Chemistry Experiments One glass bottle with 2 cups of water 1 tablespoon of sodium hydroxide inside a one rolled up small ball of aluminum foil. The aluminum foil ball is placed on top of water and moves around in circles for a few minutes while the sodium hydroxide interreacts with the aluminum foil and is powering the aluminum foil to move forward around in circles. Chemistry Chapter 1 Science is a way of knowing and understanding the universe. The scientific method is the process by which science operates. Technology is the art, skill, or craft used to apply the knowledge provided by science. Chapter 1 Exercises For Review 1. Following are a statement containing a number of blanks and a list of words and phrases. The number of words equals the number of blanks within the statement, and all but two of the words fit correctly into these blanks. Fill in the blanks of the statement with those words that do fit, then complete the state-ment by filling in the two remaining blanks with correct words (not in the list) in place of the two words that don't fit. _ are substances that conduct electricity when dissolved in_water or when . They consist of _ ( charged ions) and (positively charged ions). Common table salt, , is an example of an electrolyte, while table sugar,_ , is a . That is, table sugar does not _when dissolved in water. We conclude that table sugar is not composed of _ anions cations chemistry compound electrolytes ions melted nonelectrolyte sodium chloride sucrose water Technology: A cellular telephone brings the applications of Technology is the art, skill, or craft used to apply the science into our daily lives. knowledge provided by science.  For Review 2. Complete this statement using the same conditions as described for the preceding exercise. _, which is the study of the composition and properties of matter, and of the changes that it undergoes, is a branch of , which itself provides us with a way of knowing and understanding the universe we live in. In the operation of the we ask questions of the universe through tests and . By observing the results that we get, we can formulate additional questions, perform additional experiments, and finally develop a ten-tative explanation of what we have learned. If this tenta tive explanation or is confirmed by others and becomes widely accepted it becomes a and helps us understand better the world about us. chemistry experiments hypothesis science scientific method theory gained through science works to our benefit or to our detri-ment through the technology we use to put it to work. We'I I see in Chapters 4 and 5, for example, that the knowledge of how atoms are constructed and how they behave can be applied through one form of technology to build powerful weapons of destruction or through another technology to detect and cure disease. • Science is a way of knowing and understanding the universe. The scientific method is the process by which science operates. 3. Match each item in group A with one in group B. Group A Group B a. chloride anion 1. assembly of atoms b. compound 2. chemical particle that carries c. electrolyte either a positive or a negative electrical charge d. ion 3. conducts electricity when it is e. dissolved in water or when it is f. molecule molten ionic bond g. sodium cation 4. element h. sulfur 5. negatively charged ion 6. positively charged ion 7. pure substance formed by com-bination of two or more ele-ments in a specific ratio 8. results from the attraction of oppositely charged ions Exercises • 13 14 • Chapter 1 An Introduction to Chemistry 4. What characteristic determines whether or not a small particle is be classified as (a) an ion, (b) a cation, (c) an anion? 5. What characteristic determines whether or not a substance can be classified as an electrolyte or a nonelectrolyte? An electrolyte is a substance that conducts electricity when it is dissolved in water or when it is melted. A nonelectrolyte does not conduct electricity when it is dissolved in water or when it is melted. In Figure 1.3 shows An electric light bulb. Pure water is a very poor conductor of electricity as is a solution of sucrose table sugar in water. A solution of sodium chloride table salt in water is a good conductor of electricity. 6. What is the distinction between an element and a compound? 7. a. Name three elements. A compound is a pure substance formed by the chemical combination of two or more different elements in a specific ratio. Magnesium Sodium Elements mercury, copper, and carbon. helium hydrogen Matter consists of all the different kinds of substances that make up the material things of the universe. b. Name three different compounds, each of which contains at least one of these elements. 8. What kind of chemical bond holds the sodium cations and chloride anions in place, close to each other, in a crystal of table salt? An anion is a negatively charged ion a cation is a positivley charged ion. An ionic bond is a chemical bond resulting from the mutual attraction of oppositely charged ions. 9. Name five elements found in the human body, describe their functions in the body, and identify a good dietary source for each of these elements. Calcium Magnesium 1 O. In your own words, describe briefly the steps of the scientific method. The scientific method is the process by which science operates. 11. What is the difference between a hypothesis and a theory? 12. What is the difference between science and technology? Science is a way of knowing and understanding the universe. Technology is the art, skill, or craft used to apply the knowledge provided by science. Science itself is a way of knowing and understanding the universe we live in. The word science comes to us from the Latin scire to know. Asking questions of the universe. Technology comes from a greek word tekno meaning art, craft, or skill. Science gives us the ability to know and to understand the physical universe. 13. In what way are water and hydrogen peroxide similar in chemical composition? In what way are they different? (See Section 1.4.) Water and hydrogen peroxide are both chemical liquids. Both contain oxygen. the body converts food into skin, hair, and other body tissue; (g) looking for a correlation between hyperactivity in children _., and seasonal changes in daylight. 18. Suppose you discovered a new substance and weren't sure whether you should classify it as a new element or a new com-pound. How would you go about determining whether you had discovered a new element or a new compound? 19. The following summarizes the results we described for the light bulb, water, sodium chloride, and sucrose early in this chapter: Condition of the Light Bulb pure water only dim or dark water and sucrose dim or dark water and sodium chloride bright What would you have concluded for each of the following results: A. Condition of the Light Bulb pure water only dim or dark water and sucrose bright water and sodium chloride dim or dark A Little Arithmetic and Other Quantitative Puzzles 14. Suppose you carry out a large number of tests as follows. In each experiment you use 10.0 g of sodium. In the first ex- periment you allow the 10 g of sodium to react with 0.1 g of chlorine; in the second you allow 10 g of sodium to react with 0.2 g of chlorine; in the third, with 0.3 g of chlorine; and so with an additiona10.1 g of chlorine until the series ends with 10 g of sodium and 20.0 g of chlorine. Describe qualitatively how the product(s) of the individual reactions change(s) as the series of experiments progresses from 0.1 g of chlorine to 20.0 g of chlorine. B. Condition of the Light Bulb pure water only dim or dark pure water and sucrose bright water and sodium chloride bright C. Condition of the Light Bulb pure water only bright water and sucrose g of sodium to react pure water and sodium chloride bright bright forth. In each subsequent test you allow 10 15. How much chlorine would you have to use if you want- ed 10.0 g of sodium to react with it to produce pure sodium chloride, with neither excess sodium nor excess chlorine left over? 16. Water is composed of hydrogen and oxygen in the ratio 1 g z hydrogen to 8 g oxygen. Hydrogen peroxide is composed of hydrogen and oxygen in the ratio 1 g hydrogen to 16 g oxygen (Section 1.4). What would result from the reaction of a mixture of 1 g hydrogen and 12 g oxygen? 17. Which of the following are suitable subjects for the sci- ence of chemistry? (a) determining the composition of rocks; , (b) analyzing the effects of a day's experiences on the nature of dreams; (c) designing a low-calorie sweetener that is also an electrolyte; (d) preparing a plastic that decomposes readi- ly to environmentally harmless products; (e) defining the dif- ference between music and random noise; (f) determining how the body converts food into skin, hair, and other body tissue g looking for a correlation between hyperactivity in children and seasonal changes in daylight. 20. Why was it necessary to test the electrical conductivity of pure water before adding sodium chloride and sucrose? 21. Suppose water itself were a very good conductor of elec- tricity. How might you then determine whether table sugar, table salt, or any other substance is an electrolyte or a non- electrolyte? 22. Would you expect seawater to be a good conductor of electricity? Explain. Seawater contains salt, and other types of substances. 23. Is it possible to determine whether air is an electrolyte? If Your answer is yes, explain how you might do it; if no ex- Plain why not. 24. Several centuries ago, it was generally believed that heavy objects fall faster than lighter objects, that the more an object weighs the faster it falls. According to one legend, the Italian scientist Galileo Galilei, who lived from 1564 to 1642, correct-17. Which of the following are suitable subjects for the sci- ed this error by dropping two spheres of different weight si- multaneously from a high point on the LeaningTower of Pisa and demonstrating that they reach the ground at the same time. Describe what Galileo supposedly did in terms of the sci- entific method. What question did he ask of the universe? What test did he use to obtain an answer? What did he observe? How did he interpret this observation? Think, Speculate, Reflect, and Ponder Energy is the ability to do work. Chemicals give us energy form the clothes materials. Aspirin can relieve pain in recommended doses. swelling, fever. In overdoses aspirin can cause nausea, bleeding, even death. Chemical reactions that provide energy and materials. pollutants that can foul the air. Chemicals can cause illness, and death. Describe a circumstance in which water H2O is (a) a life sustaining or a life saving substance. (b) a hazardous or life threatening substance. Chapter 1 compositions, properties, changes. What do you think would be the result of placing wires into a solution made up of a mixture of equal parts of sucrose and sodium chloride? Chemistry is the branch of science devoted to the study of matter its composition, its properties, and changes it undergoes. 500,000,000 atoms of gold to stretch across a dollar bill. Table salt makes the light bulb light up, and sugar doesn't. Table Salt in water. Light bulb, salt, and Sugar. Web Questions • 15 25. The old saying "A watched pot never boils" comes from a. Give examples of two other chemicals that are ordinari- the observation that a pot of water seems to take longer to ly beneficial yet can produce undesirable, even deadly come to a boil if you are watching it than if you aren't. De- effects. scribe how you could use the scientific method to learn b. Give examples of two chemicals that are ordinarily whether water really does take longer to boil if you are watch- thought of as hazardous or harmful, yet in the right cir- ing it. If water takes just as long to boil whether or not you are cumstances can be beneficial. watching it, how could you use the scientific method to deter- mine whether water actually does seem to take longer if you a"'`'e Wฐ6 are, indeed, watching it, and just how much longer it seems to ' "' eb Questions take? Describe what questions you would ask, how you would go about finding experimental tests that would give you an- Use the Web to answer or accomplish each of the following. Re- , swers to these questions, and how you would interpret the port your Web source for each response. ti answers. 1. Describe a scientific contribution made by Michael Fara- 26. Describe another popular belief or perception, similar to day, in addition to his work with ions and electrolytes. the one about the watched pot or falling objects, that you could 2. The terms "chemistry," "energy," "matter," "technology," investigate by application of the scientific method. and "science" are all defined in this chapter. Present alterna- 27. Give an example of a benefit brought to us through the tive definitions derived from Web sources. operation of science. Do the same for a benefit brought 3. Show how application of the steps of the scientific method through the operation of technology. led to a scientific discovery made: (a) during the 19th century; 28. Water can be considered to be a "good" chemical in the (b) during the past 10 years. sense that we cannot live without it. Yet it is "bad" when floods 4. Illustrate each of the themes discussed in Section 1.2 with destroy property or when someone drowns. Similarly, aspirin examples obtained from the Web. is "good" in the sense that it relieves headaches, yet it is "bad" 5. Find when each of the elements of Table 1.1 was discover- in that children have mistaken it for candy, taken overdoses, ed and who made the discovery. If the date or the discoverer and died. is unknown, describe early sources and uses for the element. Exercises • 31 E X E R C I S E S ., 1. Following are a statement containing a number of blanks and a list of words and phrases. The number of words equals the number of blanks within the statement, and all but two ~ of the words fit correctly into these blanks. Fill in the blanks of the statement with those words that do fit, then complete the statement by filling in the two remaining blanks with ~'-orrect words (not in the list) in place of the two words that von't fit. ? are the smallest electrically neutral particles of ~ an , a fundamental substance of chemistry and of the world, that can be identified as that element. All atoms consist of two parts: (1) a that contains 6. In terms of the number of atoms present, hydrogen is the most abundant element in the universe and also in our bodies. What is the second most abundant element in the universe, again in terms of the number of atoms present? What is the second most abundant element in our bodies? Helium is the second most abundant element in the universe. 7. Given the atomic number and the mass number of an atom, how do we determine the number of protons in the nucleus? The number of neutrons in the nucleus? The number of elec- trons in the surrounding shells? 8. Do an atom of protium and an atom of deuterium repre- sent atoms of two different elements? Explain. d e ! P positively charged and (except for , an of hydrogen) electrically neutral ; and (2) , which lie in surrounding the nucleus. The number of protons in the nu- cleus defines an atom's and is represented by the symbol . The sum of the protons and neu- trons in the nucleus determines the atom's and is represented by . As the atomic number of the atom increases, the number of electrons in the shells also in- creases so that the number of electrons always equals the . The first quantum shell can contain a maxi- mum of A negative atomic number neutral atoms neutrons deuterium nucleus eight protons element quantum shells isotope two mass number Z electrons. 9. (a) Name the three isotopes of the element whose atomic number is 1. (b) What collective name do we give to a mixture of these three isotopes when they are present in the same ra- tios as in the universe as a whole? 10. What is a name used for the isotope of hydrogen indicat- ed by iH? 11. What chemical symbol is used as the equivalent of 1H? 12, Name and give the chemical symbols for the elements with the first 10 atomic numbers. number of protons and the atom remains electrically 13. Atoms of what element are used to define the atomic mass electrons; the second a maximum of unit? 14. Can any isotope of any element have a mass number of zero? Explain. 15. (a) What would remain if we removed an electron from a hydrogen atom? What charge would this particle bear? What would its mass be? (b) How do you think we could convert a sodium atom into one of the sodium cations discussed in Chapter 1? 16. Write the chemical symbol, showing the atomic number and the mass number, for atoms of two different elements each of which has two neutrons in its nucleus. 17. Name: a. three elements that have only a single electron in their outermost quantum shell b. two elements that have exactly two electrons in their outermost quantum shell c. three elements with filled outermost quantum shells d. one element that has only a single electron in its inner-most quantum shell  v2. Name an element that is a. the major gas of the air we breathe j~ b. used in small, long-lasting batteries t' c. used to harden the enamel of teeth d. present in graphite, diamonds, petroleum, and all living things 3. Of the first 10 elements, which are metals? 4. Exercise 3 contains the phrase "the first 10 elements." What does this refer to? 18. The nucleus of 16C and the nucleus of t~N contain the 5. How many elements are currently known to exist? - same number of but different numbers of 32 • Chapter 2 Atoms and Elements . The nucleus of t6C and the nucleus of t6C contain the same number of but different numbers of . 19. (a) Which element was found on the sun before it was found on the earth? (b) Which element has a name that in-dicates its presence in many acids or sour-tasting sub-stances? (c) How many years passed between the identification of hydrogen as an element and the discovery of its isotope deuterium? (d) Which of the first 10 elements are gases? (e) Which is the most reactive of the first 10 elements? 20. What do diamonds and ficllerenes have in common? b. Helium is an unreactive gas and neon is a gas of ex-tremely low reactivity. What, if anything, do their atoms have in common? 27. Suppose we could combine one electron with one proton to form a single, new subatomic particle. What mass, in amu, would the resulting subatomic particle have? What electrical charge would it carry? What known subatomic particle would the resulting particle be equivalent to? 28. Suppose someone discovered a particle that consisted o a single neutron surrounded by a shell containing a single ele~ tron. Would you classify this as an atom? Would you classify as an ion? Would it represent a new element? Explain yc answers. A Little Arithmetic and Other Quantitative Puzzles 21. Give the number of protons and the number of neutrons in the nucleus of each of the following atoms and the number of electrons in their first and second quantum shells: (a) 1sB; (b) 16C; (c) iHe; (d) i9K; (e)'s0~ 22. Section 2.5 tells us that hydrogen atoms make up two-thirds of all atoms in water but just over 11 % of the water's weight. Given that there are twice as many hydrogen atoms in water as there are oxygen atoms and that virtually all the hy-drogen atoms in water are iH and virtually all the oxygen atoms are 1g0, how do you explain this apparent discrepancy? 23. What is the weight of a sheet of gold atoms 1 atom thick and with the same dimensions as this page? You can answer this question by measuring the width and length of this page and carrying out a calculation similar to the one in the exam-ple of Section 2.2. 24. Using 3 x 10-8 cm as the diameter of a gold atom and 3.3 x 10-22 g as its weight, calculate the weight of 1 cm3 of gold. (You can start by finding how many gold atoms fit on a line 1 cm long; see Section 2.2.) How does your calculated value compare with the measured density of gold,19.3 g/cm3? Suggest some factors that might account for the difference. 29. a. What is the difference between an object's mass anc weight? b. A bag of table sugar (sucrose) weighs 10 kg on the moon. What is its weight on the earth? c. A bag of table salt (sodium chloride) has a mass of 5 kg on the moon. What is its mass on the earth? d. A piece of charcoal has a mass of 1 kg on the earth. What is its weight on the moon? 30. You have two spheres, one made of lead and one made of ` cork. They are standing next to each other at some spot on the sur- e face of the earth. At that location each weighs 7 kg. Compare their masses at that location. Does one have a greater mass than thc•, .,,_ other? If so, which has the greater mass? Now move both sphera ~ to one particular location on the surface of the moon and agait.v compare their masses. Does one have a greater mass? If so, which one? Does one weigh more than the other on the moon? If so,L, which? Finally, leave the cork sphere on the moon and move the lead sphere back to its original location on earth.Again,compare both their masses and their weights.  31. Suppose you discovered how to produce an isotopea drogen containing three neutrons in its nucleus. a. Write its elemental symbol, showing its atomic numbe~- _ and its mass number. b. What name might you give this new isotope to distin-guish it from protium, deuterium, and tritium. Think, Speculate, Reflect, and Ponder 25. (a) If you split the nucleus of a gold atom into two parts, would you now have two smaller gold atoms? Explain. (b) If you combined the nuclei of two gold atom into a sin-gle nucleus, would you now have one, larger gold atom? Explain. 26. a. Lithium, sodium, and potassium are all metals that react with water to liberate hydrogen gas. What, if any-thing, do atoms of each of these metals have- in - common? c. What new letter-symbol would you give this new iso-tope to distinguish it from D and T, but without repeat-ing the symbol of another element. d. Explain or give a reason for your responses to parts b and c. 32. The description of the atom that we have used in this chapter resembles in some ways our own solar system. What part of our solar system corresponds to the nucleus of an atom? What part corresponds to the electron shells surrounding the nucleus? What are some of the other similarities between the structure of the atom, as described in this chapter, and our own solar system? What are some of the more obvious differences? Web Questions • 33 `a~,~ae w 6 eb Questions Use the Web to answer or accomplish each of the following. Re-port your Web source for each response. 1. The modern view of the atom originated with the work of John Dalton. Write a brief biography of John Dalton, includ-ing the dates of his birth and death, his nationality, background, education, and a description of his view of the atom and how he arrived at it. 2. What is the principal factor affecting a planet's gravita-tional force? If a person weighs 60 kg on earth, what would that same person weigh on Mercury, Venus, Mars, Saturn, and Jupiter? 3. Who discovered each of the following? How and when was the discovery made? (a) the electron, (b) the neutron, (c) the proton? Who discovered the electron Joseph John Thomson J. J. Thomson, 1856-1940 Thomson did carry out this measurement and (later) the measurement of the particles's charge, and he recognized its importance as a constituent of ordinary matter.Joseph John Thomson (J. J. Thomson, 1856-1940; see photo at the Science Museum, London) is widely recognized as the discoverer of the electron. Thomson worked on various aspects of the conduction of electricity through gases. In 1897 he reported that "cathode rays" were actually negatively charged particles in motion In 1899, he measured the charge of the particles, and speculated on how they were assembled into atoms [Thomson 1899]. the neutron the neutron was not discovered until 1932 when James Chadwick used scattering data to calculate the mass of this neutral particle. the proton In 1919 Ernest Rutherford discovered the proton as a product of the disintegration of the atomic nucleus. The antiproton, the proton's antiparticle, was discovered in 1955. When found in the nucleus of an atom, protons and neutrons are called nucleons. Neutrons and protons belong to a class of particles called baryons which are made up of three quarks. Hadrons are any particles composed of quarks and which take part in the strong interaction, so a proton is also a hadron. 4. The Perspective summarizes the occurrence, history, prop-erties, etc., of the first 10 elements, those with atomic numbers 1-10. Write similar short paragraphs for the next five elements, those with atomic numbers 11-15. Mass is a measure of how much material is in an object, but weight is a measure of the gravitational force exerted on that material in a gravitational field 5. Henry Moseley, Isaac Newton, and Harold Urey each made a major contribution to the topics discussed in this chapter. Identify the topic associated with each of these three scientists and describe the scientist's contribution. Henry Moseley Henry Moseley (1887-1915). In 1913 Henry Moseley conducted X-ray experiments on elements. The outcome of his work was the introduction of the atomic number. It was found that if Mendeleev's table was ordered by atomic number instead of atomic mass the inconsistencies in the table were eliminated. This is the blueprint for the modern periodic table. Isaac Newton the Universal Law of Gravitation. Newton's 2nd Law there must be a force that acts on the apple to cause this acceleration. Let's call this force "gravity", and the associated acceleration the "accleration due to gravity". the orbit of the Moon about the Earth could be a consequence of the gravitational force, because the acceleration due to gravity could change the velocity of the Moon in just such a way that it followed an orbit around the earth. Harold Clayton Urey April 29, 1893 - January 5, 1981 including his discovery of deuterium and work on isotope chemistry, isotope separation, isotope geology, and cosmochemistry. Chapter 2 Atoms and Paper Clips Piles of paper clips individual paper clips, and fragments of a paper clip. The fragments no longer represent a paper clip. 15 - 20 paper clips. 113 known elements. pure gold. Gold ingot Gold nuggets Gold dust gold atom in dust. Ancient All matter can be subdivided into atoms which cannot be subdivided further. Modern Further subdivision is possible the identity of the original element is lost. A atom is the smallest electrically neutral particle of a element can be identified as a element. The size and abundance of Atoms. Atoms are small. Be seen with a powerful optical microscope. gold atom is 3 x 10 -8cm in diameter. mass is 3.3 x 10 -22 g. 0.00000003 cm diameter or mass with 22 0s 33g. Relative sizes of helium, gold, and cesium atoms. every 200 atoms in the universe 182 atoms of hydrogen 18 atoms of helium. less than half of other elements. 132 lb 60 kg on earth would weigh 10 kg 22 lb on the moon. A bodys weight depends on where it is. Mass is observed as a body's resistance to acceleration. Weight results from the pull of gravity. spaceship mass 60 kg or 132 lb 0 weight. Small mass small force needed for acceleration. Large mass large force needed for acceleration. A=1 mass number hydrogen. a The nucleus of a hydrogen atom contains only a single proton. What is the mass of the hydrogen atom in atomic mass units? b The nucleus of a fluorine atom con- tains 9 protons and 10 neutrons. What is the mass of a fluorine atom in amu? The proton forms the nucleus of the atom. electron occupies a spherical shell surrounding the nucleus. The mass number of a atom is the sum of the protons and neutrons in its nucleus. The atomic number is the sum of all of a atom's proton's. A element is a substance whose atoms all have the same atomic number. Relative distances and masses in the hydrogen atom. Filled with the flammable element hydrogen for buoyancy the German airship Hindenburg burned in May 1937. The hydrogen ignited as the airship approached its dock in Lakehurst, New Jersey. 36 people died as a result. 1 electron 54 • Chapter 3 Chemical Bonding Name a element that is harmless or beneficial to us in its elemental form. Name a different element that can be hazardous in its elemental form. Now switch things around and name a hazardous compound of the harmless or beneficial element and a harmless or beneficial compound of the hazardous element. Sodium chloride the compound that forms when elemental sodium reacts with elemental chlorine is a relatively harmless electrolyte that is used daily to modify the taste of food. It isn't completely without hazard. What are the name and the chemical symbol of the alkaline earth metal with the smallest atomic number? Valence Shells and Chemical Reactivity. Figure 3.3 The reaction of sodium and chlorine to produce sodium chloride. Full electronic structures are shown on the top. Lewis structures are on bottom. A sodium atom Na + A chloride atom Cl A sodium cation a How many electrons must a magnesium atom lose to acquire a valence shell with eight electrons? b How many electrons must oxygen gain to form an octet? c Would you expect magnesium and oxygen to react with each other to form a chem- ical compound? Why? Potassium can react with any of the halogens to form a compound similar to NaCl. Astatine. At is a very rare element of the halogen family. Ionic compounds are com- pounds composed of ions. Fluoride, chloride, bromide, iodide are the names of the halide. Sodium atom contains 11 protons in its nucleus 11 electrons in the surrounding shells. Cl atom contains 17 protons in its nucleus equal number of electrons in three quantum shells. valence shells hold 7 electrons in the Cl atom completes the octet with eighth electron. The electronic structure of the sodium cation two electrons in the first quantum shell and eight in the second resembles the electronic structure of what inert or noble gas element? The electronic structure of the chloride anion resembles that of what inert or noble gas element? The crystals of the sodium chloride. equal numbers of sodium cations chloride anions. Crystals are solid shapes of substance. crystal lattice. What do we call the structures shown enlarged in figure 3.6 that form as water crystallizes in the atmosphere in cold weather? ice and snow. Crystals of sodium chloride a ionic compound and a electrolyte. Crystals of water support a popular sport. A crystal lattice is the orderly three dimensional arrangement of the chemical particles that make up a crystal. A ionic bond results from the attraction of oppositely charged ions. Chemical formula is a sequence of chemical symbols and subscripts show the elements present in a compound. Binary compound is made up of 2 elements. Scouring pads and kitchen magnets The attraction that iron has for a magnet isn't carried over into the iron oxides it forms as its rusts. Iron oxygen and carbon are elements. in their free state. Chlorine is deadly and can be hazardous destroys tissue. Elemental sodium is a metallic acid. Chlorine is a yellow gas. Sodium reacts explosively with water. Chlorine and Sodium are poisonous. Valence electrons are the electrons of the valence shell which is the outermost electron shell of a atom. The octal rule states that atoms often react so as to obtain exactly eight electrons in their valence shells. (b) carbon, (c) sodium chloride, (d) propane, (e) lithium io- dide, (f) sucrose, (g) potassium. 5. Write chemical formulas for (a) lithium bromide, (b) cal- cium sulfide, (c) sodium sulfide, (d) beryllium oxide, (e) the chlorine molecule, and (f) the compound formed on reaction of silicon and hydrogen. 6, Write the chemical formulas of all the ionic compounds is an organization of all that could result from reaction of a mixture of lithium and potassium with a mixture of fluorine and bromine. 7. Name a commercial product that contains (a) elemental , have the same number of chlorine, (b) the iodide ion, (c) both the element nitrogen and the element chlorine, (d) the element fluorine, (e) the chloride , atomic number, ion, (f) the element sulfur, (g) elemental iodine. , which is the average mass of all the 8, Which of the following contain (or are a form of) elemen- tal carbon? Which contain the element carbon? (Reviewing the perspective of Chapter 2 may be helpful.) (a) carbon dioxide, (b) graphite, (c) water, (d) diamond. 9. Where might you find (a) elemental oxygen, (b) elemental gold, (c) the element carbon, (d) sodium ions, (e) the element hydrogen, and (f) the elements carbon, hydrogen, nitrogen, and oxygen in a single compound? 1. Following are a statement containing a number of blanks and a list of words and phrases. The number of words equals the number of blanks within the statement, and all but two of the words fit correctly into these blanks. Fill in the blanks of the statement with those words that do fit, then complete the state- ment by filling in the two remaining blanks with correct words (not in the list) in place of the two words that don't fit. In its modern form the the known elements arranged in order of increasing . Elements that lie in the same have similar and belong to the same chemical . The table shows the element's chemical and of the element, weighted for the of each. The table is particularly useful for predicting the out- come of chemical reactions between since an atom of any element tends to react so as to convert its elec- tronic structure to that of a nearby . When atoms react by a complete of electrons, the products are . When they react by pairs of electrons, the result is a . While ionic compounds exist as crystals made up of extensive 10. What element has the following: of ions, covalent compounds are composed of a. an atomic weight of almost exactly 14 discrete . If the atoms that form the covalent b. an atomic number of 16 bonds have significantly different , the bond that c. one electron in its first quantum shell forms is a d. two quantum shells, both of which are filled with abundance isotopes electrons atomic number lattices e. the electron structure 2 8 2 atomic weight molecules ^ a valence shell filled with a total of two electrons column noble gas 11. a total of three quantum shells, with two electrons in its covalent bond periodic table valence shell crystals polar covalent bond h. a total of two quantum shells, with three electrons in its electronegativities properties valence shell elements symbol i. twice as many electrons in its second shell as in its first halogens transfer 11. Each of the following pairs of elements reacts to form a bi-nary compound. Which form an ionic compound and which ions valence electrons form a covalent compound? 12, Write the chemical symbols of the following elements: 2. Define, illustrate, or explain each of the following: a. alkaline earth metal b. binary compound c. chemical family d. chemical formula e. covalent bond f. halogen g. lithium and iodine h. magnesium and oxygen (a) aluminum, (b) argon, (c) calcium, (d) carbon, (e) cesium, j. molecule a. sulfur and oxygen b. hydrogen and fluorine c. barium and chlorine d. sodium and bromine e. nitrogen and oxygen f. hydrogen and carbon g. ionization h. molecular formula i. molecular weight k. valence electron (f) fluorine, (g) gold, (h) hydrogen, (i) lead, (j) manganese. 3. Identify the elements and the compounds among the fol- lowing: (a) oxygen, (b) water, (c) chlorine, (d) sucrose, (e) hy- drogen, (f) sodium chloride, (g) sulfur, (h) propane, (i) argon, . (j) carbon. 13. Name the elements that the following chemical symbols represent: (a) Ag, (b) Be, (c) He, (d) I, (e) Kr, (f) Mg, (g) Na, (h) Si, (i) Zn Argon Beryllium Helium Iodine Krypton Magnesium N Strontium Zinc 14. Write the Lewis structures of (a) a chlorine atom, (b) a 4. Identify each of the following as consisting principally of fluorine atom, (c) a fluoride anion, (d) a sodium atom, (e) a molecules, principally of ions, or principally of atoms: (a) water, magnesium atom, (f) a carbon atom, (g) an aluminum atom, (h) a boron atom, (i) a molecule of HCI, (j) a water molecule, (k) a molecule of hydrogen peroxide, H202. 15. How many electrons would an oxygen atom have to lose to obtain the same electronic structure as an inert gas? Why doesn't an oxygen atom lose these electrons, rather than ac-quire two, when it reacts with other elements? 16. a. What are two properties that all elements in the same column of the periodic table as helium have in common? b. What are two properties that all elements in the same column of the periodic table as lithium have in common? 17. What would you expect to happen if you place a small piece of potassium metal into water? 18. What change occurs in the valence shells of elements as we move from left to right in any given row of the periodic table? 31. Many compounds, such as carbon dioxide, CO2, methane, CH4, water, H20, and sucrose, C1ZH22011, exist as molecules. 19. What change occurs in the valence shells of elements as we Hydrogen gas, H2, also exists as molecules. Does this mean move down a column in the periodic table? that the gas HZ is a compound? Explain. 20. Why do elements in the same column of the periodic table 32. The covalent compound acetylene, the fuel of the oxy- show similar chemical behavior? acetylene torch used by welders, has the molecular formula 21. What is the valence of sulfur in the gas sulfur dioxide, CZH2. The covalent compound benzene, a commercial solvent, SOZ? In the gas sulfur trioxide, S03? has the molecular formula C6H6. Each of these compounds 22. The element oxygen can exist in two molecular forms. In contains carbon and hydrogen atoms in a one-to-one ratio. its most common form, it exists as a diatomic molecule, O2, Would it be correct to write the chemical formula of each as but it can also exist as ozone, in which three atoms of oxygen CH? Explain your answer. combine to form a covalent molecule. Write the molecular for- mula of ozone. 23. Like water, hydrogen peroxide (Fig. 3.18) ionizes slight- ly to produce a hydrogen cation and an anion. What is the chemical structure of the anion resulting from the ionization 34. Arranging the elements in order of increasing atomic of H202? Show the structure in two ways: (1) with pairs of number also places the elements in order of increasing atom- electrons represented by pairs of dots and (2) with covalent ic weight, with a few exceptions. One of these appears in the bonds represented by dashes. sequence of tellurium (Te) and iodine (I). The atomic weight of tellurium (atomic number 52) is 127.6. The atomic weight of iodine (atomic number 53) is 126.9. How do you account Figure 3.18 The hydrogen peroxide for this? molecule, HZOZ. 33. Elemental oxygen exists as a diatomic gas, O2. How many electrons do the two oxygen atoms have to share between them to form this diatomic molecule? How many covalent bonds unite the two oxygen atoms of the OZ molecule? 35. Hydrogen chloride, HCI, exists as a gas composed of co-valent molecules. If we dissolve this gas in water, the water conducts an electric current well. If we dissolve HCl in ben zene, a solvent of molecular formula C6H6, the solution does not conduct an electric current. (Pure benzene does not con-duct an electric current either.) What do you conclude from this observation? 24. Pure hydrogen chloride is a gas under ordinary conditions. Molecules of pure, gaseous hydrogen chloride consist of a hy-drogen atom covalently bonded to a chlorine atom. When hy-drogen chloride gas dissolves in water, the resulting solution easily conducts an electric current. As the hydrogen chloride molecules enter the water, what process occurs to generate an electrolyte? A Little Arithmetic and Other Quantitative Puzzles 25. Give the valence of the cation in each of the following com-pounds: (a) SrF2, (b) ZnCIZ, (c) A1C13, (d) C~O, (e) Fe203. 26. What is the total number of electrons being shared among all the covalent bonds of a molecule of methane, CH4? 27. What would you write as the molecular formula for the nitrogen dioxide of Section 3.3? (Di- is a prefix meaning "two.") What is the valence of the nitrogen of this molecule? Exercises • 55 28. Bromine's atomic weight is 79.9. Two isotopes make up virtually all the bromine in the universe. One, with a mass num-ber of 79, makes up 50.69% of all the bromine atoms. What is the mass number of the other isotope? 29. The permanganate anion, Mn04, bears a single negative charge. Knowing that oxygen acquires an octet by acquiring two electrons, what do you calculate as the valence of the man-ganese atom in this ion? , 30. What is the valence of neon? Think, Speculate, Reflect, and Ponder 36. The element carbon, as we will see later, forms the basis for all life as we know it. Science fiction writers sometimes speculate on the properties of different forms of life based on an element other than carbon. What element do you think they usually choose, and why? (Referring to Fig. 3.2 may help you answer this question.) 37. Some forms of the periodic table show hydrogen twice, once at the top of the column of the alkali metals and once again at the top of the column of the halogens. Suggest a reason for putting hydrogen into both families. (Kint.~ Consider the structure of the hydrogen atom and its similarities to the other elements of each of these families.) 56 • Chapter 3 Chemical Bonding 38. Silver chloride, AgCl, is not soluble in water. Explain how Identify two other scientists who reported a periodic repeti- you might be able to determine whether this is an ionic or a co- tion of properties among elements before Mendeleev devised valent compound. (Hint. Refer to Section 1.1.) his periodic table. What repetitions did they find? Among 39. Are there any exceptions to the octet rule? If your an- what elements? swer is no, explain why there aren't any. If your answer is yes, 2. Figure 3.2 represents one of several modern versions of the describe one and explain why it is an exception. periodic table. Find two other versions, one of which repre-sents a three-dimensional periodic table.  3. Identify three different compounds each of which has the molecular formula C6H1206. Describe briefly some similari Use the Web to answer or accomplish each of the following. Re- ties and some differences among them. eb Questions port your Web source for each response. 4. Find the molecular formulas of the pain-relievers aspirin 1. Section 3.6 contains the sentence "Although others had and ibuprofen; the antibiotics penicillin and erythromycin; the also noted the same sort of periodic repetition of properties sweeteners aspartame and saccharin. even before Mendeleev's inspiration, none had pursued the 5. Write a brief summary of the life of Linus Pauling. Include idea as vigorously or in as much detail as the Russian chemist." descriptions of his contributions to the topics of this chapter. 82 • Chapter 4 Discovering the Secrets of the Nucleus and energy are interconvertible, that mass can literally van- In its descriptions of the material of our world, what ish, to be replaced by its equivalent in energy. follows asks us to use letters of the English alphabet to In another sense, chemistry asks us to look at the phys- represent the nuclei and electrons shel Is of atoms that ical structures of our world not with our eyes but with our are invisible to our eyes; numerical subscripts to repre- minds. As it explains the behavior of the matter that makes sent clusters of these atoms; and straight lines to repre- up our world, chemistry invokes structures-atoms and sent the clouds of electrons that hold these atoms into molecules-too small to be seen with even the most pow- the well-formed structures we call molecules. The same erful optical microscopes, structures that can be made vis- kind of mental activity that allows us to visualize the ible only with such uncommon devices as the scanning structure and behavior of atoms and the conversion of tunneling microscope (Sec. 2.2). In this sense, the study of matter directly into energy (and the reverse) will convert chemistry asks us to use our imagination to give shape and the letters, lines, and subscripts that follow into the in- structure to the nucleus and its surrounding electrons and credibly small particles that form us and everything else the bonds they form. in our everyday world. • E X E R C 1 S E S For Review 1. Following are a statement containing a number of blanks and a list of words and phrases. The number of words equals the number of blanks within the statement, and all but two of the words fit correctly into these blanks. Fill in the blanks of the statement with those words that do fit, then complete the state-ment by filling in the two remaining blanks with correct words (not in the list) in place of the two words that don't fit. Antoine Henri Becquerel discovered the phenomenon of , which occurs when the nucleus of a emits an , a , andlor a . Each of these forms of radiation can cause the ionization of matter so each is an example of . When an atom-ic nucleus loses either an a particle, which is a high-energy , or a (3 particle, which is a high-energy , the nucleus undergoes a change in its atomic number and becomes transformed into a nucleus of a dif-ferent element in a process known as . If the newly formed isotope is also radioactive, it too emits radiation and is transformed into still another element. Eventually, after a series of these transformations, a non-radioactive is formed, and this comes to an end.  a particle neutron (3 particle proton y ray radioactivity chain of radioactive decay radioisotope electron stable isotope ionizing radiation a. A. H. Becquerel 1. derived the equation b. James Chadwick E = mc2 2. Repeat the instructions of Exercise 1 for the following 2. discovered a and ra s statement and list of words and phrases. c. Marie Curie R Y The first atomic weapons-the bombs tested near Alam- d. Albert Einstein 3. discovered the neutron ogordo, New Mexico, and those dropped on Hiroshima and e. Otto Hahn 4. discovered nuclear fission Nagasaki-derived their explosive power from the con- f. Ernest Rutherford 5~ discovered radioactivity version of into through 6. discovered radium and the process of . The first atomic bomb detonat- , ._ - polonium ed was made of , an artificially produced iso-tope that does not occur naturally (in more than trace amounts). The bomb dropped on Hiroshima contained , which was separated from its more common ' isotope, , by the process of . Each of these weapons was detonated by setting off a convention-al explosion that compressed subcritical portions of the metal into a and set off a , which produced the nuclear blast. Still another kind of nuclear weapon, which harnesses the power of the sun, relies on for its energy. In one form, and nuclei come together at very high temperatures to produce and release nuclear power. critical mass nuclear fission deuterium nuclear fusion energy plutonium-239 helium tritium hydrogen uranium-235 initiator uranium-238 matter 3. Each of the following scientists or groups of scientists in the left-hand column received a Nobel Prize for contributing to our understanding of the structure and properties of the atomic nucleus. Match each of these individuals or groups with one of their major accomplishments (often, but not in every case, the one for which the prize was awarded), shown in the right-hand column. Exercises • 83 11. (a) What results from the collision of an electron with a positron? (b) Explain why this is an example of the conver-sion of mass into energy. 12. Protons and neutrons are the particles that make up the atomic nucleus. What particles make up protons and neutrons? 4. Place the following events in chronological order: a. detonation of the first atomic bomb b. discovery of a, (3, and y rays c. discovery of the neutron d. discovery of nuclear fission e. discovery of radioactivity 13. Describe a commercial use for y radiation that is not a f. the first planned, successful transmutation of an element medical application. 5. In the process of unlocking the secrets of the nucleus and 14• What does the implosion accomplish in the plutonium _.__. ____._. __ bomb? m the story of the atomic bomb, what imp process is associated with each of the following cities? 15. In the initiator of both the uranium and plutonium bombs, a. Alamogordo, New Mexico what function does the polonium-210 serve? What function b. Berlin does the beryllium serve?  c. Hanford, Washington 16. In what way did Ernest Rutherford bring the dreams of d. Los Alamos, New Mexico the alchemists to reality? e. Oak Ridge, Tennessee f. Paris A Little Arithmetic and Other 6. a. What element was the first one found to be radioactive? Uranium Quantitative Puzzles b. What element was the first one found to undergo nu- clear fission? Uranium 17. Using the form of notation shown in Figure 4.3 and (if c. What radioisotope was the first to be produced artifi- needed) data obtained from the periodic table or lists of atom- cially on an industrial scale? ic symbols, atomic numbers, and mass numbers, write complete d. Why was the element of part (c) produced in such large quantities? e. What element is produced on the sun through a nuclear fusion reaction? Hydrogen and Helium sYmbols for (a) radon-222, (b) carbon-13, (c) the most com-mon isotope of lithium, (d) the isotope of chlorine of mass number 37, (e) an atom containing 43 protons and 56 neutrons, (f) a helium nucleus, (g) a proton, (h) a y ray, (i) a R particle, (j) a chloride ion, and (k) a sodium ion. ^ What isotope forms the final, stable product of the chain 18. (a) When a radioactive nucleus ejects an a particle, both of radioactive decay that starts with U-238? the atomic number and the mass number decrease. By what g. What element forms when carbon-14 undergoes radio- quantity does each decrease? (b) When a radioactive nucleus active decay? ejects a (3 particle, only one of these (atomic number or mass h. What element forms initially on radioactive decay of number) changes. Which one? Does it increase or decrease? By radon? what quantity? i. What element served as the starting material for the first 1 g. (a) What effect does ejection of a y ray have on atomic planned, successful, transmutation of one element into number? On mass number? (b) What effect does ejection of a another? positron have on atomic number? On mass number? j. What element was produced as a result of the first planned, successful transmutation? 2~• Tritium is a radioactive isotope of hydrogen. Explain why tritium cannot decay with the loss of an a particle. 7. What is phosphorescence and what event revealed to A. H. Becquerel that the mysterious spot on his photographic plates did not originate in the phosphorescence of uranium? 21. What form of radioactivity, if any, occurs with an increase in the mass number of the radioactive nucleus? Explain. 22. The experimentally measured mass of an atom is always less than the mass calculated as the sum of the masses of all the Protons, neutrons, and electrons that compose it. Why? 23. If U-238 absorbed one neutron and the resulting U-239 then underwent fission to generate three neutrons and two (and only two) mutually equivalent nuclear particles that were equal in their mass numbers and atomic numbers, what iso- tope of what element would these two new atomic particles represent? Do you think they would be stable isotopes ox radioisotopes? Explain. 24. Per unit of atomic mass, Fe-56, the most common isotope of iron, has one of the greatest mass defects and one of the highest binding energies of all atoms. 8. What one characteristic is common to all end products of all possible chains of radioactive decay? 9. How does the ratio of neutrons to protons in an atomic nu- cleus affect the stability of the nucleus? 10. A neutron bomb is a proposed nuclear weapon that would explode with very little force (and therefore do little physical damage to buildings and equipment) but would release im- mense amounts of neutrons as ionizing radiation that would disable and kill troops and civilians. Which would you expect to penetrate matter more effectively: (a) a beam of high-speed neutrons or a beam of y radiation? (b) a beam of high-speed neutrons or a beam of a radiation? Give reasons for your choices. 84 • Chapter 4 Discovering the Secrets of the Nucleus a. Given that the experimentally measured atomic mass work in common in making discoveries or must the use of one of this isotope of iron is 55.9349, calculate its mass defect. exclude the use of the other? The atomic number of iron is 26. 33. In the operation of the scientific method the questions b. What is the mass defect of Fe-56 per atomic mass unit? that scientists ask of the universe (in their experiments) are c. What is the mass defect of U-235 per atomic mass unit? almost always based on something already known of the uni- (See Sec. 4.12.) verse. The questions are chosen carefully, so that there is a d. Which has the greater binding energy per atomic mass good chance that the answers (the results of the experi- unit, Fe-56 or U-235? ments) will yield interesting or important information. With this in mind, why do you think that Otto Hahn chose to bom- bard Complete the following equations with the symbol for bard uranium nuclei with neutrons rather than with a or (3 the atom or particle represented by the question mark. Show particles? the mass numbers and atomic numbers of the isotopes formed or the symbols of the subatomic particles: 34. It has been suggested that in areas with certain kinds of zlo soil and underground rock and mineral deposits, it may be a. g4Po ---> ? + a more hazardous to live in a house that is well sealed against b. 294 Pa ~ ? + R drafts than in one with loose-fitting doors and windows that c. 153 Pa ------ s4Xe + ? allow a continual flow of air into and out of the house. Sug- d. z~Th -~ zgBRa + ? gest a reason why this may be so. e. ? _ z94Pu + a 35. Explain why radioactivity is hazardous to humans. f. ? , 292U + R 36. Radioactivity does considerable biological damage and 26. Why was a source of neutrons needed in the detonation can be harmful to living things. Of the three forms of radia- of the atomic bombs? tion discussed in this section, a, (3, and y rays, which would be the most hazardous to a person standing a few feet from a ra-dioactive substance that emits all three of these forms of radi-Think, Speculate, Reflect, and Ponder ation? Which would be the least hazardous? 27. Describe one difference between the way the laws of the 37. The first significant application of newly discovered nu- physical universe operate within the nucleus and the way they clear energy was in the construction of an atomic bomb. Sug- operate in our everyday world, gest a reason why this was so. 28. Describe Becquerel's use of the scientific method as he 38. Nuclear weapons tests in space, in the atmosphere, and sought to establish a connection between phosphorescence in the ocean are prohibited by international treaty, but under- and X-rays. How did he explain the observation of an exposed ground tests are still permitted. Why are underground tests of spot on the photographic film that had been wrapped in black nuclear weapons considered to be different from the other paper and kept in a drawer with the crystal of the uranium tests? compound, out of contact with sunlight? How did this obser- 39. Detonations of high explosives such as dynamite and TNT vation affect the idea that a phosphorescing substance emits are used for peaceful purposes, in demolition and in construc- X-rays along with visible light? If Becquerel wished to contin- tion, for example, as well as in weapons of war. Suggest and ue his investigation of a connection between phosphorescence describe peaceful uses for detonations of fission or fusion nu- and X-ray emission, what test(s) might he have used next? clear explosives. 29. Suppose that instead of using crystals of a uranium com- 40. As we saw in Exercise 10, a neutron bomb produces a pound in his investigations of phosphorescence, Becquerel had very small blast when it explodes but releases very large used crystals of a compound that was not radioactive but that numbers of neutrons. Would you classify a neutron bomb as did nonetheless phosphoresce. With your own knowledge that a more humane weapon or a less humane weapon than a phosphorescence and the generation of X-rays are not con- uranium bomb of the power that exploded over Hiroshima? nected, what do you think Becquerel would have observed? Explain. What do you think his conclusion would have been? 41, Chemical reactions release and absorb far less energy (per 30. Was Columbus's discovery of the American continent an atom involved) than the nuclear reactions of fission and fu- example of serendipity? If the American continent did not sion. Using this observation as a basis, suggest a reason why exist and Columbus had indeed reached the Orient by sailing the Law of Conservation of Mass might not be valid. westward, as he had expected, would that have been an ex- ample of serendipity? Explain your answers. 31. Give an example of a discovery (other than those dis-cussed in this chapter) made through serendipity.The example you use may come from outside the field of science. 32. Contrast and compare the use of serendipity and the use of the scientific method in making discoveries. Can the two 42. As we saw in Section 4.8, Otto Hahn and Fritz Strass-mann carried out certain experiments on uranium late in 1938 in Berlin, and Lise Meitner identified the results of these ex-periments as newly discovered nuclear fission, a process that could release incredible amounts of energy. In September 1939, Germany invaded Poland and World War II began. Not quite a month before the outbreak of war, believing that Germany Web Questions • 85 . ~ - w - m ~ . ~ ~~ , -. -~ m . ,- •~~ ~ _ m ~ . ~~ ~ _ .- . ~ •~ i ~ •~ i i i - , m ~ •i i i •~ m w • m , , •1 . -~ _•.. m- -~ '~. ~ .- ~ ~ m- • - .- , ;. , -. .. . - m ~ . . . . w ~ -. . v -~ ~ .- .w . . ~ ~ - o . .~~ ~ ~ .- . ~ ~ -~ - w .w .. - . w w ~. ~ ~ ~ .m W ~ ' m ~ ~ . ~ ~~ ~ ~ - , ,- _ • ~ w • ~ m ~ ~ ~ .~ w w ~ ~ ~ ~ ~ w. .m ~~ ~ ~ m - - .m ~ ~w ~ ~- ~. ~ w ~ w ~ w w ~ m ~ ~ .~~ - . ~ w ~- w ~ •~ ~ -~ m „ - - w ~ . - w w . - . ~ v . . ,- ,•. ,- •,. m . ~ ~ ~~ _ ~ fi- ~- 44. One of the motives for dropping atomic bombs on Japan at the end of World War II was to save the lives of American troops who might otherwise have had to invade the home is-lands of Japan. There is still dispute about whether such an in-vasion would have been necessary. Regardless of the likelihood that such an invasion might have been required, suppose that one would indeed have been necessary and that the lives of American troops would have been lost as a re-sult. Suppose you had been President of the United States in 1945 and that the best military estimates were that dropping the bombs would save the lives of 1 million U.S. troops. Knowing what you do now of the effects of the bombs that dropped on Hiroshima and Nagasaki, would you have au-thorized their use? Suppose that the best estimates were that Japan was lightly defended and that our troops were so well prepared that no more than 10 U.S. lives were likely to be lost. Under those conditions, would you have authorized the use of nuclear weapons? If you would have authorized their use at the level of 1 million casualties, but not at a level of 10, can you cite a specific number of casualties that would have been a dividing line between your decision to authorize and your refusal to authorize the use of the atomic bombs? Explain your answers. 7. Identify each of the following, describe how each was in-volved in the creation of the atomic bomb, and describe a sci-entific contribution of each that is unrelated to the atomic bomb: (a) Leo Szilard, (b) Edward Teller, (c) John von Neu-mann, (d) Eugene Wigner. 8. What were some of the arguments used to justify the use of atomic bombs at the close of World War II? What were some of the criticisms of their use? What alternatives to dropping them on occupied cities were proposed before their actual use? 9. What is the current state of nuclear armaments among the world's nations? What publicly available information now ex-ists about the kinds and numbers of nuclear weapons that each nation now holds? What international agreements are now in effect concerning the construction and/or testing of nuclear weapons? What agreements, if any, are now under considera-tion or review?  In Chapter 1 we defined chemistry as the branch of science defect. We've seen that much of the importance of nuclear that sfudies the composition and properties of matter and transformations (and associated changes in binding ener- the changes that matter undergoes.This definition properly gies) lies in the energy they release-instantaneously in focuses on the matter, the material substance, of the world nuclear weapons, more slowly in nuclear reactors and in about us and the universe in general. But when we look at medical applications. We've seen that this energy can do "the changes that matter undergoes" we are also looking harm when it destroys biological molecules vital to health at energy. Virtually without exception, when there's a change and life, or provide lifesaving benefits when it kills cancer in matter, there's movement of energy, into or out of the mat- cel Is. e` ter that's changing. We must remove energy from water The next several chapters, and those further ahead, (cool it) to freeze it. We must add energy to water (heat it) continue examining this connection between changes in to boil it. When atoms split (fission) or combine (fusion), matter and the release or absorption of energy, and carry it they release energy. When we burn gasoline in a car's en- beyond nuclear transformations to changes in the structure gine or oxidize food in our own bodies, we release the en- of molecules, especial ly the organic molecules of our fuels ergy stored in the gasoline and in the food. and of the food we eat. We'll define what energy itself is, As Einstein pointed out with E = mc2, matter and en- learn how molecules store and release it, examine how the ergy are in a real sense equivalent to each other. In Section chemicals of our food provide us with our own biological 4.12 we saw that the energy that holds a nucleus together, energy, and trace the energy of our life back to its ultimate the atom's binding energy, is derived from the atom's mass origin. •    For Review Exercises • 111 1. Following are a statement containing a number of blanks, and a list of words and phrases. The number of words equals the number of blanks within the statement, and all but two of the words fit correctly in these blanks. Fill in the blanks of the statement with those words that do fit, then complete the state-ment by filling in the two remaining blanks with correct words (not in the list) in place of the two words that don't fit. atomic pile half-lives carbon-14 iodine-131 control rods plutonium-239 diagnosis and therapy potassium-40 Peaceful uses of nuclear reactions include the generation of electrical power radioisotopic dating , medical , and . C~rrently fission reactor uranium-235 the most practical form of nuclear power plant is the , in which heat produced by an creates fusion reactor uranium-238 steam, which turns a turbine attached to an electrical gener- 2, Identify, describe, or explain each of the following: ator. Although most nuclear power plants use a uranium fuel, which is enriched in the more highly fissionable isotope a~ background radiation e. meltdown , a converts the more common, but b. film badge f. PET , less efficient isotope into fissionable c. Geiger counter g. rem as it simultaneously generates power. Someday electrical d. LMFB reactor h. scintillation counter power may be produced by an environmentally cleaner , in which small nuclei, such as hydrogen isotopes, 3• In what way was Enrico Fermi's nuclear pile at Stagg Field combine to form larger nuclei, such as helium atoms. important to building the first atomic bomb? In what way was Medically, is valuable in the diagnosis and con- it important to the development of nuclear-powered electric trol of hyperthyroidism; is used widely as a generating plants? source of diagnostic y rays. 4. Describe the steps involved in the conversion of the heat Since the of radioisotopes are well known and produced in a nuclear pile into electricity by a commercial are constants, unaffected by physical or chemical condi- power plant. Energy, From the Nucleus to the World We Liue In  tions, naturally occurring radioisotopes are useful in deter-mining the age of ancient materials. The dating of objects made of wood, paper, and linen, for example, is often ac-complished by analysis of their content. 112 • Chapter 5 Harnessing the Secrets of the Nucleus exposed if: (a) standing in a well-sealed room with walls of thick lead; (b) buried deep within a mine. 5. Describe how electricity is generated through the action of steam. The steam pushes or turns the waterwheel which the waterwheel is attached to a rod that turns a disk with magnets on the disk on the other end of the rod, and the magnets are slightly above coils of wire that when the magnets are moving in a circular path around the coils of wire electricity is generated in the coils of wire. 6. Describe how a source of energy other than heat is used to generate electric power on a commercial scale. 25. List a rays, (3 rays, and y rays in order of increasing abil- ity to pass through a thick wooden wall. List them in order of increasing ability to generate ions over equivalent paths of travel within that wooden wall. stacle yet to be overcome in building a fusion reactor? 7. What is the principal advantage of nuclear fusion over nu- clear fission for generating power? What is the principal ob- 8. List four factors that have slowed the expected growth of A Little Arithmetic and Other nuclear power as a source of commercial electricity. Quantitative Puzzles 9. What would result if all the control rods of a commercial 26. Using the data in Table 5.3, calculate how long it would fission reactor were removed from the nuclear pile and not take 1 kg of Tc-99m to be reduced to just under 1 g of Tc-99 by reinserted? What would happen if all the rods were fully in- the process of radioactive decay. serted into the pile and allowed to remain? 27, Ten grams of krypton-93 were prepared through the use 10. Explain why a nuclear explosion cannot occur in a com- of nuclear reactions. A measurement taken after a certain pe- mercial fission reactor. What kinds of accidents can occur? riod passed showed that radioactive decay left a total of 0.625 g What happens during a meltdown? of this radioisotope. How long a period elapsed between the 11. (a) Was the accident at Three Mile Island the result of a formation of the 10 g of krypton-93 and the measurement? nuclear explosion of fissionable material? (b) Was the accident 28. you have a balance that will weigh masses down to 0.1 g at Chernobyl the result of a nuclear explosion of fissionable but gives a reading of zero for anything less than that. Using material'? Explain your answers. that balance, you have just measured out 100.0 g of each of the 12. Of the accidents at Seascale, England, Three Mile Island, radioisotopes in Table 5.3. What weight of each of these iso- Pennsylvania, and Chernobyl, Ukraine, which released the topes will be left (using the same balance) after 20 years have greatest amount of radioactive fallout? passed? 13. Write the three sequential nuclear reactions that convert 29. Section 4.9 informs us that U-235 can undergo the fol- U-238 into Pu-239 in a breeder reactor. lowing mode of fission: 14. In the conversion of U-238 to Pu-239 in the breeder re-i 137 actor, another element is produced momentarily from the ura- 92U + on -~ SZTe + 4~~Zr + 2 (1)n nium and decays quickly to plutonium. What is this transient Suppose that as Otto Hahn bombarded uranium with neu- element produced on the path from U-238 to Pu-239? trons, some of the fission had followed this route. Suppose 15. In the term "liquid metal fast breeder reactor," what does further that Hahn had taken about 4 days to analyze the the word "fast" refer to? products of this study. Do you think he might have found any 16. Describe two hazards associated with a breeder reactor tellurium-137? Do you think he might have found any zirco- that converts uranium to plutonium. nium-97? (Te-137 has a half-life of 4 seconds; Zr-97 has a half- 17. Why is it important that high-level nuclear wastes be life of 16.8 hours.) , stored in an area that is completely dry? 30. You have just examined a wooden utensil recovered 18. What was the first new element to be produced by artifi- from an ancient archeological site and have found that the cial means? How does its name reflect its origin? ratio of C-14 to C-13 is less than 0.,1% of the ratio of C-14 to 19. Describe how ionizing radiation can be used to cure or C-13 measured in a branch just cut from a nearby tree. What, control hyperthyroidism. if anything, can you conclude about the age of the wooden 20. What property of radioisotopes of iodine makes them utensil? What assumptions do you make in arriving at your answer? particularly useful for diagnosis and therapy of disorders of the thyroid gland? 31. In determining the age of the earth by measuring the ratio 21. How does the emission of a positron affect the atomic of lead-206 atoms to uranium-238 atoms in the earth's crust, we number of an atom? How does it affect the mass number of an made the assumption that all of the lead-206 in the rock sam- atom? ples came from the radioactive decay of uranium-238. How would our calculations of the earth's age be affected if some of 22. What form of radiation is detected by the instruments the lead-206 atoms were formed at the same instant the ura- used in PET? nium-238 atoms were formed? Suppose, that is, that at least 23. Describe how ionizing radiation can cause (a) somatic some of the lead-206 atoms that we found along with the ura- damage and (b) genetic damage. nium did not come from radioactive decay of the U-238 but 24. Name four sources of background radiation that might were formed along with the U-238. Would the earth be older affect someone standing outside in a rocky field. Name one or younger than our calculations would show? Describe your source of background radiation to which someone would be reasoning. Exercises • 113 .2. Plutonium-239 has a half-life of about 24,000 years. How rather than a (3 emitter for the treatment of deep-seated tu- ~ong will it take for 99.9% of the plutonium wastes of a breed- mors. What would your response be? Would you (a) pro- er reactor to decay into other substances? If we assume that mote or (b) fire the research scientist who proposed the there are four generations of humans in each century, how idea? Why? many generations will this period cover? 44. Of a radiation, (3 radiation, and y radiation, which is most 33. Using the graph of Figure 5.2 and the data of Table 5.3, damaging to living things when it is emitted by a nearby, ex- determine how long it will take for 100 g of U-235 to decay to ternal source? Explain your answer. Of the three, which is most 90 g of U-235. dangerous to a living thing when it is emitted by a radioiso-tope located within the body? Explain your answer. 45. Describe the similarities and the differences in the use of y radiation (a) to determine the shape and size of an internal organ and to detect the presence of tumors in it; (b) to deter-mine how well the organ is performing its biological functions, such as metabolizing a particular nutrient; (c} to kill a cancer-ous tumor in the organ. 35. If the Shroud of Turin were analyzed for C-14 today, what 46. Suggest three possible reasons why genetic damage by percentage of the C-14 originally present at its formation ionizing radiation has not yet been observed in humans. ; would you expect to be present? (Figure 5.2 may be useful to 47• Suppose there were to be a vote soon in your state to you.) ban all forms of production of ionizing radiation by human 36. Would it make any difference in calculations of the age of activities, such as in the production of electricity by nuclear rocks, based on the isotopic ratio of U-238 and Pb-206, if the Po~'~'er plants, the production of radioisotopes for medical decay step with the longest half-life were at the end of the se- use, and the use of X-rays in medical and dental examina- quence rather than at the beginning? Use an hourglass analo- tions. Would you vote for or against the proposal? Explain gy in arriving at your answer. your answer. - 48. Which one of the four factors that have slowed the growth of commercial nuclear power do you think provides the most Think, Speculate, Reflect, and Ponder important argument against further development of commer-cial nuclear power? Which one earries the least weight in ar- 37. What was the function of the graphite in Fermi's pile? guments against further development? What was the function of the cadmium? 49. Suppose a commercial electric utility wanted to build a 38. How did Enrico Fermi's studies of nuclear reactions con- nuclear power plant a few miles from where you live and your tribute to the use of atomic energy for the production of com- county or municipal government held a referendum to deter- mercial power? mine whether to permit the construction and operation of the 39. Why do health professionals working in radiology de- plant. This would give you the opportunity to cast a vote in partments of hospitals wear film badges on their coats? favor of the plant or against it. What factor(s) would sway you 40. Describe the operation of each of the following radiation toward voting for the construction and operation of the nu- detection devices: (a) a Geiger counter; (b) a scintillation clear power plant? What factor(s) would sway you toward vot- counter; (c) a film badge. How would you use each to estimate ing against the plant? the quantity of ionizing radiation that is present? Which one of 50. Is there any way to detect an actual difference between these detectors do you think is the best for determining the the electricity that is generated by a nuclear power plant and amount of accumulated radiation exposure a person receives the electriciry generated by a plant run with oil? If your an- over a long period, a week for example? Describe your swer is yes, how would you go about detecting the difference? reasoning. If your answer is no, how would you go about convincing some- 41. How could you construct a crude but effective radiation one (who believes otherwise) that you are right? detector out of common consumer materials readily available 51. What's the major difference between a pressurized water to you? Would this deviee measure radiation the moment it reactor and a boiling water reactor? Whieh do you think would occurs or would it measure cumulative radiation, detected over be less expensive to build and operate? Why? Which do you a period of time'? think would present less hazard of an accident or of radioac- 42. What properties should a radioisotope have if it is to be tive contamination of the environment? Why? administered internally in a medical diagnostic procedure? 52. Do you think that the continued production of electrici- 43. You are the administrator of a major research insti- ty by nuclear plants justifies the accumulation of high-level tute. One of your research scientists presents a plan to build nuclear wastes? Explain. an instrument much like that used for cobalt radiation ther- 53. lf you had a choice between connecting your home or apy, except that this new instrument would use an a emitter apartment to electric power provided by a plant that burns 34. You have 10 g of a mixture made up of exactly 5 g of I-131 and 5 g of K-40 and you also have a radiation detector that is able to detect radiation down to a level of 0.10% of the current level of radiation given off by the sample. How long do you estimate it will take for the level of radiation of the 10-g sam-ple to drop to (a) 75% of its current level? (b) half of its cur-rent level? (c) 0.10% of its current level? 114 • Chapter 5 Harnessing the Secrets of the Nucleus  imported petroleum or a plant powered by nuclear reactions, ~a"',` which would you choose? Why? ; ฐ eb Questions 54. Among the various proposals suggested for the disposal Use the Web to answer or accomplish each of the following. Re- of high-level nuclear wastes is the possibility of sealing them port your Web source for each response. in drums and transporting them by rocket to the moon, to re- 1, Describe the current state of plans or expectations for the main on its surface forever. What would be the advantages of use of nuclear fusion to produce commercial electric power. such a plan? What would be the drawbacks? Would you sup- 2. What is the current condition of the nuclear power plant at port a plan of this sort? Explain. p p 55. It's possible to convert the energy of steam into elec- tricitand it' Chernobyl, Ukraine? Does it currently produce electric power? Are there current plans for rebuilding it? For tearing y, s p ossible to reverse the process by using elec- it down? For replacing it with a new power plant? tricity to produce steam from water. It's possible to convert g• Describe another reported accident at a nuclear power - the energy of falling water into electricity, and it's possible to reverse the process by using electricity to pump water plant anywhere in the world, in addition to those discussed in from a lower level to a higher level. It's possible to convert Section 5.2. the energy of the wind into electricity with a windmill con- 4• Find the location, history, and current status of a breeder re- nected to a generator, and it's possible to reverse the process actor in current use, either for experimental, research, or com- by using a fan to convert electricity into a stream of moving mercial purposes. air. It's possible to convert the energy of fissioning atoms 5• What is the current status of the proposal for the use of Yucca into electricity. Do you think it might be possible to reverse Mt., Nevada, for the long-term storage of nuclear wastes? the process and use electricity to produce fusion? Describe 6. Identify a radioisotope other than those discussed in this ' your reasoning. chapter that is used for medical diagnosis or treatment. De- 56. Suppose that the isotopic analysis of the Shroud of scribe its medical application. Turin had dated its origin to a few years earlier than the 7• Find a positron emission tomogram posted on the Web and birth of Jesus. What conclusion(s) could be drawn from this describe the medical condition or study it illustrates. result? 8. Radioisotopes of elements other than carbon and urani- 57. The ability of different kinds of ionizing radiation to um have been used for the dating of various substances. Iden- penetrate human tissue varies from one form of radiation to tify an isotope of one of these other elements that has been another. Gamma rays penetrate the entire body readily, a used for dating and describe an example of its use. rays are stopped by the skin, while (3 rays lie between these 9. Section 5.11 ends with the sentence, "Claims and counter- two. Yet 1 rem of any one of these forms of radiation does claims for the authenticity of the Shroud and of the radiocar- • the same amount of damage as 1 rem of either of the other bon dating have continued since the 1988 analysis." Summarize two. Explain why this is so despite the differences in pene- some of the arguments supporting and opposing the conclusion trating ability. discussed in this chapter. Exercises • 143     Figure 6.21 A burning candle. Water droplets coat the sides of The candle flame dies as the the beaker as the burning candle oxygen in the beaker converts oxygen and alkanes to is replaced by carbon water and carbon dioxide dioxide. marize our thoughts in the form of chemical equations. to express the chemical reactions in terms of balanced These are no more than shorthand expressions for our ideas chemical equations, placing our explanations of what we `. that atoms and molecules can interact with each other to be observe on a quantitative foundation. converted from one set of chemical structures to another This applies to the entire range of material substances set, with entirely different properties. of the world we live in, from solids like the hard wax of our All this takes place within the context of still other ob- burning candle to invisible gases such as those within the servations and still other interpretations. That is, we know beaker. In Chapter 8 we'll move beyond these material sub- that the Law of Conservation of Mass holds in all chemical stances to the energy they consume and release as they reactions and that under the usual conditions of our every- react with each other, like the heat and light given off by the day world atoms are neither created nor destroyed, nor is candle's flame. • one element converted into another element.This leads us v For Review Different compounds that share the same molecular for- 1. 1. Following are a statement containing a number of blanks, mula are known as . The molecular formula and a list of words and phrases. The number of words equals CaHio, for example, applies to two different compounds, the number of blanks within the statement, and all but two of known by their IUPAC names as and the words fit correctly into these blanks. Fill in the blanks of the statement with those words that do fit, then complete the state- alkanes IUPAC ment by filling in the two remaining blanks with correct words butane organic (not in the list) in place of the two words that don't fit. hydrocarbons paraffins Any compound containing the element carbon is an isobutane stereochemistry compound. Those compounds containing both carbon and hydrogen, but with no other element present, 2. Define, describe, or give an example of each of the following: are . Those containing carbon and hydrogen in a ratio that fits the general formula C„HZn+2 are known as a~ 1ฐ carbon f. double bond or, by an older system of nomenclature, b. alkene g. heptane . The modern system of naming organic c. alkyl group h. saturated hydrocarbon compounds, the system, came about as a re- d. aromatic compound i. stereochemistry sult of an international gathering of chemists at Geneva, e. cycloalkane j. unsaturated Switzerland, in 1892. Because the component atoms of all but the smallest mol- 3. Name three carbon-containing compounds that have been ecules can be joined to each other in a variety of ways, most obtained for centuries from living or once-living substances. molecular formulas can represent a variety of molecules. Describe their uses. 144 • Chapter 6 Introduction to Organic Chemistry 4. Using the chemical definition described in this chapter, c. propane 3. Related to a very highly identify each of the following as organic or inorganic: (a) table tlammable compound salt, (b) table sugar, (c) methyl alcohol, (d) oxygen gas, (e) the d. butane 4. Related to an alcohol isotope of uranium used in nuclear reactors, (f) the dye henna, obtained from wood (g) urea, (h) the carbon dioxide of your exhaled breath, (i) the carbon dioxide of a carbonated soft drink. 13. How can you determine whether any particular organic 5. Given a specific molecular structure, describe how you compound is a member of the alkane family? would determine whether it represents an alkane, an alkene, 14' Describe a property or a bit of chemistry: (a) common to or an alkyne. the entire hydrocarbon family; (b) common to all alkenes but 6. What do all aromatic compounds have in common? not to alkanes. 7. Name three consumer products that are composed exclu- 15' What compound is produced when: (a) diatomic hydrogen sively or largely of hydrocarbons. Describe the properties of is added to ethylene, (b) water is added to ethylene. alkanes that are most important to eaeh of the three consumer 16' Classify each of the following as to whether it is (1) a hy- products. drocarbon or not a hydrocarbon, (2) an alkane or not an alkane, 8. Name each of the following: and (3) an aromatic compound or not an aromatic compound. a. isobutane e. carbon dioxide a. CH3-CHz-CHz-CHz-CHZ-CH3 b. acetylene f, benzene b. CH3-CHz-CH-CHZ-CH3 c. hexane g. C1~H~6 d. cyclohexane h. cinnamaldehyde CH3 17. What's the difference between the molecular structures c. CH3-CHz-CH-CHZ-CH3 ~ of ethene and ethyne? CHZ 18. Draw the molecular structure of 2-pentyne. 19. How would you determine whether a chemical equation CH3 is balanced or unbalanced? d. CH3-CHZ-CH-CHZ-CHz-CH-CH3 A Little Arithmetic and Other I I Quantitative Puzzles CH3 CII3 e. CH3-CH-CH-CH3 20. Write balanced equations for the combustion of (a) me-thane, (b) ethylene, (c) propane, (d) propyne, (e) benzene. CH~ CH3 f. CH3-CH=CH-CHZ-CHZ-CH3 g. ~CH\ CHZ CHz 21. Balance each of the following equations: a. Na + Clz -~ NaCI b. Hz + C12 ---~ HCl c. Ca + Oz --~ Ca0 d. Na + Oz -> NazO e. Mg + Brz -~ MgBrz CHz ~CHz ~CHZ 9. Identify five organic compounds that are isolated from plants. Identify one organic compound that is generated by an-imals or animal products. 1 O. What are three properties of carbon that result in the large number and great variety and complexity of organic compounds? 11. In what way do free radicals react when two of them en-counter each other? 12. Match each of the following organic compounds with the property or source that is the origin of its common name: 22. Draw condensed molecular structures for all the isomers of heptane, C~H16, that have exactly six 1ฐ hydrogens. 23. The number of 1ฐ hydrogens in a molecule must be a mul- l tiple of 3, and the number of 2ฐ hydrogens in a molecule must be a multiple of 2. Why is this so'? 24. Hydrocarbon molecules that contain two carbon-carbon double bonds are called dienes. What is the general molecular formula for the family of dienes? What other family of hydro-carbons has this same general molecular formula'? 25. How many molecules of hydrogen would have to be - ; added to a molecule of benzene to produce cyclohexane? Compound Property or source 26. To what class or classes of compounds might each of the ; a. methane 1. Reiated to the first in a following hydrocarbons belong: (a) CSHlo, (b) CgHlg, series of acids found in fats (c) C6Hlo, (d) C~oHzo> (e) C9Hzo? b. ethane 2. Related to an acid found in 27. Draw all the isomers of C3H6 that can exist and name rancid butter each. Exercises • 145 28. Why can't a compound with a molecular formula of 40. Can two different compounds have the same name? Can C3Hlo exist? two compounds identical in every other way have different 29. Can an alkane molecule contain an odd number of hy- names? Explain. drogens? Explain. 41. Because alkanes burn readily in air they are useful as com- ponents of commercial fuels. What is another property or char- acteristic of alkanes, especially the higher alkanes, that makes matic rings and carbons joined by triple bonds (Sec. 6.11). them useful in consumer products, even in products that are Write the balanced equations for its combustion to water and not used as fuels? 30. The largest hydrocarbon discovered to date has the mo- lecular formula C139sH127s and is composed largely of aro- carbon dioxide. 42. Both the methyl free radical and the chlorine atom con- 31. How many straight-chain isomers of CSOH l02 can there tain an unpaired electron. When two methyl free radicals com- ; be? Explain your answer. bine they form ethane, CH3-CH3. When two chlorine atoms the condensed structure of the molecule formed when a methyl free radical combines with a chlorine atom. Think, Speculate, Reflect, and Ponder 32. Methane and ethane are both members of the alkane fam- 43• Write the molecular formula of heptadecane. ily of hydrocarbons. Describe one characteristic that methane 44. How would using a warm beaker rather than a cool one and ethane have in common. Identify one difference between in the demonstration that opened this chapter have affected methane and ethane. our observations of a candle burning in an inverted beaker? 33. Draw the structure of cyclohexene. 45. How would you distinguish between food that is "organ- 34. Are 1-butene and cyclobutane isomers? Explain. ic" and food that is not "organic"? Apply the chemist's defini- 35. Draw the structure of two isomers of C4H6 that contain tion of "organic" to food and describe how this affects your a triple bond. Draw one isomer that contains a ring. interpretation of the term organic food. 36. Draw the structure and give the IUPAC name of the alka- 46• Can any inorganic substance be isolated from living or ne of lowest molecular weight that contains a 4ฐ (quaternary) once-living material? Exnlain. carbon. 47. Give the molecular structures and the IUPAC names of all five isomeric hexanes. 37. Name the following two compounds (Sec. 6.3 may pro-vide help for part b):  a. CH3-CH-CI CH3 b. CH3-CHZ-CHZ-OH 38. What would be one danger of using pure methane as a household fuel for heating and cooking? 39. Name each of the following compounds: a. CH3-CH-CHZ-CH3 "12-CH3 b. CH3-CH-CH3 CH3-CH-CH3 c. CH3-CH-CHZ-CHZ-CH-CHZ-CH3 52. We can speculate that life exists in some other part of the universe, perhaps in a form far different from what we find here on Earth. On Earth, life is based on compounds of the el-ement carbon. If life were to occur in another part of the uni-verse, and if that life were based on an element other than carbon, suggest what element that might be. Justify your an-swer with reference to the periodic table and the relationships among elements within it. ' combine, they form a diatomic chlorine molecule, C12. Write Compare compound (a) with compound (b) of Exercise 8. Are these two compounds isomeric alkanes? Are they mutually identical? Are they identical compounds with different names? Are they different compounds with the same names? Answer 53. Suppose that the carbon atoms of alkanes weren't tetra- these questions after comparing compound (b) with compound hedral but were square planar instead. That is, suppose the car- (e) of Exercise 8. Repeat for a comparison of compound bon atom were at the center of a simple square and the (c) with compound (d) of Exercise 8. hydrogens or other carbons bonded to it were at the corners 48. Draw molecular structures for all the isomers of (a) CZH6 (one isomer), (b) CZHSCl (one isomer), (c) C3H7C1(two iso-mers), (d) C4Hlo (two isomers), and (e) CSH12 (three isomers). 49. Should we classify benzene as a saturated hydrocarbon or as an unsaturated hydrocarbon? Explain. 50. What was the significance of Wohler's laboratory syn-thesis of urea? 51. Suppose a sealed vial of a liquid is recovered from an an-cient tomb in Egypt and writing on a clay tablet accompany-ing the vial is translated to indicate that the liquid was made from the juice of berries, but there is no indication of the age of the liquid. How might you go about determining how long ago the liquid was prepared from the berries? What technique might you use? 146 • Chapter 6 Introduction to Organic Chemistry of the square and that they all lay in the same plane, as they do 4. Where are the official headquarters of the IUPAC? Where on this sheet of paper. Knowing that atoms and groups bond- are its administrative headquarters? Where and when was the ed to each other by covalent bonds can rotate freely around latest meeting of its general membership held? Where and those bonds, predict how many isomeric methanes could exist when is the next meeting scheduled? if all carbons of alkanes were square planar. How many 5, What is the IUPAC name for the unbranch.ed hydrocar- ethanes? Propanes? Butanes? bon Cq6Hq4? 6. Write a brief history and description of benzene. Discuss the contributions of Michel Faraday and Friedrich August Kekule to our knowledge and understanding of benzene. De Use the Web to answer or accomplish each of the following. scribe where benzene was discovered, where or how it is cur- ' Report your Web source for each response. rently obtained, what it looks like and how it behaves under 1. Section 6.1 describes the red-orange dye henna and the an- ordinary conditions of temperature and pressure, and what it timalarial agent quinine as organic compounds that can be ex- is used for. Discuss the hazards of handling the compound and , tracted directly from plants. Identify two other useful organic of absorbing it into the body. compounds that can be extracted directly from plants. 7. In addition to those presented in this chapter, identify aro- v,; 2. Many Web sites offer "organic" foods for sale. Describe some matic compounds: a) isolated from plant material, b) not found common characteristics of these foods described as "organic." in nature but manufactured commercially, used c) in prescrip- tion medicines, d) as food additives, e) in the manufacture of 3. Find commercial sources for samples of each of the first 10 alkanes, methane through decane. plastics, f) in dyes.  eb Questions  1. Following are a statement containing a number of blanks, and a list of words and phrases. The number of words equals the number of blanks within the statement, and all but two of ; the words fit correctly into these blanks. Fill in the blanks of the statement with those words that do fit, then complete the state-ment by filling in the two remaining blanks with correct words '' (not in the list) in place of the two words that don't fit. is a mixture of that provide power to a car as they react with oxygen within the cylinders of the to produce and and to release energy. In a four-stroke engine, the ignites the gasoline-air mixture at the end of the sending the piston downward. The , which fol-lows, translates the energy of the gasoline into the power that moves the vehicle. What are the three products of the complete oxidation of a "isooctane." hdb? Wht lthlbt idd on im yrocaronaea susances proucenco- Gasoline itself is derived from a naturally occurring mix- plete oxidation of a hydrocarbon? ture of hydrocarbons known as . Al- though a certain amount of gasoline hydrocarbons (known 5. What two characteristics of a hydrocarbon's molecular as natural or straight-run gasoline) can be obtained direct- structure affect its volatility?  Exercises • 169 batteries. In the end a balance of cost, convenience, and cleanliness will probably determine our choice of fuel forto-morrow's car. "Cost" will include the cost of the fuel and the engine, and the expense of maintaining a clean environment. "Convenience" will reflect both the car's driving range and the simplicity of charging or exchanging a battery or filling a tank with fuel. "Cleanliness" will be a matter of the kind of en-vironment in which we choose to live. In any case, we will have choices before us, both as individuals and as a society. Whatever fuel or combination of fuels we do choose, it will be chemistry, in one form or another, that delivers the ener-gy. Making the choices intelligently will require an under-standing of the chemistry that lies behind them. • , are broken down into smaller molecules that have properties more suitable to gasoline. benzene kerosene catalytic cracking knock compression ratio octane rating compression stroke methyl tert-butyl ether distillation petroleum gasoline power stroke hydrocarbons spark plug internal combustion 2,2,4-trimethylpentane engine water 2. Define or identify each of the following: taining fuel carried on the vehicle. Although not truly a zero-emission device-it produces water as a product-the cell is essentially pollution free. As with other forms of alterna-tive power, fuel cells come with their own disadvantages. They are currently large, heavy, and much more expensive than other sources of power. Combinations, Cost, Convenience, and Cleanli-ness Still another possibility is the hybrid electric vehicle (HEV), which carries both gasoline and electric engines. In a parallel HEV both engines are connected to the wheels; driving conditions determine which one is running. In a series HEV the gasoline engine serves principally to recharge the For Review a. catalyst b. catalytic converter As the (the ratio of the maximum volume of c. crude petroleum d. fossil fuel the gasoline-air ratio at the beginning of the compression e. intake stroke ^ isomerization stroke to that of the fully compressed mixture at the end of g, oxygenate h. petroleum refining the compression stroke) of an engines increases, the ten- i, reforming j. tetraethyllead dency of a gasoline to also increases. The abil- k, ZEV ity of a particular gasoline blend to resist this tendency is reflected by its , which is measured by compar- 3. Identify the four strokes of the internal combustion engine ing the gasoline blend to a mixture of and describe what happens during each. and ' which is also known as "octane" ly from this mixture by , additional 6. What is a major advantage of increasing the compression gasoline can be produced by , a process ratio of an engine? What characteristic of a gasoline must be in which the molecules of higher boiling fractions, such as changed as the compression ratio increases? 170 • Chapter 7 Petroleum 7. What purpose does the catalytic converter of an automo- 22. What correlation do you think may exist between the bile serve? ratio of primary and secondary carbons on a pair of iso- 8. Into which chemical is the carbon monoxide (CO) of ex- meric alkanes and the relative magnitude of their octane haust gases converted as the gases pass through the catalytic numbers? Explain. converter? 23. Isopentane (2-methylbutane) is a major component of 9. (a) Why was tetraethyllead added to gasoline? (b) What gasoline. Give its molecular structure and write a balanced was the original reason for discontinuing the addition of equation for its combustion (see Sec. 6.8). tetraethyllead? (c) What additional benefit comes from re- 24. (Note: This exercise deals with data presented in Sec- moving this additive? (d) Name another chemical additive that tion 7.1.) Assuming that the number of vehicles on the road can serve the same function as tetraethyllead. (e) What refin- and the number of miles we drive remain constant, how many ing process produces the same characteristic in gasoline as that gallons of gasoline would we save each year for each obtained by adding tetraethyllead? mile-per-gallon increase in the energy efficiency of our cars? 10. What is the function of distillation in the refining of petroleum? Think, Speculate, Reflect, and Ponder 11. In what way do compounds that occur naturally in petro- leum but that are not hydrocarbons contribute to environ- 25. The distillation of water from the tea in the pot of the mental pollution? opening demonstration allows you to collect water that is quite pure, except for possible contamination by the more volatile 12. Petroleum, which does not contain large quantities of components of the tea. What is left behind in the pot as you dis- aromatic hydrocarbons, is a major source of aromatic hy- till the water from the pot and collect it in the glass? drocarbons. Explain why and describe the chemistry involved. 26. Arrange the following hydrocarbons in order of increas-ing boiling point, with the lowest boiling hydrocarbon first and 13. Does the catalytic cracking of petroleum produce straight- the highest boiling last: (a) nonane, (b) ethane, (c) butane, run gasoline? Explain. (d) heptane, (e) methane. 14. What two refining steps are needed to convert hexane 27, Arrange the following hydrocarbons in order of increas- into benzene? ing boiling point, with the lowest boiling hydrocarbon first 15. What is the function of: (a) an oxygenate, (b) an octane. and the highest boiling last: (a) 2-methylbutane, (b) butane, enhancer? (c) 2,2-dimethylpropane, (d) 2-methylpropane, (e) pentane. 16. Identify an oxygenate that is not an ether. What functional 28. Arrange the following hydrocarbons in order of increas- group does it possess? ing boiling point, with the lowest boiling hydrocarbon first and 17. What is one disadvantage to the use of ethanol as an the highest boiling last: (a) octane, (b) 2-methylbutane, oxygenate? (c) hexane, (d) 2,2-dimethylpropane, (e) heptane. 29. Arrange the following hydrocarbons in order of increas-ing boiling point, with the lowest boiling hydrocarbon first A Little Arithmetic and Other and the highest boiling last: (a) 2,2-dimethylpentane, (b) 2- Quantitative Puzzles methylhexane, (c) 2,2,3-trimethylbutane, (d) heptane. 18. On average, how many cylinders are in the power stroke at any given moment in a four-cylinder engine? In an eight-cylinder engine? In a six-cylinder engine? 19. Using the data presented in Section 7.1, calculate the num-ber of miles per gallon provided by the average motor vehicle in the United States. Identify at least one source of error in this calculation. 30. Based on what you know of the effect of the molecular structure of alkanes on their boiling points, why is it difficult to predict whether 2,2,3-trimethylheptane or octane will have the lower boiling point? 31. Aromatization of a cyclic hydrocarbon, A, molecular for-mula C7H14, produces toluene, C7Hg. Write the name of hy-drocarbon A and give its molecular structure. 32. In Section 6.10 we saw that adding water to an alkene produces an alcohol. Methyl tert-butyl ether is manufactured by adding a certain organic compound to 2-methyl-l-propene: 20. Draw the condensed structure of the isomer of C8H18 that has the greatest number of methyl groups. Write the IUPAC name of this isomer. What prediction can you make about the probable numerical value of its octane number? CI-12=C-CI-13 21. Repeat Exercise 20 for the isomer of C$Hl$ that has the smallest number of methyl groups. CH3 Exercises • 171 What compound is added to the double bond of this alkene to 45. (a) If the combination of a new engine design and the de- produce methyl tert-butyl ether? velopment of the ideal hydrocarbon fuel produced only C02 33. You have a mixture of two different liquid compounds and HZO as combustion products, would you agree to the re- and you attempt to separate them from each other by distilla- moval of catalytic converters from automobiles or to the sale tion. You find, however, that no matter how carefully you dis- of new cars without them? Explain. (b) If catalytic converters till them and no matter how complex and intricate a distillation were removed, would you agree to the return of leaded gaso apparatus you use, you cannot separate the two components. line to raise octane ratings? What can you conclude about these two liquids? 46. Suppose that you now own a car and could replace it with a new one that is equivalent or better in all respects, is far less ex-pensive to own and operate, and doesn't pollute the atmosphere in any way. Suppose, though, that this new car has to be refueled (or recharged if it is an electric car) every 10 miles you drive. Would you replace your current car with this one? Would you re-place it if the new car required refueling or recharging every 20 miles? 50 miles? 100 miles? 250 miles? 1000 miles? How does the range of a car affect your attitude toward it? 34. Which of the following components of auto exhaust emis-sions would you expect to be decreased by the use of a cat-alytic converter: H2O, isopentane, C02, CO? 35. Which of the components of exhaust emissions described in Exercise 34 would you expect to be increased by the use of catalytic converters? 36. Would you expect the chemical composition-the spe-cific hydrocarbons used to blend the gasoline and their pro-portions in the mixture-of a specific brand of gasoline to be the same in Miami in July as it is for the same brand sold in Chicago in January? Explain. 37. Suppose you were given samples of two different liquids. Describe how you could determine which one is the more volatile. 38. Engines are more likely to stall as the result of vapor lock after the car has been traveling for a while than when it is just started. Why? 39. You are in charge of designing a new form of the internal combustion engine. One of your workers has suggested mov- ing the valves and the spark plug from the top of the cylinder -qniWveb Questions to the side of the cylinder, midway between the top and the Use the Web to answer or accomplish each of the following. bottom of the piston's travel. Are there any advantages to this idea? Are there any disadvantages? Explain. port your wed source jor eacn response. 1. When and where was the first oil well drilled within the continental United States? Is it still in operation? 40. Describe one way our society can produce a significant decrease in our consumption of petroleum. Describe your reasoning. 41. In the event of a severe and prolonged petroleum short-age, we may have to choose between producing enough heating oil to keep us warm during a particularly cold win-ter and producing enough gasoline to keep our cars run-ning. Explain why we might have to make this choice and describe the chemistry involved. 42. What would be a major advantage of using the combus-tion of hydrogen (HZ) as a source of energy in a car's engine? What might be a major disadvantage? 4. What octane enhancers have been used or proposed for gasoline, in addition to methyl tert-butyl ether? What are the advantages and disadvantages of each? ti 43. Which of the compounds in the question at the end of Section 7.3 would you expect to have the highest octane num-ber? The lowest? Describe your reasoning. 44. Can a compound have an octane rating higher than 100? 6• Prepare a graph showing the total amount of gasoline used Lower than zero? If your answer to either of these is no, ex- by cars in the United States each year since 1920. 5. What is the location of the nearest petroleum refinery? What is its annual output of refined petroleum products? plain why not. If your answer to either of these is yes, explain 7. Describe the current prospects for the use of solar power their significance. in automobiles. 47. Prepare a table listing sources of energy that may replace today's gasoline for our cars of tomorrow. List several of the advantages and disadvantages of each. 48. Suppose that all motor vehicles that now run on fuels derived from petroleum were replaced by electric, battery-powered cars. How would you suggest we produce the elec-tricity needed to recharge the battery so as to minimize pollution of all kinds? What source of energy would you use for the production of the large quantities of electricity that would be needed? 2. What's the average, typical, or most common compression ratio of the cars that drive on our highways? What's the range of compression ratios of racing cars that participate in events like the Indy 500? What fuels do the racing cars use? What are their octane ratings? 3. Describe the concerns about air quality that led to the pas-sage of the Clean Air Act of 1970. What amendments, if any, have been added to the act since 1970? Exercises • 197 E X E R C I S E S  For Review d. an electric battery standing alone on the floor of a room e. a stream of a particles f. a coiled, compressed spring g. the earth as it orbits the sun h. a car moving at 0.5 mile per hour 1. Following are a statement containing a number of blanks, and a list of words and phrases. The number of words equals the number of blanks within the statement, and all but two of the words fit correctly into these blanks. Fill in the blanks of the statement with those words that do fit, then complete the state-ment by filling in the two remaining blanks with correct words (}~ot in the list) in place of the two words that don't fit. is a form of , which is simply the ca pacity to do . The , which is the amount of energy needed to raise the temperature of by , is a common unit of nutrition-al energy. Another unit, the , is more widely used in the physical sciences. It is the amount of work done by 1 watt of in 1 second. Chemical energy is stored as the energy of . If the total amount of energy stored among all the of a chemical re-action is less than the total amount of energy stored among the , energy is released as the reaction occurs. The actual measurement of energy and work is accom-plished through the technique of Carbohydrates, proteins, and are the macronu-trients that provide us with all of our bodily energy. We use the energy that they and our other macronutrients provide to do physical work, for the 5. Write the Energy Equation for human nutrition and de-scribe each of its terms. 6. Using the terms of the Energy Equation, describe the conditions under which a person's weight (a) increases; (b) de-creases; (c) remains constant. 7. What are the three processes by which we use or expend the energy provided by food? 8. What is resting metabolism? necessary to the digestion and metabolism of our food and for the that keeps our organs running and our bodies alive. 9. What are the three macronutrients of our foods? Carbohydrates, proteins, and are the macronutrients that provide us with all of our bodily energy. 1 O. Which macronutrient contributes the greatest amount of energy per gram to the body? proteins 11. How do our bodies store unused energy? 12. Label each of the following as exothermic or endothermic: a. burning hydrocarbons of a candle b. nuclear fission c. steam condensing to water d. ice melting to water e. electricity passing through the filament of a light bulb f. water boiling to steam g. nuclear fusion h. chlorine gas reacting with sodium metal i. electrolysis of water to hydrogen and oxygen 1 g of water heat 1ฐ Celsius joule basal metabolism products 13. Give an example of a substance produced by nature, other Calorie reactants ~ than food or petroleum products such as gasoline, that we calorimetry specific dynamic action value for its chemical potential energy. chemical bonds watt 14. Describe the connection between the Industrial Revolu- electricity work tion and the average temperature of the earth's surface. energy 15. Describe the atmospheric greenhouse effect and explain t 2. Identify the contribution made by each to our under- ~'~'hY carbon dioxide is classified as a greenhouse gas. ~ standing of the physical nature of heat: (a) Francis Bacon; 16. Name three other gases, in addition to carbon dioxide, ,, (b) Benjamin Thompson, Count Rumford; (c) James Prescott that are classified as greenhouse gases and describe their prin- Joule. cipal sources. 3. How might Francis Bacon have explained the results of 17. In what way does the use of gasoline as a fuel contribute Count Rumford's experiment? to the greenhouse effect? Why doesn't the use of corn-derived ~~ 4. Which of the following are examples primarily of kinetic ethanol as a fuel contribute to the greenhouse effect? ; energy and which are examples primarily of potential energy: 18. Suppose we discovered a way to modify the combustion ;~ a. a waterfall products of fossil fuels by converting COZ emissions into CH4 1 b. a person standing on a diving board, about to jump into emissions through the chemical reaction a swimming pool catalyst c. a diver who is in the process of entering the water at the COZ + 2H20 -~ CH4 + 20Z end of the dive What effect, if any, would this have on the greenhouse effect? 198 • Chapter 8 Working with Chemistry A Little Arithmetic and Other 24. Suppose you weigh 154 Ib and have just eaten a Iunch Quantitative Puzzles consisting of a glass of orange juice, a hamburger, a malted 19. A person in normai health and weighing 165 Ib (75 kg) milk shake, and a serving of potato chips. How long would you fasts for 36 hours while lying still in bed. What is the total num- have to run to use up the calories you absorbed from the ber of Calories lost during the last 24 hours of the fast? lunch? (Refer to Table 8.3.) 25. Repeat Exercise 24, but this time for a lunch consisting of 20. Suppose this same 165-Ib person chooses to lie in bed for a glass of orange juice, a tuna fish sandwich, a raw carrot, and a month, without engaging in any of the normal, daily physical a glass of soda. activities that constitute exercise in its broadest sense. Taking into account all the factors involved in resting metabolism, cal- 26• How many calories does it take to heat 25 g of water from culate the average daily intake of food Calories needed by this 40 to 50ฐC? individual to maintain body weight at a constant level. 27. How many calories are released as 25 g of water cools 21. The following are the amounts of each of the macronu- from 60 to 50ฐC? trients provided by one standard serving of several common- 28. What is the final temperature of the 50 g of water formed ly available packaged foods. How many Calories does one when 25 g of water at 60ฐC is mixed with 25 g of water at 40ฐC? serving of each of these foods provide? Assume that all of the heat released by the warmer water is ab- a. Bumble Bee chunk light tuna in water sorbed by the cooler water. carbohydrate 0 g 29. What is the final temperature of the 50 g of water formed protein 12 g when 10 g of water at 60ฐC is mixed with 40 g of water at 40ฐC? fat 2 g 30. A 100-watt electric light bulb was placed in a calorimeter b. V8 vegetable juice and turned on. After a period the temperature of 1000 g of carbohydrate 9 g water in the calorimeter rose by exactly 10ฐC. Using the in- protein 1 g ` formation in Section 8.5, calculate the length of time the light fat 0 g bulb was on. c. Campbell's chicken broth 31. How long would the nutritional energy provided by one carbohydrate 2 g serving of the potato chips described in Exercise 21 g keep a protein 3 g 100-watt light bulb burning? fat 2 g g2, Which is larger, the total annual production of energy by d. Farm Best low-fat milk all the commercial and industrial plants on earth or the total carbohydrate 11 g annual production of energy by all the people on earth, protein 8 g through the combination of exercise and basal metabolism. fat 5 g 'I'he Question at the end of Section 8.9 may be useful here. e. Breyers mint chocolate chip ice cream carbohydrate 17 g protein 3 g Think, Speculate, Reflect, and Ponder fat 9 g f Planter's Sweet-N-Crunchy peanuts carbohydrate 15 g protein 4 g fat 8 g g. Charles Chips potato chips 34. You have an electric hot plate that transfers heat di- carbohydrate 15 g rectly to whatever is on it with negligible losses. How could protein 1 g you determine the wattage rating of the hot plate experi- fat 10 g mentally? 33. A person who is ill with a fever is releasing energy more rapidly than normal. This energy raises the body temperature, which we detect as the fever. Which one of the three energy-expending processes increases as a result of the illness? 35. It takes energy to accelerate a car from zero to 50 miles 22. How long would it take a 70-kg person to burn up the en- an hour. Through the Law of Conservation of Energy we know ergy provided by one standard serving of each of the foods that the kinetic energy of the car traveling at 50 miles an hour (a-g) in Exercise 21 through the operation of basal metabo- has to come from the transformation of some other form of lism alone? energy into the car's kinetic energy. Where does the car's en- 23. How long would it take this same 70-kg person to burn ergy come from? It also takes energy to bring a car traveling up the energy provided by one standard serving of each of the at 50 miles an hour to a complete stop. The kinetic energy of foods (a-g), in Exercise 21 through the energy expenditure of the car has to be transformed into some other form of energy. 5 Cal per minute during a moderate exercise such as brisk Into what kind of energy is the car's kinetic energy transformed walking? as it slows to a stop? Web Questions • 199 36. Table 8.3 shows that a fried egg provides 110 Cal, while a each step you would take in the conversion of the C-11 into su- boiled egg gives us 77 Cal. Since eggs are often fried in butter, crose containing this isotope. margarine, or vegetable oil, what do you suppose is the source 43. Suggest some benefits that might come from a gradual of the additional calories in the fried egg? What do you think warming of the earth's surface through the greenhouse effect. would be the calorie content of an egg fried without the use of de we butter, margarine, or oil (in a nonstick frying pan)? 37. Describe a device or a process by which the following `~eb Questions transformations occur: Use the Web to answer or accomplish each of the following. a. chemical energy is transformed into electrical energy Report your Web source for each response. b. chemical energy is transformed into heat 1. In addition to the calorie and the joule, another unit of heat c. chemical energy is transformed into kinetic energy or energy in widespread use, especially outside the sciences, is the british thermal unit or btu. Write a brief description of the d. electrical energy is transformed into chemical energy btu, including its definition, its origin, and the areas in which e. electrical energy is transformed into heat it is principally used. f. electrical energy is transformed into kinetic energy 2. Describe how a person's basal metabolism is measured in g. kinetic energy is transformed into electrical energy a medical setting. h. kinetic energy is transformed into heat 3. Summarize briefly federal regulations for the listing of 38. Francis Bacon and Count Rumford used the scientific macronutrients and their associated Calories on the labels of method in the investigations described in this chapter. State packages of processed foods. the question each asked and describe the experiment each de- 4• What is the estimated mass, in kilograms, of the earth's en-vised to answer the question, the results each obtained (or tire biomass? ; would have obtained, had Bacon lived), and the conclusions 5. What is the estimated mass, in kilograms, of all the carbon drawn. dioxide currently present in the earth's atmosphere? 39. Using commonly available materials, how would you : demonstrate that (a) work produces heat and (b) heat can be ; used to do work? 6. What is the temperature of the moon's surface when it is lit by the sun, during the lunar day? What is the temperature when the surface is dark, during the lunar night? How do these temperatures differ from comparable temperatures on earth? What is the source or cause of this difference between the moon's surface temperatures and the earth's? = 40. Planting 100 million trees has been suggested as a means for decreasing the greenhouse effect of our atmosphere. Describe the reasoning behind this proposal. 41. What would have been the fate of the carbon of plank- 7• Describe additional evidence for the greenhouse effect, be- ton if the plankton had been completely metabolized by other yond the phenomena discussed in Section 8.15. organisms instead of being trapped, only partially decomposed, 8. Describe any current arguments or evidence that the green- at the bottom of bodies of water and eventually converted into house effect is not real, or that the burning of fossil fuels is not fossil fuels? a significant contributor to the greenhouse effect. 42. If you wanted to use sucrose containing C-11 in a PET 9. Describe the current status of each of the proposals, listed ` investigation (Sec. 5.9), how might you obtain a quantity? As- in the Perspective, for achieving a balance of energy produc- sume that you have a supply of C-11 on hand and describe tion and climate stability. Exercises • 225 ฐ molecule of contaminant per 79 x 1023 molecules of water the water an offensive taste, odor, or appearance, but we (Fig. 9.6), our language provides no terms of reference equiv- cannot realistically expect the total and complete absence alentto parts per million, parts per billion, orthe like. Would of anything but molecules of H20 in our drinking water. we realistically call the water "polluted"? Surely not. When we consider the arithmetic of pollution we can Nor would we consider a glass of water to be polluted better understand the questions of the opening demon- if it contained two, three, or ten molecules of another sub- stration. What must be asked is not "Is there any contami- stance. Yet at some higher level, some threshold concen- nant in our drinking water?" but rather "What are the limits tration, we would just as surely call the water polluted and of contamination we can reasonably accept?" Understand- `'~ unfit to drink. We do, indeed, expect the concentrations of ing the answer to this more critical question requires an un- any contaminants in our drinking water to remain well below derstanding of how we count chemical particles and what ~ the levels at which they might be hazardous or might give their concentration terms mean. •  ~`~ For Review 4. (a) What is the danger in heating a closed room by burn- 1. Following are a statement containing a number of blanks, ing charcoal briquettes in a grill, placed in the room? (b) Why ~ and a list of words and phrases. The number of words equals isn't this a hazard when the grill is used outdoors? the number of blanks within the statement, and all but two of 5• Is it necessary to know the numerical value of Avogadro's num- the words fit correctly in these blanks. Fill in the blanks of the ber to carry out calculations using quantities of moles? Explain. ratement with those words that do fit, then complete the state- 6. Write the balanced reaction for the combustion of methane :ent by filling in the two remaining blanks with correct words to produce carbon dioxide and water. aot in the list) in place of the two words that don't fit. 7. Why are concentrations expressed in molarity particularly Y One of a substance is equal to its atomic or mo- useful to chemists? lecular weight expressed in and contains g. What unit of concentration is used most frequently in con- 6.02 x lOZ3 chemical particles, which is also known as sumer products? of particles. Since 1 mole of any chemical substance g, What unit of concentration is equivalent to 1 milligram of contains the same number of as 1 mole of any solute per kilogram of solution? - other chemical substance, we can calculate the weight of one chemical that will react completely with a given weight of an- 1 W Name a unit of concentration useful in discussions of ex- other by using their in our calculations. We can tremely small concentrations, as in pollution studies.   also use of solutions rather than weights in these 11 • Describe three processes that remove freshly fallen rain calculations as long as we know the of the so- water from the ground. lution, which is a measure of the amount of dissolved in a specific volume of the .A solution A Little Arithmetic and Other that contains 1 mole of solute per of solu- Quantitative Puzzles tion has a concentration of 1 . 12. How many (a) left shoes are there in 15 pairs of shoes? atomic or molecular weights mole (b) dozen yolks would you get from half a dozen eggs? (c) moles Avogadro's number ppm of sodium cations are there in half a mole of sodium chloride? concentration solute 13. How many moles of hydrogen atoms does it take to pro- grams solution duce 1 mole of diatomic hydrogen molecules? kilogram vofumes 14. What is the weight of: liter a. 1 mole of neon 2. Explain, define, or describe the significance of each of the b. 2 moles of zinc following: . c. 1 mole of diatomic nitrogen a. agricultural runoff d. 3 moles of diatomic hydrogen gas b. groundwater e. 1/2 mole of chloride ions c. ppm ^ 1 mole of chlorine atoms d. The Safe Drinking Water Act of 1974 g. 1 mole of diatomic chlorine molecules 4 e. weight/weight percentage (w/w %) concentration h. 2 moles of neutrons 3. Write the chemical equation for the reaction that occurs 15. What weight of (a) sodium contains 1 mole of sodium as charcoal burns (a) in the open air; (b) in an enclosed space, atoms? (b) chlorine atoms contains 1 mole of chlorine atoms? with a limited supply of air. (c) sodium chloride contains 1 mole of sodium ions? (d) sodium 226 • Chapter 9 Arithmetic of Chemistry 9.8 Molarities of Common Solutions: Vinegar, Hydrogen Peroxide, and Sweet Coffee • 217 As far as the language of chemistry is concerned, water is the solute in rubbing al-cohol since water is the minor component of the mixture. Isopropyl alcohol is the solvent in this case. In chemical usage the only difference between "solute" and "solvent" lies in the relative proportions of the two. Figure 9.8 shows the percentage compositions (by weight) of vinegar, com-mercial hydrogen peroxide, and rubbing alcohol. A typical 8-fluid-ounce cup of coffee weighs about 240 g, while a teaspoon of sugar • QUEST1ON weighs about 5 g. What is the weight-percentage concentration of sugar in the cof- fee when you sweeten a typical cup of coffee with two teaspoons of sugar? (Don't forget to add the weight of the added sugar to the total weight of the solution.) 9.8 Molarities of Common Solutions: Vinegar, Hydrogen Peroxide, and Sweet Coffee To get a sense of the range of molarities of some common solutions, we'11 calcu-late the molarities of • acetic acid in vinegar, • hydrogen peroxide in the commercial solution we might find in a drugstore, and • the sucrose in a cup of sweet coffee. To simplify all our calculations, we'll assume that each of these has a density of exactly 1 (Sec. 13.1). That is, we'll assume that 1 liter of each has a mass of exact-ly 1000 grams. While this isn't quite true, it's close enough for a calculation of ap-proximate molarities. Since these are only very rough calculations, we'll find the molarities to only one significant figure (Appendix D). For vinegar, we'll also assume that all of the acidity of vinegar is due to acetic acid, which has the molecular formula CZH402, and that the acetic acid is present 1, as a 5% (w/w) solution: 5 g of acetic acid per 100 g of vinegar. E X A M PLE With the assumptions made above, what is the molarity of acetic acid in vinegar? Acetic Acid in Vinegar  ~ The molecular weight of acetic acid is C: 2 x 12.O1 amn = 24.02 amu H: 4 x 1.008 amu = 4.032 amu O: 2 x 16.00 amu = 32.00 amu 60.05 amu, which we round off to 60 amu ~t a concentration of 5% (w/w) and with the assumptions we've made, there are ` > g of acetic acid per 1(~ g of vinegar. Starting with this eoneentration we get S g C2H40~ 1 mol C2H402 1000 g vinegar x x 100 g vinegar 60 g C,H402 liter vinegar   c~ncentration nf ~c~ti~ arid in vinegar ia 0.8 M. f... ~.w~~ ;.~ .. , , , , . ~„,~ , 218 • Chapter 9 Arithmetic of Chemistry E X A M P L E Now for the hydrogen peroxide, HZO2, Drugstore Hydrogen Peroxide • The molecular weight of H202 is: H: 2 x 1.008 amu = 2:016 amu O: 2 x -16.00 amu = 32.00 amu 34:02 amu, whieh we'll round off to 34 amu At a concentration of 3% (w/w) and with the assumptions we've made, there are 3 g of hydrogen peroxide per i00 g of the commercial solution. Starting with this concentration, we get  3 g H2O2 1 mol H202 1000 g solution 100 g solution x 34 g H202 x liter solution 0.9 moles H2O2 - = 0.9 M ^ liter hydrogen peroxide solution  The concentration of hvdrogen peroxide in the commercial solution is 0.9 ~'hl. • Q U E S T I O N Which represents the greatest number of molecules of solute per liter of solutior (a) the acetic acid in vinegar, (b) the hydrogen peroxide in the commercial solutior or (c) the sucrose in the coffee of the preceding example? Commercially bottled water. of us at their typical levels in natural and in commercially bottled drinking water, and at even higher levels as well. Some of us, for example, take mineral supplements that provide calcium, iron, or magnesium at levels far higher than those found in drinking water. There are hazards, though. A few of the chemicals that can enter our water sup-plies are particularly toxic even at what may seem to be very low concentrations. Contamination by these substances comes as rainwater picks up residues of agricultural fertilizers and pesticides (known as agricultural runoff) and from industrial, urban, and household wastes dumped onto the surface or injected just below it. Any of these can be carried by the natural flow of rainwater into groundwater. To ensure the safety and high quality of public drinking water, the U.S. Congress passed the Safe Drinking Water Act of 1974, which establishes, among other things, maximum drinking water levels for specific, potentially hazardous chemical con taminants. Some of the minerals controlled by the Act appear in Table 9.2, while rep-resentative organic compounds appear in Table 9.3. When present in concentrations Table 9.3 Maximum Contamination Levels of Organic Compounds in Community Water Systems Permitted by the Safe Drinking Water Act of 1974 Maximum Permitted Level Compound and Use (mg/liter) Endrin (an insecticide no longer 0.0002 manufactured or used in the United States) Lindane (an insecticide) 0.004 Methoxychlor (an insecticide) 0.1 2,4-D (an herbicide) 0.1 Silvex (an herbicide) 0.01 Trihalomethanes (solvents and other uses): 0.10 bromodichloromethane dibromochloromethane bromoform chloroform 9.8 Molarities of Common Solutions: Vinegar, Hydrogen Peroxide, and Sweet Coffee • 217 As far as the language of chemistry is concerned, water is the solute in rubbing alcohol since water is the minor component of the mixture. Isopropyl alcohol is the solvent in this case. In chemical usage the only difference between "solute" and "solvent" lies in the relative proportions of the two. Figure 9.8 shows the percentage compositions (by weight) of vinegar, com-mercial hydrogen peroxide, and rubbing alcohol. A typical 8-fluid-ounce cup of coffee weighs about 240 g, while a teaspoon of sugar QUESTION weighs about 5 g. What is the weight-percentage concentration of sugar in the cof- fee when you sweeten a typical cup of coffee with two teaspoons of sugar? Don't forget to add the weight of the added sugar to the total weight of the solution. 9.8 Molarities of Common Solutions: Vinegar, Hydrogen Peroxide, and Sweet Coffee To get a sense of the range of molarities of some common solutions, we'11 calcu-late the molarities of • acetic acid in vinegar, • hydrogen peroxide in the commercial solution we might find in a drugstore, and • the sucrose in a cup of sweet coffee. To simplify all our calculations, we'll assume that each of these has a density of ` exactly 1 (Sec. 13.1). That is, we'll assume that 1 liter of each has a mass of exact-ly 1000 grams. While this isn't quite true, it's close enough for a calculation of ap-proximate molarities. Since these are only very rough calculations, we'll find the molarities to only one significant figure (Appendix D). For vinegar, we'll also assume that all of the acidity of vinegar is due to acetic acid, which has the molecular formula C2H402, and that the acetic acid is present 1, as a 5% (w/w) solution: 5 g of acetic acid per 100 g of vinegar. E X A M P 1-. E  With the assumptions made above, what is the molarity of acetic acid in vinegar? Acetic Acid in Vinegar ~ The molecular weight of acetic acid is C: 2 x 12.O1 amn = 24.02 amu H: 4 x 1.008 amu = 4.032 amu O: 2 x 16.00 amu = 32.00 amu 60.05 amu, which we round off to 60 amu ~t a concentration of 5% (w/w) and with the assumptions we've made, there are ` > g of acetic acid per 1(~ g of vinegar. Starting with this eoneentration we get S g C2H40~ 1 mol C2H402 1000 g vinegar x x 100 g vinegar 60 g C,H402 liter vinegar   c~ncentration nf ~c~ti~ arid in vinegar ia 0.8 M. f... ~.w~~ ;.~ .. , , , , . ~„,~ , 218 • Chapter 9 Arithmetic of Chemistry E X A M P L E Now for the hydrogen peroxide, HZO2, Drugstore Hydrogen Peroxide • The molecular weight of H202 is: H: 2 x 1.008 amu = 2:016 amu O: 2 x -16.00 amu = 32.00 amu 34:02 amu, whieh we'll round off to 34 amu  At a concentration of 3% (w/w) and with the assumptions we've made, there are 3 g of hydrogen peroxide per i00 g of the commercial solution. Starting with this concentration, we get  3 g HZOZ 1 mol H202 1000 g solution 100 g solution x 34 g H202 x liter solution 0.9 moles HZO2 - = 0.9 M ^ liter hydrogen peroxide solution  The concentration of hvdrogen peroxide in the commercial solution is 0.9 ~'hl. E X A M P L E Using the information given in the question at the end of Section 9.7, a ma Sweet Coffee molecular formula of CIZH,ZOll for sucrose (table sugar), and units conversian data taken from Appendix B, we can calculate the approximate molarity of the sugar in the cup of eoffee.  • For the molecular weight of the sucrose we-have C: 12 x 12.01 amu = 144.12 amu H: 22 x 1.008 amu = 22.176 amu O: 11 x 26.00 amu = 176.00 amu 342.29b amu, which we'll round off to 342 amu Recalling that we use two teaspoons of sugar, at 5,g eaeh, we get 10 g sucrose 1 mol sucrose 1000 g coffee _ 250 g coffee x 342 g sucrose x liter of coffee 0~1 M Two teaspoons of table sugar in an 8-oz cup of coffee produces coffee that's about 0.1 M in sucrose. • Q U E S T I O N  Which represents the greatest number of molecules of solute per liter of solution (a) the acetic acid in vinegar, (b) the hydrogen peroxide in the commercial solutior or (c) the sucrose in the coffee of the preceding example? 9.9 You're 167 in a Trillion: Expressing Exceedingly Small Concentrations Even though molarity is a useful concentration term for chemists, and per ages are informative for many consumer products, the very small concentt-of the pollutants that affect our environment require a different approac' 9.9 You're 167 in a Trillion: Expressing Exceedingly Small Concentrations • 219 It's useful to express exceedingly small concentrations, such as those of food contaminants and environmental pollutants, in terms of parts per thousand, parts per million, parts per billion, and so on. These terms are closely related to the per centages we've already examined. The term percent literally means "per hundred." A one percent solution contains one unit of solute in each 100 units of solution, whatever the units happen to be. We can also speak of concentrations in terms of parts per thousand, which are the same as tenths of a percent. The coffee in the question at the end of Section 9.7, for example, contains 10 g of sugar in 250 g of the entire mixture. That amounts to 4%, or 4 parts per hundred, which is the same as 40 parts per thousand. One part per million (one ppm) represents a particularly convenient concen-tration unit since it's the concentration of one milligram of one substance distrib-uted throughout one kilogram of another. A concentration of 1 ppm, then, is the same as a concentration of one milligram per kilogram,l mg/kg. One milligram is a thousandth part of a gram and a gram is a thousandth part of a kilogram. One-thousandth of one-thousandth is one-millionth: 1 1 1 X = 1000 1000 1,000,000 one-thousandth one-thousandth one-millionth As an illustration, 35 mg of one substance in every kilogram of another would amount to a concentration of 35 mg/kg, or 35 parts per million, or 35 ppm. Consumer products provide plenty of examples of concentration terms. Labels of canned fruit drinks, for example, often reveal the presence of 0.1 % sodium ben-zoate, the sodium salt of benzoic acid (Sec.10.8), as an added preservative. A tenth of one percent amounts to a concentration of one part per thousand. The concentration of potassium iodide, KI, in iodized table salt is even small-er. Traces of iodide ion in the diet help prevent the enlargement of the thyroid gland, a condition known as goiter. To provide this dietary iodide, KI is added to commercial table salt, NaCl, to the extent of about 7.6 X 10-5 g of KI per gram ~ of NaCI. The following example shows how we can convert this concentration ~into ppm. The concentration term ppm refers to parts per million, or milligrams of solute per kilo-gram or liter of solution. E X A M P t.. E 7.6 X 10-5 g KI = 106 7.6 X 10 g KI 1 g table salt X 106 106 g table salt Translate the cancentration of potassium iodide in table salt into ppm. nd we want to know how many grams of KI there are in 106 g of table salt. The quickest way to get the answer is to multiply both the numeratar and ie denaminator by 10~. ,000, or 106. We knaw that the caneentration of Kl in table 7.6 x 10-5 g KI 1 g table salt Concentrate on Salt   220 • Chapter 9 Arithmetic of Chemistry  • Q U E S T 1 O N Zinc is important to human health. A deficiency of zinc can lead to stunted growth, incomplete development of the sexual organs, and poor healing of wounds. Among foods richest in this element are liver, eggs, and shellfish, which contain zinc at lev els ranging from about 2 to 6 mg per 100 g. Express this range of zinc concentrations in parts per million. (Note that an excess of zinc can be just as bad as a deficiency. Dietary excesses of this element can cause anemia, which is a deficiency of red blood cells, kidney failure, joint pain, and other medical problems. A balanced diet provides most of us with all the zinc we need.) Even the very purest rain contains dissolved carbonic acid, HZC03. Botulinum toxin, the virulent poison of spoiled food, provides us with anoth-er illustration of the importance of even very low concentrations of substances. As we'll see in Section 20.4, botulinum toxin is the most powerful biologically pro- duced toxin known. A dose of as little as 1 x 10-y g of this substance can kill a ` 20-g mouse. At that level the concentration of the poison in the mouse's body amounts to 1 g of toxin per 20 x 109 g of mouse. To state this more directly, we can multiply both the weight of the toxin and the weight of the mouse by 50, which re-veals that the toxin is lethal to the mouse at a concentration of only 50 parts per trillion! For comparison, consider yourself as one individual person among all the people on earth. With the world's total population of about 6 billion humans, you yourself make up roughly one person in 6 billion, or 167 parts per trillion of all of those alive today on our planet. Remarkably, the lethal concentration of botulinum toxin in a mouse's body is even less than your own "concentration" among all those now living. 9.10 The Very Purest Water on Earth The presence of dissolved minerals and organic compounds in the water we drink provides a fine example of the significance of the concentrations of solutes. When we think of pure water we may imagine fresh rainwater falling from a crisp sky or clear water bubbling up from a mountain spring. The very purest water on earth isn't either of these.The very purest of all water comes from a chemist's laboratory. It's water that has passed through columns of specially prepared cleansing resins or water that has been distilled repeatedly under carefully controlled laboratory conditions to remove all traces of contaminants, as demonstrated in the opening demonstration of Chapter 7 All other water, including pristine rainwater and the very purest drinking water, carries a variety of chemical impurities in a range of concentrations. To clarify the nature and origin of these impurities, we'll follow the rain as drops to earth and becomes part of our water supply. As rain falls it absorbs, to vat ing degrees, the gases that make up our atmosphere (Section 14.1). The nitrog( oxygen, and carbon dioxide of air all dissolve to a very small extent in water. No room temperature a maximum of about 0.01 g of nitrogen, 0.05 g of oxygen, a 3.4 g of carbon dioxide can dissolve in 1 liter of water. (The small bubbles that) from heated tap water just before it starts to boil are bubbles of these very sa dissolved gases. Almost all gases are much less soluble in hot water than in c water. They tend to escape from their water solutions as the water warms up.) Part of the carbon dioxide that enters rainwater reacts with the water itsel form carbonic acid (Chapter 10); C02 + H20 ---~ H2C03 carbon dioxide water - - _.:..__carbonic acid 224 • Chapter 9 Arithmetic of Chemistry 9.12 That's the Glass Where Pollution Begins We can return now to the seven glasses of salt water we prepared in our opening demonstration and point directly to the glass where pollution begins. Here's how ,we can identify it. First, since we can expect variations in our sense of taste and our sensitivity to any contaminant, we have to find a reference or a criterion for pollution that's common to all of us. Perhaps the most useful is the legal standard of Table 9.2, 160 ppm sodium. Having chosen 160 ppm as the standard for pollution, we can now apply a little simple arithmetic. Since the mass of a sodium ion is about 23.0 amu and the mass of a chloride ion is about 35.5 amu, the sodium ion makes up about 23.0 amu (23.0 + 35.5) amu or roughly 39% of the mass of any quantity of NaCI. Like the teaspoon of sugar in the question that follows Section 9.7, a teaspoon of table salt has a mass of about 5 g. This means that the sodium in the teaspoon of table salt we added to the first glass has a mass of about 39% of 5 g, or roughly 2 g. Although glasses vary quite a bit in size, we wouldn't be far off if we estimated that the glass holds about 250 mL of water. Estimating that the density of the so-lution is about 1 g per mL, we can conclude that our solution contains about 2 g of sodium in about 250 g of solution. Even though these are rough approxima-tions, we can see now that the concentration of the sodium in the first glass is close to 8 g per kilogram of solution, or since there are 1000 milligrams per gram 8000 ppm. That's real pollution by any standard. In each succeeding glass the concentration of sodium chloride, and of sodium, drops by a factor of 10. The sodium concentration in the second glass, then, is 800 ppm, which is still above the legal limit. For the third glass the sodium con centration is 80 ppm, which is now below the standard for sodium in drinking water. Working our way backward from glass 7, which holds the most dilute solu-tion, we can now point to glass 2 and say "That's the glass where pollution begins." This entire approach illustrates the use of a combination of fundamental chemistry and simple arithmetic to help us work through environmental problems. • Q U E S T I O N Suppose we were off by 50% in any of our estimates. Suppose, for example, that the teaspoon of table salt has a mass of 7.5 g, or the glasses hold only 125 g of water. How would this affect our determination that glass 2 is the glass where pollution begins? The Arithmetic of Pollution Given the variety of sources of water pollution and the vari- cated, we become able to detect contaminants at concent ety of the pollutants themselves, it's unrealistic to expect that tions far below those we could smell or taste or see or that our water can ever be made completely free of every foreign might reasonably expect to be hazardous. We could imagi substance imaginable. Moreover, we'd have to understand for example, a method of detection that would reveal the pr~ what it would mean for water to be completely free of every ence of a single molecule of, say, a pesticide, or a compc- other substance. As our means of chemical detection and of gasoline, or a dry cleaning fluid, or a noxious ind, measurement become increasingly sensitive and sophisti- waste in an 8-oz glass of water. At that concentrati 250 • Chapter 10 Acids and Bases Figure 10.8 Le Chatelier's Principle in operation. 232 • Chapter 10 Acids and Bases material to learn whether it's sour or bitter or rubbing it between your fingers to determine whether it feels slippery is a dangerous activity. Although many of our foods-lemons and vinegar, for example-contain acids and taste distinctly acidic, other substances may be composed of acids (or bases) powerful enough -~_ to destroy skin and mucous membranes and cause great harm. Some substances we may come in contact with are highly poisonous in ways that have nothing to do with acidity or basicity. Even many consumer products are toxic and/or corrosive and can cause much damage if used carelessly or in ways other than those specified by their labels. Never taste or touch any material you aren't sure of. It could be quite dangerous. We'll examine some of our ideas about safe-ty in more detail in Chapter 20. The remaining phenomenon, the reaction of acids with metals like iron and zinc, can also be hazardous. The product is hydrogen gas, which is dangerous in itself because of its flammability. In addition to the characteristics we've just described, another useful proper-Pieces of zinc metal react with ty that distinguishes acids from all other kinds of chemical substances is their abil hydrochloric acid to produce ity to neutralize bases. Similarly, bases can neutralize acids. In this acid-base hydrogen gas. neutralization an acid and a base react chemically with each other to produce a salt, a compound that has no (or much weaker) acidic or basic properties. A salt is a In neutralization an acid and compound (other than water) produced by the reaction of an acid and a base. a base react to produce a sa/t. A particularly simple acid-base neutralization occurs, for example, when hy- A salt is a compound (other drochloric acid (HCl, hydrogen chloride) reacts with sodium hydroxide (NaOH). than water) produced by the Hydrochloric acid, usually available in hardware stores by its commercial name, reaction of an acid with a muriatic acid, is a strong acid useful for cleaning metals, masonry, cement, and stuc base. co. Sodium hydroxide, better known as household lye, is a powerful base often effective in clearing clogged drains. Both sodium hydroxide and hydrochloric acid are dangerous, corrosive chemicals that must be handled with great care. Hydrochloric acid and sodium hydroxide react with each other to form sodium chloride (a salt) and water: HCl + NaOH NaCI + H20 hydrogen and sodium react sodium and water chloride hydroxide to produce chloride, a salt Notice that the hydrogen of the HCl and the OH of the NaOH combine to form water, while a combination of the Cl of the HCl and the Na of the NaOH pro-duces NaCI. This resulting sodium chloride is a salt in two closely related senses. It's not only the common table salt that we use on our food and that began our study of chemistry in Chapter 1, but it's also a salt in the generic sense. That is. sodium chloride is produced, along with water, by the reaction of HCl (an acid) witr NaOH (a base). Sodium chloride is a perfectly neutral salt, neither acidic nor basi~ in any sense at all. Other salts include potassium iodide, KI, which provides the iodide of iodize salt (Sec. 9.9); magnesium sulfate, MgSOq, better known as epsom salts and somy times used as a laxative; monosodium glutamate (MSG), an additive that enhancE or intensifies the flavor of food and is often used in Chinese food; and calciw carbonate, CaC03, common chalk. Acid Base Salt HI + KOH KI + H20 hydrogen potassium potassium iodide hydroxide - iodide 10.8 The Acids of Everyday Life • 245 Benzoic acid consists of a carboxyl group bonded directly to a benzene ring: O 11 C-OH benzoic acid 250 • Chapter 10 Acids and Bases Figure 10.8 Le Chatelier's Principle in operation.  COZ + H20 ~ H2C03 The original equilibrium  As COz is absorbed its concentration tends to grow above its original equilibrium value . . .  ~+ H20 ~ HZC03 -- Carbon dioxide is absorbed, shifting . . . causing the equilibrium to shift so as to the equilibrium to the right decrease the COZ concentration and increase the HZC03 concentration. COZ + Hzo ~= H2C03 New equilibrium, with higher concentration of carbonic acid numerical value of the ratio is held constant. In this case the very large quantity of carbonic acid that is produced puts a stress on the system, which is relieved as carbonic acid decomposes into carbon dioxide and water (Fig. 10.9). Le Chatelier's Principle also describes how your blood's pH is maintained within a narrow range. Blood is slightly basic; its pH, normally 7.4, doesn't vary by more than about one-tenth of a pH unit in a healthy person. In maintaining this narrow range of pH through all the stresses of a normal life, the body uses an acid-base equilibrium, with carbonic acid as the acid and water as the base. (Recall that water is amphoteric; Sec.10.4.):  HZC03 + HZO H30+ + HC03- Figure 10.9 The chemistry of the fizz. NdHC03 + H+ - Na+ + H2C03 Sodium bicarbonate reacts with citric acid producing carbonic acid . . . C02 + H20 ~ H2C03 COZ + H20 . . . which equilibrates with carbon dioxide and water. As the concentration of carbonic acid grows, through continuing reaction of sodium bicarbonate and acid, the equilibrium shifts toward carbon dioxide . . .   . . . which grows in concentration and escapes from the water as bubbles fizz. 232 • Chapter 10 Acids and Bases material to learn whether it's sour or bitter or rubbing it between your fingers to determine whether it feels slippery is a dangerous activity. Although many of our foods-lemons and vinegar, for example-contain acids and taste distinctly acidic, other substances may be composed of acids (or bases) powerful enough - _to destroy skin and mucous membranes and cause great harm. Some sub-stances we may come in contact with are highly poisonous in ways that have nothing to do with acidity or basicity. Even many consumer products are toxic and/or corrosive and can cause much damage if used carelessly or in ways other than those specified by their labels. Never taste or touch any material you aren't sure of. It could be quite dangerous. We'll examine some of our ideas about safe-ty in more detail in Chapter 20. The remaining phenomenon, the reaction of acids with metals like iron and zinc, can also be hazardous. The product is hydrogen gas, which is dangerous in itself because of its flammability. In addition to the characteristics we've just described, another useful proper-Pieces of zinc metal react with ty that distinguishes acids from all other kinds of chemical substances is their abil hydrochloric acid to produce ity to neutralize bases. Similarly, bases can neutralize acids. In this acid-base hydrogen gas. neutralization an acid and a base react chemically with each other to produce a salt, a compound that has no (or much weaker) acidic or basic properties. A salt is a In neutralization an acid and compound (other than water) produced by the reaction of an acid and a base. a base react to produce a salt. A particularly simple acid-base neutralization occurs, for example, when hy- A salt is a compound (other drochloric acid (HCl, hydrogen chloride) reacts with sodium hydroxide (NaOH). than water) produced by the Hydrochloric acid, usually available in hardware stores by its commercial name, reaction of an acid with a muriatic acid, is a strong acid useful for cleaning metals, masonry, cement, and stuc base. co. Sodium hydroxide, better known as household lye, is a powerful base often effective in clearing clogged drains. Both sodium hydroxide and hydrochloric acid are dangerous, corrosive chemicals that must be handled with great care. Hydrochloric acid and sodium hydroxide react with each other to form sodium chloride (a salt) and water: HCl + NaOH NaCI + H20 hydrogen and sodium react sodium and water chloride hydroxide to produce chloride, a salt Notice that the hydrogen of the HCl and the OH of the NaOH combine to form water, while a combination of the CI of the HCl and the Na of the NaOH pro-duces NaCI. This resulting sodium chloride is a salt in two closely related senses. It's not only the common table salt that we use on our food and that began our study of chemistry in Chapter 1, but it's also a salt in the generic sense. That is, sodium chloride is produced, along with water, by the reaction of HCl (an acid) witr NaOH (a base). Sodium chloride is a perfectly neutral salt, neither acidic nor basi( in any sense at all. Other salts include potassium iodide, KI, which provides the iodide of iodize salt (Sec. 9.9); magnesium sulfate, MgSOq, better known as epsom salts and somy times used as a laxative; monosodium glutamate (MSG), an additive that enhancE or intensifies the flavor of food and is often used in Chinese food; and calciw carbonate, CaC03, common chalk. Acid Base Salt HI + KOH KI + H20 hydrogen potassium potassium iodide hydroxide - iodide 10.8 The Acids of Everyday Life • 245 Benzoic acid consists of a carboxyl group bonded directly to a benzene ring: O C-OH benzoic acid To consumers, benzoic acid is less important in itself than as its sodium salt, sodium benzoate (also known as benzoate of soda). This salt is used as a preservative in canned and bottled fruit drinks and also in baked goods. Lactic acid is the acid that gives sour milk its sharp taste. Bacterial fermenta-tion of lactose, the principal sugar of milk, produces the acid: O bacterial fermentation II lactose (milk sugar) CH3-CH-C-OH OH lactic acid, the acid of sour milk Lactic acid is also important to us in another, more immediate way: in our own bod-ies. As we've seen in Chapter 8, our biological energy comes from chemical oxidation of the foods we eat. We've seen that we obtain energy from our nutrients by oxidiz-ing them to carbon dioxide and water, much as a car's engine derives energy from the hydrocarbons of gasoline. But our bodies are far more complex than the internal ~ombustion engine. Converting the chemicals of our foods to carbon dioxide and water requires an enormous variety of steps involving a huge assortment of inter- ;ediate compounds. For example, as we metabolize glucose (a sugar) through muscular activity, lactic acid is generated in our muscle tissue and is then decomposed .nto C02 and H20. With heavy exercise, our metabolic chemistry forms lactic acid more rapidly than it decomposes. It's this transient accumulation of lactic acid that ~ causes an aching, tired sensation in our muscles when we use them vigorously. As our t body disposes of the accumulated lactic acid, the discomfort disappears and we sense a recovery from the muscular ache and fatigue. Figure 10.7 summarizes the occurrences of some representative carboxylic ? acids. Figure 10.7 Common acids include the citric acid of limes, lemons, oranges, grapefruit, and citrus juices, the propionic acid of Swiss cheese, and the oxalic acid of rhubarb. 246 • Chapter 10 Acids and Bases In terms of commercial production, sulfuric acid (HZS04) is by far our lead-ing industrial chemical. In raw tonnage produced, about 44 million tons in the United States in 2000, it swamps any of its rivals. Most of it ends up as a reactant or a catalyst (Sec. 7.7) in the manufacture of various consumer products, including pharmaceuticals, plastics, synthetic fibers, and synthetic detergents. More calcium oxide (CaO, or lime; roughly 22 million tons in 2000) is produced than any other base. Much of it goes into the production of building materials, the generation of still other industrial chemicals, and water and sewage treatment. Q U E S T I O N Name or identify each of the following carboxylic acids: (a) gives rancid butter its foul odor; (b) toxic, it is found in small concentrations in raw spinach and rhubarb; (c) forms in our muscles as the result of metabolic activity; (d) produces the flavor of Swiss cheese; (e) used as its sodium salt to preserve canned and bottled fruit drinks; (f) responsible for the taste of sour milk; (g) produces the acidity of citrus fruit; (h) generates the sting of red ant bites; (i) the major organic acid of vinegar. 10.9 Antacids: Bases That Fight Cannibalism Carbon dioxide is released when an Alka-Seltzer tablet is dropped into water. As the sodium bicarbonate and citric acid of the tablet react in water, they form carbonic acid. With increasing concentration the carbonic acid decomposes to carbon dioxide and water. Although an acidic stomach is necessary for good health, excessive stomach acid-ity can produce the discomforts commonly called "acid indigestion" and "heart-burn" as well as contribute to the pain of gastric ulcers. Like much of our food, our body tissues and organs, including the walls of the stomach itself, are made of pro-tein. The enzymes of the stomach fluids that help digest protein can't discriminate between the protein of food and the protein of the stomach walls. They would di-gest the stomach itself as easily as a steak if it weren't for special protective devices such as an alkaline mucous lining that resists the action of the stomach's acid an its enzymes. This barrier keeps the stomach from being eaten away by its ov juices. Sometimes, though, things get out of hand. When the body's defenses faii. a combination of stomach acid and pepsin (perhaps accompanied by certain bac-teria) can attack the stomach wall in an act of chemical cannibalism. The result is a gastric ulcer. Relief from the discomforts of excess stomach acid, which can include the pain of ulcers, can often be obtained from antacids such as Alka-Seltzer, Milk of Magnesia, Rolaids, Titralac, and Turns, or simply some baking soda in water. Each year Americans buy a quarter of a billion dollars worth of these and other antacid products simply for the relief of pain brought on by maverick hydronium ions of the stomach. (Baking soda is the commercial term for sodium hydrogen carbonate, NaHC03, which is also known by an older name, sodium bicarbonate. The anion HC03- can be called the hydrogen carbonate or the bicarbonate ion. For simplicity, and to be consistent with the term most often used commercially, we'll use the older bicarbonate here.) The antacid's function isn't to bring the stomach fluids to a complete acid-base neutrality of pH 7. Such an action would shut down digestion completely and could shock the walls into flooding the stomach with fresh acid in what's called "acid re bound." Instead, a good antacid neutralizes enough of the HCI in the gastric juices to alleviate the pain and discomfort yet allows normal stomach action to proceed. Even if as much as 90% of the stomacVs HCl were to be neutralized, the pH would still be a healthy 2.3. The bases most widely used in antacids, providing an inexpensive combination of safety, effectiveness, and efficiency, include: 246 • Chapter 10 Acids and Bases In terms of commercial production, sulfuric acid (H2S04) is by far our lead-ing industrial chemical. In raw tonnage produced, about 44 million tons in the United States in 2000, it swamps any of its rivals. Most of it ends up as a reactant or a catalyst (Sec. 7.7) in the manufacture of various consumer products, including pharmaceuticals, plastics, synthetic fibers, and synthetic detergents. More calcium oxide (CaO, or lime; roughly 22 million tons in 2000) is produced than any other base. Much of it goes into the production of building materials, the generation of still other industrial chemicals, and water and sewage treatment. Q U E S T I O N Name or identify each of the following carboxylic acids: (a) gives rancid butter its foul odor; (b) toxic, it is found in small concentrations in raw spinach and rhubarb; (c) forms in our muscles as the result of metabolic activity; (d) produces the flavor of Swiss cheese; (e) used as its sodium salt to preserve canned and bottled fruit drinks; (f) responsible for the taste of sour milk; (g) produces the acidity of citrus fruit; (h) generates the sting of red ant bites; (i) the major organic acid of vinegar. Aluminum hydroxide, Al(OH)3 Magnesium hydroxide, Mg(OH)Z Calcium carbonate, CaC03 Sodium bicarbonate, NaHC03 Magnesium carbonate, MgC03 Potassium bicarbonate, KHC03 Magnesium oxide, MgO, is also used as an antacid ingredient since it reacts with water to form magnesium hydroxide: Mg0 + H20 -> Mg(OH)2 Table 10.5 Common Antiacids Principal Active Representative Ingredient Antiacid Neutralization Reaction  Sodium bicarbonate Alka-Seltzer NaHC03 + HCl -~ NaCI + H2C03 1 Potassium bicarbonate (HZC03 --j HZO + COZ) Magnesium hydroxide Phillips' Milk Mg(OH)2 + 2HC1 -~ MgCIZ + 2H20 of Magnesia Dihydroxyaluminum Rolaids Al(OH)ZNaC03 + 4HC1 -~ A1C13 + sodium carbonate NaCI + 2 H20 + HZC03 Calcium carbonate Titralac CaC03 + 2HC1 ~ CaC12 + HZC03 Tums Aluminum hydroxide Di-Gel Magnesium carbonate Magnesium hydroxide Al(OH)3 + 3 HCl ~ A1C13 + 3 H20 MgC03 + 2 HCl -~ MgC12 + HZC03 Mg(OH)Z + 2HC1 ~ MgC12 + 2H20 248 • Chapter 10 Acids and Bases • QUESTION Some commercial antacids claim only to neutralize "excess" stomach acidity. Why is it undesirable to neutralize completely all stomach acidity? What would result from bringing the pH of stomach fluids all the way up to 7? 10.10 Red Cabbage, Antacid Fizz, and Le Chatelier's Principle We're now in a position to understand why the cabbage breath test works and how the color change of the cabbage extract is connected to the fizz that an Alka-Seltzer tablet produces. In addition we'll also see how breathing helps maintain a stable pH for your blood. In the opening demonstration, the ammonia that's added to the deep blue so-lution of cabbage extract makes the solution slightly basic and turns the color of the indicator solution to an emerald green. As someone blows into the basic test solution of the opening demonstration, the carbon dioxide of the exhaled breath dissolves in the water to form carbonic acid, which immediately reacts with the dissolved ammonia, neutralizing it. Formation of carbonic acid as carbon dioxide dissolves in water: O 11 COZ + H20 ' HO-C-011 carbon carbonic dioxide acid Neutralization of ammonia by carbonic acid to form a salt, ammonium carbonate 11 11 HO-C-OH + 2NH3 - NH4+-O-C-O-+NH4 carbonic ammonium carbonate acid Then, after all the ammonia has been converted to ammonium carbonate, the excess carbonic acid ionizes and produces hydronium cations and bicarbonate anions, and the indicator turns to a light blue color as the test solution becomes slightly acidic. Ionization of excess carbonic acid, with water acting as a base as it accepts the proton released by the carbonic acid and forms the hydronium ion:  II II HO-C-OH + H20 H30+ + -O-C-OH carbonic hydronium bicarbonate acid ion anion Adding the vinegar at the end of the demonstration introduces acetic acid into the solution. The acetic acid is a much stronger acid than carbonic acid; it makes the test solution far more acidic than the carbon dioxide of breath does. With the marked increase in acidity, the indicator turns a vivid pink or red. Ionization of acetic acid to form a hydronium ion and an acetate anion:  11 11 CH3-C-OH + H20 CH3-C-O- + H30+  acetic acid anion acetate 11.10 Why Batteries Work • 269 Again in the opening demonstration we saw that adding a chlorine bleaeh to the nearly colorless solution causes the color of the iodine to return. To see why-and knowing that the oxidizing agent in the bleach is C10-, as we saw in the discussion of the opening demonstration-we'll now ask: Will the C10-oxidize the iodide ion to molecular iodine and therefore restore the color? For the oxidation of iodide ion to molecular iodine, the oxidation half-ce11 is: oxidation: 2I- ' I2 + 2e (-0.54 volt) With C10- as the oxidizing agent, the reduction half-cell is:  reduction: C10- + Hz0 + 2e- ~ Cl- + 2 OH- (+0.84 volxj Thus the redox reaction is: redox: 2I- + C10- + FIzO ~ IZ + Cl- + 20H- (+(1.30volt)  With a positive redox potential, the C10- of the bleach oxidizes the iodide ion spontaneously; regenerating the IZ as the deep color oI the molecular io-dine returns.   Now for another question. Why don't the sodium cations and the chloride anions of table salt react with eaeh other to form sodium metal and chlorine gas? In this case, we're asking why the following redax reaction doesn't occur spontaneously in a salt-shaker: 2hTa+ + 2C1- ~ 2Na~ + ClZ Once again we add an oxidation potential and a reduction potential to get a redox potential. (Notice that although it's necessary to double all the chemi-cal species in the reduction reaction so that the number of electrons matches the number used in the oxidation, the reduction voltage remains unchanged.) oxidation: reduction: 2 Cl- ~~ C12 + 2e (-1:36 volts) E X A IYi I' L E The Color Returns  Stable Salt  2Na+ + 2e ---~ 2NaQ (-2.71 voltsj 2 Na} + 2 Cl- ~ 2 :  -+~ Cl~ (-4.07 voltsj''  re negative redox potential explains why the sodium cations and the chlo-~; anions don't react with each other spontaneously. And it's a good thing .y don't. If they did, all the table salt in our kitchens and restaurants wauld '~hurning away right now, with sodium cations and chloride anions inter-ing with each other, producing very dangerous sodium metal and poison-gas (Sec 3.2).  n Section 10.2 we saw that acids liberate hydrogen gas when in contact with certain metals, such as iron and zinc. Using the data ofTable 11.1, show that the reactions of iron and zinc with an acid spontaneously generate hydrogen gas by redox reac- - tions. Identify three other metals that will spontaneously liberate hydrogen gas from an acid. Identify three metals that will not. CO2 + H20 ~ H2C03 The original equilibrium As CO2 is absorbed its concentration tends to grow above its original equilibrium value . . . ~+ H20 ~ H2C03 -- Carbon dioxide is absorbed, shifting . . . causing the equilibrium to shift so as to the equilibrium to the right decrease the COZ concentration and increase the HZC03 concentration. CO2 + H2o ~= H2C03 New equilibrium, with higher concentration of carbonic acid numerical value of the ratio is held constant. In this case the very large quantity of carbonic acid that is produced puts a stress on the system, which is relieved as carbonic acid decomposes into carbon dioxide and water (Fig. 10.9). Le Chatelier's Principle also describes how your blood's pH is maintained within a narrow range. Blood is slightly basic; its pH, normally 7.4, doesn't vary by more than about one-tenth of a pH unit in a healthy person. In maintaining this narrow range of pH through all the stresses of a normal life, the body uses an acid-base equilibrium, with carbonic acid as the acid and water as the base. Recall that water is amphoteric; Sec.10.4. HZC03 + HZO H30+ + HC03- Figure 10.9 The chemistry of the fizz. NdHC03 + H+ - Na+ + H2C03 Sodium bicarbonate reacts with citric acid producing carbonic acid . . . C02 + H20 ~ H2C03 COZ + H20 . . . which equilibrates with carbon dioxide and water. As the concentration of carbonic acid grows, through continuing reaction of sodium bicarbonate and acid, the equilibrium shifts toward carbon dioxide .  . . . which grows in concentration and escapes from the water as bubbles fizz. Table 9.1 Concentration of Several Minerals in Natural Spring Water of the French Alps  Mineral Concentration, mg/liter (ppm) Calcium 78 Magnesium 24 Sodium ~ ~ . 5 Potassium 1 222 • Chapter 9 Arithmetic of Chemistry Table 9.2 Maximum Contamination Levels of Minerals in Community Water Systems Permitted by the Safe Drinking Water Act of 1974 Maximum Permitted Level, Contaminant mg/liter (ppm) Arsenic .OS Barium 1 Cadmium 0.010 Chromium 0.05 Lead 0.05 Mercury 0.002 Selenium 0.01 Silver 0.05 Sodium 160 Commercially bottled water. of us at their typical levels in natural and in commercially bottled drinking water, and at even higher levels as well. Some of us, for example, take mineral supplements that provide calcium, iron, or magnesium at levels far higher than those found in drinking water. There are hazards, though. A few of the chemicals that can enter our water sup-plies are particularly toxic even at what may seem to be very low concentrations. Contamination by these substances comes as rainwater picks up residues of agri cultural fertilizers and pesticides (known as agricultural runoff) and from indus-trial, urban, and household wastes dumped onto the surface or injected just below it. Any of these can be carried by the natural flow of rainwater into groundwater. To ensure the safety and high quality of public drinking water, the U.S. Congress passed the Safe Drinking Water Act of 1974, which establishes, among other things, maximum drinking water levels for specific, potentially hazardous chemical con taminants. Some of the minerals controlled by the Act appear in Table 9.2, while rep-resentative organic compounds appear in Table 9.3. When present in concentrations Table 9.3 Maximum Contamination Levels of Organic Compounds in Community Water Systems Permitted by the Safe Drinking Water Act of 1974 Maximum Permitted Level Compound and Use (mg/liter) Endrin (an insecticide no longer 0.0002 manufactured or used in the United States) Lindane (an insecticide) 0.004 Methoxychlor (an insecticide) 0.1 2,4-D (an herbicide) 0.1 At a concentration of 3% (w/w) and with the assumptions we've made, there are 3 g of hydrogen peroxide per i00 g of the commercial solution. Starting with this concentration, we get  3 g HZOZ 1 mol H202 1000 g solution 100 g solution x 34 g H202 x liter solution 0.9 moles HZO2 - = 0.9 M ^ liter hydrogen peroxide solution  The concentration of hvdrogen peroxide in the commercial solution is 0.9 ~'hl. E X A M P L E Using the information given in the question at the end of Section 9.7, a ma Sweet Coffee lecular formula of CIZH,ZOll for sucrose (table sugar), and units conversian data taken from Appendix B, we can calculate the approximate molarity of the sugar in the cup of eoffee.  • For the molecular weight of the sucrose we-have C: 12 x 12.01 amu = 144.12 amu H: 22 x 1.008 amu = 22.176 amu O: 11 x 26.00 amu = 176.00 amu 342.29b amu, which we'll round off to 342 amu Recalling that we use two teaspoons of sugar, at 5,g eaeh, we get 10 g sucrose 1 mol sucrose 1000 g coffee _ 250 g coffee x 342 g sucrose x liter of coffee 0~1 M Two teaspoons of table sugar in an 8-oz cup of coffee produces coffee that's about 0.1 M in sucrose. • Q U E S T I O N  Which represents the greatest number of molecules of solute per liter of solutior (a) the acetic acid in vinegar, (b) the hydrogen peroxide in the commercial solutior or (c) the sucrose in the coffee of the preceding example? 9.9 You're 167 in a Trillion: Expressing Exceedingly Small Concentrations Even though molarity is a useful concentration term for chemists, and per ages are informative for many consumer products, the very small concentt-of the pollutants that affect our environment require a different approac' 9.9 You're 167 in a Trillion: Expressing Exceedingly Small Concentrations • 219  It's useful to express exceedingly small concentrations, such as those of food contaminants and environmental pollutants, in terms of parts per thousand, parts per million, parts per billion, and so on. These terms are closely related to the per centages we've already examined. The term percent literally means "per hundred." A one percent solution contains one unit of solute in each 100 units of solution, whatever the units happen to be. We can also speak of concentrations in terms of parts per thousand, which are the same as tenths of a percent. The coffee in the question at the end of Section 9.7, for example, contains 10 g of sugar in 250 g of the entire mixture. That amounts to 4%, or 4 parts per hundred, which is the same as 40 parts per thousand. One part per million (one ppm) represents a particularly convenient concen-tration unit since it's the concentration of one milligram of one substance distrib-uted throughout one kilogram of another. A concentration of 1 ppm, then, is the same as a concentration of one milligram per kilogram,l mg/kg. One milligram is a thousandth part of a gram and a gram is a thousandth part of a kilogram. One-thousandth of one-thousandth is one-millionth: 1 1 1 X = 1000 1000 1,000,000 one-thousandth one-thousandth one-millionth As an illustration, 35 mg of one substance in every kilogram of another would amount to a concentration of 35 mg/kg, or 35 parts per million, or 35 ppm. Consumer products provide plenty of examples of concentration terms. Labels of canned fruit drinks, for example, often reveal the presence of 0.1 % sodium ben-zoate, the sodium salt of benzoic acid (Sec.10.8), as an added preservative. A tenth of one percent amounts to a concentration of one part per thousand. The concentration of potassium iodide, KI, in iodized table salt is even small-er. Traces of iodide ion in the diet help prevent the enlargement of the thyroid gland, a condition known as goiter. To provide this dietary iodide, KI is added to commercial table salt, NaCl, to the extent of about 7.6 X 10-5 g of KI per gram ~ of NaCI. The following example shows how we can convert this concentration ~into ppm. The concentration term ppm refers to parts per million, or milligrams of solute per kilo-gram or liter of solution. E X A M P t.. E 7.6 X 10-5 g KI = 106 7.6 X 10 g KI 1 g table salt X 106 106 g table salt Translate the cancentration of potassium iodide in table salt into ppm. nd we want to know how many grams of KI there are in 106 g of table salt. The quickest way to get the answer is to multiply both the numeratar and ie denaminator by 10~. ,000, or 106. We knaw that the caneentration of Kl in table 7.6 x 10-5 g KI 1 g table salt Concentrate on Salt 220 • Chapter 9 Arithmetic of Chemistry • QUEST1ON Zinc is important to human health. A deficiency of zinc can lead to stunted growth, incomplete development of the sexual organs, and poor healing of wounds. Among foods richest in this element are liver, eggs, and shellfish, which contain zinc at lev els ranging from about 2 to 6 mg per 100 g. Express this range of zinc concentrations in parts per million. (Note that an excess of zinc can be just as bad as a deficiency. Dietary excesses of this element can cause anemia, which is a deficiency of red blood cells, kidney failure, joint pain, and other medical problems. A balanced diet provides most of us with all the zinc we need.) Even the very purest rain contains dissolved carbonic acid, HZC03. Botulinum toxin, the virulent poison of spoiled food, provides us with anoth-er illustration of the importance of even very low concentrations of substances. As we'll see in Section 20.4, botulinum toxin is the most powerful biologically pro- duced toxin known. A dose of as little as 1 x 10-y g of this substance can kill a ` 20-g mouse. At that level the concentration of the poison in the mouse's body amounts to 1 g of toxin per 20 x 109 g of mouse. To state this more directly, we can multiply both the weight of the toxin and the weight of the mouse by 50, which re-veals that the toxin is lethal to the mouse at a concentration of only 50 parts per trillion! For comparison, consider yourself as one individual person among all the people on earth. With the world's total population of about 6 billion humans, you yourself make up roughly one person in 6 billion, or 167 parts per trillion of all of those alive today on our planet. Remarkably, the lethal concentration of botulinum toxin in a mouse's body is even less than your own "concentration" among all those now living. 9.10 The Very Purest Water on Earth The presence of dissolved minerals and organic compounds in the water we drink pro-vides a fine example of the significance of the concentrations of solutes. When we think of pure water we may imagine fresh rainwater falling from a crisp sky or clear water bubbling up from a mountain spring. The very purest water on earth isn't either of these. The very purest of all water comes from a chemist's laboratory. It's water that has passed through columns of specially prepared cleansing resins or water that has been distilled repeatedly under carefully controlled laboratory conditions to remove all traces of contaminants, as demonstrated in the opening demonstration of Chapter 7 All other water, including pristine rainwater and the very purest drinking water, car ries a variety of chemical impurities in a range of concentrations. To clarify the nature and origin of these impurities, we'll follow the rain as drops to earth and becomes part of our water supply. As rain falls it absorbs, to vat ing degrees, the gases that make up our atmosphere (Section 14.1). The nitrog( oxygen, and carbon dioxide of air all dissolve to a very small extent in water. Ne room temperature a maximum of about 0.01 g of nitrogen, 0.05 g of oxygen, a 3.4 g of carbon dioxide can dissolve in 1 liter of water. (The small bubbles that) from heated tap water just before it starts to boil are bubbles of these very sa dissolved gases. Almost all gases are much less soluble in hot water than in c water. They tend to escape from their water solutions as the water warms up.) Part of the carbon dioxide that enters rainwater reacts with the water itsel form carbonic acid (Chapter 10); C02 + H20 ---~ H2C03 carbon dioxide water - - _.:..__carbonic acid 9.11 The Water We Drink • 221 As a result all rainwater is very slightly acidic. The absorption of still other at-mospheric gases, especially industrial pollutants and automobile exhaust gases, can increase the acidity of rainwater sharply, well beyond its normal acidity, to produce what is known as acid rain. We'll have more to say about acids and about how acid rain affects our environment in Chapter 14. Rain that falls onto land soaks into the earth, runs off to our rivers, lakes, and other bodies of water, or simply evaporates and reenters the atmosphere. Even some of the rain that seeps into the ground finds its way, underground, to lakes and rivers. Much of it, though, enters layers of porous rock and earth lying just below the surface of the land, where it accumulates as large reservoirs of fresh water known as groundwater. Assuming that drinking water has a density of 1000 g per liter, what is the maximum •QUESTION concentration, in ppm, of N2 and of 02 in the water we drink? 9.11 The Water We Drink Despite the abundance of rivers, streams, and lakes throughout most of the pop-ulated land area, chances are that the water coming from your kitchen faucet or from a public water fountain was drawn up from the reservoir of groundwater. Reaching the surface through wells or springs, this source provides the drinking water for about half the people in the United States and about three-quarters of , those of us who live in large cities. More water is present in this subsurface layer than in all of our rivers, streams, and lakes combined. In chemical terms, groundwater and the water we draw from our rivers and other bodies of water are solutions of solutes in a solvent. Water is the solvent; the substances the water picks up in its travels from the clouds, through the earth, and into our faucets are the solutes. It's a combination of the chemistry of the solutes and their concentrations that determines whether the water is polluted. Some of the solutes have been in earth's water since rain began to fall on the newly formed planet. Partly because of rainwater's normal acidity (resulting from the carbonic acid it contains) and partly because water itself is a very good solvent. Pollution in a rural stream. mercially bottled "natural" or "mineral" drinking water, contain a variety of min- ~rals in a range of concentrations. Among these are calcium, iron, magnesium, potassium, and sodium cations and fluoride anions. The concentrations of repre-;ntative minerals found in natural spring water of the French Alps appear in ~ble 9.1. Minerals such as these are usually harmless or even beneficial to most Table 9.1 Concentration of Several Minerals in Natural Spring Water of the French Alps Mineral Concentration, mg/liter (ppm) Calcium 78 Magnesium 24 Sodium ~ ~ . 5 Potassium 1 222 • Chapter 9 Arithmetic of Chemistry Table 9.2 Maximum Contamination Levels of Minerals in Community Water Systems Permitted by the Safe Drinking Water Act of 1974 Commercially bottled water. of us at their typical levels in natural and in commercially bottled drinking water, and at even higher levels as well. Some of us, for example, take mineral supplements that provide calcium, iron, or magnesium at levels far higher than those found in drinking water. There are hazards, though. A few of the chemicals that can enter our water sup-plies are particularly toxic even at what may seem to be very low concentrations. Contamination by these substances comes as rainwater picks up residues of agri cultural fertilizers and pesticides (known as agricultural runoff) and from indus-trial, urban, and household wastes dumped onto the surface or injected just below it. Any of these can be carried by the natural flow of rainwater into groundwater. To ensure the safety and high quality of public drinking water, the U.S. Congress passed the Safe Drinking Water Act of 1974, which establishes, among other things, maximum drinking water levels for specific, potentially hazardous chemical con taminants. Some of the minerals controlled by the Act appear in Table 9.2, while rep-resentative organic compounds appear in Table 9.3. When present in concentrations Table 9.3 Maximum Contamination Levels of Organic Compounds in Community Water Systems Permitted by the Safe Drinking Water Act of 1974 Maximum Permitted Level Compound and Use (mg/liter) Endrin (an insecticide no longer 0.0002 manufactured or used in the United States) Lindane (an insecticide) 0.004 Methoxychlor (an insecticide) 0.1 2,4-D (an herbicide) 0.1 Silvex (an herbicide) 0.01 Trihalomethanes (solvents and other uses): 0.10 bromodichloromethane dibromochloromethane bromoform chloroform a. How many moles of S03 are there in 8 g of sulfur trioxide? b. How many moles of sulfuric acid form when 8 g of sul- fur trioxide dissolve in water? chloride contains 1 mole of chloride ions? (e) CO2 is produced when 1 mole of carbon combines with 1 mole of diatomic oxy- gen molecules? 16. Assuming that rubbing alcohol is 70% (w/w) isopropyl al- cohol, and that its density is 1 kg/liter: a. How many grams of water and how many grams of iso- propyl alcohol are there in a liter of rubbing alcohol? b. How many moles of water and how many moles of iso- propyl alcohol (molecular weight 60) are there in a liter of rubbing alcohol? c. If we decide which is the solute on the basis of weight, is isopropyl alcohol the solute or the solvent? d. If we decide on the basis of the number of moles, is iso- propyl alcohol the solute or the solvent? e. Considering water as the solute and the isopropyl alco- . hol as the solvent, what is the molarity of the water in the solution? ^ Considering isopropyl alcohol as the solute and water find Section 9.12 useful in working this problem.) ,: as the solvent, what is the molarity of the isopropyl al- c. What weight of sulfuric acid forms when 8 g of sulfur trioxide dissolve in rainwater? 22. you have l liter of a solution that contains selenium at a level of 15 parts per billion and 1liter of another solution that contains barium at a level of 3 parts per million. You now mix the two solutions together to produce 2liters of a single solu- tion. Does the new solution produced by mixing the two orig- inal liters together meet federal drinking water standards for selenium? For barium? 23. The Safe Drinking Water Act of 1974 permits a maximum of 160 mg of sodium per liter of drinking water. What is the maximum molarity of sodium chloride permitted in community drinking water by the Safe Drinking Water Act? (You may 24, How many sodium cations are there in all of the water in cohol in the solution? glass 7 of the demonstration at the beginning of the chapter? 17. Which one of the following contains the greater number of moles of sucrose, (a) or (b), or do they contain the same number? (a) 4 liters of a 0.125 M sucrose solution; (b) 0.375 stration that opened this chapter. Which glass comes close liter of a 1.5 M sucrose solution? 18. A typical aspirin tablet contains 0.325 g of the active in- gredient, acetylsalicylic acid. What is the average concentra- tion, expressed as a percentage by weight (w/w %), of the acetylsalicylic acid in the body of a 165-1b (75-kg) person who has just taken two aspirin tablets? 19. In determining the molarity of the sucrose in the coffee of the example of Section 9.8, we assumed that the coffee has a den- sity of 1, or 1000 g per liter. With all the solutes in the coffee, in- cluding the 10 g of sugar, our assumption of 1000 g per liter is liter, what molarity (to one significant figure) would we now get? 25. prepare a table showing the molarity of the sugar water each of the seven glasses of the second part of the demo~ to the molarity of two teaspoons of sugar in a cup of coffee Refer to the examples in Section 9.8. 9.8section EXAMPLE Using the information given in the question at the end of Section 9.7, a ma Sweet Coffee Molecular formula of CIZH,ZOll for sucrose (table sugar), and units conversian data taken from Appendix B, we can calculate the approximate molarity of the sugar in the cup of eoffee. • For the molecular weight of the sucrose we-have C: 12 x 12.01 amu = 144.12 amu H: 22 x 1.008 amu = 22.176 amu O: 11 x 26.00 amu = 176.00 amu 342.29b amu, which we'll round off to 342 amu Recalling that we use two teaspoons of sugar, at 5,g eaeh, we get 10 g sucrose 1 mol sucrose 1000 g coffee _ 250 g coffee x 342 g sucrose x liter of coffee 0~1 M Two teaspoons of table sugar in an 8-oz cup of coffee produces coffee that's about 0.1 M in sucrose. 20. Chlorine gas consists of diatomic molecules, C12. The bal- ' anced chemical equation for the reaction of sodium metal with chlorine gas to produce sodium chloride is 2Na + C12 -~ 2NaCl. 28, If you count all of the protons and all of the neutrons in the body of a person weighing 1651b and add the sum of all the pro- tons you have counted to the sum of all the neutrons you have counted, what is the combined total? This is not a trick question and you don't have to perform tiresome or complex calculations. pll ihat's required is a good understanding of the material in this chapter and a little thought.The solution appears in Appendix E, along with a discussion of the chemical principles involved. probably too low. If we assumed a density of, let's say,1100 g per 27. As we saw in Chapter 7, carbon monoxide is also produced by the incomplete combustion of gasoline in a car's engine. To help reduce air pollution catalytic corcverters (Sec. 7.7) are used on cars to promote the combination of carbon monoxide with oxy- gen, thus transforming the CO into CO2. Write the balanced equation for the reaction of CO with OZ to form CO2. a. What weight of chlorine gas does it take to react com- 2g, Write the balanced equation for the combustion of methane pletely with 4.6 g of sodium? in an enclosed space,with a limited amount of oxygen, to produce b. What weight of sodium does it take to react complete- carbon monoxide and water instead of carbon dioxide and water. ly with 1.42 g of chlorine gas? 29, Write balanced equations for the complete combustion of c. If we started with exactly 10 g of sodium and 10 g of di- methanol (CH3-OH), ethanol (CH3-CHZ-OH), and pen- atomic chlorine gas, would either of these elements be tane (CSHlZ, a major hydrocarbon of gasoline). Calculate the left over at the end of the reaction? If so, which one? weight of carbon dioxide produced by the complete combustion 21. The use of fuels with small amounts of sulfur-containing of 100 g of each of these compounds. Assuming that all three of impurities results in the formation of sulfur trioxide, 503, an these compounds are equally efficient when used as a fuel for atmospheric pollutant. The S03 dissolves in rain and other an internal combustion engine, rank them in order of the amount forms of atmospheric water to form sulfuric acid, HZSO4, ac- of carbon dioxide released to the atmosphere per mile of auto- cording to the chemical equation S03 + H20 --~ HzS04. mobile travel. Based on the content of Section 8.14, which would Through the generation of sulfuric acid, S03 contributes to the contribute most to an increase in the greenhouse effect if used as formation of acid rain (Sec.14.5) an automotive fuel? Which would contribute least? Web Questions • 227 30. The sun is 150,000,000 km from the earth and the diameter he welfare ought to be more important than individual wishes of a penny is 1.9 cm. If Avogadro's number of pennies were used in making these decisions? Discuss your answers. to build a road from the earth to the sun and the road were just 39. Here's breaking news, just in! It's just been discovered one layer of pennies deep, how many pennies wide would the that the value long accepted for Avogadro's number is wrong! road be? (This problem is worked in some detail in Appendix C.) The value used for so long has just been shown to be off by at least 25%, although no one knows just yet exactly how much Think, Speculate, Reflect, and Ponder or in which direction. Which answers in these end-of-chapter exercises will have to be changed as soon as we learn the cor- 31. Why is it not possible, either in theory or in practice, to rect value of Avogadro's number, and which can we let stand calibrate a scale in units of moles? as they are? 32. Suppose you have a scale you know to be accurate, but you don't know what units of weight it measures. You have a quanti- = ty of acetic acid and you want to measure a quantity of water that ;q1%.g7iVeb Questions contains the same number of water molecules as there are acetic Use the Web to answer or accomplish each of the following. acid molecules. Could you use the scale to do that? Explain. Sup- Report your Web source for each response. pose you want to prepare a 1 M solution of acetic acid in water. Could you use the scale to do that? Explain. 33. Suppose you have an analytical instrument that could tell you quickly exactly how many molecules of an agricultural in- secticide there are in a glass of water. What standard(s)-the number of insecticide molecules, the odor, color, taste of the water, or any other criterion-would you use to determine whether the water is fit to drink? (No governmental drinking- water standards have yet been set for this insecticide.) 34. Regardless of any legal definition, which glasses in the opening demonstration would you consider to be polluted with salt? Which, if any, would you consider safe to drink? 35. Define "pollution" in your own words. 36. (a) Under what conditions would you consider water be "polluted"? (b) Would you say that all "polluted" water is (c) Can water that is unfit to drink not be "pol- luted"? (d) Can water that is "polluted" be safe to drink? 37. Describe three specific actions you would recommend to to 1 Summarize the life of Amedeo Avogadro with a brief bi- ography that includes the dates of his birth and death, his na- tionality, background, education, and a summary of his scientific contributions. 2, Among the concentration terms used in chemistry is molality. Define molality. Describe how it differs from molar- ity and how and why it is used in chemistry. 3. As described in Section 9.9, both sodium benzoate and potassium iodide are added to processed foods in concentra- tions that can be reported in parts per thousand. Find another food additive included in processed foods in concentrations easily reported as parts per thousand. 4. Describe a recent incidence of botulinum poisoning (some- times referred to as botulism poisoning). Include the circum- stances under which it occurred and its effects or results. unfit to drink? 5. Identify the source of the municipal drinking water dis- tributed in your area. Does it come from surface water, ground-improve the purity of your drinking water. Which one would water, or some other source? you want carried out first? 6. Find the maximum permitted level, in community drink- ing water, of an element, ion, or compound other than those listed in Tables 9.2 and 9.3. 17. Give the details of a major accidental spill, commercial or industrial discharge, or similar event that caused or threat- ened significant environmental pollution within your state. Include any action taken by state or local authorities, and the outcome. 38. We normally think of community water purification process- es as designed to remove impurities from water. Yet they can also add chemicals to water to benefit the public health and welfare. Many communities, for example, add chlorine to water to kill disease-causing microorganisms. Some add fluoride salts to retard tooth decay. Do you favor the addition of chemicals to public drinking water to promote the public health and welfare? Do you think that small quantities of essential nutrients or vitamins ought to be added to drinking water? Do you think that nothing ought to be added to the water since everyone in the communi- ty must drink the same water and some may not wish to have anything added to their drinking water? Do you think the pub- 18. Describe national, state or local requirements or restric- tions that apply in your region for the disposal of containers of unused paint; for the disposal of used motor oil; for exhaust emissions of gasoline-powered lawn mowers or other house- hold machinery. page 184 Chapter 8 The human body uses energy in three different ways. through exercise, specific dynamic action, and basal metabolism. Exercise involves push ups, jogging, swimming, tennis, physical work. Specific dynamic action accounts for the energy consumed in digesting and metabolizing food and converting its energy. for use through exercise. refining petroleum through into gasoline, heating oil, diesel oil, other products energy extraction through distillation. Energy Equation is Energy In = Energy Out + Energy Stored. Very Light Sitting, reading 1.0 - 2.5 calories expanded per minute per hour is 60 -150. Light Slow walking, washing 2.5 - 5.0 150 - 300 Moderate Fast walking, heavy gardening, bicycling 5.0 - 7.5 300 - 450. Heavy Vigorous work swimming, running 7.5 - 12.0 450 - 720. Chemistery Chapter 1 Science is a way of knowing and understanding the universe. The scientific method is the process by which science operates. Technology is the art, skill, or craft used to apply the knowledge provided by science. 1. Following are a statement containing a number of blanks and a list of words and phrases. The number of words equals the number of blanks within the statement, and all but two of the words fit correctly into these blanks. Fill in the blanks of the statement with those words that do fit, then complete the state-ment by filling in the two remaining blanks with correct words (not in the list) in place of the two words that don't fit. _ are substances that conduct electricity when dissolved in_water or when . They consist of _ ( charged ions) and (positively charged ions). Common table salt, , is an example of an electrolyte, while table sugar,_ , is a . That is, table sugar does not _when dissolved in water. We conclude that table sugar is not composed of _ anions cations chemistry compound electrolytes ions melted nonelectrolyte sodium chloride sucrose water Technology: A cellular telephone brings the applications of Technology is the art, skill, or craft used to apply the science into our daily lives. knowledge provided by science.  For Review 2. Complete this statement using the same conditions as described for the preceding exercise. _, which is the study of the composition and properties of matter, and of the changes that it undergoes, is a branch of , which itself provides us with a way of knowing and understanding the universe we live in. In the operation of the we ask questions of the universe through tests and . By observing the results that we get, we can formulate additional questions, perform additional experiments, and finally develop a ten-tative explanation of what we have learned. If this tenta tive explanation or is confirmed by others and becomes widely accepted it becomes a and helps us understand better the world about us. chemistry experiments hypothesis science scientific method theory gained through science works to our benefit or to our detri-ment through the technology we use to put it to work. We'I I see in Chapters 4 and 5, for example, that the knowledge of how atoms are constructed and how they behave can be applied through one form of technology to build powerful weapons of destruction or through another technology to detect and cure disease. • Science is a way of knowing and understanding the universe. The scientific method is the process by which science operates. 3. Match each item in group A with one in group B. Group A Group B a. chloride anion 1. assembly of atoms b. compound 2. chemical particle that carries c. electrolyte either a positive or a negative electrical charge d. ion 3. conducts electricity when it is e. dissolved in water or when it is f. molecule molten ionic bond g. sodium cation 4. element h. sulfur 5. negatively charged ion 6. positively charged ion 7. pure substance formed by com-bination of two or more ele-ments in a specific ratio 8. results from the attraction of oppositely charged ions Exercises • 13 14 • Chapter 1 An Introduction to Chemistry 4. What characteristic determines whether or not a small particle is be classified as (a) an ion, (b) a cation, (c) an anion? 5. What characteristic determines whether or not a substance can be classified as an electrolyte or a nonelectrolyte? An electrolyte is a substance that conducts electricity when it is dissolved in water or when it is melted. A nonelectrolyte does not conduct electricity when it is dissolved in water or when it is melted. In Figure 1.3 shows An electric light bulb. Pure water is a very poor conductor of electricity as is a solution of sucrose table sugar in water. A solution of sodium chloride table salt in water is a good conductor of electricity. 6. What is the distinction between an element and a compound? 7. a. Name three elements. A compound is a pure substance formed by the chemical combination of two or more different elements in a specific ratio. Magnesium Sodium Elements mercury, copper, and carbon. helium hydrogen Matter consists of all the different kinds of substances that make up the material things of the universe. b. Name three different compounds, each of which contains at least one of these elements. 8. What kind of chemical bond holds the sodium cations and chloride anions in place, close to each other, in a crystal of table salt? An anion is a negatively charged ion a cation is a positivley charged ion. An ionic bond is a chemical bond resulting from the mutual attraction of oppositely charged ions. 9. Name five elements found in the human body, describe their functions in the body, and identify a good dietary source for each of these elements. Calcium Magnesium 1 O. In your own words, describe briefly the steps of the scientific method. The scientific method is the process by which science operates. 11. What is the difference between a hypothesis and a theory? 12. What is the difference between science and technology? Science is a way of knowing and understanding the universe. Technology is the art, skill, or craft used to apply the knowledge provided by science. Science itself is a way of knowing and understanding the universe we live in. The word science comes to us from the Latin scire to know. Asking questions of the universe. Technology comes from a greek word tekno meaning art, craft, or skill. Science gives us the ability to know and to understand the physical universe. 13. In what way are water and hydrogen peroxide similar in chemical composition? In what way are they different? (See Section 1.4.) Water and hydrogen peroxide are both chemical liquids. Both contain oxygen. the body converts food into skin, hair, and other body tissue; (g) looking for a correlation between hyperactivity in children _., and seasonal changes in daylight. 18. Suppose you discovered a new substance and weren't sure whether you should classify it as a new element or a new com-pound. How would you go about determining whether you had discovered a new element or a new compound? 19. The following summarizes the results we described for the light bulb, water, sodium chloride, and sucrose early in this chapter: Condition of the Light Bulb pure water only dim or dark water and sucrose dim or dark water and sodium chloride bright What would you have concluded for each of the following results: A. Condition of the Light Bulb pure water only dim or dark water and sucrose bright water and sodium chloride dim or dark A Little Arithmetic and Other Quantitative Puzzles 14. Suppose you carry out a large number of tests as follows. In each experiment you use 10.0 g of sodium. In the first ex- periment you allow the 10 g of sodium to react with 0.1 g of chlorine; in the second you allow 10 g of sodium to react with 0.2 g of chlorine; in the third, with 0.3 g of chlorine; and so with an additiona10.1 g of chlorine until the series ends with 10 g of sodium and 20.0 g of chlorine. Describe qualitatively how the product(s) of the individual reactions change(s) as the series of experiments progresses from 0.1 g of chlorine to 20.0 g of chlorine. B. Condition of the Light Bulb pure water only dim or dark pure water and sucrose bright water and sodium chloride bright C. Condition of the Light Bulb pure water only bright water and sucrose g of sodium to react pure water and sodium chloride bright bright forth. In each subsequent test you allow 10 15. How much chlorine would you have to use if you want- ed 10.0 g of sodium to react with it to produce pure sodium chloride, with neither excess sodium nor excess chlorine left over? 16. Water is composed of hydrogen and oxygen in the ratio 1 g z hydrogen to 8 g oxygen. Hydrogen peroxide is composed of hydrogen and oxygen in the ratio 1 g hydrogen to 16 g oxygen (Section 1.4). What would result from the reaction of a mixture of 1 g hydrogen and 12 g oxygen? 17. Which of the following are suitable subjects for the sci- ence of chemistry? (a) determining the composition of rocks; , (b) analyzing the effects of a day's experiences on the nature of dreams; (c) designing a low-calorie sweetener that is also an electrolyte; (d) preparing a plastic that decomposes readi- ly to environmentally harmless products; (e) defining the dif- ference between music and random noise; (f) determining how the body converts food into skin, hair, and other body tissue g looking for a correlation between hyperactivity in children and seasonal changes in daylight. 20. Why was it necessary to test the electrical conductivity of pure water before adding sodium chloride and sucrose? 21. Suppose water itself were a very good conductor of elec- tricity. How might you then determine whether table sugar, table salt, or any other substance is an electrolyte or a non- electrolyte? 22. Would you expect seawater to be a good conductor of electricity? Explain. Seawater contains salt, and other types of substances. 23. Is it possible to determine whether air is an electrolyte? If Your answer is yes, explain how you might do it; if no ex- Plain why not. 24. Several centuries ago, it was generally believed that heavy objects fall faster than lighter objects, that the more an object weighs the faster it falls. According to one legend, the Italian scientist Galileo Galilei, who lived from 1564 to 1642, correct-17. Which of the following are suitable subjects for the sci- ed this error by dropping two spheres of different weight si- multaneously from a high point on the LeaningTower of Pisa and demonstrating that they reach the ground at the same time. Describe what Galileo supposedly did in terms of the sci- entific method. What question did he ask of the universe? What test did he use to obtain an answer? What did he observe? How did he interpret this observation? Think, Speculate, Reflect, and Ponder Energy is the ability to do work. Chemicals give us energy form the clothes materials. Aspirin can relieve pain in recommended doses. swelling, fever. In overdoses aspirin can cause nausea, bleeding, even death. Chemical reactions that provide energy and materials. pollutants that can foul the air. Chemicals can cause illness, and death. Describe a circumstance in which water H2O is (a) a life sustaining or a life saving substance. (b) a hazardous or life threatening substance. Chapter 1 compositions, properties, changes. What do you think would be the result of placing wires into a solution made up of a mixture of equal parts of sucrose and sodium chloride? Chemistry is the branch of science devoted to the study of matter its composition, its properties, and changes it undergoes. 500,000,000 atoms of gold to stretch across a dollar bill. Table salt makes the light bulb light up, and sugar doesn't. Table Salt in water. Light bulb, salt, and Sugar. Web Questions • 15 25. The old saying "A watched pot never boils" comes from a. Give examples of two other chemicals that are ordinari- the observation that a pot of water seems to take longer to ly beneficial yet can produce undesirable, even deadly come to a boil if you are watching it than if you aren't. De- effects. scribe how you could use the scientific method to learn b. Give examples of two chemicals that are ordinarily whether water really does take longer to boil if you are watch- thought of as hazardous or harmful, yet in the right cir- ing it. If water takes just as long to boil whether or not you are cumstances can be beneficial. watching it, how could you use the scientific method to deter- mine whether water actually does seem to take longer if you a"'`'e Wฐ6 are, indeed, watching it, and just how much longer it seems to ' "' eb Questions take? Describe what questions you would ask, how you would go about finding experimental tests that would give you an- Use the Web to answer or accomplish each of the following. Re- , swers to these questions, and how you would interpret the port your Web source for each response. ti answers. 1. Describe a scientific contribution made by Michael Fara- 26. Describe another popular belief or perception, similar to day, in addition to his work with ions and electrolytes. the one about the watched pot or falling objects, that you could 2. The terms "chemistry," "energy," "matter," "technology," investigate by application of the scientific method. and "science" are all defined in this chapter. Present alterna- 27. Give an example of a benefit brought to us through the tive definitions derived from Web sources. operation of science. Do the same for a benefit brought 3. Show how application of the steps of the scientific method through the operation of technology. led to a scientific discovery made: (a) during the 19th century; 28. Water can be considered to be a "good" chemical in the (b) during the past 10 years. sense that we cannot live without it. Yet it is "bad" when floods 4. Illustrate each of the themes discussed in Section 1.2 with destroy property or when someone drowns. Similarly, aspirin examples obtained from the Web. is "good" in the sense that it relieves headaches, yet it is "bad" 5. Find when each of the elements of Table 1.1 was discover- in that children have mistaken it for candy, taken overdoses, ed and who made the discovery. If the date or the discoverer and died. is unknown, describe early sources and uses for the element. Exercises • 31 E X E R C I S E S ., 1. Following are a statement containing a number of blanks and a list of words and phrases. The number of words equals the number of blanks within the statement, and all but two ~ of the words fit correctly into these blanks. Fill in the blanks of the statement with those words that do fit, then complete the statement by filling in the two remaining blanks with ~'-orrect words (not in the list) in place of the two words that von't fit. ? are the smallest electrically neutral particles of ~ an , a fundamental substance of chemistry and of the world, that can be identified as that element. All atoms consist of two parts: (1) a that contains 6. In terms of the number of atoms present, hydrogen is the most abundant element in the universe and also in our bodies. What is the second most abundant element in the universe, again in terms of the number of atoms present? What is the second most abundant element in our bodies? Helium is the second most abundant element in the universe. 7. Given the atomic number and the mass number of an atom, how do we determine the number of protons in the nucleus? The number of neutrons in the nucleus? The number of elec- trons in the surrounding shells? 8. Do an atom of protium and an atom of deuterium repre- sent atoms of two different elements? Explain. d e ! P  positively charged and (except for , 9. (a) Name the three isotopes of the element whose atomic an of hydrogen) electrically neutral number is 1. (b) What collective name do we give to a mixture ; and (2) , which lie in of these three isotopes when they are present in the same ra- surrounding the nucleus. The number of protons in the nu- tios as in the universe as a whole? cleus defines an atom's and is represented by 1~. ~at is a name used for the isotope of hydrogen indicat- the symbol . The sum of the protons and neu- ed by iH? trons in the nucleus determines the atom's and is represented by . As the atomic number of the 11. What chemical symbol is used as the equivalent of 1H? atom increases, the number of electrons in the shells also in- 12, Name and give the chemical symbols for the elements creases so that the number of electrons always equals the with the first 10 atomic numbers. number of protons and the atom remains electrically . The first quantum shell can contain a maxi- 13. Atoms of what element are used to define the atomic mass electrons; the second a maximum of unit? mum of A negative atomic number neutral atoms neutrons deuterium nucleus eight protons element quantum shells isotope two mass number Z electrons. 14. Can any isotope of any element have a mass number of zero? Explain. 15. (a) What would remain if we removed an electron from a hydrogen atom? What charge would this particle bear? What would its mass be? (b) How do you think we could convert a sodium atom into one of the sodium cations discussed in Chapter 1? 16. Write the chemical symbol, showing the atomic number and the mass number, for atoms of two different elements each of which has two neutrons in its nucleus. 17. Name: a. three elements that have only a single electron in their outermost quantum shell b. two elements that have exactly two electrons in their outermost quantum shell c. three elements with filled outermost quantum shells d. one element that has only a single electron in its inner-most quantum shell  v2. Name an element that is a. the major gas of the air we breathe j~ b. used in small, long-lasting batteries t' c. used to harden the enamel of teeth d. present in graphite, diamonds, petroleum, and all living things 3. Of the first 10 elements, which are metals? 4. Exercise 3 contains the phrase "the first 10 elements." What does this refer to? 18. The nucleus of 16C and the nucleus of t~N contain the 5. How many elements are currently known to exist? - same number of but different numbers of 32 • Chapter 2 Atoms and Elements . The nucleus of t6C and the nucleus of t6C contain the same number of but different numbers of . 19. (a) Which element was found on the sun before it was found on the earth? (b) Which element has a name that in-dicates its presence in many acids or sour-tasting sub-stances? (c) How many years passed between the identification of hydrogen as an element and the discovery of its isotope deuterium? (d) Which of the first 10 elements are gases? (e) Which is the most reactive of the first 10 elements? 20. What do diamonds and ficllerenes have in common? b. Helium is an unreactive gas and neon is a gas of ex-tremely low reactivity. What, if anything, do their atoms have in common? 27. Suppose we could combine one electron with one proton to form a single, new subatomic particle. What mass, in amu, would the resulting subatomic particle have? What electrical charge would it carry? What known subatomic particle would the resulting particle be equivalent to? 28. Suppose someone discovered a particle that consisted o a single neutron surrounded by a shell containing a single ele~ tron. Would you classify this as an atom? Would you classify as an ion? Would it represent a new element? Explain yc answers. A Little Arithmetic and Other Quantitative Puzzles 21. Give the number of protons and the number of neutrons in the nucleus of each of the following atoms and the number of electrons in their first and second quantum shells: (a) 1sB; (b) 16C; (c) iHe; (d) i9K; (e)'s0~ 22. Section 2.5 tells us that hydrogen atoms make up two-thirds of all atoms in water but just over 11 % of the water's weight. Given that there are twice as many hydrogen atoms in water as there are oxygen atoms and that virtually all the hy-drogen atoms in water are iH and virtually all the oxygen atoms are 1g0, how do you explain this apparent discrepancy? 23. What is the weight of a sheet of gold atoms 1 atom thick and with the same dimensions as this page? You can answer this question by measuring the width and length of this page and carrying out a calculation similar to the one in the exam-ple of Section 2.2. 24. Using 3 x 10-8 cm as the diameter of a gold atom and 3.3 x 10-22 g as its weight, calculate the weight of 1 cm3 of gold. (You can start by finding how many gold atoms fit on a line 1 cm long; see Section 2.2.) How does your calculated value compare with the measured density of gold,19.3 g/cm3? Suggest some factors that might account for the difference. 29. a. What is the difference between an object's mass anc weight? b. A bag of table sugar (sucrose) weighs 10 kg on the moon. What is its weight on the earth? c. A bag of table salt (sodium chloride) has a mass of 5 kg on the moon. What is its mass on the earth? d. A piece of charcoal has a mass of 1 kg on the earth. What is its weight on the moon? 30. You have two spheres, one made of lead and one made of ` cork. They are standing next to each other at some spot on the sur- e face of the earth. At that location each weighs 7 kg. Compare their masses at that location. Does one have a greater mass than thc•, .,,_ other? If so, which has the greater mass? Now move both sphera ~ to one particular location on the surface of the moon and agait.v compare their masses. Does one have a greater mass? If so, which one? Does one weigh more than the other on the moon? If so,L, which? Finally, leave the cork sphere on the moon and move the lead sphere back to its original location on earth.Again,compare both their masses and their weights.  31. Suppose you discovered how to produce an isotopea drogen containing three neutrons in its nucleus. a. Write its elemental symbol, showing its atomic numbe~- _ and its mass number. b. What name might you give this new isotope to distin-guish it from protium, deuterium, and tritium. Think, Speculate, Reflect, and Ponder 25. (a) If you split the nucleus of a gold atom into two parts, would you now have two smaller gold atoms? Explain. (b) If you combined the nuclei of two gold atom into a sin-gle nucleus, would you now have one, larger gold atom? Explain. 26. a. Lithium, sodium, and potassium are all metals that react with water to liberate hydrogen gas. What, if any-thing, do atoms of each of these metals have- in - common? c. What new letter-symbol would you give this new iso-tope to distinguish it from D and T, but without repeat-ing the symbol of another element. d. Explain or give a reason for your responses to parts b and c. 32. The description of the atom that we have used in this chapter resembles in some ways our own solar system. What part of our solar system corresponds to the nucleus of an atom? What part corresponds to the electron shells surrounding the nucleus? What are some of the other similarities between the structure of the atom, as described in this chapter, and our own solar system? What are some of the more obvious differences? Web Questions • 33 `a~,~ae w 6 eb Questions Use the Web to answer or accomplish each of the following. Re-port your Web source for each response. 1. The modern view of the atom originated with the work of John Dalton. Write a brief biography of John Dalton, includ-ing the dates of his birth and death, his nationality, background, education, and a description of his view of the atom and how he arrived at it. 2. What is the principal factor affecting a planet's gravita-tional force? If a person weighs 60 kg on earth, what would that same person weigh on Mercury, Venus, Mars, Saturn, and Jupiter? 3. Who discovered each of the following? How and when was the discovery made? (a) the electron, (b) the neutron, (c) the proton? 4. The Perspective summarizes the occurrence, history, prop-erties, etc., of the first 10 elements, those with atomic numbers 1-10. Write similar short paragraphs for the next five elements, those with atomic numbers 11-15. 5. Henry Moseley, Isaac Newton, and Harold Urey each made a major contribution to the topics discussed in this chapter. Identify the topic associated with each of these three scientists and describe the scientist's contribution. 54 • Chapter 3 Chemical Bonding  1. Following are a statement containing a number of blanks (b) carbon, (c) sodium chloride, (d) propane, (e) lithium io- and a list of words and phrases. The number of words equals dide, (f) sucrose, (g) potassium. the number of blanks within the statement, and all but two of 5. Write chemical formulas for (a) lithium bromide, (b) cal- the words fit correctly into these blanks. Fill in the blanks of the cium sulfide, (c) sodium sulfide, (d) beryllium oxide, (e) the statement with those words that do fit, then complete the state- chlorine molecule, and (f) the compound formed on reaction ment by filling in the two remaining blanks with correct words of silicon and hydrogen. (not in the list) in place of the two words that don't fit. g, Write the chemical formulas of all the ionic compounds In its modern form the is an organization of all that could result from reaction of a mixture of lithium and the known elements arranged in order of increasing potassium with a mixture of fluorine and bromine. . Elements that lie in the same have 7, Name a commercial product that contains (a) elemental similar , have the same number of chlorine, (b) the iodide ion, (c) both the element nitrogen and and belong to the same chemical . The table the element chlorine, (d) the element fluorine, (e) the chloride shows the element's chemical , atomic number, ion, (f) the element sulfur, (g) elemental iodine. and , which is the average mass of all the g, Which of the following contain (or are a form of) elemen- of the element, weighted for the of tal carbon? Which contain the element carbon? (Reviewing the each. The table is particularly useful for predicting the out- perspective of Chapter 2 may be helpful.) (a) carbon dioxide, come of chemical reactions between since an (b) graphite, (c) water, (d) diamond. atom of any element tends to react so as to convert its elec- tronic structure to that of a nearby . When 9• Where might you find (a) elemental oxygen, (b) elemental atoms react by a complete of electrons, the gold, (c) the element carbon, (d) sodium ions, (e) the element products are . When they react by hydrogen, and (f) the elements carbon, hydrogen, nitrogen, pairs of electrons, the result is a . While ionic and oxygen in a single compound? compounds exist as crystals made up of extensive 10• What element has the following: of ions, covalent compounds are composed of a. an atomic weight of almost exactly 14 discrete . If the atoms that form the covalent b. an atomic number of 16 bonds have significantly different , the bond that c. one electron in its first quantum shell forms is a d. two quantum shells, both of which are filled with abundance isotopes electrons atomic number lattices e. the electron structure 2 8 2 atomic weight molecules ^ a valence shell filled with a total of two electrons column noble gas g. a total of three quantum shells, with two electrons in its covalent bond periodic table valence shell crystals polar covalent bond h. a total of two quantum shells, with three electrons in its electronegativities properties valence shell elements symbol i. twice as many electrons in its second shell as in its first halogens transfer 11. Each of the following pairs of elements reacts to form a bi-nary compound. Which form an ionic compound and which ions valence electrons form a covalent compound? 2. Define, illustrate, or explain each of the following: a. sulfur and oxygen e. nitrogen and oxygen a. alkaline earth metal g. ionization b. hydrogen and fluorine f. hydrogen and carbon b. binary compound h. molecular formula c, barium and chlorine g. lithium and iodine c. chemical family i. molecular weight d, sodium and bromine h. magnesium and oxygen d. chemical formula j. molecule 12, Write the chemical symbols of the following elements: e. covalent bond k. valence electron (a) aluminum, (b) argon, (c) calcium, (d) carbon, (e) cesium, f. halogen (f) fluorine, (g) gold, (h) hydrogen, (i) lead, (j) manganese. 3. Identify the elements and the compounds among the fol- 13. Name the elements that the following chemical symbols lowing: (a) oxygen, (b) water, (c) chlorine, (d) sucrose, (e) hy- represent: (a) Ag, (b) Be, (c) He, (d) I, (e) Kr, (f) Mg, (g) Na, drogen, (f) sodium chloride, (g) sulfur, (h) propane, (i) argon, (h) Si, (i) Zn. (j) carbon. 14. Write the Lewis structures of (a) a chlorine atom, (b) a 4. Identify each of the following as consisting principally of fluorine atom, (c) a fluoride anion, (d) a sodium atom, (e) a molecules, principally of ions, or principally of atoms: (a) water, magnesium atom, (f) a carbon atom, (g) an aluminum atom, (h) a boron atom, (i) a molecule of HCI, (j) a water molecule, (k) a molecule of hydrogen peroxide, H202. 15. How many electrons would an oxygen atom have to lose to obtain the same electronic structure as an inert gas? Why doesn't an oxygen atom lose these electrons, rather than ac-quire two, when it reacts with other elements? 16. a. What are two properties that all elements in the same column of the periodic table as helium have in common? b. What are two properties that all elements in the same column of the periodic table as lithium have in common? 17. What would you expect to happen if you place a small piece of potassium metal into water? 18. What change occurs in the valence shells of elements as we move from left to right in any given row of the periodic table? 31. Many compounds, such as carbon dioxide, CO2, methane, CH4, water, H20, and sucrose, C1ZH22011, exist as molecules. 19. What change occurs in the valence shells of elements as we Hydrogen gas, H2, also exists as molecules. Does this mean move down a column in the periodic table? that the gas HZ is a compound? Explain. 20. Why do elements in the same column of the periodic table 32. The covalent compound acetylene, the fuel of the oxy- show similar chemical behavior? acetylene torch used by welders, has the molecular formula 21. What is the valence of sulfur in the gas sulfur dioxide, CZH2. The covalent compound benzene, a commercial solvent, SOZ? In the gas sulfur trioxide, S03? has the molecular formula C6H6. Each of these compounds 22. The element oxygen can exist in two molecular forms. In contains carbon and hydrogen atoms in a one-to-one ratio. its most common form, it exists as a diatomic molecule, O2, Would it be correct to write the chemical formula of each as but it can also exist as ozone, in which three atoms of oxygen CH? Explain your answer. combine to form a covalent molecule. Write the molecular for- 33. Elemental oxygen exists as a diatomic gas, O2. How many mula of ozone. electrons do the two oxygen atoms have to share between 23. Like water, hydrogen peroxide (Fig. 3.18) ionizes slight- them to form this diatomic molecule? How many covalent ly to produce a hydrogen cation and an anion. What is the bonds unite the two oxygen atoms of the OZ molecule? chemical structure of the anion resulting from the ionization 34. Arranging the elements in order of increasing atomic of H202? Show the structure in two ways: (1) with pairs of number also places the elements in order of increasing atom- electrons represented by pairs of dots and (2) with covalent ic weight, with a few exceptions. One of these appears in the bonds represented by dashes. sequence of tellurium (Te) and iodine (I). The atomic weight of tellurium (atomic number 52) is 127.6. The atomic weight of iodine (atomic number 53) is 126.9. How do you account Figure 3.18 The hydrogen peroxide for this? molecule, HZOZ. 35. Hydrogen chloride, HCI, exists as a gas composed of co-valent molecules. If we dissolve this gas in water, the water conducts an electric current well. If we dissolve HCl in ben zene, a solvent of molecular formula C6H6, the solution does not conduct an electric current. (Pure benzene does not con-duct an electric current either.) What do you conclude from this observation? 24. Pure hydrogen chloride is a gas under ordinary conditions. Molecules of pure, gaseous hydrogen chloride consist of a hy-drogen atom covalently bonded to a chlorine atom. When hy-drogen chloride gas dissolves in water, the resulting solution easily conducts an electric current. As the hydrogen chloride molecules enter the water, what process occurs to generate an electrolyte? A Little Arithmetic and Other Quantitative Puzzles   25. Give the valence of the cation in each of the following com-pounds: (a) SrF2, (b) ZnCIZ, (c) A1C13, (d) C~O, (e) Fe203. 26. What is the total number of electrons being shared among all the covalent bonds of a molecule of methane, CH4? 27. What would you write as the molecular formula for the nitrogen dioxide of Section 3.3? (Di- is a prefix meaning "two.") What is the valence of the nitrogen of this molecule? Exercises • 55 28. Bromine's atomic weight is 79.9. Two isotopes make up virtually all the bromine in the universe. One, with a mass num-ber of 79, makes up 50.69% of all the bromine atoms. What is the mass number of the other isotope? 29. The permanganate anion, Mn04, bears a single negative charge. Knowing that oxygen acquires an octet by acquiring two electrons, what do you calculate as the valence of the man-ganese atom in this ion? , 30. What is the valence of neon? Think, Speculate, Reflect, and Ponder 36. The element carbon, as we will see later, forms the basis for all life as we know it. Science fiction writers sometimes speculate on the properties of different forms of life based on an element other than carbon. What element do you think they usually choose, and why? (Referring to Fig. 3.2 may help you answer this question.) 37. Some forms of the periodic table show hydrogen twice, once at the top of the column of the alkali metals and once again at the top of the column of the halogens. Suggest a reason for putting hydrogen into both families. (Kint.~ Consider the structure of the hydrogen atom and its similarities to the other elements of each of these families.) 56 • Chapter 3 Chemical Bonding 38. Silver chloride, AgCl, is not soluble in water. Explain how Identify two other scientists who reported a periodic repeti- you might be able to determine whether this is an ionic or a co- tion of properties among elements before Mendeleev devised valent compound. (Hint. Refer to Section 1.1.) his periodic table. What repetitions did they find? Among 39. Are there any exceptions to the octet rule? If your an- what elements? swer is no, explain why there aren't any. If your answer is yes, 2. Figure 3.2 represents one of several modern versions of the describe one and explain why it is an exception. periodic table. Find two other versions, one of which repre-sents a three-dimensional periodic table.  3. Identify three different compounds each of which has the molecular formula C6H1206. Describe briefly some similari Use the Web to answer or accomplish each of the following. Re- ties and some differences among them. eb Questions port your Web source for each response. 4. Find the molecular formulas of the pain-relievers aspirin 1. Section 3.6 contains the sentence "Although others had and ibuprofen; the antibiotics penicillin and erythromycin; the also noted the same sort of periodic repetition of properties sweeteners aspartame and saccharin. even before Mendeleev's inspiration, none had pursued the 5. Write a brief summary of the life of Linus Pauling. Include idea as vigorously or in as much detail as the Russian chemist." descriptions of his contributions to the topics of this chapter.   82 • Chapter 4 Discovering the Secrets of the Nucleus and energy are interconvertible, that mass can literally van- In its descriptions of the material of our world, what ish, to be replaced by its equivalent in energy. follows asks us to use letters of the English alphabet to In another sense, chemistry asks us to look at the phys- represent the nuclei and electrons shel Is of atoms that ical structures of our world not with our eyes but with our are invisible to our eyes; numerical subscripts to repre- minds. As it explains the behavior of the matter that makes sent clusters of these atoms; and straight lines to repre- up our world, chemistry invokes structures-atoms and sent the clouds of electrons that hold these atoms into molecules-too small to be seen with even the most pow- the well-formed structures we call molecules. The same erful optical microscopes, structures that can be made vis- kind of mental activity that allows us to visualize the ible only with such uncommon devices as the scanning structure and behavior of atoms and the conversion of tunneling microscope (Sec. 2.2). In this sense, the study of matter directly into energy (and the reverse) will convert chemistry asks us to use our imagination to give shape and the letters, lines, and subscripts that follow into the in- structure to the nucleus and its surrounding electrons and credibly small particles that form us and everything else the bonds they form. in our everyday world. • E X E R C 1 S E S For Review 1. Following are a statement containing a number of blanks and a list of words and phrases. The number of words equals the number of blanks within the statement, and all but two of the words fit correctly into these blanks. Fill in the blanks of the statement with those words that do fit, then complete the state-ment by filling in the two remaining blanks with correct words (not in the list) in place of the two words that don't fit. Antoine Henri Becquerel discovered the phenomenon of , which occurs when the nucleus of a emits an , a , andlor a . Each of these forms of radiation can cause the ionization of matter so each is an example of . When an atom-ic nucleus loses either an a particle, which is a high-energy , or a (3 particle, which is a high-energy , the nucleus undergoes a change in its atomic number and becomes transformed into a nucleus of a dif-ferent element in a process known as . If the newly formed isotope is also radioactive, it too emits radiation and is transformed into still another element. Eventually, after a series of these transformations, a non-radioactive is formed, and this comes to an end.  a particle neutron (3 particle proton y ray radioactivity chain of radioactive decay radioisotope electron stable isotope ionizing radiation a. A. H. Becquerel 1. derived the equation b. James Chadwick E = mc2 2. Repeat the instructions of Exercise 1 for the following 2. discovered a and ra s statement and list of words and phrases. c. Marie Curie R Y The first atomic weapons-the bombs tested near Alam- d. Albert Einstein 3. discovered the neutron ogordo, New Mexico, and those dropped on Hiroshima and e. Otto Hahn 4. discovered nuclear fission Nagasaki-derived their explosive power from the con- f. Ernest Rutherford 5~ discovered radioactivity version of into through 6. discovered radium and the process of . The first atomic bomb detonat- , ._ - polonium ed was made of , an artificially produced iso-tope that does not occur naturally (in more than trace amounts). The bomb dropped on Hiroshima contained , which was separated from its more common ' isotope, , by the process of . Each of these weapons was detonated by setting off a convention-al explosion that compressed subcritical portions of the metal into a and set off a , which produced the nuclear blast. Still another kind of nuclear weapon, which harnesses the power of the sun, relies on for its energy. In one form, and nuclei come together at very high temperatures to produce and release nuclear power. critical mass nuclear fission deuterium nuclear fusion energy plutonium-239 helium tritium hydrogen uranium-235 initiator uranium-238 matter 3. Each of the following scientists or groups of scientists in the left-hand column received a Nobel Prize for contributing to our understanding of the structure and properties of the atomic nucleus. Match each of these individuals or groups with one of their major accomplishments (often, but not in every case, the one for which the prize was awarded), shown in the right-hand column. Exercises • 83 11. (a) What results from the collision of an electron with a positron? (b) Explain why this is an example of the conver-sion of mass into energy. 12. Protons and neutrons are the particles that make up the atomic nucleus. What particles make up protons and neutrons? 4. Place the following events in chronological order: a. detonation of the first atomic bomb b. discovery of a, (3, and y rays c. discovery of the neutron d. discovery of nuclear fission e. discovery of radioactivity 13. Describe a commercial use for y radiation that is not a f. the first planned, successful transmutation of an element medical application. 5. In the process of unlocking the secrets of the nucleus and 14• What does the implosion accomplish in the plutonium _.__. ____._. __ bomb? m the story of the atomic bomb, what imp process is associated with each of the following cities? 15. In the initiator of both the uranium and plutonium bombs, a. Alamogordo, New Mexico what function does the polonium-210 serve? What function b. Berlin does the beryllium serve?  c. Hanford, Washington 16. In what way did Ernest Rutherford bring the dreams of d. Los Alamos, New Mexico the alchemists to reality? e. Oak Ridge, Tennessee f. Paris A Little Arithmetic and Other 6. a. What element was the first one found to be radioactive? Uranium Quantitative Puzzles b. What element was the first one found to undergo nu- clear fission? Uranium 17. Using the form of notation shown in Figure 4.3 and (if c. What radioisotope was the first to be produced artifi- needed) data obtained from the periodic table or lists of atom- cially on an industrial scale? ic symbols, atomic numbers, and mass numbers, write complete d. Why was the element of part (c) produced in such large quantities? e. What element is produced on the sun through a nuclear fusion reaction? Hydrogen and Helium sYmbols for (a) radon-222, (b) carbon-13, (c) the most com-mon isotope of lithium, (d) the isotope of chlorine of mass number 37, (e) an atom containing 43 protons and 56 neutrons, (f) a helium nucleus, (g) a proton, (h) a y ray, (i) a R particle, (j) a chloride ion, and (k) a sodium ion. ^ What isotope forms the final, stable product of the chain 18. (a) When a radioactive nucleus ejects an a particle, both of radioactive decay that starts with U-238? the atomic number and the mass number decrease. By what g. What element forms when carbon-14 undergoes radio- quantity does each decrease? (b) When a radioactive nucleus active decay? ejects a (3 particle, only one of these (atomic number or mass h. What element forms initially on radioactive decay of number) changes. Which one? Does it increase or decrease? By radon? what quantity? i. What element served as the starting material for the first 1 g. (a) What effect does ejection of a y ray have on atomic planned, successful, transmutation of one element into number? On mass number? (b) What effect does ejection of a another? positron have on atomic number? On mass number? j. What element was produced as a result of the first planned, successful transmutation? 2~• Tritium is a radioactive isotope of hydrogen. Explain why tritium cannot decay with the loss of an a particle. 7. What is phosphorescence and what event revealed to A. H. Becquerel that the mysterious spot on his photographic plates 21 • What form of radioactivity, if any, occurs with an increase did not originate in the phosphorescence of uranium? in the mass number of the radioactive nucleus? Explain. 8. What one characteristic is common to all end products of 22. The experimentally measured mass of an atom is always all possible chains of radioactive decay? less than the mass calculated as the sum of the masses of all the 9. How does the ratio of neutrons to protons in an atomic nu- Protons, neutrons, and electrons that compose it. Why? cleus affect the stability of the nucleus? 23. If U-238 absorbed one neutron and the resulting U-239 10. A neutron bomb is a proposed nuclear weapon that would then underwent fission to generate three neutrons and two explode with very little force (and therefore do little physical (and only two) mutually equivalent nuclear particles that were damage to buildings and equipment) but would release im- equal in their mass numbers and atomic numbers, what iso- mense amounts of neutrons as ionizing radiation that would tope of what element would these two new atomic particles disable and kill troops and civilians. Which would you expect represent? Do you think they would be stable isotopes ox to penetrate matter more effectively: (a) a beam of high-speed radioisotopes? Explain. neutrons or a beam of y radiation? (b) a beam of high-speed 24. Per unit of atomic mass, Fe-56, the most common isotope neutrons or a beam of a radiation? Give reasons for your of iron, has one of the greatest mass defects and one of the choices. highest binding energies of all atoms. 84 • Chapter 4 Discovering the Secrets of the Nucleus a. Given that the experimentally measured atomic mass work in common in making discoveries or must the use of one of this isotope of iron is 55.9349, calculate its mass defect. exclude the use of the other? The atomic number of iron is 26. 33. In the operation of the scientific method the questions b. What is the mass defect of Fe-56 per atomic mass unit? that scientists ask of the universe (in their experiments) are c. What is the mass defect of U-235 per atomic mass unit? almost always based on something already known of the uni- (See Sec. 4.12.) verse. The questions are chosen carefully, so that there is a d. Which has the greater binding energy per atomic mass good chance that the answers (the results of the experi- unit, Fe-56 or U-235? ments) will yield interesting or important information. With this in mind, why do you think that Otto Hahn chose to bom- bard Complete the following equations with the symbol for bard uranium nuclei with neutrons rather than with a or (3 the atom or particle represented by the question mark. Show particles? the mass numbers and atomic numbers of the isotopes formed or the symbols of the subatomic particles: 34. It has been suggested that in areas with certain kinds of zlo soil and underground rock and mineral deposits, it may be a. g4Po ---> ? + a more hazardous to live in a house that is well sealed against b. 294 Pa ~ ? + R drafts than in one with loose-fitting doors and windows that c. 153 Pa ------ s4Xe + ? allow a continual flow of air into and out of the house. Sug- d. z~Th -~ zgBRa + ? gest a reason why this may be so. e. ? _ z94Pu + a 35. Explain why radioactivity is hazardous to humans. f. ? , 292U + R 36. Radioactivity does considerable biological damage and 26. Why was a source of neutrons needed in the detonation can be harmful to living things. Of the three forms of radia- of the atomic bombs? tion discussed in this section, a, (3, and y rays, which would be the most hazardous to a person standing a few feet from a ra-dioactive substance that emits all three of these forms of radi-Think, Speculate, Reflect, and Ponder ation? Which would be the least hazardous? 27. Describe one difference between the way the laws of the 37. The first significant application of newly discovered nu- physical universe operate within the nucleus and the way they clear energy was in the construction of an atomic bomb. Sug- operate in our everyday world, gest a reason why this was so. 28. Describe Becquerel's use of the scientific method as he 38. Nuclear weapons tests in space, in the atmosphere, and sought to establish a connection between phosphorescence in the ocean are prohibited by international treaty, but under- and X-rays. How did he explain the observation of an exposed ground tests are still permitted. Why are underground tests of spot on the photographic film that had been wrapped in black nuclear weapons considered to be different from the other paper and kept in a drawer with the crystal of the uranium tests? compound, out of contact with sunlight? How did this obser- 39. Detonations of high explosives such as dynamite and TNT vation affect the idea that a phosphorescing substance emits are used for peaceful purposes, in demolition and in construc- X-rays along with visible light? If Becquerel wished to contin- tion, for example, as well as in weapons of war. Suggest and ue his investigation of a connection between phosphorescence describe peaceful uses for detonations of fission or fusion nu- and X-ray emission, what test(s) might he have used next? clear explosives. 29. Suppose that instead of using crystals of a uranium com- 40. As we saw in Exercise 10, a neutron bomb produces a pound in his investigations of phosphorescence, Becquerel had very small blast when it explodes but releases very large used crystals of a compound that was not radioactive but that numbers of neutrons. Would you classify a neutron bomb as did nonetheless phosphoresce. With your own knowledge that a more humane weapon or a less humane weapon than a phosphorescence and the generation of X-rays are not con- uranium bomb of the power that exploded over Hiroshima? nected, what do you think Becquerel would have observed? Explain. What do you think his conclusion would have been? 41, Chemical reactions release and absorb far less energy (per 30. Was Columbus's discovery of the American continent an atom involved) than the nuclear reactions of fission and fu- example of serendipity? If the American continent did not sion. Using this observation as a basis, suggest a reason why exist and Columbus had indeed reached the Orient by sailing the Law of Conservation of Mass might not be valid. westward, as he had expected, would that have been an ex- ample of serendipity? Explain your answers. 31. Give an example of a discovery (other than those dis-cussed in this chapter) made through serendipity.The example you use may come from outside the field of science. 32. Contrast and compare the use of serendipity and the use of the scientific method in making discoveries. Can the two 42. As we saw in Section 4.8, Otto Hahn and Fritz Strass-mann carried out certain experiments on uranium late in 1938 in Berlin, and Lise Meitner identified the results of these ex-periments as newly discovered nuclear fission, a process that could release incredible amounts of energy. In September 1939, Germany invaded Poland and World War II began. Not quite a month before the outbreak of war, believing that Germany Web Questions • 85 44. One of the motives for dropping atomic bombs on Japan at the end of World War II was to save the lives of American troops who might otherwise have had to invade the home is-lands of Japan. There is still dispute about whether such an in-vasion would have been necessary. Regardless of the likelihood that such an invasion might have been required, suppose that one would indeed have been necessary and that the lives of American troops would have been lost as a re-sult. Suppose you had been President of the United States in 1945 and that the best military estimates were that dropping the bombs would save the lives of 1 million U.S. troops. Knowing what you do now of the effects of the bombs that dropped on Hiroshima and Nagasaki, would you have au-thorized their use? Suppose that the best estimates were that Japan was lightly defended and that our troops were so well prepared that no more than 10 U.S. lives were likely to be lost. Under those conditions, would you have authorized the use of nuclear weapons? If you would have authorized their use at the level of 1 million casualties, but not at a level of 10, can you cite a specific number of casualties that would have been a dividing line between your decision to authorize and your refusal to authorize the use of the atomic bombs? Explain your answers. 7. Identify each of the following, describe how each was in-volved in the creation of the atomic bomb, and describe a sci-entific contribution of each that is unrelated to the atomic bomb: (a) Leo Szilard, (b) Edward Teller, (c) John von Neu-mann, (d) Eugene Wigner. 8. What were some of the arguments used to justify the use of atomic bombs at the close of World War II? What were some of the criticisms of their use? What alternatives to dropping them on occupied cities were proposed before their actual use? 9. What is the current state of nuclear armaments among the world's nations? What publicly available information now ex-ists about the kinds and numbers of nuclear weapons that each nation now holds? What international agreements are now in effect concerning the construction and/or testing of nuclear weapons? What agreements, if any, are now under considera-tion or review?  In Chapter 1 we defined chemistry as the branch of science defect. We've seen that much of the importance of nuclear that sfudies the composition and properties of matter and transformations (and associated changes in binding ener- the changes that matter undergoes.This definition properly gies) lies in the energy they release-instantaneously in focuses on the matter, the material substance, of the world nuclear weapons, more slowly in nuclear reactors and in about us and the universe in general. But when we look at medical applications. We've seen that this energy can do "the changes that matter undergoes" we are also looking harm when it destroys biological molecules vital to health at energy. Virtually without exception, when there's a change and life, or provide lifesaving benefits when it kills cancer in matter, there's movement of energy, into or out of the mat- cel Is. e` ter that's changing. We must remove energy from water The next several chapters, and those further ahead, (cool it) to freeze it. We must add energy to water (heat it) continue examining this connection between changes in to boil it. When atoms split (fission) or combine (fusion), matter and the release or absorption of energy, and carry it they release energy. When we burn gasoline in a car's en- beyond nuclear transformations to changes in the structure gine or oxidize food in our own bodies, we release the en- of molecules, especial ly the organic molecules of our fuels ergy stored in the gasoline and in the food. and of the food we eat. We'll define what energy itself is, As Einstein pointed out with E = mc2, matter and en- learn how molecules store and release it, examine how the ergy are in a real sense equivalent to each other. In Section chemicals of our food provide us with our own biological 4.12 we saw that the energy that holds a nucleus together, energy, and trace the energy of our life back to its ultimate the atom's binding energy, is derived from the atom's mass origin. •    For Review Exercises • 111 1. Following are a statement containing a number of blanks, and a list of words and phrases. The number of words equals the number of blanks within the statement, and all but two of the words fit correctly in these blanks. Fill in the blanks of the statement with those words that do fit, then complete the state-ment by filling in the two remaining blanks with correct words (not in the list) in place of the two words that don't fit. atomic pile half-lives carbon-14 iodine-131 control rods plutonium-239 diagnosis and therapy potassium-40 Peaceful uses of nuclear reactions include the generation of electrical power radioisotopic dating , medical , and . C~rrently fission reactor uranium-235 the most practical form of nuclear power plant is the , in which heat produced by an creates fusion reactor uranium-238 steam, which turns a turbine attached to an electrical gener- 2, Identify, describe, or explain each of the following: ator. Although most nuclear power plants use a uranium fuel, which is enriched in the more highly fissionable isotope a~ background radiation e. meltdown , a converts the more common, but b. film badge f. PET , less efficient isotope into fissionable c. Geiger counter g. rem as it simultaneously generates power. Someday electrical d. LMFB reactor h. scintillation counter power may be produced by an environmentally cleaner , in which small nuclei, such as hydrogen isotopes, 3• In what way was Enrico Fermi's nuclear pile at Stagg Field combine to form larger nuclei, such as helium atoms. important to building the first atomic bomb? In what way was Medically, is valuable in the diagnosis and con- it important to the development of nuclear-powered electric trol of hyperthyroidism; is used widely as a generating plants? source of diagnostic y rays. 4. Describe the steps involved in the conversion of the heat Since the of radioisotopes are well known and produced in a nuclear pile into electricity by a commercial are constants, unaffected by physical or chemical condi- power plant. Energy, From the Nucleus to the World We Liue In  tions, naturally occurring radioisotopes are useful in deter-mining the age of ancient materials. The dating of objects made of wood, paper, and linen, for example, is often ac-complished by analysis of their content.  112 • Chapter 5 Harnessing the Secrets of the Nucleus 5. Describe how electricity is generated through the action exposed if: (a) standing in a well-sealed room with walls of of steam. thick lead; (b) buried deep within a mine. 6. Describe how a source of energy other than heat is used to 25. List a rays, (3 rays, and y rays in order of increasing abil- generate electric power on a commercial scale. ity to pass through a thick wooden wall. List them in order of 7. What is the principal advantage of nuclear fusion over nu- increasing ability to generate ions over equivalent paths of clear fission for generating power? What is the principal ob- travel within that wooden wall. stacle yet to be overcome in building a fusion reactor? 8. List four factors that have slowed the expected growth of A Little Arithmetic and Other nuclear power as a source of commercial electricity. Quantitative Puzzles 9. What would result if all the control rods of a commercial 26. Using the data in Table 5.3, calculate how long it would fission reactor were removed from the nuclear pile and not take 1 kg of Tc-99m to be reduced to just under 1 g of Tc-99 by reinserted? What would happen if all the rods were fully in- the process of radioactive decay. serted into the pile and allowed to remain? 27, Ten grams of krypton-93 were prepared through the use 10. Explain why a nuclear explosion cannot occur in a com- of nuclear reactions. A measurement taken after a certain pe- mercial fission reactor. What kinds of accidents can occur? riod passed showed that radioactive decay left a total of 0.625 g What happens during a meltdown? of this radioisotope. How long a period elapsed between the 11. (a) Was the accident at Three Mile Island the result of a formation of the 10 g of krypton-93 and the measurement? nuclear explosion of fissionable material? (b) Was the accident 28. you have a balance that will weigh masses down to 0.1 g at Chernobyl the result of a nuclear explosion of fissionable but gives a reading of zero for anything less than that. Using material'? Explain your answers. that balance, you have just measured out 100.0 g of each of the 12. Of the accidents at Seascale, England, Three Mile Island, radioisotopes in Table 5.3. What weight of each of these iso- Pennsylvania, and Chernobyl, Ukraine, which released the topes will be left (using the same balance) after 20 years have greatest amount of radioactive fallout? passed? 13. Write the three sequential nuclear reactions that convert 29. Section 4.9 informs us that U-235 can undergo the fol- U-238 into Pu-239 in a breeder reactor. lowing mode of fission: 14. In the conversion of U-238 to Pu-239 in the breeder re-i 137 actor, another element is produced momentarily from the ura- 92U + on -~ SZTe + 4~~Zr + 2 (1)n nium and decays quickly to plutonium. What is this transient Suppose that as Otto Hahn bombarded uranium with neu- element produced on the path from U-238 to Pu-239? trons, some of the fission had followed this route. Suppose 15. In the term "liquid metal fast breeder reactor," what does further that Hahn had taken about 4 days to analyze the the word "fast" refer to? products of this study. Do you think he might have found any 16. Describe two hazards associated with a breeder reactor tellurium-137? Do you think he might have found any zirco- that converts uranium to plutonium. nium-97? (Te-137 has a half-life of 4 seconds; Zr-97 has a half- 17. Why is it important that high-level nuclear wastes be life of 16.8 hours.) , stored in an area that is completely dry? 30. You have just examined a wooden utensil recovered 18. What was the first new element to be produced by artifi- from an ancient archeological site and have found that the cial means? How does its name reflect its origin? ratio of C-14 to C-13 is less than 0.,1% of the ratio of C-14 to 19. Describe how ionizing radiation can be used to cure or C-13 measured in a branch just cut from a nearby tree. What, control hyperthyroidism. if anything, can you conclude about the age of the wooden 20. What property of radioisotopes of iodine makes them utensil? What assumptions do you make in arriving at your answer? particularly useful for diagnosis and therapy of disorders of the thyroid gland? 31. In determining the age of the earth by measuring the ratio 21. How does the emission of a positron affect the atomic of lead-206 atoms to uranium-238 atoms in the earth's crust, we number of an atom? How does it affect the mass number of an made the assumption that all of the lead-206 in the rock sam- atom? ples came from the radioactive decay of uranium-238. How would our calculations of the earth's age be affected if some of 22. What form of radiation is detected by the instruments the lead-206 atoms were formed at the same instant the ura- used in PET? nium-238 atoms were formed? Suppose, that is, that at least 23. Describe how ionizing radiation can cause (a) somatic some of the lead-206 atoms that we found along with the ura- damage and (b) genetic damage. nium did not come from radioactive decay of the U-238 but 24. Name four sources of background radiation that might were formed along with the U-238. Would the earth be older affect someone standing outside in a rocky field. Name one or younger than our calculations would show? Describe your source of background radiation to which someone would be reasoning. Exercises • 113    .2. Plutonium-239 has a half-life of about 24,000 years. How rather than a (3 emitter for the treatment of deep-seated tu- ~ong will it take for 99.9% of the plutonium wastes of a breed- mors. What would your response be? Would you (a) pro- er reactor to decay into other substances? If we assume that mote or (b) fire the research scientist who proposed the there are four generations of humans in each century, how idea? Why? many generations will this period cover? 44. Of a radiation, (3 radiation, and y radiation, which is most 33. Using the graph of Figure 5.2 and the data of Table 5.3, damaging to living things when it is emitted by a nearby, ex- determine how long it will take for 100 g of U-235 to decay to ternal source? Explain your answer. Of the three, which is most 90 g of U-235. dangerous to a living thing when it is emitted by a radioiso-tope located within the body? Explain your answer. 45. Describe the similarities and the differences in the use of y radiation (a) to determine the shape and size of an internal organ and to detect the presence of tumors in it; (b) to deter-mine how well the organ is performing its biological functions, such as metabolizing a particular nutrient; (c} to kill a cancer-ous tumor in the organ. 35. If the Shroud of Turin were analyzed for C-14 today, what 46. Suggest three possible reasons why genetic damage by percentage of the C-14 originally present at its formation ionizing radiation has not yet been observed in humans. ; would you expect to be present? (Figure 5.2 may be useful to 47• Suppose there were to be a vote soon in your state to you.) ban all forms of production of ionizing radiation by human 36. Would it make any difference in calculations of the age of activities, such as in the production of electricity by nuclear rocks, based on the isotopic ratio of U-238 and Pb-206, if the Po~'~'er plants, the production of radioisotopes for medical decay step with the longest half-life were at the end of the se- use, and the use of X-rays in medical and dental examina- quence rather than at the beginning? Use an hourglass analo- tions. Would you vote for or against the proposal? Explain gy in arriving at your answer. your answer. - 48. Which one of the four factors that have slowed the growth of commercial nuclear power do you think provides the most Think, Speculate, Reflect, and Ponder important argument against further development of commer-cial nuclear power? Which one earries the least weight in ar- 37. What was the function of the graphite in Fermi's pile? guments against further development? What was the function of the cadmium? 49. Suppose a commercial electric utility wanted to build a 38. How did Enrico Fermi's studies of nuclear reactions con- nuclear power plant a few miles from where you live and your tribute to the use of atomic energy for the production of com- county or municipal government held a referendum to deter- mercial power? mine whether to permit the construction and operation of the 39. Why do health professionals working in radiology de- plant. This would give you the opportunity to cast a vote in partments of hospitals wear film badges on their coats? favor of the plant or against it. What factor(s) would sway you 40. Describe the operation of each of the following radiation toward voting for the construction and operation of the nu- detection devices: (a) a Geiger counter; (b) a scintillation clear power plant? What factor(s) would sway you toward vot- counter; (c) a film badge. How would you use each to estimate ing against the plant? the quantity of ionizing radiation that is present? Which one of 50. Is there any way to detect an actual difference between these detectors do you think is the best for determining the the electricity that is generated by a nuclear power plant and amount of accumulated radiation exposure a person receives the electriciry generated by a plant run with oil? If your an- over a long period, a week for example? Describe your swer is yes, how would you go about detecting the difference? reasoning. If your answer is no, how would you go about convincing some- 41. How could you construct a crude but effective radiation one (who believes otherwise) that you are right? detector out of common consumer materials readily available 51. What's the major difference between a pressurized water to you? Would this deviee measure radiation the moment it reactor and a boiling water reactor? Whieh do you think would occurs or would it measure cumulative radiation, detected over be less expensive to build and operate? Why? Which do you a period of time'? think would present less hazard of an accident or of radioac- 42. What properties should a radioisotope have if it is to be tive contamination of the environment? Why? administered internally in a medical diagnostic procedure? 52. Do you think that the continued production of electrici- 43. You are the administrator of a major research insti- ty by nuclear plants justifies the accumulation of high-level tute. One of your research scientists presents a plan to build nuclear wastes? Explain. an instrument much like that used for cobalt radiation ther- 53. lf you had a choice between connecting your home or apy, except that this new instrument would use an a emitter apartment to electric power provided by a plant that burns 34. You have 10 g of a mixture made up of exactly 5 g of I-131 and 5 g of K-40 and you also have a radiation detector that is able to detect radiation down to a level of 0.10% of the current level of radiation given off by the sample. How long do you estimate it will take for the level of radiation of the 10-g sam-ple to drop to (a) 75% of its current level? (b) half of its cur-rent level? (c) 0.10% of its current level? 114 • Chapter 5 Harnessing the Secrets of the Nucleus imported petroleum or a plant powered by nuclear reactions, ~a"',` which would you choose? Why? ; ฐ eb Questions 54. Among the various proposals suggested for the disposal Use the Web to answer or accomplish each of the following. Re- of high-level nuclear wastes is the possibility of sealing them port your Web source for each response. in drums and transporting them by rocket to the moon, to re- 1, Describe the current state of plans or expectations for the main on its surface forever. What would be the advantages of use of nuclear fusion to produce commercial electric power. such a plan? What would be the drawbacks? Would you sup- 2. What is the current condition of the nuclear power plant at port a plan of this sort? Explain. p p 55. It's possible to convert the energy of steam into elec- tricitand it' Chernobyl, Ukraine? Does it currently produce electric power? Are there current plans for rebuilding it? For tearing y, s p ossible to reverse the process by using elec- it down? For replacing it with a new power plant? tricity to produce steam from water. It's possible to convert g• Describe another reported accident at a nuclear power - the energy of falling water into electricity, and it's possible to reverse the process by using electricity to pump water plant anywhere in the world, in addition to those discussed in from a lower level to a higher level. It's possible to convert Section 5.2. the energy of the wind into electricity with a windmill con- 4• Find the location, history, and current status of a breeder re- nected to a generator, and it's possible to reverse the process actor in current use, either for experimental, research, or com- by using a fan to convert electricity into a stream of moving mercial purposes. air. It's possible to convert the energy of fissioning atoms 5• What is the current status of the proposal for the use of Yucca into electricity. Do you think it might be possible to reverse Mt., Nevada, for the long-term storage of nuclear wastes? the process and use electricity to produce fusion? Describe 6. Identify a radioisotope other than those discussed in this ' your reasoning. chapter that is used for medical diagnosis or treatment. De- 56. Suppose that the isotopic analysis of the Shroud of scribe its medical application. Turin had dated its origin to a few years earlier than the 7• Find a positron emission tomogram posted on the Web and birth of Jesus. What conclusion(s) could be drawn from this describe the medical condition or study it illustrates. result? 8. Radioisotopes of elements other than carbon and urani- 57. The ability of different kinds of ionizing radiation to um have been used for the dating of various substances. Iden- penetrate human tissue varies from one form of radiation to tify an isotope of one of these other elements that has been another. Gamma rays penetrate the entire body readily, a used for dating and describe an example of its use. rays are stopped by the skin, while (3 rays lie between these 9. Section 5.11 ends with the sentence, "Claims and counter- two. Yet 1 rem of any one of these forms of radiation does claims for the authenticity of the Shroud and of the radiocar- • the same amount of damage as 1 rem of either of the other bon dating have continued since the 1988 analysis." Summarize two. Explain why this is so despite the differences in pene- some of the arguments supporting and opposing the conclusion trating ability. discussed in this chapter. Exercises • 143 Figure 6.21 A burning candle. Water droplets coat the sides of The candle flame dies as the the beaker as the burning candle oxygen in the beaker converts oxygen and alkanes to is replaced by carbon water and carbon dioxide dioxide. marize our thoughts in the form of chemical equations. that atoms and molecules can interact with each other to be observe on a quantitative foundation. converted from one set of chemical structures to another This applies to the entire range of material substances set, with entirely different properties. Different compounds that share the same molecular for- mula 1. 1. Following are a statement containing a number of blanks, are known as . The molecular formula and a list of words and phrases. The number of words equals CaHio, for example, applies to two different compounds, the number of blanks within the statement, and all but two of known by their IUPAC names as and the words fit correctly into these blanks. Fill in the blanks of the statement with those words that do fit, then complete the state- alkanes IUPAC ment by filling in the two remaining blanks with correct words butane organic (not in the list) in place of the two words that don't fit. hydrocarbons paraffins Any compound containing the element carbon is an isobutane stereochemistry compound. Those compounds containing both carbon and hydrogen, but with no other element present, 2. Define, describe, or give an example of each of the following: are . Those containing carbon and hydrogen in a ratio that fits the general formula C„HZn+2 are known as a~ 1ฐ carbon f. double bond or, by an older system of nomenclature, b. alkene g. heptane . The modern system of naming organic c. alkyl group h. saturated hydrocarbon compounds, the system, came about as a re- d. aromatic compound i. stereochemistry sult of an international gathering of chemists at Geneva, e. cycloalkane j. unsaturated Switzerland, in 1892. Because the component atoms of all but the smallest mol- 3. Name three carbon-containing compounds that have been ecules can be joined to each other in a variety of ways, most obtained for centuries from living or once-living substances. molecular formulas can represent a variety of molecules. Describe their uses. 144 • Chapter 6 Introduction to Organic Chemistry 4. Using the chemical definition described in this chapter, c. propane 3. Related to a very highly identify each of the following as organic or inorganic: (a) table tlammable compound salt, (b) table sugar, (c) methyl alcohol, (d) oxygen gas, (e) the d. butane 4. Related to an alcohol isotope of uranium used in nuclear reactors, (f) the dye henna, obtained from wood (g) urea, (h) the carbon dioxide of your exhaled breath, (i) the carbon dioxide of a carbonated soft drink. 13. How can you determine whether any particular organic 5. Given a specific molecular structure, describe how you compound is a member of the alkane family? would determine whether it represents an alkane, an alkene, 14' Describe a property or a bit of chemistry: (a) common to or an alkyne. the entire hydrocarbon family; (b) common to all alkenes but 6. What do all aromatic compounds have in common? not to alkanes. 7. Name three consumer products that are composed exclu- 15' What compound is produced when: (a) diatomic hydrogen sively or largely of hydrocarbons. Describe the properties of is added to ethylene, (b) water is added to ethylene. alkanes that are most important to eaeh of the three consumer 16' Classify each of the following as to whether it is (1) a hy- products. drocarbon or not a hydrocarbon, (2) an alkane or not an alkane, 8. Name each of the following: and (3) an aromatic compound or not an aromatic compound. a. isobutane e. carbon dioxide a. CH3-CHz-CHz-CHz-CHZ-CH3 b. acetylene f, benzene b. CH3-CHz-CH-CHZ-CH3 c. hexane g. C1~H~6 d. cyclohexane h. cinnamaldehyde CH3 17. What's the difference between the molecular structures c. CH3-CHz-CH-CHZ-CH3 ~ of ethene and ethyne? CHZ 18. Draw the molecular structure of 2-pentyne. 19. How would you determine whether a chemical equation CH3 is balanced or unbalanced? d. CH3-CHZ-CH-CHZ-CHz-CH-CH3 A Little Arithmetic and Other I I Quantitative Puzzles CH3 CII3 e. CH3-CH-CH-CH3 20. Write balanced equations for the combustion of (a) me-thane, (b) ethylene, (c) propane, (d) propyne, (e) benzene. CH~ CH3 f. CH3-CH=CH-CHZ-CHZ-CH3 g. ~CH\ CHZ CHz 21. Balance each of the following equations: a. Na + Clz -~ NaCI b. Hz + C12 ---~ HCl c. Ca + Oz --~ Ca0 d. Na + Oz -> NazO e. Mg + Brz -~ MgBrz CHz ~CHz ~CHZ 9. Identify five organic compounds that are isolated from plants. Identify one organic compound that is generated by an-imals or animal products. 1 O. What are three properties of carbon that result in the large number and great variety and complexity of organic compounds? 11. In what way do free radicals react when two of them en-counter each other? 12. Match each of the following organic compounds with the property or source that is the origin of its common name: 22. Draw condensed molecular structures for all the isomers of heptane, C~H16, that have exactly six 1ฐ hydrogens. 23. The number of 1ฐ hydrogens in a molecule must be a mul- l tiple of 3, and the number of 2ฐ hydrogens in a molecule must be a multiple of 2. Why is this so'? 24. Hydrocarbon molecules that contain two carbon-carbon double bonds are called dienes. What is the general molecular formula for the family of dienes? What other family of hydro-carbons has this same general molecular formula'? 25. How many molecules of hydrogen would have to be - ; added to a molecule of benzene to produce cyclohexane? Compound Property or source 26. To what class or classes of compounds might each of the ; a. methane 1. Reiated to the first in a following hydrocarbons belong: (a) CSHlo, (b) CgHlg, series of acids found in fats (c) C6Hlo, (d) C~oHzo> (e) C9Hzo? b. ethane 2. Related to an acid found in 27. Draw all the isomers of C3H6 that can exist and name rancid butter each. Exercises • 145 28. Why can't a compound with a molecular formula of 40. Can two different compounds have the same name? Can C3Hlo exist? two compounds identical in every other way have different 29. Can an alkane molecule contain an odd number of hy- names? Explain. drogens? Explain. 41. Because alkanes burn readily in air they are useful as com- 30. The largest hydrocarbon discovered to date has the mo- ponents of commercial fuels. What is another property or char- lecular formula C139sH127s and is composed largely of aro- acteristic of alkanes, especially the higher alkanes, that makes matic rings and carbons joined by triple bonds (Sec. 6.11). them useful in consumer products, even in products that are Write the balanced equations for its combustion to water and not used as fuels? carbon dioxide. 42. Both the methyl free radical and the chlorine atom con- 31. How many straight-chain isomers of CSOH l02 can there tain an unpaired electron. When two methyl free radicals com- ; be? Explain your answer. bine they form ethane, CH3-CH3. When two chlorine atoms the condensed structure of the molecule formed when a methyl free radical combines with a chlorine atom. Think, Speculate, Reflect, and Ponder 32. Methane and ethane are both members of the alkane fam- 43• Write the molecular formula of heptadecane. ily of hydrocarbons. Describe one characteristic that methane 44. How would using a warm beaker rather than a cool one and ethane have in common. Identify one difference between in the demonstration that opened this chapter have affected methane and ethane. our observations of a candle burning in an inverted beaker? 33. Draw the structure of cyclohexene. 45. How would you distinguish between food that is "organ- 34. Are 1-butene and cyclobutane isomers? Explain. ic" and food that is not "organic"? Apply the chemist's defini- 35. Draw the structure of two isomers of C4H6 that contain tion of "organic" to food and describe how this affects your a triple bond. Draw one isomer that contains a ring. interpretation of the term organic food. 36. Draw the structure and give the IUPAC name of the alka- 46• Can any inorganic substance be isolated from living or ne of lowest molecular weight that contains a 4ฐ (quaternary) once-living material? Exnlain. carbon. 47. Give the molecular structures and the IUPAC names of all five isomeric hexanes. 37. Name the following two compounds (Sec. 6.3 may pro-vide help for part b): a. CH3-CH-CI CH3 b. CH3-CHZ-CHZ-OH 38. What would be one danger of using pure methane as a household fuel for heating and cooking? 39. Name each of the following compounds: a. CH3-CH-CHZ-CH3 "12-CH3 b. CH3-CH-CH3 CH3-CH-CH3 c. CH3-CH-CHZ-CHZ-CH-CHZ-CH3 52. We can speculate that life exists in some other part of the universe, perhaps in a form far different from what we find here on Earth. On Earth, life is based on compounds of the el-ement carbon. If life were to occur in another part of the uni-verse, and if that life were based on an element other than carbon, suggest what element that might be. Justify your an-swer with reference to the periodic table and the relationships among elements within it. ' combine, they form a diatomic chlorine molecule, C12. Write Compare compound (a) with compound (b) of Exercise 8. Are these two compounds isomeric alkanes? Are they mutually identical? Are they identical compounds with different names? Are they different compounds with the same names? Answer 53. Suppose that the carbon atoms of alkanes weren't tetra- these questions after comparing compound (b) with compound hedral but were square planar instead. That is, suppose the car- (e) of Exercise 8. Repeat for a comparison of compound bon atom were at the center of a simple square and the (c) with compound (d) of Exercise 8. hydrogens or other carbons bonded to it were at the corners 48. Draw molecular structures for all the isomers of (a) CZH6 (one isomer), (b) CZHSCl (one isomer), (c) C3H7C1(two iso-mers), (d) C4Hlo (two isomers), and (e) CSH12 (three isomers). 49. Should we classify benzene as a saturated hydrocarbon or as an unsaturated hydrocarbon? Explain. 50. What was the significance of Wohler's laboratory syn-thesis of urea? 51. Suppose a sealed vial of a liquid is recovered from an an-cient tomb in Egypt and writing on a clay tablet accompany-ing the vial is translated to indicate that the liquid was made from the juice of berries, but there is no indication of the age of the liquid. How might you go about determining how long ago the liquid was prepared from the berries? What technique might you use? 146 • Chapter 6 Introduction to Organic Chemistry of the square and that they all lay in the same plane, as they do 4. Where are the official headquarters of the IUPAC? Where on this sheet of paper. Knowing that atoms and groups bond- are its administrative headquarters? Where and when was the ed to each other by covalent bonds can rotate freely around latest meeting of its general membership held? Where and those bonds, predict how many isomeric methanes could exist when is the next meeting scheduled? if all carbons of alkanes were square planar. How many 5, What is the IUPAC name for the unbranch.ed hydrocar- ethanes? Propanes? Butanes? bon Cq6Hq4? 6. Write a brief history and description of benzene. Discuss the contributions of Michel Faraday and Friedrich August Kekule to our knowledge and understanding of benzene. De Use the Web to answer or accomplish each of the following. scribe where benzene was discovered, where or how it is cur- ' Report your Web source for each response. rently obtained, what it looks like and how it behaves under 1. Section 6.1 describes the red-orange dye henna and the an- ordinary conditions of temperature and pressure, and what it timalarial agent quinine as organic compounds that can be ex- is used for. Discuss the hazards of handling the compound and , tracted directly from plants. Identify two other useful organic of absorbing it into the body. compounds that can be extracted directly from plants. 7. In addition to those presented in this chapter, identify aro- v,; 2. Many Web sites offer "organic" foods for sale. Describe some matic compounds: a) isolated from plant material, b) not found common characteristics of these foods described as "organic." in nature but manufactured commercially, used c) in prescrip- 3. Find commercial sources for samples of each of the first 10 tion medicines, d) as food additives, e) in the manufacture of alkanes, methane through decane. plastics, f) in dyes.  Web Questions 1. Following are a statement containing a number of blanks, and a list of words and phrases. The number of words equals the number of blanks within the statement, and all but two of ; the words fit correctly into these blanks. Fill in the blanks of the statement with those words that do fit, then complete the state-ment by filling in the two remaining blanks with correct words '' (not in the list) in place of the two words that don't fit. is a mixture of that provide power to a car as they react with oxygen within the cylinders of the to produce and and to release energy. In a four-stroke engine, the ignites the gasoline-air mixture at the end of the sending the piston downward. The , which fol-lows, translates the energy of the gasoline into the power that moves the vehicle. What are the three products of the complete oxidation of a "isooctane." hdb? Wht lthlbt idd on im yrocaronaea susances proucenco- Gasoline itself is derived from a naturally occurring mix- plete oxidation of a hydrocarbon? ture of hydrocarbons known as . Al- though a certain amount of gasoline hydrocarbons (known 5. What two characteristics of a hydrocarbon's molecular as natural or straight-run gasoline) can be obtained direct- structure affect its volatility?  Exercises • 169 batteries. In the end a balance of cost, convenience, and cleanliness will probably determine our choice of fuel forto-morrow's car. "Cost" will include the cost of the fuel and the engine, and the expense of maintaining a clean environment. "Convenience" will reflect both the car's driving range and the simplicity of charging or exchanging a battery or filling a tank with fuel. "Cleanliness" will be a matter of the kind of en-vironment in which we choose to live. In any case, we will have choices before us, both as individuals and as a society. Whatever fuel or combination of fuels we do choose, it will be chemistry, in one form or another, that delivers the ener-gy. Making the choices intelligently will require an under-standing of the chemistry that lies behind them. • , are broken down into smaller molecules that have properties more suitable to gasoline. benzene kerosene catalytic cracking knock compression ratio octane rating compression stroke methyl tert-butyl ether distillation petroleum gasoline power stroke hydrocarbons spark plug internal combustion 2,2,4-trimethylpentane engine water 2. Define or identify each of the following: taining fuel carried on the vehicle. Although not truly a zero-emission device-it produces water as a product-the cell is essentially pollution free. As with other forms of alterna-tive power, fuel cells come with their own disadvantages. They are currently large, heavy, and much more expensive than other sources of power. Combinations, Cost, Convenience, and Cleanli-ness Still another possibility is the hybrid electric vehicle (HEV), which carries both gasoline and electric engines. In a parallel HEV both engines are connected to the wheels; driving conditions determine which one is running. In a series HEV the gasoline engine serves principally to recharge the For Review a. catalyst b. catalytic converter As the (the ratio of the maximum volume of c. crude petroleum d. fossil fuel the gasoline-air ratio at the beginning of the compression e. intake stroke ^ isomerization stroke to that of the fully compressed mixture at the end of g, oxygenate h. petroleum refining the compression stroke) of an engines increases, the ten- i, reforming j. tetraethyllead dency of a gasoline to also increases. The abil- k, ZEV ity of a particular gasoline blend to resist this tendency is reflected by its , which is measured by compar- 3. Identify the four strokes of the internal combustion engine ing the gasoline blend to a mixture of and describe what happens during each. and ' which is also known as "octane" ly from this mixture by , additional 6. What is a major advantage of increasing the compression gasoline can be produced by , a process ratio of an engine? What characteristic of a gasoline must be in which the molecules of higher boiling fractions, such as changed as the compression ratio increases? 170 • Chapter 7 Petroleum 7. What purpose does the catalytic converter of an automo- 22. What correlation do you think may exist between the bile serve? ratio of primary and secondary carbons on a pair of iso- 8. Into which chemical is the carbon monoxide (CO) of ex- meric alkanes and the relative magnitude of their octane haust gases converted as the gases pass through the catalytic numbers? Explain. converter? 23. Isopentane (2-methylbutane) is a major component of 9. (a) Why was tetraethyllead added to gasoline? (b) What gasoline. Give its molecular structure and write a balanced was the original reason for discontinuing the addition of equation for its combustion (see Sec. 6.8). tetraethyllead? (c) What additional benefit comes from re- 24. (Note: This exercise deals with data presented in Sec- moving this additive? (d) Name another chemical additive that tion 7.1.) Assuming that the number of vehicles on the road can serve the same function as tetraethyllead. (e) What refin- and the number of miles we drive remain constant, how many ing process produces the same characteristic in gasoline as that gallons of gasoline would we save each year for each obtained by adding tetraethyllead? mile-per-gallon increase in the energy efficiency of our cars? 10. What is the function of distillation in the refining of petroleum? Think, Speculate, Reflect, and Ponder 11. In what way do compounds that occur naturally in petro- leum but that are not hydrocarbons contribute to environ- 25. The distillation of water from the tea in the pot of the mental pollution? opening demonstration allows you to collect water that is quite pure, except for possible contamination by the more volatile 12. Petroleum, which does not contain large quantities of components of the tea. What is left behind in the pot as you dis- aromatic hydrocarbons, is a major source of aromatic hy- till the water from the pot and collect it in the glass? drocarbons. Explain why and describe the chemistry involved. 26. Arrange the following hydrocarbons in order of increas-ing boiling point, with the lowest boiling hydrocarbon first and 13. Does the catalytic cracking of petroleum produce straight- the highest boiling last: (a) nonane, (b) ethane, (c) butane, run gasoline? Explain. (d) heptane, (e) methane. 14. What two refining steps are needed to convert hexane 27, Arrange the following hydrocarbons in order of increas- into benzene? ing boiling point, with the lowest boiling hydrocarbon first 15. What is the function of: (a) an oxygenate, (b) an octane. and the highest boiling last: (a) 2-methylbutane, (b) butane, enhancer? (c) 2,2-dimethylpropane, (d) 2-methylpropane, (e) pentane. 16. Identify an oxygenate that is not an ether. What functional 28. Arrange the following hydrocarbons in order of increas- group does it possess? ing boiling point, with the lowest boiling hydrocarbon first and 17. What is one disadvantage to the use of ethanol as an the highest boiling last: (a) octane, (b) 2-methylbutane, oxygenate? (c) hexane, (d) 2,2-dimethylpropane, (e) heptane. 29. Arrange the following hydrocarbons in order of increas-ing boiling point, with the lowest boiling hydrocarbon first A Little Arithmetic and Other and the highest boiling last: (a) 2,2-dimethylpentane, (b) 2- Quantitative Puzzles methylhexane, (c) 2,2,3-trimethylbutane, (d) heptane. 18. On average, how many cylinders are in the power stroke at any given moment in a four-cylinder engine? In an eight-cylinder engine? In a six-cylinder engine? 19. Using the data presented in Section 7.1, calculate the num-ber of miles per gallon provided by the average motor vehicle in the United States. Identify at least one source of error in this calculation. 30. Based on what you know of the effect of the molecular structure of alkanes on their boiling points, why is it difficult to predict whether 2,2,3-trimethylheptane or octane will have the lower boiling point? 31. Aromatization of a cyclic hydrocarbon, A, molecular for-mula C7H14, produces toluene, C7Hg. Write the name of hy-drocarbon A and give its molecular structure. 32. In Section 6.10 we saw that adding water to an alkene produces an alcohol. Methyl tert-butyl ether is manufactured by adding a certain organic compound to 2-methyl-l-propene: 20. Draw the condensed structure of the isomer of C8H18 that has the greatest number of methyl groups. Write the IUPAC name of this isomer. What prediction can you make about the probable numerical value of its octane number? CI-12=C-CI-13 21. Repeat Exercise 20 for the isomer of C$Hl$ that has the smallest number of methyl groups. CH3 Exercises • 171 What compound is added to the double bond of this alkene to 45. (a) If the combination of a new engine design and the de- produce methyl tert-butyl ether? velopment of the ideal hydrocarbon fuel produced only C02 33. You have a mixture of two different liquid compounds and HZO as combustion products, would you agree to the re- and you attempt to separate them from each other by distilla- moval of catalytic converters from automobiles or to the sale tion. You find, however, that no matter how carefully you dis- of new cars without them? Explain. (b) If catalytic converters till them and no matter how complex and intricate a distillation were removed, would you agree to the return of leaded gaso apparatus you use, you cannot separate the two components. line to raise octane ratings? What can you conclude about these two liquids? 46. Suppose that you now own a car and could replace it with a new one that is equivalent or better in all respects, is far less ex-pensive to own and operate, and doesn't pollute the atmosphere in any way. Suppose, though, that this new car has to be refueled (or recharged if it is an electric car) every 10 miles you drive. Would you replace your current car with this one? Would you re-place it if the new car required refueling or recharging every 20 miles? 50 miles? 100 miles? 250 miles? 1000 miles? How does the range of a car affect your attitude toward it? 34. Which of the following components of auto exhaust emis-sions would you expect to be decreased by the use of a cat-alytic converter: H2O, isopentane, C02, CO? CO 35. Which of the components of exhaust emissions described in Exercise 34 would you expect to be increased by the use of catalytic converters? 36. Would you expect the chemical composition-the spe-cific hydrocarbons used to blend the gasoline and their pro-portions in the mixture-of a specific brand of gasoline to be the same in Miami in July as it is for the same brand sold in Chicago in January? Explain. 37. Suppose you were given samples of two different liquids. Describe how you could determine which one is the more volatile. 38. Engines are more likely to stall as the result of vapor lock after the car has been traveling for a while than when it is just started. Why? 39. You are in charge of designing a new form of the internal combustion engine. One of your workers has suggested mov- ing the valves and the spark plug from the top of the cylinder -qni Web Questions to the side of the cylinder, midway between the top and the Use the Web to answer or accomplish each of the following. bottom of the piston's travel. Are there any advantages to this idea? Are there any disadvantages? Explain. port your wed source jor eacn response. 1. When and where was the first oil well drilled within the continental United States? Is it still in operation? 40. Describe one way our society can produce a significant decrease in our consumption of petroleum. Describe your reasoning. 41. In the event of a severe and prolonged petroleum short-age, we may have to choose between producing enough heating oil to keep us warm during a particularly cold win-ter and producing enough gasoline to keep our cars run-ning. Explain why we might have to make this choice and describe the chemistry involved. 42. What would be a major advantage of using the combus-tion of hydrogen (HZ) as a source of energy in a car's engine? What might be a major disadvantage? 4. What octane enhancers have been used or proposed for gasoline, in addition to methyl tert-butyl ether? What are the advantages and disadvantages of each? ti 43. Which of the compounds in the question at the end of Section 7.3 would you expect to have the highest octane num-ber? The lowest? Describe your reasoning. 44. Can a compound have an octane rating higher than 100? 6• Prepare a graph showing the total amount of gasoline used Lower than zero? If your answer to either of these is no, ex- by cars in the United States each year since 1920. 5. What is the location of the nearest petroleum refinery? What is its annual output of refined petroleum products? plain why not. If your answer to either of these is yes, explain 7. Describe the current prospects for the use of solar power their significance. in automobiles. 47. Prepare a table listing sources of energy that may replace today's gasoline for our cars of tomorrow. List several of the advantages and disadvantages of each. 48. Suppose that all motor vehicles that now run on fuels derived from petroleum were replaced by electric, battery-powered cars. How would you suggest we produce the elec-tricity needed to recharge the battery so as to minimize pollution of all kinds? What source of energy would you use for the production of the large quantities of electricity that would be needed? 2. What's the average, typical, or most common compression ratio of the cars that drive on our highways? What's the range of compression ratios of racing cars that participate in events like the Indy 500? What fuels do the racing cars use? What are their octane ratings? 3. Describe the concerns about air quality that led to the pas-sage of the Clean Air Act of 1970. What amendments, if any, have been added to the act since 1970? Exercises • 197 EXERCISES For Review d. an electric battery standing alone on the floor of a room e. a stream of a particles. 198 • Chapter 8 Working with Chemistry A Little Arithmetic and Other 24. Suppose you weigh 154 Ib and have just eaten a Iunch Quantitative Puzzles consisting of a glass of orange juice, a hamburger, a malted 19. A person in normai health and weighing 165 Ib (75 kg) milk shake, and a serving of potato chips. How long would you fasts for 36 hours while lying still in bed. What is the total num- have to run to use up the calories you absorbed from the ber of Calories lost during the last 24 hours of the fast? lunch? (Refer to Table 8.3.) 25. Repeat Exercise 24, but this time for a lunch consisting of 20. Suppose this same 165-Ib person chooses to lie in bed for a glass of orange juice, a tuna fish sandwich, a raw carrot, and a month, without engaging in any of the normal, daily physical a glass of soda. activities that constitute exercise in its broadest sense. Taking into account all the factors involved in resting metabolism, cal- 26• How many calories does it take to heat 25 g of water from culate the average daily intake of food Calories needed by this 40 to 50ฐC? individual to maintain body weight at a constant level. 27. How many calories are released as 25 g of water cools 21. The following are the amounts of each of the macronu- from 60 to 50ฐC? trients provided by one standard serving of several common- 28. What is the final temperature of the 50 g of water formed ly available packaged foods. How many Calories does one when 25 g of water at 60ฐC is mixed with 25 g of water at 40ฐC? serving of each of these foods provide? Assume that all of the heat released by the warmer water is ab- a. Bumble Bee chunk light tuna in water sorbed by the cooler water. carbohydrate 0 g 29. What is the final temperature of the 50 g of water formed protein 12 g when 10 g of water at 60ฐC is mixed with 40 g of water at 40ฐC? fat 2 g 30. A 100-watt electric light bulb was placed in a calorimeter b. V8 vegetable juice and turned on. After a period the temperature of 1000 g of carbohydrate 9 g water in the calorimeter rose by exactly 10ฐC. Using the in- protein 1 g ` formation in Section 8.5, calculate the length of time the light fat 0 g bulb was on. c. Campbell's chicken broth 31. How long would the nutritional energy provided by one carbohydrate 2 g serving of the potato chips described in Exercise 21 g keep a protein 3 g 100-watt light bulb burning? fat 2 g g2, Which is larger, the total annual production of energy by d. Farm Best low-fat milk all the commercial and industrial plants on earth or the total carbohydrate 11 g annual production of energy by all the people on earth, protein 8 g through the combination of exercise and basal metabolism. fat 5 g 'I'he Question at the end of Section 8.9 may be useful here. e. Breyers mint chocolate chip ice cream carbohydrate 17 g protein 3 g Think, Speculate, Reflect, and Ponder fat 9 g f Planter's Sweet-N-Crunchy peanuts carbohydrate 15 g protein 4 g fat 8 g g. Charles Chips potato chips 34. You have an electric hot plate that transfers heat di- carbohydrate protein 1 g fat 10 g 15 g rectly to whatever is on it with negligible losses. How could you determine the wattage rating of the hot plate experi- mentally? 33. A person who is ill with a fever is releasing energy more rapidly than normal. This energy raises the body temperature, which we detect as the fever. Which one of the three energy-expending processes increases as a result of the illness? 35. It takes energy to accelerate a car from zero to 50 miles an hour. Through the Law of Conservation of Energy we know that the kinetic energy of the car traveling at 50 miles an hour has to come from the transformation of some other form of energy into the car's kinetic energy. Where does the car's en- ergy come from? It also takes energy to bring a car traveling at 50 miles an hour to a complete stop. The kinetic energy of the car has to be transformed into some other form of energy. Into what kind of energy is the car's kinetic energy transformed as it slows to a stop? each step you would take in the conversion of the C-11 into su- crose containing this isotope. 43. Suggest some benefits that might come from a gradual warming of the earth's surface through the greenhouse effect. de we butter, margarine, or oil (in a nonstick frying pan)? 22. How long would it take a 70-kg person to burn up the en- ergy provided by one standard serving of each of the foods (a-g) in Exercise 21 through the operation of basal metabo- lism alone? 23. How long would it take this same 70-kg person to burn up the energy provided by one standard serving of each of the foods (a-g), in Exercise 21 through the energy expenditure of 5 Cal per minute during a moderate exercise such as brisk walking? Web Questions • 199 36. Table 8.3 shows that a fried egg provides 110 Cal, while a boiled egg gives us 77 Cal. Since eggs are often fried in butter, margarine, or vegetable oil, what do you suppose is the source of the additional calories in the fried egg? What do you think would be the calorie content of an egg fried without the use of 37. Describe a device or a process by which the following Web Questions transformations occur: Use the Web to answer or accomplish each of the following. a. chemical energy is transformed into electrical energy Report your Web source for each response. b. chemical energy is transformed into heat c. chemical energy is transformed into kinetic energy d. electrical energy is transformed into chemical energy e. electrical energy is transformed into heat f. electrical energy is transformed into kinetic energy g. kinetic energy is transformed into electrical energy a medical setting. h. kinetic energy is transformed into heat 38. Francis Bacon and Count Rumford used the scientific method in the investigations described in this chapter. the question each asked and describe the experiment each de- 1. In addition to the calorie and the joule, another unit of heat or energy in widespread use, especially outside the sciences, is the british thermal unit or btu. Write a brief description of the btu, including its definition, its origin, and the areas in which it is principally used. 2. Describe how a person's basal metabolism is measured in 3. Summarize briefly federal regulations for the listing of macronutrients and their associated Calories on the labels of State packages of processed foods. 4. What is the estimated mass, in kilograms, of the earth's en-vised to answer the question, the results each obtained (or tire biomass? ; would have obtained, had Bacon lived), and the conclusions drawn. 39. Using commonly available materials, how would you : demonstrate that (a) work produces heat and (b) heat can be ; used to do work? 5. What is the estimated mass, in kilograms, of all the carbon dioxide currently present in the earth's atmosphere? 6. What is the temperature of the moon's surface when it is lit by the sun, during the lunar day? What is the temperature when the surface is dark, during the lunar night? How do these temperatures differ from comparable temperatures on earth? What is the source or cause of this difference between the moon's surface temperatures and the earth's? = 40. Planting 100 million trees has been suggested as a means for decreasing the greenhouse effect of our atmosphere. Describe the reasoning behind this proposal. 41. What would have been the fate of the carbon of plank- ton if the plankton had been completely metabolized by other organisms instead of being trapped, only partially decomposed, at the bottom of bodies of water and eventually converted into fossil fuels? a 7. Describe additional evidence for the greenhouse effect, be- yond the phenomena discussed in Section 8.15. 8. Describe any current arguments or evidence that the green- house effect is not real, or that the burning of fossil fuels is not significant contributor to the greenhouse effect. 42. If you wanted to use sucrose containing C-11 in a PET ` investigation (Sec. 5.9), how might you obtain a quantity? sume that you have a supply of C-11 on hand and describe 9. Describe the current status of each of the proposals, listed As- in the Perspective, for achieving a balance of energy produc- tion and climate stability. Exercises • 225 ฐ molecule of contaminant per 79 x 1023 molecules of water the water an offensive taste, odor, or appearance, but we cannot realistically expect the total and complete absence of anything but molecules of H20 in our drinking water. When we consider the arithmetic of pollution we can better understand the questions of the opening demon- stration. What must be asked is not "Is there any contami- nant in our drinking water?" but rather "What are the limits of contamination we can reasonably accept?" Understand- ing the answer to this more critical question requires an un- derstanding of how we count chemical particles and what their concentration terms mean. • (Fig. 9.6), our language provides no terms of reference equiv- alentto parts per million, parts per billion, orthe like. Would we realistically call the water "polluted"? Surely not. Nor would we consider a glass of water to be polluted if it contained two, three, or ten molecules of another sub- stance. Yet at some higher level, some threshold concen- tration, we would just as surely call the water polluted and `'~ unfit to drink. We do, indeed, expect the concentrations of any contaminants in our drinking water to remain well below ~ the levels at which they might be hazardous or might give Chapter 9 Exercises For Review 1. Following are a statement containing a number of blanks, and a list of words and phrases. The number of words equals the number of blanks within the statement, and all but two of the words fit correctly in these blanks. Fill in the blanks of the ratement with those words that do fit, then complete the state- :ent by filling in the two remaining blanks with correct words aot in the list) in place of the two words that don't fit. One___of a substance is equal to its atomic or mo- lecular weight expressed in ___ and contains 6.02 x lO 23 chemical particles, which is also known as ___ of particles. Since 1 mole of any chemical substance contains the same number of ___ as 1 mole of any other chemical substance, we can calculate the weight of one chemical that will react completely with a given weight of an- other by using their ____ in our calculations. We can also use ___ of solutions rather than weights in these calculations as long as we know the ___ lution, which is a measure of the amount of ___ dissolved in a specific volume of the ___ A solution that contains 1 mole of solute per ___ of solu- tion has a concentration of 1 ___. atomic or molecular weights mole Avogadro's number ppm concentration solute grams solution kilogram volumes liter a. 1 mole of neon 2. Explain, define, or describe the significance of each of the following: . a. agricultural runoff b. groundwater c. ppm d. The Safe Drinking Water Act of 1974 4 e. weight/weight percentage (w/w %) concentration 3. Write the chemical equation for the reaction that occurs as charcoal burns (a) in the open air; (b) in an enclosed space, with a limited supply of air. 4. (a) What is the danger in heating a closed room by burn- ing charcoal briquettes in a grill, placed in the room? (b) Why isn't this a hazard when the grill is used outdoors? 5. Is it necessary to know the numerical value of Avogadro's num- ber to carry out calculations using quantities of moles? Explain. 6. Write the balanced reaction for the combustion of methane to produce carbon dioxide and water. 7. Why are concentrations expressed in molarity particularly useful to chemists? 8. What unit of concentration is used most frequently in con- sumer products? 9. What unit of concentration is equivalent to 1 milligram of solute per kilogram of solution? 10. Name a unit of concentration useful in discussions of ex- tremely small concentrations, as in pollution studies. 11 • Describe three processes that remove freshly fallen rain water from the ground. A Little Arithmetic and Other Quantitative Puzzles 12. How many (a) left shoes are there in 15 pairs of shoes? (b) dozen yolks would you get from half a dozen eggs? (c) moles of sodium cations are there in half a mole of sodium chloride? 13. How many moles of hydrogen atoms does it take to pro- duce 1 mole of diatomic hydrogen molecules? 14. What is the weight of: a. 1 mole of neon b. 2 moles of zinc c. 1 mole of diatomic nitrogen d. 3 moles of diatomic hydrogen gas e. 1/2 mole of chloride ions f 1 mole of chlorine atoms g. 1 mole of diatomic chlorine molecules h. 2 moles of neutrons 15. What weight of (a) sodium contains 1 mole of sodium atoms? (b) chlorine atoms contains 1 mole of chlorine atoms? (c) sodium chloride contains 1 mole of sodium ions? (d) sodium 226 • Chapter 9 Arithmetic of Chemistry chloride contains 1 mole of chloride ions? (e) CO2 is produced when 1 mole of carbon combines with 1 mole of diatomic oxy- gen molecules? 16. Assuming that rubbing alcohol is 70% (w/w) isopropyl al- cohol, and that its density is 1 kg/liter: a. How many grams of water and how many grams of iso- propyl alcohol are there in a liter of rubbing alcohol? b. How many moles of water and how many moles of iso- propyl alcohol (molecular weight 60) are there in a liter of rubbing alcohol? c. If we decide which is the solute on the basis of weight, is isopropyl alcohol the solute or the solvent? d. If we decide on the basis of the number of moles, is iso- propyl alcohol the solute or the solvent? e. Considering water as the solute and the isopropyl alco- hol as the solvent, what is the molarity of the water in the solution? Considering isopropyl alcohol as the solute and water as the solvent, what is the molarity of the isopropyl al- cohol in the solution? a. How many moles of S03 are there in 8 g of sulfur trioxide? b. How many moles of sulfuric acid form when 8 g of sul- fur trioxide dissolve in water? c. What weight of sulfuric acid forms when 8 g of sulfur trioxide dissolve in rainwater? 22. you have l liter of a solution that contains selenium at a level of 15 parts per billion and 1liter of another solution that contains barium at a level of 3 parts per million. You now mix the two solutions together to produce 2liters of a single solu- tion. Does the new solution produced by mixing the two orig- inal liters together meet federal drinking water standards for selenium? For barium? 23. The Safe Drinking Water Act of 1974 permits a maximum of 160 mg of sodium per liter of drinking water. What is the maximum molarity of sodium chloride permitted in community drinking water by the Safe Drinking Water Act? (You may find Section 9.12 useful in working this problem.) ,: 24, How many sodium cations are there in all of the water in glass 7 of the demonstration at the beginning of the chapter? 25, prepare a table showing the molarity of the sugar wate each of the seven glasses of the second part of the demo~ stration that opened this chapter. Which glass comes close 17. Which one of the following contains the greater number of moles of sucrose, (a) or (b), or do they contain the same number? (a) 4 liters of a 0.125 M sucrose solution; (b) 0.375 liter of a 1.5 M sucrose solution? to the molarity of two teaspoons of sugar in a cup of coffee 18. A typical aspirin tablet contains 0.325 g of the active in- Refer to the examples in Section 9.8. gredient, acetylsalicylic acid. What is the average concentra- 2g, If you count all of the protons and all of the neutrons in the tion, expressed as a percentage by weight (w/w %), of the body of a person weighing 1651b and add the sum of all the pro- acetylsalicylic acid in the body of a 165-1b (75-kg) person who tons you have counted to the sum of all the neutrons you have has just taken two aspirin tablets? counted, what is the combined total? This is not a trick question 19. In determining the molarity of the sucrose in the coffee of and you don't have to perform tiresome or complex calculations. the example of Section 9.8, we assumed that the coffee has a den- pll ihat's required is a good understanding of the material in this sity of 1, or 1000 g per liter. With all the solutes in the coffee, in- chapter and a little thought.The solution appears in Appendix E, cluding the 10 g of sugar, our assumption of 1000 g per liter is along with a discussion of the chemical principles involved. probably too low. If we assumed a density of, let's say,1100 g per liter, what molarity (to one significant figure) would we now get? 27. As we saw in Chapter 7, carbon monoxide is also produced by the incomplete combustion of gasoline in a car's engine. To 20. Chlorine gas consists of diatomic molecules, C12. The bal- help reduce air pollution catalytic corcverters (Sec. 7.7) are used on ' anced chemical equation for the reaction of sodium metal with cars to promote the combination of carbon monoxide with oxy- chlorine gas to produce sodium chloride is 2Na + C12 -~ gen, thus transforming the CO into CO2. Write the balanced 2NaCl. equation for the reaction of CO with OZ to form CO2. a. What weight of chlorine gas does it take to react com- 2g, Write the balanced equation for the combustion of methane pletely with 4.6 g of sodium? in an enclosed space,with a limited amount of oxygen, to produce b. What weight of sodium does it take to react complete- carbon monoxide and water instead of carbon dioxide and water. ly with 1.42 g of chlorine gas? 29, Write balanced equations for the complete combustion of c. If we started with exactly 10 g of sodium and 10 g of di- methanol (CH3-OH), ethanol (CH3-CHZ-OH), and pen- atomic chlorine gas, would either of these elements be tane (CSHlZ, a major hydrocarbon of gasoline). Calculate the left over at the end of the reaction? If so, which one? weight of carbon dioxide produced by the complete combustion 21. The use of fuels with small amounts of sulfur-containing of 100 g of each of these compounds. Assuming that all three of impurities results in the formation of sulfur trioxide, 503, an these compounds are equally efficient when used as a fuel for atmospheric pollutant. The S03 dissolves in rain and other an internal combustion engine, rank them in order of the amount forms of atmospheric water to form sulfuric acid, HZSO4, ac- of carbon dioxide released to the atmosphere per mile of auto- cording to the chemical equation S03 + H20 --~ HzS04. mobile travel. Based on the content of Section 8.14, which would Through the generation of sulfuric acid, S03 contributes to the contribute most to an increase in the greenhouse effect if used as formation of acid rain (Sec.14.5) an automotive fuel? Which would contribute least? Web Questions • 227   30. The sun is 150,000,000 km from the earth and the diameter he welfare ought to be more important than individual wishes of a penny is 1.9 cm. If Avogadro's number of pennies were used in making these decisions? Discuss your answers. to build a road from the earth to the sun and the road were just 39. Here's breaking news, just in! It's just been discovered one layer of pennies deep, how many pennies wide would the that the value long accepted for Avogadro's number is wrong! road be? (This problem is worked in some detail in Appendix C.) The value used for so long has just been shown to be off by at least 25%, although no one knows just yet exactly how much Think, Speculate, Reflect, and Ponder or in which direction. Which answers in these end-of-chapter exercises will have to be changed as soon as we learn the cor- 31. Why is it not possible, either in theory or in practice, to rect value of Avogadro's number, and which can we let stand calibrate a scale in units of moles? as they are? 32. Suppose you have a scale you know to be accurate, but you don't know what units of weight it measures. You have a quanti- = ty of acetic acid and you want to measure a quantity of water that ;q1%.g7iVeb Questions contains the same number of water molecules as there are acetic Use the Web to answer or accomplish each of the following. acid molecules. Could you use the scale to do that? Explain. Sup- Report your Web source for each response. pose you want to prepare a 1 M solution of acetic acid in water. Could you use the scale to do that? Explain. 33. Suppose you have an analytical instrument that could tell you quickly exactly how many molecules of an agricultural in- secticide there are in a glass of water. What standard(s)-the number of insecticide molecules, the odor, color, taste of the water, or any other criterion-would you use to determine whether the water is fit to drink? (No governmental drinking- water standards have yet been set for this insecticide.) 34. Regardless of any legal definition, which glasses in the opening demonstration would you consider to be polluted with salt? Which, if any, would you consider safe to drink? 35. Define "pollution" in your own words. 36. (a) Under what conditions would you consider water be "polluted"? (b) Would you say that all "polluted" water is (c) Can water that is unfit to drink not be "pol- luted"? (d) Can water that is "polluted" be safe to drink? 37. Describe three specific actions you would recommend to to 1 Summarize the life of Amedeo Avogadro with a brief bi- ography that includes the dates of his birth and death, his na- tionality, background, education, and a summary of his scientific contributions. 2, Among the concentration terms used in chemistry is molality. Define molality. Describe how it differs from molar- ity and how and why it is used in chemistry. 3. As described in Section 9.9, both sodium benzoate and potassium iodide are added to processed foods in concentra- tions that can be reported in parts per thousand. Find another food additive included in processed foods in concentrations easily reported as parts per thousand. 4. Describe a recent incidence of botulinum poisoning (some- times referred to as botulism poisoning). Include the circum- stances under which it occurred and its effects or results. unfit to drink? 5. Identify the source of the municipal drinking water dis- tributed in your area. Does it come from surface water, ground-improve the purity of your drinking water. Which one would water, or some other source? you want carried out first? 6. Find the maximum permitted level, in community drink- ing water, of an element, ion, or compound other than those listed in Tables 9.2 and 9.3. 17. Give the details of a major accidental spill, commercial or industrial discharge, or similar event that caused or threat- ened significant environmental pollution within your state. Include any action taken by state or local authorities, and the outcome. 38. We normally think of community water purification process- es as designed to remove impurities from water. Yet they can also add chemicals to water to benefit the public health and welfare. Many communities, for example, add chlorine to water to kill disease-causing microorganisms. Some add fluoride salts to retard tooth decay. Do you favor the addition of chemicals to public drinking water to promote the public health and welfare? Do you think that small quantities of essential nutrients or vitamins ought to be added to drinking water? Do you think that nothing ought to be added to the water since everyone in the communi- ty must drink the same water and some may not wish to have anything added to their drinking water? Do you think the pub- 18. Describe national, state or local requirements or restric- tions that apply in your region for the disposal of containers of unused paint; for the disposal of used motor oil; for exhaust emissions of gasoline-powered lawn mowers or other house- hold machinery. page 184 Chapter 8 The human body uses energy in three different ways. through exercise, specific dynamic action, and basal metabolism. Exercise involves push ups, jogging, swimming, tennis, physical work. Specific dynamic action accounts for the energy consumed in digesting and metabolizing food and converting its energy. for use through exercise. refining petroleum through into gasoline, heating oil, diesel oil, other products energy extraction through distillation. Energy Equation is Energy In = Energy Out + Energy Stored. Very Light Sitting, reading 1.0 - 2.5 calories expanded per minute per hour is 60 -150. Light Slow walking, washing 2.5 - 5.0 150 - 300 Moderate Fast walking, heavy gardening, bicycling 5.0 - 7.5 300 - 450. Heavy Vigorous work swimming, running 7.5 - 12.0 450 - 720. 30 • Chapter 2 Atoms and Elements Helium, the second element, is a gas of extraordinari- rings of carbon unite to form large spheres, the most ly low reactivity. It's used to dilute gaseous anesthetics dur- common of which contain 60 carbon atoms. Fullerenes ing surgery and to inflate lighter-than-air blimps and are currently under intense study for their properties and balloons. One of its most important properties is its inabil- potential uses. Carbon itself has been used by humans ityto burn; helium is completely nonflammable. In one sense probably since the discovery of fire and the burning of helium has the most unusual history of all the elements: It wood. The word "carbon" comes from a Latin term for was found on the sun before it was discovered on the earth. coal or charcoal. In 1868 analysis of light radiating from the sun led scien- Nitrogen, a gas that makes up about 78% of the air we tists to conclude that a previously unreported element ex- breathe, was discovered independently in the early 1770s isted on the sun.The British astronomer J. Norman Lockyer by two British chemists, Joseph Black and Joseph called the newly discovered element helium, which he took Priestly, and a Swedish chemist, Karl Wilhelm Scheele. from the Greek word for the sun, helios. Its name reflects its occurrence in nitre, known also as Lithium is a reactive metal that forms hydrogen gas on potassium nitrate or saltpeter, a component of gunpowder. contact with water. First isolated in 1818, it's used com- Nitrogen is found in an enormous number of compounds mercially in long-lasting batteries (Section 2.7) and med- important to life and good health, including medications, ically in the compound lithium carbonate to moderate the agricultural fertilizers, and the vitamins and proteins of swings of manic depression. The element's name comes our foods. from the Greek word for stone, lifhos, and reflects its orig- Oxygen, which makes up almost 21% of our atmos- inal isolation from a mineral, petalite. phere, was also discovered by Priestly and Scheele, again Like lithium, beryllium was also discovered (in 1797) in independently and again in the early 1770s. Like nitrogen, a mineral, in this case beryl. A hard but very toxic metal, oxygen occurs in a large variety of important compounds, f beryllium has few uses in consumer goods. Combined with including the proteins, carbohydrates, and fats and oils of t copper, it increases the strength of various specialized our foods.The name "oxygen" comes from Greek words and, tools, springs, and electrical components; because of its reflects its presence in many acidic or sharp-tastin~o low absorption of X-rays, it's used to make the casings of substances. X-ray tubes. It's also used in the construction of spacecraft Fluorine, a gas, is one of the most reactive elemen.ts and nuclear reactors (Chapter 5). known. Although it was recognized as an element in the Boron is a semimetallic element, which means that if early 1800s, its ability to react with virtually anythinq it it's isolated under certain conditions, it's a solid with a dull, touches delayed the preparation of sizable quantitiea of metallic shine; under other conditions it's a black powder pure fluorine until 1886, when Henri Moissan, a French that's very much unlike any metal. Although boron was first chemist, first isolated it. Compounds of fluorine known as prepared in a very crude form by the French chemist Joseph fluorides are important for hardening the enamel of teeth. Louis Gay-Lussac and a co-worker in 1808, the pure element It's also a component ofTeflon, a compound used as a coat-wasn't obtained until 1909. Pure boron has few if any uses. Consumers use boron largely as a component of the anti-septic boric acid. The origin of the element's name is uncertain. Carbon is a nonmetallic element found in every com-pound (except water) that's important to sustaining life and health. Because of its widespread occurrence in liv ing things, the chemistry of carbon is called "organic chemistry." (We'll examine this in greater detail in Chap-ter 6,) The element itself exists in four distinct forms: charcoal, the black material formed when wood and other living or once-living materials are heated to high tem-peratures; graphite, a slippery form of carbon that's used as a solid lubricant and that forms the "lead" of pencils; diamond, the precious gem; and fullerenes, a form of car-bon discovered in 1985 in which five- and six-membered ing on machine parts and kitchen utensils to make thei r sur-faces nearly friction-free. Fluorine's name is taken f,rom a group of minerals in which it occurs. Neon, the tenth element of our series, is a gas as inert as helium.The British chemistWilliam Ramsay and his as-sistant M.Travers discovered the element in 1898 by isolat ing it from air and named the new element neon from a Greek word meaning new. Its principal consumer applica-tion lies in generating the glow of neon signs. All of these are elements since, using the description of Section 1.4, they can't be produced from any other sub-stances (that don't already contain them), nor can they be decomposed or broken down to any other substances by any of the common forces of our everyday world. Next, in Chapter 3, we'll examine how these and other elements combine to f ro~compounds. 0  64 • Chapter 4 Discovering the Secrets of the Nucleus  y radiation  High-energy electromagnetic radiation In an interesting commercial application, y rays are used to detect flaws in metal parts and structures in much the same way as X-rays are used to detect and diagnose fractures in bones or cavities in teeth, or to examine luggage at security stations. A sample of the radioisotope cobalt-60, enclosed in a protective capsule, is placed in or near the metal part under examination. The y rays from the ra-dioisotope pass through the metal and strike a sheet of photographic film or an electronic detector on the other side. Examining the image produced on the film or on a video screen reveals flaws, much as medical and dental X-rays show the in-terior of a bone or a tooth or the contents of luggage. When high-energy a or (3 particles or y rays collide with electrically neutral matter, they can knock electrons away from atoms or molecules and generate pairs of ions. Along with other forms of radiation that are powerful enough to do this, including cosmic rays and X-rays, these components of radioactivity are known as ionizing radiation. Figure 4.4 and Table 4.1 sum up their characteristics. Table 4.1 The lonizing Radiation of Radioactivity Penetrating Radiation Component Symbols Velocity Power Figure 4.4 The components of a rays, (3 rays, and y rays. lonizing radiation is any form of radiation capable of con-verting electrically neutral matter into ions. a rays Helium nuclei (3 rays Electrons y rays Electromagnetic oy, y waves ZHe2+, Za, a 1-ฐe, i-ฐR, R , R 5% to 7% of the Low speed of light Varies; up to 90% of the speed of light Speed of light :~ i Moderate ~~ High  • Q U E S T I O N How does an atom's atomic number change when its nucleus loses a(n): (a) a par-ticle, (b) (3 particle, (c) y ray? How does that atom's mass number change with` ~ the loss of each of these?  4.5 Naturally Occurring Radioactive Decay: From Tritium to Helium, from Carbon to Nitro gen, from Uranium to Lead We can now use our knowledge of nuclear radiation and its symbols to ex,~mine a few representative illustrations of naturally occurring radioactive decay. Aa we do, we'll use nuclear notation to write the kinds of equations that will help explain, both here and in the next chapter, how the mysteries of the nucleus were explored, how the atomic bomb was built, and how we now use nuclear reactions in medicine, in commerce, and in the study of history. Tritium, the simplest of all the radioisotopes, decays by ~3 emission (the loss of a (3 particle) to form ZHe, a stable isotope of helium: iH ~ 2He + 1_ฐR  When the tritium nucleus loses the electron, one of the neutrons of its nucleus is transformed into a proton. Although its mass number remains unchanged at 3, the atom increases by one unit in atomic number and becomes the element helium 4.4 a Particles, R Particles, and y Rays • 63 With their high speed, single negative charge, and extremely small mass, the high-energy P particles pass through matter much more easily than do a particles and are stopped only by heavy clothing or thick walls. They have about 100 times the penetrating power of a particles. The loss of a single R particle produces an increase of one unit in the atomic number of the nucleus. This follows from the requirement that the creation or de-struction of net electrical charge can never occur in a chemical reaction, or in any other process for that matter. No positive (or negative) charge can appear or van-ish unless the opposite charge also appears or vanishes at the same time. The ap-pearance or disappearance of charges occurs through the formation of pairs of ions or of subatomic particles bearing opposite electrical charges, or their combi-nation and destruction or neutralization. With this in mind we can see that if the nucleus of an atom loses a (3 particle, which carries a single unit of negative charge, then the nucleus must balance this loss of one unit of negative charge by simultaneously increasing in positive charge, again by one unit. For a physical picture of the ejection of a R particle from the nu-cleus, we can think of a neutron as a combination of a proton and an electron. Since the electron's mass is negligible compared with the mass of a proton or a neu-tron (Sec. 2.4), combining an electron with a proton (or removing an electron from ',a neutron) would hardly affect the mass of the particle. Moreover, as a union of one _ positive and one negative charge the combination would be electrically neutral, as a i neutron indeed is. In effect, then, the loss of a (3 particle converts a neutron to a p_ xoton without substantially changing the total mass of the nucleus but nonethe-le; 5s increasing its atomic number by one unit. Like visible light, radio and television waves, and X-rays, the y rays that con-stit ute the third member of this set of radioactive emissions are a form of electro-maL gnetic radiation. Because of their high energies (even greater than the energies carr ied by X-rays) and their ability to penetrate deeply into matter, they can do com;iderable biological damage, as we'll see in Chapter 5. Without either mass or charl ;e, y rays are written py or simply y. V he physical characteristics of this kind of radiation help explain its very great pene;trating power. Traveling with high energy at the speed of light and without ei-ther n aass or charge, ,y rays penetrate matter easily. Complete protection from their effe&; requires the use of thick lead or concrete shields. They have about 100 times the pelnetrating power of (3 rays.  Beta particles are high-energy electrons emitted by radioactive nuclei and moving at up to 90% the speed of light. Gamma rays are a form of high-energy electromagnetic radiation.They have no mass and carry no electrical charge.  X-ray examination of luggage at a security station. Gamma ray analysis of a fitting for a medical device shows it to be free of flaws. 30 • Chapter 2 Atoms and Elements Helium, the second element, is a gas of extraordinari- rings of carbon unite to form large spheres, the most ly low reactivity. It's used to dilute gaseous anesthetics dur- common of which contain 60 carbon atoms. Fullerenes ing surgery and to inflate lighter-than-air blimps and are currently under intense study for their properties and balloons. One of its most important properties is its inabil- potential uses. Carbon itself has been used by humans ityto burn; helium is completely nonflammable. In one sense probably since the discovery of fire and the burning of helium has the most unusual history of all the elements: It wood. The word "carbon" comes from a Latin term for was found on the sun before it was discovered on the earth. coal or charcoal. In 1868 analysis of light radiating from the sun led scien- Nitrogen, a gas that makes up about 78% of the air we tists to conclude that a previously unreported element ex- breathe, was discovered independently in the early 1770s isted on the sun.The British astronomer J. Norman Lockyer by two British chemists, Joseph Black and Joseph called the newly discovered element helium, which he took Priestly, and a Swedish chemist, Karl Wilhelm Scheele. from the Greek word for the sun, helios. Its name reflects its occurrence in nitre, known also as Lithium is a reactive metal that forms hydrogen gas on potassium nitrate or saltpeter, a component of gunpowder. contact with water. First isolated in 1818, it's used com- Nitrogen is found in an enormous number of compounds mercially in long-lasting batteries (Section 2.7) and med- important to life and good health, including medications, ically in the compound lithium carbonate to moderate the agricultural fertilizers, and the vitamins and proteins of swings of manic depression. The element's name comes our foods. from the Greek word for stone, lifhos, and reflects its orig- Oxygen, which makes up almost 21% of our atmos- inal isolation from a mineral, petalite. phere, was also discovered by Priestly and Scheele, again Like lithium, beryllium was also discovered (in 1797) in independently and again in the early 1770s. Like nitrogen, a mineral, in this case beryl. A hard but very toxic metal, oxygen occurs in a large variety of important compounds, f beryllium has few uses in consumer goods. Combined with including the proteins, carbohydrates, and fats and oils of t copper, it increases the strength of various specialized our foods.The name "oxygen" comes from Greek words and, tools, springs, and electrical components; because of its reflects its presence in many acidic or sharp-tastin~o low absorption of X-rays, it's used to make the casings of substances. X-ray tubes. It's also used in the construction of spacecraft Fluorine, a gas, is one of the most reactive elemen.ts and nuclear reactors (Chapter 5). known. Although it was recognized as an element in the Boron is a semimetallic element, which means that if early 1800s, its ability to react with virtually anythinq it it's isolated under certain conditions, it's a solid with a dull, touches delayed the preparation of sizable quantitiea of metallic shine; under other conditions it's a black powder pure fluorine until 1886, when Henri Moissan, a French that's very much unlike any metal. Although boron was first chemist, first isolated it. Compounds of fluorine known as prepared in a very crude form by the French chemist Joseph fluorides are important for hardening the enamel of teeth. Louis Gay-Lussac and a co-worker in 1808, the pure element It's also a component ofTeflon, a compound used as a coat-wasn't obtained until 1909. Pure boron has few if any uses. Consumers use boron largely as a component of the anti-septic boric acid. The origin of the element's name is uncertain. Carbon is a nonmetallic element found in every com-pound (except water) that's important to sustaining life and health. Because of its widespread occurrence in liv ing things, the chemistry of carbon is called "organic chemistry." (We'll examine this in greater detail in Chap-ter 6,) The element itself exists in four distinct forms: charcoal, the black material formed when wood and other living or once-living materials are heated to high tem-peratures; graphite, a slippery form of carbon that's used as a solid lubricant and that forms the "lead" of pencils; diamond, the precious gem; and fullerenes, a form of car-bon discovered in 1985 in which five- and six-membered ing on machine parts and kitchen utensils to make thei r sur-faces nearly friction-free. Fluorine's name is taken f,rom a group of minerals in which it occurs. Neon, the tenth element of our series, is a gas as inert as helium.The British chemistWilliam Ramsay and his as-sistant M.Travers discovered the element in 1898 by isolat ing it from air and named the new element neon from a Greek word meaning new. Its principal consumer applica-tion lies in generating the glow of neon signs. All of these are elements since, using the description of Section 1.4, they can't be produced from any other sub-stances (that don't already contain them), nor can they be decomposed or broken down to any other substances by any of the common forces of our everyday world. Next, in Chapter 3, we'll examine how these and other elements combine to f ro~compounds. 0  64 • Chapter 4 Discovering the Secrets of the Nucleus  y radiation  High-energy electromagnetic radiation In an interesting commercial application, y rays are used to detect flaws in metal parts and structures in much the same way as X-rays are used to detect and diagnose fractures in bones or cavities in teeth, or to examine luggage at security stations. A sample of the radioisotope cobalt-60, enclosed in a protective capsule, is placed in or near the metal part under examination. The y rays from the ra-dioisotope pass through the metal and strike a sheet of photographic film or an electronic detector on the other side. Examining the image produced on the film or on a video screen reveals flaws, much as medical and dental X-rays show the in-terior of a bone or a tooth or the contents of luggage. When high-energy a or (3 particles or y rays collide with electrically neutral matter, they can knock electrons away from atoms or molecules and generate pairs of ions. Along with other forms of radiation that are powerful enough to do this, including cosmic rays and X-rays, these components of radioactivity are known as ionizing radiation. Figure 4.4 and Table 4.1 sum up their characteristics. Table 4.1 The Ionizing Radiation of Radioactivity Penetrating Radiation Component Symbols Velocity Power Figure 4.4 The components of a rays, (3 rays, and y rays. Ionizing radiation is any form of radiation capable of con-verting electrically neutral matter into ions. a rays Helium nuclei (3 rays Electrons y rays Electromagnetic o y, y waves ZHe2+, Z 4(X, a 1-ฐe, i-ฐR, P-, R 5% to 7% of the Low speed of light Varies; up to 90% of the speed of light Speed of light  High  • Q U E S T I O N How does an atom's atomic number change when its nucleus loses a(n): (a) a par-ticle, (b) (3 particle, (c) y ray? How does that atom's mass number change with` ~ the loss of each of these?  4.5 Naturally Occurring Radioactive Decay: From Tritium to Helium, from Carbon to Nitrogen, from Uranium to Lead We can now use our knowledge of nuclear radiation and its symbols to ex,hmine a few representative illustrations of naturally occurring radioactive decay. Aa we do, we'll use nuclear notation to write the kinds of equations that will help explain, both here and in the next chapter, how the mysteries of the nucleus were explored, how the atomic bomb was built, and how we now use nuclear reactions in medicine, in commerce, and in the study of history. Tritium, the simplest of all the radioisotopes, decays by ja emission (the loss of a (3 particle) to form Z He, a stable isotope of helium: iH - 2 He + 1_ฐR  When the tritium nucleus loses the electron, one of the neutrons of its nucleus is transformed into a proton. Although its mass number remains unchanged at 3, the atom increases by one unit in atomic number and becomes the element helium 4.4 a Particles, R Particles, and y Rays • 63 With their high speed, single negative charge, and extremely small mass, the high-energy P particles pass through matter much more easily than do a particles and are stopped only by heavy clothing or thick walls. They have about 100 times the penetrating power of a particles. The loss of a single R particle produces an increase of one unit in the atomic number of the nucleus. This follows from the requirement that the creation or de-struction of net electrical charge can never occur in a chemical reaction, or in any other process for that matter. No positive (or negative) charge can appear or van-ish unless the opposite charge also appears or vanishes at the same time. The ap-pearance or disappearance of charges occurs through the formation of pairs of ions or of subatomic particles bearing opposite electrical charges, or their combi-nation and destruction or neutralization. With this in mind we can see that if the nucleus of an atom loses a (3 particle, which carries a single unit of negative charge, then the nucleus must balance this loss of one unit of negative charge by simultaneously increasing in positive charge, again by one unit. For a physical picture of the ejection of a R particle from the nu-cleus, we can think of a neutron as a combination of a proton and an electron. Since the electron's mass is negligible compared with the mass of a proton or a neu-tron (Sec. 2.4), combining an electron with a proton (or removing an electron from ',a neutron) would hardly affect the mass of the particle. Moreover, as a union of one _ positive and one negative charge the combination would be electrically neutral, as a i neutron indeed is. In effect, then, the loss of a (3 particle converts a neutron to a p_ xoton without substantially changing the total mass of the nucleus but nonethe-le; 5s increasing its atomic number by one unit. Like visible light, radio and television waves, and X-rays, the y rays that con-stit ute the third member of this set of radioactive emissions are a form of electro-maL gnetic radiation. Because of their high energies (even greater than the energies carr ied by X-rays) and their ability to penetrate deeply into matter, they can do com;iderable biological damage, as we'll see in Chapter 5. Without either mass or charl ;e, y rays are written py or simply y. V he physical characteristics of this kind of radiation help explain its very great pene;trating power. Traveling with high energy at the speed of light and without ei-ther n aass or charge, ,y rays penetrate matter easily. Complete protection from their effe&; requires the use of thick lead or concrete shields. They have about 100 times the pelnetrating power of (3 rays.  Beta particles are high-energy electrons emitted by radioactive nuclei and moving at up to 90% the speed of light. Gamma rays are a form of high-energy electromagnetic radiation.They have no mass and carry no electrical charge.  X-ray examination of luggage at a security station. Gamma ray analysis of a fitting for a medical device shows it to be free of flaws. ~ with Chemistry 8.3 How Francis Bacon Died Attempting to Discover the Benefits of Refrigeration In the history of science, ideas sometimes get lost for a while. Even an especially shrewd and perceptive idea, one that could lead to great advances in our under-standing of the world around us, can vanish for a period of time. It's ignored and it goes underground while other, less useful and sometimes more bizarre theories blossom, attract the best minds, and then wither away as the earlier, more pro-ductive idea comes forth once again to revitalize the exploration of science. That's exactly what happened to Francis Bacon's theory of heat. Francis Bacon, born in 1561 to a family of considerable influence and power in the court of Queen Elizabeth I of England, was a statesman, an essayist, and ~ rhe father of inductive logic and modern experimental science. Back in 1620, with , ,;onsiderable insight, Bacon wrote about his idea that heat results quite simply from motion: a Cold Hot i~Q" ('~, ccE~~> Applying Bacon's theories of heat in a modern context, suppose you have a cold piece of copper and a hot piece of copper. Using the terminology of modern chem-istry, what would you say is moving more "briskly" in the hot piece of copper than in the cold one? ซซ~~a~~ ~u`~ €cectd~~y~3 ,,,, Figure 8.3 Heat results from the "brisk agitation" of the particles of matter. 8.4 What Happened When Count Rumford Bored Cannons Bacon's theory-that the basis of what we call heat lies in the motion of particles of matter-was overwhelmed for over 150 years by the caloric theory of heat. (Calorie and caloric come from the Latin calor, meaning heat.) Until nearly the very last year of the eighteenth century most scholars believed that heat wa~ mysterious sort of fluid, which they called "caloric," that flowed spontaneoi from a hot body to a cooler one. This "caloric" was a very strange substance. 8.2 Potential Energy, Kine+ r Potential energy can be stored in two different ways: • through a body's location or position, and • through a substance's composition. If you climb up onto a diving board over a swimming pool, for example, your body acquires a certain amount of potential energy. The higher you climb-the higher your location above the water-the more potential energy you have. As you stand at the end of the board, motionless, your energy is potential since nothing is hap-pening. You have the potential for doing work, but you aren't doing any as long as you stand motionless. When you jump off the board you convert your potential en-ergy into kinetic energy, the energy of motion. As you land in the water the kinet-ic energy of your falling body does work in moving the water, creating a splash and generating noise. iagine a child swinging on a playground swing. At what point(s) does the child i we the greatest amount of kinetic energy?The greatest amount of potential energy? 4.5 Naturally Occurring Radioactive Decay • 65   /3 particle, a igh-speed electron Figure 4.5 Radioactive decay of tritium. (Fig. 4.5). Tritium itself is a key component of the hydrogen bomb. The combina-tion of tritium with deuterium at extremely high temperatures provides the ex-plosive force of one version of the hydrogen bomb (Sec. 4.14). Decay of carbon-14 also occurs with loss of a (3 particle. The result 14 . 14 0 6C ,lv + 1_R  in this case is the transformation of a radioactive carbon atom into the most com-mon isotope of nitrogen (Fig. 4.6). As in the case of tritium's decay, the mass of the nucleus remains unchanged while its atomic number increases by one unit. The radioactive decay of carbon-14 is useful for establishing the dates of ancient ob-jects, as we'll see in detail in Section 5.11. Uranium, which formed an image on the photographic plate in Becquerel's desk drawer and led him and the Curies to radioactivity, also provided the explo-sive force of one of the first atomic bombs. Its most common isotope, 298U, makes up over 99% of the uranium found in nature-mostly in pitchblende, an ore of the earth's crust-and represents the radioisotope of highest mass and highest atom- The universal trident symbol for ' ic number of any found (in more than trace amounts) in nature. The radioactive radioactivity decay of U-238 to thorium by loss of an a particle and emission of y radiation rep- ` resents the first step in one particular sequence of radioactive decay. Since the y ,radiation that accompanies uranium's decay has neither mass nor charge and there-ore doesn't affect the mass number or atomic number of any of the nuclei pro 'aced, it's often omitted from the equations. The equation for the decay of uranium o thorium is usually written as 29sU _ _ 29oTh + 2 He    Figure 4.6 Radioactive decay of carbon-14. 4.5 Naturally Occurring Radioactive Decay • 65   /3 partide, a igh-speed clectron Figure 4.5 Radioactive decay of tritium. (Fig. 4.5). Tritium itself is a key component of the hydrogen bomb. The combina-tion of tritium with deuterium at extremely high temperatures provides the ex-plosive force of one version of the hydrogen bomb (Sec. 4.14). Decay of carbon-14 also occurs with loss of a (3 particle. The result 14 . 14 0 6C ,lv + 1_R  in this case is the transformation of a radioactive carbon atom into the most com-mon isotope of nitrogen (Fig. 4.6). As in the case of tritium's decay, the mass of the nucleus remains unchanged while its atomic number increases by one unit. The radioactive decay of carbon-14 is useful for establishing the dates of ancient ob-jects, as we'll see in detail in Section 5.11. Uranium, which formed an image on the photographic plate in Becquerel's desk drawer and led him and the Curies to radioactivity, also provided the explo-sive force of one of the first atomic bombs. Its most common isotope, 298U, makes up over 99% of the uranium found in nature-mostly in pitchblende, an ore of the earth's crust-and represents the radioisotope of highest mass and highest atom- The universal trident symbol foF ' ic number of any found (in more than trace amounts) in nature. The radioactive radioactivity decay of U-238 to thorium by loss of an a particle and emission of y radiation rep- ` resents the first step in one particular sequence of radioactive decay. Since the y v-adiation that accompanies uranium's decay has neither mass nor charge and there-ore doesn't affect the mass number or atomic number of any of the nuclei pro '~tced, it's often omitted from the equations. The equation for the decay of uranium o thorium is usually written as 29sU _ _ 29oTh + 2He Figure 4.6 Radioactive decay of carbon-14. 66 • Chapter 4 Discavering ths Secrets of the Nucleus Figure 4.7 The sequence of radioactive decay from 292U to ZgZPb. 238 236 234 232 230 228 226 ~ 224 ~~ 222 ~ 220 218 216 214 212 210 208 206 Z~Po z82Pb --w283Bi -i2~Po Z~Pb ~Z~Bi -+Z~Po z82Pb 82 83 84 (Stable isotope) z~z~, a~ Notice that: • the sum of the mass numbers to the left of the arrow, the 238 of the U-238, equals the sum of the mass numbers to the right of the arrow, 234 + 4. • the sum of the atomic numbers to the left of the arrow, the 92 of the uranium, equals the sum of the atomic numbers to the right of the arrow, 90 + 2. After 13 additional steps the entire chain finally comes to an end with the forma-tion of a stable isotope of lead, 2g2Pb. The entire sequence appears in Figure 4.7. Notice in Figure 4.7 that the radioactive element radon (Rn) is a transier part of this decay chain, forming from the radioactive decay of radium (Ra) an decaying, in turn, to polonium (Po). Radon itself is a gaseous element, a membe of the inert family of elements of the periodic table. What subatomic partiele is lost as radon-222 is converted tt~ poloniumi218? Again, the equation What subatomic particle is lost from Ra-226 as it decays to Rn-222? We can Sinee the mass 'number drops by 4 and the atomic number drops by 2 as radium-226 is transformed into radon 222, the subatomic particle that is lost must be a combination of two protons-and two neutrons. Thus, it must be a he-lium nucleus, which is the same in this ease as saying that it is an a particle. The complete nuclear reaction is shows us that a particle with an atomic number of 2 and a mass number of 4 is lost. It must once again be a helium nucleus. The complete equation is What subatomie particle is lost as bismuth-210 is converted to polonium-210 in the next-to-last step of the sequence shown in Figure 4.7? Hete the equation ls  Since there is no change in the mass number and an increase by 1 in atomie number, an electron must have been ldst from the nucleus as a ~3 particle. The equation is therefore ite the reaction that occurs here as Zg$Ra ' Zg~Rn + subatomic particle Z88Ra -~ Zg6R~ + a ~gbRn ~ Zg4Po + subatomic particle Zg6Rn ~ ZgqPO -~ a '~3Bi -~ ~~Po + subatomie particle 2g~Bi -> 2~4Po + j3 4.5 Naturally Occurring Radioactive Decay • 67 P L E  Subatomic Loss E X A M P L E In its radioactive decay, curium-245 (Cm-245) loses an c~ particle; What radioisotope results from the decay of Cm-245? Curium's First Step  Reforenee t€i the periodic table shows that curium's atomic number is 96. Since an a particle has a mass number of 4 and an atomie-number of 2, curium-245 loses 4 units of mass and two units of atomic number. The result is an isotope with a mass number of 241 (245 - 4) and an atomic number of 94 (96 - 2). The element with an atomic number of 94 is plutonium (Puj. Thus the first step in the ehain of radioactive decay of curium-245 pro-duces plutonium-241;  Other naturally occurring radioisotopes decay by paths different from the one shown in Figure 4.7. Uranium-235, for example, decays initially to thorium-231, by a emission, and then, through an additiona113 steps, to the stable leau-207. After a total of 15 steps, radioactive curium-245 ends up as a stable isotope of bismuth, Bi-209. (The curie, the unit of radioactivity mentioned in Section 4.1, represents the rate of decay of a radioisotope: 1 curie = 3.7 x lOt~ radioactive disintegrations per second.) 68 • Chapter 4 Discovering the Secrets of the Nucleus • Q U E S T 1 O N   Although scientists could observe the changes that naturally occurring radioiso-topes undergo, as Becquerel and the Curies had done, unti11919 no one had as yet planned and carried out an artificial nuclear transformation that would convert a stable isotope of one element into another element. In that year Ernest Rutherford (Sec. 4.2) published a report of the first artificial transformation of one element to another. By bombarding nitrogen-14, a stable (and the most common) isotope of nitrogen, with a particles emitted by radium, Rutherford transformed the nitrogen atom into an atom of oxygen. In the process, the nitrogen nucleus absorbs the two protons and two neutrons of the a particle and then loses a proton, all with a net gain of 3 in mass number and 1 in atomic number. The entire procedure results in Transmutation is the conver- a transmutation, the conversion of one element into another: sion of one element into an- other element. 1~N + ZHe ~ lg0 + 1H • Q U E S T I O N What subatomic particle is lost by 28ฐPo as it is converted into 282Po in the final step of the decay sequence of U-238? W rite the reaction for this step. 4.6 Rutherford's Transmutation of Nitrogen As we saw for the decay of uranium-238 (Sec. 4.5), the sum of the mass numbers to the left of the arrow equals the sum of the mass numbers to the right, and the sum of the atomic numbers to the left equals the sum of the atomic numbers to the right. With his conversion of nitrogen into oxygen, Rutherford had achieved the age-old dream of the transmutation of the elements. One of the goals of alchemy, an ancient, mystical practice that preceded the sci-ence of chemistry and in many respects prepared its way was the transmutation of one elemental substance into another. The alchemists sought especially to convert a common, inexpensive metal such as lead into precious gold. Through nuclear transformations much like Rutherford's, the alchemical dream has by now been re-alized, but without fulfilling the promise of the riches the ancients sought. Not only is expensive platinum (rather than lead) used as the starting metal for the forma-tion of gold, but the cost of the highly purified platinum needed for the modern transmutation is far greater than the value of the gold that's generated. The conversion of platinum into gold has been achieved by bombarding platinum-198 with neutrons to produce platinum-199.This isotope, in turn, decays to gold-199 with the loss of a subatomic particle: ~98Pt + on -> ~98Pt ~~$Pt ~ ~99Au + a subatomic particle What subatomic particle is lost by the platinum as it becomes an atom of gold? 4.7 A Nuclear Wonderland As the 20th century progressed, science probed ever more deeply into the struc-ture and behavior of the atom, continuously stripping away its secrets. Today the nucleus stands as a strange and complex world, seemingly no less bizarre than the one Alice found when she fell down the rabbit hole of Lewis Carroll's Alice's Adventures in Wonderland. 4.12 The Matter of the Missing Mass: Mass Defect and Binding Energy • 77 we can calculate the mass of an atom of U-235. With the periodic table or a table of atomic weights and atomic numbers, we find that the atomic number of uranium is 92.Thus, there must be 92 protons in the nueleus and 92 electrons in the surrounding shells. Furthermore, since its mass number is 235, the total, combined number of protons and neutrons in the nucleus must be 235. With 92 protons in the nucleus, the number of neutrons in U-235 is neutrons = 235 - 92 = 143 The subatomic particles that make up an atom of U-235 are thus 92 protons 92 electrons 143 neutrons With a mass of 1.007 amu each, the protons contribute 92 protons x 1.007 amu/proton = 92.64 amu With a mass of 0.0005 each, the eleetrons contribute 92 electrons x 0.0005 amu/eleetron = 0.0460 amu With a mass of 1.009 eaeh, the neutrons contribute 143 neutrons x 1.009 amu/neutron = 144.29 amu Combining these individual contributipns, we find that the calculated mass of the U-235 atom is protons 92.64 amu electrons 0.05 amu neutrons 144:29 amu 236.98 amu We can round this off to 237.0 amu for the calculated mass of the U-235 atom. As we've just seen, the calculated mass of the U-235 atom arrived at by adding up the masses of all the subatomic particles that compose it is 237.0 amu. Yet the actual mass of an atom of U-235 as measured experimentally (and extremely ac curately) is only 235.043924 amu, which we can round off here to 235.0 amu. The difference between the calculated mass of all the protons, neutrons, and electrons present in an atom and the actual, measured mass is known as the atom's mass defect. For U-235 the binding energy is the energy equivalent of 2.0 amu, the difference between the sum of the masses of its individual particles and the mass of the whole atom itsel^ An atom's binding energy is the energy equivalent of its mass defect. Similar calculations and measurements for atoms of other elements show that the mass defect per atomic mass unit (and therefore the binding energy per atomic An atom's mass defect is the difference between the mass of the atom as a whole and the mass of all the individual pro-tons, neutrons, and electrons that compose it. The binding energy of an atom, the energy that holds the nucleus together as a co-herent whole, is the energy equivalent of its mass defect. 78 • Chapter 4 Discovering the Secrets of the Nucleus mass unit) rises sharply as mass numbers increase, reaches its maximum at mass numbers of 50 to 60, and then drops slowly as mass numbers increase further. • QUESTION Calculate the mass defect of an atom of Pu-239.The measured mass of an atom of Pu-239 is 239.05 amu. 4.13 The Energy of Uranium Fission E X A M P L E Now we can turn to the source of the energy released by nuclear fission, once again using the equivalence of mass and energy. We use the neutron-induced fission of U-235 to barium, krypton, and three neutrons as an illustration (Sec. 4.9): 29z U + on ~ 156Ba + 36Kr + 3 on Using accurately measured masses of the neutron and the atoms that take part in this reaction Particle Precise Mass (amu) the neutron 1.009 U-235 235.044 Ba-140 139.911 Kr-93 92.931 we can calculate the total mass of all the particles that enter into this reaction (one U-235 atom and one neutron) and all the particles that result from the fission (one Ba-140 atom, one Kr-93 atom, and three neutrons), and the difference between the two sets. Calculate the difference in mass between the reactants and the products in the fission of U-235 just shown. The reactants and their masses are Particle Mass 1 U-235 atom 235.044 1 neutron 1.009 Total 236.053 amu The products and their masses are Particle Mass 1 Ba-140 atom 134,911 1 Kr-93 atom 92:931 3 neutrons 3.027 Total 235.869 amu There's concern that gaseous radon formed by the decay of very small amounts of radioisotopes that occur naturally in some kinds of rocks and soils may seep upward through the ground, enter homes and other buildings, and pres- ent an indoor pollution hazard. Ordinarily, we might expect that any radon gas we inhale would leave our lungs when we exhale. But radioactive decay of radon as it remains inside our lungs, during the moment between inhaling and exhal-ing, would produce minuscule amounts of Any traces of these radioactive elements that might remain within our bodies could do considerable biological damage through ionizing radiation. What subatomic particle is lost as radon-222 is converted to polonium-218? polonium and other radioisotopes. the radioactive decay of radium (Ra) an decaying, in turn, to polonium (Po). Radon itself is a gaseous element Again, the equation What subatomic particle is lost from Ra-226 as it decays to Rn-222? We can Since the mass 'number drops by 4 and the atomic number drops by 2 as radium-226 is transformed into radon 222, the subatomic particle that is lost must be a combination of two protons and two neutrons. Thus, it must be a he-lium nucleus, which is the same in this ease as saying that it is an a particle. The complete nuclear reaction is shows us that a particle with an atomic number of 2 and a mass number of 4 is lost. It must once again be a helium nucleus. The complete equation is What subatomic particle is lost as bismuth-210 is converted to polonium-210 in the next-to-last step of the sequence shown in Figure 4.7? Here the equation is  Since there is no change in the mass number and an increase by 1 in atomic number, an electron must have been lost from the nucleus as a P particle. The equation is therefore ite the reaction that occurs here as Zg$Ra ' 222 88 ,Rn + subatomic particle Z88Ra -~ Zg6Rn + a 2gbRn ~ Zg4Po + subatomic particle Zg6Rn ~ ZgqPO + a '~3Bi -~ ~~Po + subatomic particle 2g~21013i ->2~ 4 P o +j3 4.5 Naturally Occurring Radioactive Decay • 67 P L E  Subatomic Loss E X A M P L E In its radioactive decay, curium-245 (Cm-245) loses an ct particle; What radioisotope results from the decay of Cm-245? Curium's First Step curium's atomic number is 96. Since an a particle has a mass number of 4 and an atomic number of 2, curium-245 loses 4 units of mass and two units of atomic number. The result is an isotope with a mass number of 241 (245 - 4) and an atomic number of 94 (96 - 2). The element with an atomic number of 94 is plutonium (Pu). Thus the first step in the chain of radioactive decay of curium-245 pro-duces plutonium-241;  Other naturally occurring radioisotopes decay by paths different from the one shown in Figure 4.7. Uranium-235, for example, decays initially to thorium-231, by a emission, and then, through an additional 13 steps, to the stable leau-207. After a total of 15 steps, radioactive curium-245 ends up as a stable isotope of bismuth, Bi-209. (The curie, the unit of radioactivity mentioned in Section 4.1, represents the rate of decay of a radioisotope: 1 curie = 3.7 x 1010 radioactive disintegrations per second.) 68 • Chapter 4 Discovering the Secrets of the Nucleus • Q U E S T 1 O N Although scientists could observe the changes that naturally occurring radioiso-topes undergo, as Becquerel and the Curies had done, unti1 1919 no one had as yet planned and carried out an artificial nuclear transformation that would convert a stable isotope of one element into another element. In that year Ernest Rutherford (Sec. 4.2) published a report of the first artificial transformation of one element to another. By bombarding nitrogen-14, a stable (and the most common) isotope of nitrogen, with a particles emitted by radium, Rutherford transformed the nitrogen atom into an atom of oxygen. In the process, the nitrogen nucleus absorbs the two protons and two neutrons of the a particle and then loses a proton, all with a net gain of 3 in mass number and 1 in atomic number. The entire procedure results in Transmutation is the conver- a transmutation, the conversion of one element into another: sion of one element into an- other element. 1~N + ZHe ~ lg0 + 1H • Q U E S T I O N What subatomic particle is lost by 28ฐPo as it is converted into 282Po in the final step of the decay sequence of U-238? W rite the reaction for this step. Plutonium 4.6 Rutherford's Transmutation of Nitrogen As we saw for the decay of uranium-238 (Sec. 4.5), the sum of the mass numbers to the left of the arrow equals the sum of the mass numbers to the right, and the sum of the atomic numbers to the left equals the sum of the atomic numbers to the right. With his conversion of nitrogen into oxygen, Rutherford had achieved the age-old dream of the transmutation of the elements. One of the goals of alchemy, an ancient, mystical practice that preceded the sci-ence of chemistry and in many respects prepared its way was the transmutation of one elemental substance into another. The alchemists sought especially to convert a common, inexpensive metal such as lead into precious gold. Through nuclear transformations much like Rutherford's, the alchemical dream has by now been realized, but without fulfilling the promise of the riches the ancients sought. Not only is expensive platinum (rather than lead) used as the starting metal for the forma-tion of gold, but the cost of the highly purified platinum needed for the modern transmutation is far greater than the value of the gold that's generated. The conversion of platinum into gold has been achieved by bombarding platinum-198 with neutrons to produce platinum-199.This isotope, in turn, decays to gold-199 with the loss of a subatomic particle: ~98Pt + on -> ~98Pt ~~$Pt ~ ~99Au + a subatomic particle What subatomic particle is lost by the platinum as it becomes an atom of gold? 4.7 A Nuclear Wonderland As the 20th century progressed, science probed ever more deeply into the struc-ture and behavior of the atom, continuously stripping away its secrets. Today the nucleus stands as a strange and complex world, seemingly no less bizarre than the one Alice found when she fell down the rabbit hole of Lewis Carroll's Alice's Adventures in Wonderland.  4.12 The Matter of the Missing Mass: Mass Defect and Binding Energy • 77  we can calculate the mass of an atom of U-235. With the periodic table or a table of atomic weights and atomic numbers, we find that the atomic number of uranium is 92.Thus, there must be 92 protons in the nucleus and 92 electrons in the surrounding shells. Furthermore, since its mass number is 235, the total, combined number of protons and neutrons in the nucleus must be 235. With 92 protons in the nucleus, the number of neutrons in U-235 is neutrons = 235 - 92 = 143 The subatomic particles that make up an atom of U-235 are thus 92 protons 92 electrons 143 neutrons With a mass of 1.007 amu each, the protons contribute 92 protons x 1.007 amu/proton = 92.64 amu With a mass of 0.0005 each, the electrons contribute 92 electrons x 0.0005 amu/eleetron = 0.0460 amu With a mass of 1.009 each, the neutrons contribute 143 neutrons x 1.009 amu/neutron = 144.29 amu Combining these individual contributions, we find that the calculated mass of the U-235 atom is protons 92.64 amu electrons 0.05 amu neutrons 144:29 amu 236.98 amu We can round this off to 237.0 amu for the calculated mass of the U-235 atom. As we've just seen, the calculated mass of the U-235 atom arrived at by adding up the masses of all the subatomic particles that compose it is 237.0 amu. Yet the actual mass of an atom of U-235 as measured experimentally (and extremely ac curately) is only 235.043924 amu, which we can round off here to 235.0 amu. The difference between the calculated mass of all the protons, neutrons, and electrons present in an atom and the actual, measured mass is known as the atom's mass defect. The mass defect for the U-235 atom, then, is about 2.0 amu. Where did the missing mass go? It has been converted from mass into energy, the very energy that binds all of the protons and neutrons together to form a com-pact, coherent nucleus. This binding energy-the cement that holds the nucleus together-comes from the conversion into energy of a very small fraction of the masses of the subatomic particles that compose the atom. For U-235 the binding energy is the energy equivalent of 2.0 amu, the difference between the sum of the masses of its individual particles and the mass of the whole atom itself. An atom's binding energy is the energy equivalent of its mass defect. Similar calculations and measurements for atoms of other elements show that the mass defect per atomic mass unit (and therefore the binding energy per atomic An atom's mass defect is the difference between the mass of the atom as a whole and the mass of all the individual pro-tons, neutrons, and electrons that compose it. The binding energy of an atom, the energy that holds the nucleus together as a co-herent whole, is the energy equivalent of its mass defect. 78 • Chapter 4 Discovering the Secrets of the Nucleus mass unit) rises sharply as mass numbers increase, reaches its maximum at mass numbers of 50 to 60, and then drops slowly as mass numbers increase further. • Q U E S T I O N Calculate the mass defect of an atom of Pu-239.The measured mass of an atom of Pu-239 is 239.05 amu.  4.13 The Energy of Uranium Fission E X A M P L E Now we can turn to the source of the energy released by nuclear fission, once again using the equivalence of mass and energy. We use the neutron-induced fission of U-235 to barium, krypton, and three neutrons as an illustration (Sec. 4.9): 29z U + on ~ 156Ba + 36Kr + 3 on Using accurately measured masses of the neutron and the atoms that take part in this reaction Particle Precise Mass (amu) the neutron 1.009 U-235 235.044 Ba-140 139.911 Kr-93 92.931 we can calculate the total mass of all the particles that enter into this reaction (one U-235 atom and one neutron) and all the particles that result from the fission (one Ba-140 atom, one Kr-93 atom, and three neutrons), and the difference between the two sets. Calculate the difference in mass between the reactants and the products in the fission of U-235 just shown. The reactants and their masses are Particle Mass 1 U-235 atom 235.044 1 neutron 1.009 Total 236.053 amu The products and their masses are Particle Mass 1 Ba-140 atom 134,911 1 Kr-93 atom 92:931 3 neutrons 3.027 Total 235.869 amu   As a result of this particular fission reaction, there is a loss of mass equal to ' total mass of reactants 236.053 al mass of products -235.869 mass lost 0.184 amu 8.2 Potential Energy, Kine+ r Potential energy can be stored in two different ways: • through a body's location or position, and • through a substance's composition.  ~agine a child swinging on a playground swing. At what point(s) does the child i we the greatest amount of kinetic energy?The greatest amount of potential energy? 4.5 Naturally Occurring Radioactive Decay • 65   /3 particle, a igh-speed electron Figure 4.5 Radioactive decay of tritium. (Fig. 4.5). Tritium itself is a key component of the hydrogen bomb. The combina-tion of tritium with deuterium at extremely high temperatures provides the ex-plosive force of one version of the hydrogen bomb (Sec. 4.14). Decay of carbon-14 also occurs with loss of a (3 particle. The result 14 . 14 0 6C ,lv + 1_R  in this case is the transformation of a radioactive carbon atom into the most com-mon isotope of nitrogen (Fig. 4.6). As in the case of tritium's decay, the mass of the nucleus remains unchanged while its atomic number increases by one unit. The radioactive decay of carbon-14 is useful for establishing the dates of ancient ob-jects, as we'll see in detail in Section 5.11. Uranium, which formed an image on the photographic plate in Becquerel's desk drawer and led him and the Curies to radioactivity, also provided the explo-sive force of one of the first atomic bombs. Its most common isotope, 298U, makes up over 99% of the uranium found in nature-mostly in pitchblende, an ore of the earth's crust-and represents the radioisotope of highest mass and highest atom- The universal trident symbol for ' ic number of any found (in more than trace amounts) in nature. The radioactive radioactivity decay of U-238 to thorium by loss of an a particle and emission of y radiation rep- ` resents the first step in one particular sequence of radioactive decay. Since the y ,radiation that accompanies uranium's decay has neither mass nor charge and there-ore doesn't affect the mass number or atomic number of any of the nuclei pro 'aced, it's often omitted from the equations. The equation for the decay of uranium o thorium is usually written as 29sU _ _ 29oTh + 2 He Figure 4.6 Radioactive decay of carbon-14. 66 • Chapter 4 Discavering ths Secrets of the Nucleus Figure 4.7 The sequence of radioactive decay from 292U to ZgZPb. Z~Po z82Pb --w283Bi -i2~Po Z~Pb ~Z~Bi -+Z~Po z82Pb 82 83 84 (Stable isotope) z~z~, a~ Notice that: • the sum of the mass numbers to the left of the arrow, the 238 of the U-238, equals the sum of the mass numbers to the right of the arrow, 234 + 4. • the sum of the atomic numbers to the left of the arrow, the 92 of the uranium, equals the sum of the atomic numbers to the right of the arrow, 90 + 2. After 13 additional steps the entire chain finally comes to an end with the forma-tion of a stable isotope of lead, 2g2Pb. The entire sequence appears in Figure 4.7. Notice in Figure 4.7 that the radioactive element radon (Rn) is a transier part of this decay chain, forming from the radioactive decay of radium (Ra) an decaying, in turn, to polonium (Po). Radon itself is a gaseous element, a membe of the inert family of elements of the periodic table. There's concern that gaseous radon formed by the decay of very small amounts of radioisotopes that occur naturally in some kinds of rocks and soils may seep upward through the ground, enter homes and other buildings, and pres- ent an indoor pollution hazard. Ordinarily, we might expect that any radon gas we inhale would leave our lungs when we exhale. But radioactive decay of radon as it remains inside our lungs, during the moment between inhaling and exhal-ing, would produce minuscule amounts of polonium and other radioisotopes. Any traces of these radioactive elements that might remain within our bodies could do considerable biological damage through ionizing radiation (Chapter 5). g6 g7 88 89 90 91 92 Atomic number What subatomic partiele is lost as radon-222 is converted tt~ poloniumi218? Again, the equation What subatomic particle is lost from Ra-226 as it decays to Rn-222? We can Sinee the mass 'number drops by 4 and the atomic number drops by 2 as radium-226 is transformed into radon 222, the subatomic particle that is lost must be a combination of two protons-and two neutrons. Thus, it must be a he-lium nucleus, which is the same in this ease as saying that it is an a particle. The complete nuclear reaction is shows us that a particle with an atomic number of 2 and a mass number of 4 is lost. It must once again be a helium nucleus. The complete equation is What subatomie particle is lost as bismuth-210 is converted to polonium-210 in the next-to-last step of the sequence shown in Figure 4.7? Hete the equation ls  Since there is no change in the mass number and an increase by 1 in atomie number, an electron must have been ldst from the nucleus as a ~3 particle. The equation is therefore ite the reaction that occurs here as Zg$Ra ' Zg~Rn + subatomic particle Z88Ra -~ Zg6R~ + a ~gbRn ~ Zg4Po + subatomic particle Zg6Rn ~ ZgqPO -~ a '~3Bi -~ ~~Po + subatomie particle 2g~Bi -> 2~4Po + j3 4.5 Naturally Occurring Radioactive Decay • 67 P L E  Subatomic Loss E X A M P L E In its radioactive decay, curium-245 (Cm-245) loses an c~ particle; What radioisotope results from the decay of Cm-245? Curium's First Step  Reforenee t€i the periodic table shows that curium's atomic number is 96. Since an a particle has a mass number of 4 and an atomie-number of 2, curium-245 loses 4 units of mass and two units of atomic number. The result is an isotope with a mass number of 241 (245 - 4) and an atomic number of 94 (96 - 2). The element with an atomic number of 94 is plutonium (Puj. Thus the first step in the ehain of radioactive decay of curium-245 pro-duces plutonium-241;  Other naturally occurring radioisotopes decay by paths different from the one shown in Figure 4.7. Uranium-235, for example, decays initially to thorium-231, by a emission, and then, through an additiona113 steps, to the stable leau-207. After a total of 15 steps, radioactive curium-245 ends up as a stable isotope of bismuth, Bi-209. (The curie, the unit of radioactivity mentioned in Section 4.1, represents the rate of decay of a radioisotope: 1 curie = 3.7 x lOt~ radioactive disintegrations per second.) 68 • Chapter 4 Discovering the Secrets of the Nucleus • Q U E S T 1 O N   Although scientists could observe the changes that naturally occurring radioiso-topes undergo, as Becquerel and the Curies had done, until 1919 no one had as yet planned and carried out an artificial nuclear transformation that would convert a stable isotope of one element into another element. In that year Ernest Rutherford (Sec. 4.2) published a report of the first artificial transformation of one element to another. By bombarding nitrogen-14, a stable (and the most common) isotope of nitrogen, with a particles emitted by radium, Rutherford transformed the nitrogen atom into an atom of oxygen. In the process, the nitrogen nucleus absorbs the two protons and two neutrons of the a particle and then loses a proton, all with a net gain of 3 in mass number and 1 in atomic number. The entire procedure results in Transmutation is the conver- a transmutation, the conversion of one element into another: sion of one element into an- other element. 1~N + Z He ~ lg0 + 1H agine a child swinging on a playground swing. At what point(s) does the child i we the greatest amount of kinetic energy? The greatest amount of potential energy? 4.5 Naturally Occurring Radioactive Decay • 65 /3 particle, a igh-speed electron Figure 4.5 Radioactive decay of tritium. (Fig. 4.5). Tritium itself is a key component of the hydrogen bomb. The combina-tion of tritium with deuterium at extremely high temperatures provides the explosive force of one version of the hydrogen bomb (Sec. 4.14). Decay of carbon-14 also occurs with loss of a (3 particle. The result 14 . 14 0 6C ,lv + 1_R in this case is the transformation of a radioactive carbon atom into the most common isotope of nitrogen (Fig. 4.6). As in the case of tritium's decay, the mass of the nucleus remains unchanged while its atomic number increases by one unit. The radioactive decay of carbon-14 is useful for establishing the dates of ancient ob-jects, as we'll see in detail in Section 5.11. Uranium, which formed an image on the photographic plate in Becquerel's desk drawer and led him and the Curies to radioactivity, also provided the explo-sive force of one of the first atomic bombs. Its most common isotope, 298U, makes up over 99% of the uranium found in nature-mostly in pitchblende, an ore of the earth's crust-and represents the radioisotope of highest mass and highest atom- The universal trident symbol for ' ic number of any found (in more than trace amounts) in nature. The radioactive radioactivity decay of U-238 to thorium by loss of an a particle and emission of y radiation rep- ` resents the first step in one particular sequence of radioactive decay. Since the y ,radiation that accompanies uranium's decay has neither mass nor charge and there-ore doesn't affect the mass number or atomic number of any of the nuclei pro 'aced, it's often omitted from the equations. The equation for the decay of uranium o thorium is usually written as 29sU _ _ 29oTh + 2 He Figure 4.6 Radioactive decay of carbon-14. 66 • Chapter 4 Discavering ths Secrets of the Nucleus Figure 4.7 The sequence of radioactive decay from 292U to ZgZPb. Z~Po z82Pb --w283Bi -i2~Po Z~Pb ~Z~Bi -+Z~Po z82Pb 82 83 84 (Stable isotope)  z~z~, a~  Notice that: • the sum of the mass numbers to the left of the arrow, the 238 of the U-238, equals the sum of the mass numbers to the right of the arrow, 234 + 4. • the sum of the atomic numbers to the left of the arrow, the 92 of the uranium, equals the sum of the atomic numbers to the right of the arrow, 90 + 2. After 13 additional steps the entire chain finally comes to an end with the forma-tion of a stable isotope of lead, 2g2Pb. The entire sequence appears in Figure 4.7. Notice in Figure 4.7 that the radioactive element radon (Rn) is a transier part of this decay chain, forming from the radioactive decay of radium (Ra) an decaying, in turn, to polonium (Po). Radon itself is a gaseous element, a membe of the inert family of elements of the periodic table. There's concern that gaseous radon formed by the decay of very small amounts of radioisotopes that occur naturally in some kinds of rocks and soils may seep upward through the ground, enter homes and other buildings, and pres- ent an indoor pollution hazard. Ordinarily, we might expect that any radon gas we inhale would leave our lungs when we exhale. But radioactive decay of radon as it remains inside our lungs, during the moment between inhaling and exhal-ing, would produce minuscule amounts of polonium and other radioisotopes. Any traces of these radioactive elements that might remain within our bodies could do considerable biological damage through ionizing radiation (Chapter 5). There's still much dispute about whether radon actually constitutes a significant indoor hazard. Nevertheless, the simple possibility of harm from indoor radon has spurred the design and manufacture of various radon detectors for use in homes and other buildings. The following example illustrates some of the steps in the sequence of radio-active decay shown in Figure 4.7. g6 g7 88 89 90 91 92 Atomic number t What subatomic partiele is lost as radon-222 is converted tt~ poloniumi218? Again, the equation What subatomic particle is lost from Ra-226 as it decays to Rn-222? We can Sinee the mass 'number drops by 4 and the atomic number drops by 2 as radium-226 is transformed into radon 222, the subatomic particle that is lost must be a combination of two protons-and two neutrons. Thus, it must be a he-lium nucleus, which is the same in this ease as saying that it is an a particle. The complete nuclear reaction is shows us that a particle with an atomic number of 2 and a mass number of 4 is lost. It must once again be a helium nucleus. The complete equation is What subatomie particle is lost as bismuth-210 is converted to polonium-210 in the next-to-last step of the sequence shown in Figure 4.7? Hete the equation ls  Since there is no change in the mass number and an increase by 1 in atomie number, an electron must have been ldst from the nucleus as a ~3 particle. The equation is therefore ite the reaction that occurs here as Zg$Ra ' Zg~Rn + subatomic particle Z88Ra -~ Zg6R~ + a ~gbRn ~ Zg4Po + subatomic particle Zg6Rn ~ ZgqPO -~ a '~3Bi -~ ~~Po + subatomie particle 2g~Bi -> 2~4Po + j3 4.5 Naturally Occurring Radioactive Decay • 67 P L E  Subatomic Loss E X A M P L E In its radioactive decay, curium-245 (Cm-245) loses an c~ particle; What radioisotope results from the decay of Cm-245? Curium's First Step  Reforenee t€i the periodic table shows that curium's atomic number is 96. Since an a particle has a mass number of 4 and an atomie-number of 2, curium-245 loses 4 units of mass and two units of atomic number. The result is an isotope with a mass number of 241 (245 - 4) and an atomic number of 94 (96 - 2). The element with an atomic number of 94 is plutonium (Puj. Thus the first step in the ehain of radioactive decay of curium-245 pro-duces plutonium-241;  Other naturally occurring radioisotopes decay by paths different from the one shown in Figure 4.7. Uranium-235, for example, decays initially to thorium-231, by a emission, and then, through an additiona113 steps, to the stable leau-207. After a total of 15 steps, radioactive curium-245 ends up as a stable isotope of bismuth, Bi-209. (The curie, the unit of radioactivity mentioned in Section 4.1, represents the rate of decay of a radioisotope: 1 curie = 3.7 x lOt~ radioactive disintegrations per second.) 68 • Chapter 4 Discovering the Secrets of the Nucleus • Q U E S T 1 O N Although scientists could observe the changes that naturally occurring radioiso-topes undergo, as Becquerel and the Curies had done, until 1919 no one had as yet planned and carried out an artificial nuclear transformation that would convert a stable isotope of one element into another element. In that year Ernest Rutherford (Sec. 4.2) published a report of the first artificial transformation of one element to another. By bombarding nitrogen-14, a stable (and the most common) isotope of nitrogen, with a particles emitted by radium, Rutherford transformed the nitrogen atom into an atom of oxygen. In the process, the nitrogen nucleus absorbs the two protons and two neutrons of the a particle and then loses a proton, all with a net gain of 3 in mass number and 1 in atomic number. The entire procedure results in Transmutation is the conver- a transmutation, the conversion of one element into another: sion of one element into an- other element. 1~N + Z He ~ lg0 + 1H • Q U E S T I O N What subatomic particle is lost by 28ฐPo as it is converted into 282Po in the final step of the decay sequence of U-238? Write the reaction for this step. Positron or Plutonium. 4.6 Rutherford's Transmutation of Nitrogen As we saw for the decay of uranium-238 (Sec. 4.5), the sum of the mass numbers to the left of the arrow equals the sum of the mass numbers to the right, and the sum of the atomic numbers to the left equals the sum of the atomic numbers to the right. With his conversion of nitrogen into oxygen, Rutherford had achieved the age-old dream of the transmutation of the elements. One of the goals of alchemy, was the transmutation of one elemental substance into another. The alchemists sought especially to convert a common, inexpensive metal such as lead into precious gold. Through nuclear transformations much like Rutherford's, the alchemical dream has by now been re-alized, but without fulfilling the promise of the riches the ancients sought. Not only is expensive platinum (rather than lead) used as the starting metal for the forma-tion of gold, but the cost of the highly purified platinum needed for the modern transmutation is far greater than the value of the gold that's generated. The conversion of platinum into gold has been achieved by bombarding platinum-198 with neutrons to produce platinum-199.This isotope, in turn, decays to gold-199 with the loss of a subatomic particle: 198 Pt + on -> 198Pt '~$Pt - '99 Au + a subatomic particle What subatomic particle is lost by the platinum as it becomes an atom of gold? 4.7 A Nuclear Wonderland As the 20th century progressed, science probed ever more deeply into the struc-ture and behavior of the atom, continuously stripping away its secrets. Today the nucleus stands as a strange and complex world, seemingly no less bizarre than the one Alice found when she fell down the rabbit hole of Lewis Carroll's Alice's Adventures in Wonderland. r. with Chemistry 8.3 How Francis Bacon Died Attempting to Discover the Benefits of Refrigeration In the history of science, ideas sometimes get lost for a while. Even an especially shrewd and perceptive idea, one that could lead to great advances in our under-standing of the world around us, can vanish for a period of time. It's ignored and it goes underground while other, less useful and sometimes more bizarre theories blossom, attract the best minds, and then wither away as the earlier, more pro-ductive idea comes forth once again to revitalize the exploration of science. That's exactly what happened to Francis Bacon's theory of heat. Francis Bacon, born in 1561 to a family of considerable influence and power in the court of Queen Elizabeth I of England, was a statesman, an essayist, and 'the father of inductive logic and modern experimental science. Back in 1620, with considerable insight, Bacon wrote about his idea that heat results quite simply from motion: "The very essence of heat," he proposed, "is motion, and nothing else." Heat, Francis Bacon concluded, is neither more nor less than a "brisk agitation" of the very particles that compose matter. , cold-simple cold-might prevent the decay of meat. He stopped his carriage and rushed out into the snow to buy a freshly butchered piece of poultry. To test his the-ory, Bacon gathered up some snow with his bare hands and stuffed it into the an-imal. He never knew the results. Instead of discovering the modern technique of preserving food by refrigeration, a Cold Hot 00" (01, (0)> Applying Bacon's theories of heat in a modern context, suppose you have a cold piece of copper and a hot piece of copper. Using the terminology of modern chem-istry, what would you say is moving more "briskly" in the hot piece of copper than in the cold one? "Nam' €c(ctdaffi)3 Figure 8.3 Heat results from the "brisk agitation" of the particles of matter.  8.4 What Happened When Count Rumford Bored Cannons Bacon's theory-that the basis of what we call heat lies in the motion of particles of matter-was overwhelmed for over 150 years by the caloric theory of heat. (Calorie and caloric come from the Latin calor, meaning heat.) Until nearly the very last year of the eighteenth century most scholars believed that heat wa, mysterious sort of fluid, which they called "caloric," that flowed spontaneoi from a hot body to a cooler one. This "caloric" was a very strange substance. It 8.2 Potential Energy, Kine+ r Potential energy can be stored in two different ways: • through a body's location or position, and • through a substance's composition. If you climb up onto a diving board over a swimming pool, for example, your body acquires a certain amount of potential energy. The higher you climb-the higher your location above the water-the more potential energy you have. As you stand at the end of the board, motionless, your energy is poterztial since nothing is hap-pening. You have the potential for doing work, but you aren't doing any as long as you stand motionless. When you jump off the board you convert your potential en-ergy into kinetic energy, the energy of motion. As you land in the water the kinet-ic energy of your falling body does work in moving the water, creating a splash and generating noise. Before you jump, your potential energy lies in your position, your location some distance above the surface of the water. But potential energy can come from the composition of a substance as well as from its position. The hydrocarbons of gasoline and paraffin wax, for example, contain great amounts of chemical poten-tial energy, regardless of their location. Igniting a mixture of these hydrocarbons and oxygen releases this potential energy, which can be converted (for gasoline) into the kinetic energy of a moving car or (for paraffin wax) into the heat and light of a candle's flame. Similarly, food contains chemical potential energy that's con-verted into a body's heat, the actions of the muscles, the functioning of the organs, and so on-all involving chemical processes. This potential energy of gasoline, paraffin wax, and food derives from their chemical composition. While energy presents itself in many forms-biological, chemical, electrical, thermal, and more-energy itself is usually described most simply and most con-veniently in terms of its equivalent in heat (Fig. 8.2). We'll look now at the origins of our modern view of heat and we'll see how heat is related to work and to chem-ical energy. 4~Hi~N~t~NN ~~(l~NNlI~N~fi~;;l~(il~ ih~nnrvnmrloVrmnPrti~Yttn:nnm :LUwiiiiiiill~uu.~s~trltllllliluY~iiu1  ~agine a child swinging on a playground swing. At what point(s) does the child i we the greatest amount of kinetic energy?The greatest amount of potential energy? 4.5 Naturally Occurring Radioactive Decay • 65   /3 particle, a igh-speed electron Figure 4.5 Radioactive decay of tritium. (Fig. 4.5). Tritium itself is a key component of the hydrogen bomb. The combina-tion of tritium with deuterium at extremely high temperatures provides the ex-plosive force of one version of the hydrogen bomb (Sec. 4.14). Decay of carbon-14 also occurs with loss of a (3 particle. The result 14 . 14 0 6C ,lv + 1_R  in this case is the transformation of a radioactive carbon atom into the most com-mon isotope of nitrogen (Fig. 4.6). As in the case of tritium's decay, the mass of the nucleus remains unchanged while its atomic number increases by one unit. The radioactive decay of carbon-14 is useful for establishing the dates of ancient ob-jects, as we'll see in detail in Section 5.11. Uranium, which formed an image on the photographic plate in Becquerel's desk drawer and led him and the Curies to radioactivity, also provided the explo-sive force of one of the first atomic bombs. Its most common isotope, 298U, makes up over 99% of the uranium found in nature-mostly in pitchblende, an ore of the earth's crust-and represents the radioisotope of highest mass and highest atom- The universal trident symbol for ' ic number of any found (in more than trace amounts) in nature. The radioactive radioactivity decay of U-238 to thorium by loss of an a particle and emission of y radiation rep- ` resents the first step in one particular sequence of radioactive decay. Since the y ,radiation that accompanies uranium's decay has neither mass nor charge and there-ore doesn't affect the mass number or atomic number of any of the nuclei pro 'aced, it's often omitted from the equations. The equation for the decay of uranium o thorium is usually written as 29sU _ _ 29oTh + 2 He Figure 4.6 Radioactive decay of carbon-14. 80 • Chapter 4 Discovering the Secrets of the Nucleus -JJJ ,W? -vjg 4.14 Nuclear Fusion: Another Bomb, with the Power of the Sun Nuclear fusion is the process by which several nuclei of small mass combine to form a single nucleus of larger mass.  A flare ejected from the surface of the sun. The sun's energy comes from a fusion reaction that converts hydrogen to helium. Gone Fusion We've seen that in nuclear fission the nuclei of certain isotopes of relatively large mass split apart into smaller fragments, releasing energy in the process through the conversion of matter into energy. In nuclear fusion, a transforma-tion resembling the reverse of fission, several atoms of small mass come together at extremely high temperatures, 10 million to 100 million degrees Celsius, to form larger nuclei. As in fission, nuclear fusion also results in the conversion of matter into energy. The fusion of four hydrogen nuclei to a helium nucleus and two positrons (Sec. 4.7) produces the energy of the sun. As in all other reactions, this fusion reaction occurs with the preservation of electrical neutrality: The two positive charges of the ejected positrons are balanced by the two neg-ative charges of two electrons lost from valence shells. (The four hydrogen atoms taking part in the fusion reaction contain a total of four valence electrons; the single helium atom produced has only two. Thus, two electrons are lost from valence shells as a result of the fusion.) 41H ~ 2 He + 21'e+ + 21_ฐe The oppositely charged positrons and electrons combine with each other; each pair of these subatomic particles is transformed into a pair of y rays (Sec. 4.7): o++loe `2y The overall fusion reaction of the sun becomes 41H ~ ZHe + 4y  In Section 4.13 we saw that the fission of 1 kg of U-235 converts about 0:78 g of matter into energy. How much matter is converted to energy by the fusion of i kg of hydrogen, or more specifically, protium? The experimentally deter-mined mass of a helium-4 atom is 4.0026 amu; for an atom of protium, it's 1:0078 amu. We've just seen that 4 protium atoms fuse to form one atom of He-4. The mass of 4 protium atoms is 4 x 1.0078 amu = 4:0312 amu Since the measured mass of a He-4 atom is 4.0026 amu, the amount of ma: converted into energy is mass of 4 protium atoms 4.0312 amu 4:0026 amu mass converted into energy 0.0286 ainu On a percentage basis, the amount of mass converted into energy mass of 1 He-4 atom 0.0286 amu X 100 = 0.709% of the mass of the 4 protium atoms 4.0312 amu Applying this percentage to 1 kg of protium, we get' 0.709% x 1000 g = 7.09 g of matter 5.9 Positron Emission Tomography • 103 PET operates through the emission of positrons by nuclei with unstable neutron-proton ratios. As we saw in Section 4.7, a positron is a subatomic particle indistinguish-able from an electron except for its positive charge. We also saw, in Section 4.8, that the stability of a nucleus depends partly on the ratio of its neutrons to its protons. Certain radioisotopes, especially those containing relatively few neutrons, emit positrons, which disappear in a burst of y radiation when they collide with electrons. (The electrons van-ish as well.) Whenever a nucleus emits a positron, one of the protons within the nucle-us is transformed into a neutron and thereby improves the ratio.To keep track of these nuclear transformations we can think of a proton as a combination of a neutron and a positron. Looking at it in this way, the loss of a positron from the combination (the pro-ton) leaves the neutron behind, with the net conversion of one proton to one neutron. a neutron as a combination of a proton and an electron. R-particle emission does convert a neutron to a proton, and positron emission does convert a proton to a neutron.) In PET, a positron-emitting radioisotope-most often carbon-11, nitrogen-13, oxygen-15, or fluorine-l8-is incorporated into the molecular structure of a com-pound normally used by the organ under examination or into a closely related compound that travels along the same biological paths. The compound containing the radioisotope is administered to the patient and travels into the organ. Positrons emitted by the isotope collide with nearby electrons and disappear (along with the electrons) in bursts of energy consisting of two y rays traveling in opposite directions. Nearby detectors and computers convert these unusual bursts into images of planes or slices of the organ and reveal the molecular activity within it. (Tomography comes from the Greek word tomos, meaning slice or section.) In this way PET provides views of the molecular traffic within organs such as the brain and the heart and shows what's going on inside them. As an illustration, PET reveals graphically that the human brain processes the names of different kinds of objects-simple tools and common animals, for example-in different re-gions. It also shows the effects of various drugs and medications on an organ. In one of PET's most useful applications, an atom of fluorine-18 is attached to a mol-ecule of glucose, the sugar used by the brain as its exclusive nutritional fuel. This tagged glucose enters the brain along with ordinary glucose and emits its positrons, which collide with electrons and emit bursts of y rays. Analysis of images obtained in this way allows physicians to follow the path of the glucose within the brain and to diagnose and treat abnormalities of this organ. Among the advantages of PET are the very short half-lives of the more com-mon positron-emitting isotopes, ranging from 2 minutes for oxygen-15 to 110 min-utes for fluorine-18. With isotopes of such short half-lives, the source of ionizing ,, radiation soon disappears from the body. Figure 5.4 illustrates the positron-emitting activity of fluorine-18. Into what element is an atom of Q-15 converted when it emits ~ positron? , Oxygen's atomic number is 8. There must therefore be 8 protons in oxygen's nucleus. Sinee positron emission converts a proton into a neutron, the atomic number must decrease by 1 unit as the positron leaves the nucleus. Thus oxv-gen, with its atomic number of 8, is eonverted into the element whose atomic numbc;r is 7, nitrogerr. Positron emission tomogra-phy, or PET, produces images of planes, within an organ, generated through the analy-sis of y rays emitted by colli-sions of positrons and electrons. E X A M P ~ E Positively Positron 104 • Chapter 5 Harnessing the Secrets of the Nucleus Figure 5.4 Positron emission by fluorine-18. Nearby electron -y , Positron .  Neutrnn -1- + - - Proton + -f" ..---i t   18F 9 A fluorine-18 nucleus an oxygen-18 nucleus. vanishes in a burst emits a positron, The ejected positron collides of two y rays. becoming . . . with a nearby electron and . . . Into what element is an atom of nitrogen-13 transformed when it emits a positron? 5.10 The Nuclear Calendar: Uranium and the Age of the Earth With their individual, predictable, and immutable rates of de.cay, naturally occur-ring radioisotopes provide an important tool for dating ancient objects, ranging in age from artifacts created a few thousand years ago to bodies as old as the earth and the solar system. We can estimate the earth's age from our knowledge of the half-lives of the ra-dioisotopes that constitute the decay chain of U-238 (Table 5.3) and from a chem-ical analysis of the oldest known rocks.To understand how, suppose that the oldest sample of rock we can find contains exactly equal numbers of atoms of lead-206 (the stable isotope of lead at the end of the U-238 decay series) and of uranium-238. If we assume that all of the lead-206 came from decay of the U-238, then we have evidence that exactly one half-life of the U-238 has passed since the rock was formed. This amounts to 4.5 X 109 years (Table 5.3). If we find a ratio of three atoms of Pb-206 for every atom of U-238, then two half-lives (9.0 X 109 years) have passed, and so on. By measuring the ratio of the atoms of each of these iso-topes and by making several critical assumptions (especially that all the lead atoms were formed from decay of uranium atoms), we can calculate the age of the rock containing the U-238. Analysis of a piece of meteorite shows that it contains seven Pb-206 atoms for every atom of U-238. How old is the meteorite? To calculate the age of the meteorite we make the same sort of -assump-tions described in this section. We assume that no Pb-206 was present at the formation of the meteorite and that all the Pb-206 now present in the meteorite came from radioactive decay of the U-238. t t This technique, as well as others that are based on different chains of ra-dioactive decay and that require different assumptions, give estimates of the age of the earth's surface that fall in the broad range of 3.5 billion to 4 billion years (3.5 x 109 to 4 x 109 years). We might expect, at first, that the half-lives of all the other radioisotopes in the chain have to be used in the calculation as well, but this isn't the case at all. The U-238 decays so much more slowly than any of the other isotopes that its half-life alone reveals the age of the rock. To see why, we can use an analogy involving an hourglass with an unusual shape. Imagine a sand-filled hourglass shaped like the one shown in Figure 5.5. The time it takes for the sand to fall from the top bulb to the bottom is determined ex-clusively by the width of the narrowest neck, which happens to be the first in the series. The remaining necks are much wider than the first one, so they don't affect p;gurQ 5.5 An unusual the rate at which the sand falls. Similarly, the rate of decay of U-238 to Pb-206 is hourglass. determined exclusively by the slowest step in the sequence, which again happens to be the first step. With this analogy, both the rate at which the sand falls through the narrowest (first) constriction and the rate of decay of the U-238 through the slowest (first) f A rate-determining step is . decay step determine the time it takes for each process to occur.The slowest step the slowest step in a sequence ~; of a sequence that proceeds through other, much faster steps as well-the single of steps that, by itself alone, a step that determines the rate of the entire sequence-is called the rate-determining determines the rate of the en- ; step of the overall process. tire, multistep process. 5.10 The Nuclear Calendar: Uranium and the Age of the Earth • 105 We can now' construct a table showing the number of half-lives of U-238 that have passed, and the number and ratio of U-238 and Pb-206 atoms. To simplify the arithmetic, we'll assume that we start with 64 U-238 atoms. Notiee =,y that sinee each U-238 atom decays eventually to one Pb-206 atom, the total number of U-?38 and Pb-206 atoms must remain constant: Half-Lives Number of Number of Pb/U of U-238 U-238 Atoms Pb-206 Atoms Ratio 0 ~ 0 0 Since the observed ratio is 7 atoms of Pb-206 for every U-238 atom in the sample, 3 half-lives must have passed since this sample of the mete-orite was formed. As the half-life of U-238 is 4.5 x 10y years (Table 5.3), 3 half-lives are 3 x 4.5 x 109 years = 13.5 x 109 years. If our assumptions are correct, the sample of the meteorite is 13.5 x 109 years The slowest or rate-determining step What would the ratio of Pb-206 to U-238 atoms be if the sample of meteorite in the • Q U E S T I O N exercise were 18.0 x 109 years old?  106 • Chapter 5 Harnessing the Secrets of the Nucleus 5.11 The Nuclear Calendar: Carbon-14 and the Shroud of Turin A variation of this dating technique allows us to determine the age of carbon-containing objects made of materials derived from plants. Unlike uranium-238, which decays without being replenished by any natural phenomenon, the ra-dioactive isotope carbon-14 (16C) is formed continuously by the action of cosmic radiation on the earth's atmosphere. Neutrons generated by the cosmic radiation react with atmospheric nitrogen atoms to produce carbon-14 and a proton: pn + 14N ----- 164C + With its half-life of 5730 years, this newly formed C-14 • combines with atmospheric oxygen to form 1~COZ, • migrates (as part of the carbon dioxide) down to the surface of the earth, and • becomes incorporated into the cellulose and other carbohydrates of plant life. In this way the C-14 becomes part of our cotton, paper, and wooden products and enters the bodies of all animals through the food chain. With the death of the plant-through its use as food or its conversion into fabric, paper, or wooden objects-the plant's incorporation of atmospheric 16COZ into its carbohydrates stops. Yet the C-14 already present within it continues its long decay to nitrogen, thereby continually decreasing the ratio of the radioactive C-14 to the stable isotopes of carbon, C-12 and C-13. The carbon dating technique itself begins with a measurement of the relative amounts of C-12 and C-13 (both of which are stable, naturally occurring isotopes) and the radioactive C-14 still present in the organic material. By comparing these measured ratios with ratios normally present in the atmosphere, radiocarbon dating provides good estimates of the age of substances composed of organic materials. In 1988 this form of dating was applied to the Shroud of Turin, a 14-foot-long piece of linen in the shape of a burial cloth. The shroud first appeared in France sometime between 1350 and 1360 and was later transferred to the Italian city of Turin. Imprinted on it is the distinct image of a man. Many have believed that the image is that of Jesus and that the shroud is the actual burial cloth of Jesus, which would make the shroud approximately 2000 years old. 5.12 The Source of the Static at Stagg Field: Detecting Radiation • 107 •QUEST1ON Which of the following can be dated by radiocarbon techniques: (a) a rock; (b) a leather slipper; (c) a wooden boat; (d) a mummified body; (e) a silver spoon. Describe your reasoning. a rock due to rocks have been on Earth for more than 4 billion years. 5.12 The Source of the Static at Stagg Field: Detecting Radiation Even with its remarkable abilities to produce ions, to destroy tissue, and to kill, as ~`R ' well as to diagnose and heal, there are nonetheless some important things that nu- clear radiation doesn't do. It doesn't produce any taste, odor, sound, or any other kind of immediate sensation. You can't see, hear, taste, smell, or feel it. To detect nuclear radiation you have to use a device or instrument designed specifically for this purpose. Some are complex and expensive; others are as simple as a piece of film wrapped in plastic. It was the steady clicking of one of these more complex instruments that produced the static under Stagg Field as Enrico Fermi's atomic pile began its controlled chain reaction. That historic device resembled a Geiger counter, which consists of a gas-filled cylinder connected to a high-voltage battery and to a sounding device and a meter. A gap between the wall of the cylinder and an electrode passing into its center serves to break an electrical circuit connecting the battery to the rest of the counter. In the absence of ionizing radiation this gap keeps the battery from activating the sounding device or the meter. Any ionizing radiation that passes through the cylinder produces a stream of ions in the gas, which tem-porarily completes the circuit between the cylinder's wall and the central electrode and registers as a click from a speaker. The frequency of the resulting clicks and the meter reading indicate the intensity of the radiation (Fig. 5.6). The Geiger A medical worker wearing a fihn counter is named for one of its inventors, Hans Geiger, a German scientist who had badge. The badge records the been a student of Ernest Rutherford (Sec. 4.2). accumulated radiation exposure. Gap between electrodes Figure 5.6 The Geiger ! keeps circuit open Central electrode counter. Ionizing 4 Insulation \ / Inert gas radiation, _  Thin window   Cylindrical outer electrode \ High-voltage battery Electronic amplifier Ionized gas momentarily completes the electrical circuit 108 • Chapter 5 Harnessing the Secrets of the Nucleus Girl being scanned with a Geiger counter after a nuclear accident.   Another kind of detector, a scintillation counter, uses a material that fluoresces, or emits an instantaneous flash of light when the invisible radiation strikes it. Zinc sulfide, ZnS, is a substance of this sort. A light-sensitive detector in the counter registers the intensity of radiation through the amount of light emitted by the flu-orescing material. Both the Geiger counter and the scintillation counter are par-ticularly useful for detecting and measuring radiation as it occurs. Still another device, the film badge, is worn by medical personnel and others who work near radiation in order to monitor the amount of radiation they receive over a period of time, rather than at any particular moment. These badges respond to radiation much as Becquerel's sealed photographic plate did when it produced an image as it shared a desk drawer with radioactive ore (Chapter 4). Developing the film of the film badge reveals the wearer's cumulative exposure to radiation. Which one or more of the detection devices described in this Section would you use if you wished to determine immediately whether the residue left by a spilled chemical is radioactive? Which would you use if you wanted to determine the total, cumulative amount of radiation you might be exposed to in the course of an entire month? 5.13 Ionizing Radiation in Everyday Life radiation I-131 released by the Chernobyl explo-sion (Sec. 5.2) caused an increase in thyroid cancer in children, yet this same ra-diation from I-131 provides medically useful images of the thyroid and can cure or alleviate the medical condition of hyperthyroidism (Sec. 5.8). These are spe-cific illustrations of the generality that ionizing radiation can cause illness and 166 • Chapter 7 Petroleum Figure 7,11 Cyclization of H~ hexane to cyclohexane. , C HZC CHZ CH3-CHz-CHZ-CHZ-CHZ-CH3  HZC~ ~CHZ C HZ Figure 7.12 Aromatization of HZ cyclohexane to benzene.  HZC CHZ / + 3H2 H2C~ iCH2 \ C _. HZ • Q U E S T I O N Name two products produced by the isomerization of pentane. What is produced through the aromatization of cyclohexane?  S P E C T 1 Y E  Energy for the Cars of Tomorrow in this chapter we have examined hydrocarbons as a several forms. Automobile manufacturers can improve the source of energy, with particular emphasis on the hydro- fuel efficiency of new cars so that they consume less gaso- carbons of gasoline and their use in the internal combus- line and produce less exhaust gas. Gasoline manufactur- tion engine. It's an appropriate emphasis since more than ers can formulate cleaner burning gasolines with improved 40% of all the petroleum used in the United States now methods of refining and improved gasoline formulations. ends up as gasoline for our cars. Overall, two-thirds of all Still another route would be to abandon hydrocarbon-rich the petroleum used goes, in one form or another, into gasoline and turn instead to other sources of energy, the transportation of all kinds. alternative fuels. Driving is a dirty business. We add more pollutants to our environment by running our internal combustion en- Liquified Petroleum Gas (LPG) Liquified petrole- gines than we do with any other single activity. Auto ex- um gas (LPG), often referred to simply (and erroneously) as haust, even exhaust presumed to be clean, contributes propane, is a liquified mixture of hydrocarbons that normally about a quarter of all the carbon dioxide discharged into exist as gases. Its composition varies, but it's usualiy large- the air above the United States, as well as almost all of ly propane with the isomeric butanes and smaller amounts the carbon monoxide in and above our cities. (Although of methane, ethane, and other low-molecuiar-weight hy- carbon dioxide isn't a health hazard, we'll examine its role drocarbons also present. as an atmospheric pollutant in Sec. 8.14,) Moreover ben- Liquified petroleum gas has been used extensively as zene, one of the hydrocarbons of gasoline, is a known car- a fuel, in general applications for more than 90 years and to cinogen, a cancer-causing agent. Next time you fill your propel vehicles for more than 60 years.Today it's the most tank, look for a note on the gas dispenser telling you that widely used alternative fuel. Only gasoline and diesel fuel "Long-term exposure to vapors has caused cancer in some surpass LPG as a fuel for transportation. It's a clean- laboratory animals." burning fuel, producing little carbon monoxide and fewer It seems clear that improving the health of our envi- oxides of nitrogen than gasoline. But it is still a fossil fuel, ronment (and ourselves) requires, among other things, lim- with all the disadvantages that this implies (Chapter 8). iting or eliminating tailpipe emissions. This can take Leaks of LPG result in a dense, flammable, low-lying, in- Perspective • 167  Installing a tank of natural gas. visible cloud of gas that ignites easily. In some localities cars powered by LPG are prohibited from entering tunnels or parking garages. i Compressed Natural Gas Compressed natural gas is another fossil fuel that's used as an alternative fuel. Com-posed principally of methane, with small amounts of other alkanes, natural gas is used widely for cooking and heating. Plentiful, clean burning, and often at a cost not far from gaso-line's, it ranks with LPG as a major competitorto gasoline. For use in vehicles, natural gas must be compressed and stored in heavy, sturdytanks. Its disadvantages arethe short driving range it provides-about 100 miles-the heavy and awkward fuel tanks it requires, and the complexity of refueling. It is more suitable to fleet vehicles than to private automobiles. i  Ethanol Ethanol (ethyl alcohol) belongs to a class of , fuels known as renewable fuels. Unlike fuels obtained from petroleum, natural gas, or coal, ethanol comes prin-cipally from the fermentation of grain and other crops, in-cluding potatoes and corn, and is thus a renewable resource. (Grain alcohol is another name for ethanol.)The fossil fuels, on the other hand, are nonrenewable; none are being formed today to regenerate what we draw from A bus powered by methanol.  the earth's current reserves. Add to this ethanol's octane rating of 105, its low impact on the environment, and its relatively low toxicity, and ethanol becomes an attractive replacement for hydrocarbon fuels. Among its disadvantages are its relatively high cost (compared to gasoline), low energy content (which would require large fuel tanks), and scarcity. Converting all the grain grown in the United States each year into ethanol would supply only about a quarter of the fuel needed. One practical solution to the problem of scarcity is the use of mixtures of ethanol and gasoline, such as 85% ethanol-15% gasoline, a blend known commercially as E85. Major auto-mobile manufacturers currently produce a limited number of cars designed to run on either gasoline or gasoline-ethanol blends. Methanol Methanol (methyl alcohol) can be produced from a variety of sources, including wood, the fossil fuels coal and natural gas, and even garbage. (Originally gener-ated by heating wood to a high temperature, methanol is sometimes known as woodalcohol.) Methanol's octane rat-ing is high, close to ethanol's, and it generally burns more cleanly than gasoline. A mixture of 85% methanol-15% gasoline is available commercially as M85. But methanol also comes with a few disadvantages. It corrodes common varieties of steel, has a relatively low en-ergy content, and is toxic. As a result, fuel tanks would have to be large, made of expensive, corrosion-resistant stainless steel, and well sealed. Moreover, one of the few pollutants methanol does produce is especially nasty. I ncomplete com-bustion of methanol generates formaldehyde, which is a car-cinogen, an irritant, and an air pollutant. Exhaust systems would have to be redesigned to keep it out of the environment. 168 • Chapter 7 Petroleum  An electric car. ate it from some other, primary source such as fossil fuels, nuclear reactions, falling water, sunlight, the wind, or chemical reactions. Switching from burning hydrocarbons to electric batteries won't, in itself, decrease the total amount of energy we consume; it will simply shift the bur-den of producing that energy from the internal combus-tion engine to some other power source. Unless we use wisdom in addition to technical knowledge, we might find that in replacing gasoline with electric batteries we have simply moved our problems of energy production from one location to another. Fuel Cells The fuel cell can be described as a "gaseous Electricity No matter how efficient the engine, a car battery," a term applied to it by its English inventor, William that get its power from the combustion of a hydrocarbon or Grove, in 1839. It's designed not to accept, store, and re- an alcohol or some other kind of organic compound must lease electricity, as a common battery does, but rather to produce exhaust gas emissions of some sort, even if they're induce chemical reactions to release energy in the form of no more than water and carbon dioxide. Cars that meet the electricity rather than heat. In a common form of the cell, ideal of no emissions whatever, that produce no exhaust hydrogen combines with oxygen on the surface of the cell's gases, that add nothing at all to the atmosphere, are known catalysts (Sec. 7.7) to form water and produce electricity as zero-emission vehicles, or ZEVs. One source of power (Fig. 7.13): that meets this test is electricity, released by storage bat- 2H2 + 02 - 2H20 + energy (electricity) teries mounted in the car. Electric cars are classified as ZEVs. Because of concerns about air pollution, the state of The oxygen forthe cell is obtained from the atmosphere; the California requires that by 2003 at least 10% of all cars sold hydrogen can either be stored on the vehicle or produced within the state must be ZEVs. catalytically from a hydrocarbon or other hydrogen-con-Despite the absence of emissions, electric cars come with problems of their own. The major disadvantages of electric cars are their short driving ranges, the long times required for recharging their batteries, and the uncer-tainty of where all the electric power needed to recharge large numbers of batteries will come from. Part of the so-lution to the last problem comes from the nature of ener-gy itself. Moving vehicles powered by other sources of energy are slowed and stopped by the force of the brakes. These convert the energy of the motion to heat as they press against the rotating wheels. Electric cars use a process known as regenerative braking, in which an elec-tric generator slows the moving car by converting its en-ergy of motion into electricity rather than heat. This regenerated electricity is fed to the battery to help main-tain its charge. We'll have more to say about the various forms of energy in the next chapter. Despite energy economies produced by regenerative braking and similar techniques, the wholesale conversion of our transportation system from fossil fuels (or other fuels that rely on combustion) to electric power could pro-duce the most serious problem of all. Electricity itself is a secondary source of energy in the sense that we gener- Figure 7.13 The essentials of a typical fuel cell.  9.4 Counting Atoms and Molecules: Part II • 209   1~16 of a mole of oxygen atams. On the other hand,l gram of hydrogen, atom-ic weight 1.008, represents very nearly 1 mole of hydrogen atoms. Since 1 mole of any chemical substance must contain exactly the same number of chemical particles as 1 mole of any other chemical substance, there must be almost 16 times as many atoms of hydrogen in 1 gram of hydrogen as there are oxygen atoms in 1 gram of o?~yge; What's the mass of one gold atom? .. We know that the atomic weight of an element, expressed in grams, contains 1 mole of that element. We also know that 1 mole of any chemical substance contains 6.02 x 1(1~3 atoms, molecuies, or ions of that substance. Since the atomic weight of gold is 197 amu (a value we can find in the pe-riodic table or in any table of atomic weights),197 grams of gold must contain 1 mole of gold, or 6.02 x 102' atoms of gold. The product of the two fractions, 197 grams of gold mole of gold mole of gold x 6.02 x 1023 gold atams gives the result 3 grams of gold Z2 32:7 x 10 = or 3.27 x 10- grams per gold atom gold,atom One gold atom has a mass of 3.27 x 10-ZZ grams. Compare this Example with ~he Question at the end of Section 2.2  How many hydrogen atoms are there in 18.02 g of water? • The molecular weight of water is H: 2 x 1.008 amu = 2.016 amu O: 1 x 16.00 amu = 16.00 amu 18.02 amu E X A I~1 P L E One Gold Atom E X A MI P L E Hydrogen Atoms This mass of water (18.02 g) represents 1 mole of water. Since there are two : hydrogen atoms €or each water moleeule, there must be twice as many hy-~; drogen atoms as there are water molecules in any quantity of water molecules. - , In 18.02 g of water (1 mole of H20) there must be two moles of hydrogen = atoms, or 2 x 6.02 x 1023, or 12.04 x 102~ hydrogen atoms.  'Which contains the greater number of carbon atoms: 1 gram of CO2 (atomic weight • Q U E S T I O N 44 amu) or 1 gram of CO (atomic weight 28 amu)? Explain your reasoning. ;`.4 Counting Atoms and Molecules: Part II ow, by using the mole and understanding its connection to Avogadro's number, ~ can count out the chemical particles that take part in any reaction. '~_One of the most important of all the reactions our society uses is the burning y hydrocarbons of gasoline, natural gas, kerosene, jet fuel, diesel fuel, and other 210 • Chapter 9 Arithmetic of Chemistry products derived from petroleum (Chapter 7). In Chapter 8 we saw evidence that the carbon dioxide produced by this combustion contributes to the gradual warm-ing of the earth's surface. We'll look now at the quantitative connection between the amount of the fuel that's used and the amount of carbon dioxide generated. We'll look specifically at the combustion of methane, a relatively simple com-pound with the molecular formula CH4. Methane is the principal component of natural gas, a fuel widely used for cooking and heating and in many industrial processes, including the manufacture of steel. Methane burns according to the bal-anced equation CH4 + 202 ) C0Z + 2H20 This equation tells us that one molecule (or 1 mole) of methane reacts with two mol-ecules (or 2 moles) of diatomic oxygen to produce one molecule (or 1 mole) of ear-bon dioxide and two molecules (or 2 moles) of water (Fig. 9.7). (Naturally, other quantities of these chemicals can react with each other as well, but always in that same ratio.) This must be the case since in this balanced equation every atom of every ele-ment that appears among the products also appears among the reactants.  Figure 9.7 The reaction of one H molecule of methane with two molecules of oxygen to form H-C-H + 0=0 -~ 0=C=0 + H-O-H one molecule of carbon dioxide I 0=0 H-O-H and two molecules of water. H 1 carbon atom, 1 carbon atom, 4 hydrogen atoms, 4 hydrogen atoms, and 4 oxygen atoms and 4 oxygen atoms CH4 + 202 -) C0Z + ZHZ0 We can summarize the logic of all this as follows: Since matter may be neither created nor destroyed in a chemical reaction (Sec. 4.11), every atom appearing on one side of the arrow must appear on the other side as well. To obtain this condi tion, we balance equations. A balanced equation, in turn, tells us the ratio of the moles (or atoms or molecules or ions) of all the substances that make up its reac-tants and its products. From this information we can calculate the mass of each chemical involved in the reaction, given the mass of any one of them. The follow-ing example shows how. What weight of carbon dioxide is generated for every 103-g of methane that ` we use as fuel? We can solve this problem in five simple steps, represented graphically as :ollows: Step 5 Weight of carbon dioxide Step 1 Step 2 Weight of methane Balanced equation: CH4 + 202 - COZ + 2H20- :     Step 4 Moles of carbon dioxide 168 • Chapter 7 Petroleum  An electric car. ate it from some other, primary source such as fossil fuels, nuclear reactions, falling water, sunlight, the wind, or chemical reactions. Switching from burning hydrocarbons to electric batteries won't, in itself, decrease the total amount of energy we consume; it will simply shift the bur-den of producing that energy from the internal combus-tion engine to some other power source. Unless we use wisdom in addition to technical knowledge, we might find that in replacing gasoline with electric batteries we have simply moved our problems of energy production from one location to another. Fuel Cells The fuel cell can be described as a "gaseous Electricity No matter how efficient the engine, a car battery," a term applied to it by its English inventor, William that get its power from the combustion of a hydrocarbon or Grove, in 1839. It's designed not to accept, store, and re- an alcohol or some other kind of organic compound must lease electricity, as a common battery does, but rather to produce exhaust gas emissions of some sort, even if they're induce chemical reactions to release energy in the form of no more than water and carbon dioxide. Cars that meet the electricity rather than heat. In a common form of the cell, ideal of no emissions whatever, that produce no exhaust hydrogen combines with oxygen on the surface of the cell's gases, that add nothing at all to the atmosphere, are known catalysts (Sec. 7.7) to form water and produce electricity as zero-emission vehicles, or ZEVs. One source of power (Fig. 7.13): that meets this test is electricity, released by storage bat- 2H2 + 02 - 2H20 + energy (electricity) teries mounted in the car. Electric cars are classified as ZEVs. Because of concerns about air pollution, the state of The oxygen forthe cell is obtained from the atmosphere; the California requires that by 2003 at least 10% of all cars sold hydrogen can either be stored on the vehicle or produced within the state must be ZEVs. catalytically from a hydrocarbon or other hydrogen-con-Despite the absence of emissions, electric cars come with problems of their own. The major disadvantages of electric cars are their short driving ranges, the long times required for recharging their batteries, and the uncer-tainty of where all the electric power needed to recharge large numbers of batteries will come from. Part of the so-lution to the last problem comes from the nature of ener-gy itself. Moving vehicles powered by other sources of energy are slowed and stopped by the force of the brakes. These convert the energy of the motion to heat as they press against the rotating wheels. Electric cars use a process known as regenerative braking, in which an elec-tric generator slows the moving car by converting its en-ergy of motion into electricity rather than heat. This regenerated electricity is fed to the battery to help main-tain its charge. We'll have more to say about the various forms of energy in the next chapter. Despite energy economies produced by regenerative braking and similar techniques, the wholesale conversion of our transportation system from fossil fuels (or other fuels that rely on combustion) to electric power could pro-duce the most serious problem of all. Electricity itself is a secondary source of energy in the sense that we gener- Figure 7.13 The essentials of a typical fuel cell.  212 • Chapter 9 Arithmetic of Chemistry 44.0 g COZ 6.25 mol C02 x mol COZ = 275 g C02 100g 275g CH4 + 2 02 ~ C02 + 2 H20 6.25 mol 6.25 mol  We have now answered the original question. Every 100 g of CH4 that disap-' pears during combustion generates 275 g of COZ.  E X A M P L E Water, Too and Two Water, too, is formed as methane burns. How much water is generated by the 100 g of methane?  • Here, we can repeat the first three steps of the preceding example. But for the fourth step we must recognize that two molecules (or moles) of water form for every one molecule (mole) of methane that reacts:  100 g cH4 + 202 ~ Co2 + 2x20 6.25 mol Step 4; Since 6.25 moles of methane exist among the reactants, twice this amount of water-12.5 moles of HZO-must be formed: 100 g CH4 + 2 02 --~ C02 + 2 H20 6.23 mol 12.5 mol Step 5: Since the molecular weight of water is H: 2 x 1.008 amu = 2.016 amu O: 1 x 16.0 amu = 16:0 amu 18.016 arnui or 18:0 amu to three significant figures a rnass of 18.0 g H20 12.5 mol HZO x mol = 225 g H20 results from the reaction: 100 g 225 g   9.5 Getting to the Right Solution Takes Concentration • 213 Using this five-step approach, determine how many grams of oxygen it takes to react • Q U E S T I O N completely with 100 g of methane. 9.5 Getting to the Right Solution Takes Concentration Although weighing quantities of chemicals provides a fine method for counting out atoms, molecules, and ions, we can often count chemical particles far more conveniently and easily by measuring volumes of liquid solutions. You make up a solution by dissolving one substance, the solute, in another substance, the solvent. The result is a solution of the solute in the solvent. Solutions are completely ho-mogeneous mixtures of solutes and solvents. That is, the composition and prop-erties of any solution are perfectly uniform throughout the entire solution. Sometimes it takes a bit of stirring or shaking to achieve this homogeneity, as when you dissolved the salt and sugar in water in the opening demonstration. With enough stirring, the sodium and chloride ions of the salt and the sucrose molecules of the sugar were distributed evenly throughout the water. The sodium chloride and the sucrose were the solutes; the water was the solvent; and the salt water and the sugar water were the solutions. If we know how much of the solute is dissolved in a specific volume of the so-lution, we know the concentration of the solute. Knowing this value allows us to measure out an exact quantity of solute by measuring a volume of the solution it self. In effect, we can count out chemical particles by measuring volumes of solutions. In the demonstration that opened this chapter we saw examples of various concentrations of a solute (salt) in a solution (salt water). As we dissolved one tea-spoon of sodium chloride in a glass of water, we prepared a solution whose A solution is a homogeneous mixture of one substance, the solute, dissolved in another, the solvent.The solute is present in a smaller propor-tion than the solvent. The concentration of a solu-tion expresses the quantity of solute dissolved in a specific quantity solution.The quantity of solution is usually stated as a volume. The five steps in preparing a solution of a specific concentration. (a) Adding a known weight of solute to a flask etched with a mark to allow filling it to an accurately measured, predetermined volume. (b) Adding a portion of the solvent. (c) Swirling the ; mixture to dissolve the solute in the solvent. (d) Adding enough solvent to bring the S surface of the solution exactly to the etched mark. This produces an accurately measured ivolume of solution, usually a multiple or simple fraction of a liter. (e) Shaking the , stoppered flask to distribute the solute uniformly throughout the solution.      (a) (b) (c) (d) (e) 214 • Chapter 9 Arithmetic of Chemistry concentration was one teaspoon per glass. While we don't normally use units of this sort, our measurements with the standard glass of water in that demonstration make this a perfectly valid, if nonstandard and not very precise, description of the concentration of salt water in glass 1. Recall that we transferred 1/10 of the salt from the first glass into glass 2 by pouring out 1/10 of the solution. The concen-tration of the sodium chloride in glass 2 thus became 0.1 teaspoon per glass. In the next glass the concentration was 0.01 teaspoon per glass. The same principles and definitions of that demonstration apply equally to the much more accurate meas-urements carried out in scientific laboratories. • Q U E S T 1 O N What's the concentration of the sodium chloride in glass 7? 9.6 Molarity  The terms and units available for expressing concentrations are almost as varied as the kinds of solutions we can prepare. They range from the not-very-scientific and imprecise "teaspoon per glass" of our demonstration, through some of the terms that appear on the labels of our consumer products (which we'll examine in the next section), to well-defined units based on the concept of the mole. This last unit-the mole-makes it particularly easy to get a quick count of chemical par-ticles of a solute by measuring the volume of a solution in an inexpensive, readily available, calibrated cup, beaker, flask, or cylinder. That beats carrying around a heavy, cumbersome, and expensive balance or scale. For counting chemical particles by measuring volumes of solutions we com-The molarity of a solution monly use concentrations expressed in molarity (M). The molarity of a solution refers to the number of moles refers simply to the number of moles of solute per liter of solution. A 1 M (one of solute per liter of solution. molar) solution contains one mole of solute in each liter of solution; a 2 M solu-tion contains two moles of solute per liter of solution; and so on. Molariry provides an especially easy way to count chemical particles. Simply multiply the volume of a solution (in liters) by its concentration (in molarity) and you have the number of moles of solute in the volume of solution at hand. Two liters of a 1 M solution contain a total of 2 mol of the solute, but then so does 1 liter of a 2 M solution, or 0.5 liter of a 4 M solution: Volume of Concentration Solution of Solution 2liters x 1 mol/liter 1 liter x 2 mol/liter O.S liter x 4 mol/liter Number of Moles of Solute 2 mol of solute 2 mol of solute 2 mol of solute Cleaning Up Solutions of ammonia are sometimes used as household cleaners. How man~ moles of ammonia; NH3, are there in 1.2 liters of a solution that is 0.50 M ir ammonia? Using the definition of molarity as the number of moles of salute per lite} of solution, we have 0.50 mol NH3 1':2liters x , . = 0.60 mol NH3 9.6 Molarity • 215 We are still using this same 0.50 M solution of ammonia, but this time we need 1.8 mol of the solute. What voIume of the solution do we use to get i.8 mol of ammonia? E X A M P L E More Ammonia ~ This time we start with the number of moles we need and we divide by the value of the molarity to give us the answer in liters:  1.8 mol NH3 x liter = 3.6liters R' 0.50 mol NH3  We have just run out of the 0.50 M solution of ammonia and must make up more. We prepare the solution 5 liters at a time. What weight of ammonia do we need to prepare S.O liters of 0.50 M ammonia? To convert between moles of ammonia and grams of ammonia, we use the molecular weight of ammonia: < E X A M P L E Mixing Up More N: 1 x 14.01 amu = 14.01 amu 3 x 1.008 amu = 3.024 amu 17.03 amu, which we round off to 17 amu since we're using only two significant figures for volume and concentration ฎ In this ease we know that we need 5':O liters of solution; we know that the solution must contain 0.50 mol of ammonia per liter, and we know that there are 17 g of ammonia per mole: Tbis knowledge gives us 0.50 mol 17 g NH3 _ S.O liters x liter x mol - 42 g NH3 With a density of 1000 g per liter for water and a molecular weight of 18.0 amu ir the water molecule, we have 1000 g water mol of water x = 55.6 mol of water per liter liter of water 18.0 g water ith 55.6 mol of water molecules per liter of water, the molarity of water is 55.6 M. ~is gives water, of all our common liquids, the highest concentration of mole-les in a given volume. i ~~ Calculate the molarity of the salt water and the sugar water of glass 1 of the •QUESTION measuring demonstration. Assume that the standard glass holds 400 mL of each 216 • Chapter 9 Arithmetic of Chemistry solution and that the rounded teaspoons of sodium chloride and sucrose you used in preparing the solutions weighed 23.4 g and 17.1 g, respectively. Use 23.0 for the atomic weight of Na, 35.5 for CI, and 342 for the molecular weight of sucrose. (b) Cal-culate the molarity of the solution of glass 7. Although molarity is a common measure of concentration in scientific studies, the solutions we prepare in our daily lives employ more common units. We use a tea-spoon or two of sugar in our coffee or tea and a couple shakes of salt (if any at all) in our soup. A quarter-cup of detergent does the wash, and a squeeze of the plastic bottle does the dishes. We take medicines a tablet or two or a teaspoon at a time. In each of these cases we're dealing with the concentration of a solute in a solution. A teaspoon of sugar in coffee or tea produces a concentration of one teaspoon per cup. The single teaspoon of sugar is the solute and the single cup of sweetened bev-erage is the solution. A quarter-cup of detergent gives us a concentration of 0.25 cup per laundry tub. A squeeze of dishwashing detergent into a sinkful of dishes gives us an imprecise concentration of one squeeze per sink. Even two aspirin tablets and a glass of water produce a certain concentration of acetylsalicylic acid, the active com-ponent of the tablet, per human body (Sec. 23.1). The unit of concentration of the salt water we prepared in our opening demonstration was "teaspoon per glass." concentrations of solutes expressed as a percentage (%) of weight or volume. The acidity of vinegar, for example, results from a combination of simple organic acids, principally acetic acid, dissolved in water. The label of a typical bottle of ordinary vinegar reveals that the product is "diluted with water to 5 % acidity." This is a form of commercial shorthand (or maybe simply jargon) that's meant to indicate the concentration of acids in vinegar. Commercial vinegar normally contains 5 g of acetic acid (Fig. 9.8) in every 100 g of vinegar. 5% or 7% Red Wine Vinegar interreacts with baking soda. A percentage concentration ex-Vinegar contains acetic acid at a pressing the weight of solute for every 100 units of weight of the solution is a concentration of 5% by weight. weight/weight percentage, or w/w %. A 3% solution of H202 in water forms the common antiseptic hydrogen per-oxide, while rubbing alcohol is a solution of 70% isopropyl alcohol and 30% water.  Figure 9.8 Commercial solutes, solvents, and solutions. ~C - OH O O O- 11 11 C-CH3 CH3-C-OH H-O-O-H . CH3-CH-CH3 Acetylsalicylic Acetic acid Hydrogen I acid peroxide Vinegar Water 95% Hydrogen peroxide  Water 97% Rubbing alcohol 9.7 Percentage Concentrations Acetic acid a other acids Isopropyl alcohol Chapter 11 232 • Chapter 10 Acids and Bases material to learn whether it's sour or bitter or rubbing it between your fingers to determine whether it feels slippery is a dangerous activity. Although many of our foods-lemons and vinegar, for example-contain acids and taste distinctly acidic, other substances may be composed of acids (or bases) powerful enough to destroy skin and mucous membranes and cause great harm. Some substances we may come in contact with are highly poisonous in ways that have nothing to do with acidity or basicity. Even many consumer products are toxic and/or corrosive and can cause much damage if used carelessly or in ways other than those specified by their labels. Never taste or touch any material you aren't sure of. It could be quite dangerous. We'll examine some of our ideas about safety in more detail in Chapter 20. The remaining phenomenon, the reaction of acids with metals like iron and zinc, can also be hazardous. The product is hydrogen gas, which is dangerous in itself because of its flammability. Hydrochloric acid, usually available in hardware stores by its commercial name, reaction of an acid with a muriatic acid, is a strong acid useful for cleaning metals, masonry, cement, and stuc base. co. Sodium hydroxide, better known as household lye, is a powerful base often effective in clearing clogged drains. Both sodium hydroxide and hydrochloric acid are dangerous, corrosive chemicals that must be handled with great care. Hydrochloric acid and sodium hydroxide react with each other to form sodium chloride (a salt) and water: HCl + NaOH NaCI + H20 hydrogen and sodium react sodium and water chloride hydroxide to produce chloride, a salt Notice that the hydrogen of the HCl and the OH of the NaOH combine to form water, while a combination of the Cl of the HCl and the Na of the NaOH pro-duces NaCI. This resulting sodium chloride is a salt in two closely related senses. Other salts include potassium iodide, KI, which provides the iodide of iodize salt (Sec. 9.9); magnesium sulfate, MgSOq, better known as epsom salts and somy times used as a laxative; monosodium glutamate (MSG), an additive that enhancE or intensifies the flavor of food and is often used in Chinese food; and calciw carbonate, CaC03, common chalk. Acid Base Salt HI + KOH KI + H20 hydrogen potassium potassium iodide hydroxide - iodide 10.8 The Acids of Everyday Life • 245 Benzoic acid consists of a carboxyl group bonded directly to a benzene ring: O 11 C-OH benzoic acid 250 • Chapter 10 Acids and Bases Figure 10.8 Le Chatelier's Principle in operation.  COZ + H20 ~ H2C03 The original equilibrium  As COz is absorbed its concentration tends to grow above its original equilibrium value . . . ~+ H20 ~ HZC03 -- Carbon dioxide is absorbed, shifting . causing the equilibrium to shift so as to the equilibrium to the right decrease the COZ concentration and increase the HZC03 concentration. COZ + Hzo ~= H2C03 New equilibrium, with higher concentration of carbonic acid numerical value of the ratio is held constant. In this case the very large quantity of carbonic acid that is produced puts a stress on the system, which is relieved as carbonic acid decomposes into carbon dioxide and water (Fig. 10.9). Le Chatelier's Principle also describes how your blood's pH is maintained within a narrow range. Blood is slightly basic; its pH, normally 7.4, doesn't vary by more than about one-tenth of a pH unit in a healthy person. In maintaining this narrow range of pH through all the stresses of a normal life, the body uses an acid-base equilibrium, with carbonic acid as the acid and water as the base. (Recall that water is amphoteric; Sec.10.4.):  HZC03 + HZO H30+ + HC03- Figure 10.9 The chemistry of the fizz. NdHC03 + H+ - Na+ + H2C03 Sodium bicarbonate reacts with citric acid producing carbonic acid . . . C02 + H20 ~ H2C03 which equilibrates with carbon dioxide and water. As the concentration of carbonic acid grows, through continuing reaction of sodium bicarbonate and acid, the equilibrium shifts toward carbon dioxide. which grows in concentration and escapes from the water as bubbles fizz. 232 • Chapter 10 Acids and Bases material to learn whether it's sour or bitter or rubbing it between your fingers to determine whether it feels slippery is a dangerous activity. Although many of our foods-lemons and vinegar, for example-contain acids and taste distinctly acidic, other substances may be composed of acids (or bases) powerful enough to destroy skin and mucous membranes and cause great harm. Some sub-stances we may come in contact with are highly poisonous in ways that have nothing to do with acidity or basicity. Even many consumer products are toxic and/or corrosive and can cause much damage if used carelessly or in ways other than those specified by their labels. Never taste or touch any material you aren't sure of. It could be quite dangerous. The product is hydrogen gas, which is dangerous in itself because of its flammability. Similarly, bases can neutralize acids. In this acid-base hydrogen gas. neutralization an acid and a base react chemically with each other to produce a salt, a compound that has no (or much weaker) acidic or basic properties. A salt is a In neutralization an acid and compound other than water produced by the reaction of an acid and a base. a base react to produce a salt. Sodium hydroxide, better known as household lye, is a powerful base often effective in clearing clogged drains. Both sodium hydroxide and hydrochloric acid are dangerous, corrosive chemicals that must be handled with great care. Hydrochloric acid and sodium hydroxide react with each other to form sodium chloride (a salt) and water: HCl + NaOH NaCI + H20 hydrogen and sodium react sodium and water chloride hydroxide to produce chloride, a salt Notice that the hydrogen of the HCl and the OH of the NaOH combine to form water, while a combination of the CI of the HCl and the Na of the NaOH pro-duces NaCI. This resulting sodium chloride is a salt in two closely related senses. It's not only the common table salt that we use on our food and that began our study of chemistry in Chapter 1, but it's also a salt in the generic sense. That is, sodium chloride is produced, along with water, by the reaction of HCl (an acid) witr NaOH (a base). Sodium chloride is a perfectly neutral salt, neither acidic nor basi( in any sense at all. Other salts include potassium iodide, KI, which provides the iodide of iodize salt (Sec. 9.9); magnesium sulfate, MgSOq, better known as epsom salts and somy times used as a laxative; monosodium glutamate (MSG), an additive that enhancE or intensifies the flavor of food and is often used in Chinese food; and calciw carbonate, CaC03, common chalk. Acid Base Salt HI + KOH KI + H20 hydrogen potassium potassium iodide hydroxide - iodide 10.8 The Acids of Everyday Life • 245 Benzoic acid consists of a carboxyl group bonded directly to a benzene ring: O C-OH benzoic acid To consumers, benzoic acid is less important in itself than as its sodium salt, sodium benzoate (also known as benzoate of soda). This salt is used as a preservative in canned and bottled fruit drinks and also in baked goods. Lactic acid is the acid that gives sour milk its sharp taste. Bacterial fermenta-tion of lactose, the principal sugar of milk, produces the acid: O bacterial fermentation II lactose (milk sugar) CH3-CH-C-OH OH lactic acid, the acid of sour milk Lactic acid is also important to us in another, more immediate way: in our own bod-ies. As we've seen in Chapter 8, our biological energy comes from chemical oxidation of the foods we eat. Figure 10.7 Common acids include the citric acid of limes, lemons, oranges, grapefruit, and citrus juices, the propionic acid of Swiss cheese, and the oxalic acid of rhubarb. 246 • Chapter 10 Acids and Bases In terms of commercial production, sulfuric acid (HZS04) is by far our lead-ing industrial chemical. In raw tonnage produced, about 44 million tons in the United States in 2000, it swamps any of its rivals. Most of it ends up as a reactant or a catalyst (Sec. 7.7) in the manufacture of various consumer products, including pharmaceuticals, plastics, synthetic fibers, and synthetic detergents. More calcium oxide (CaO, or lime; roughly 22 million tons in 2000) is produced than any other base. Much of it goes into the production of building materials, the generation of still other industrial chemicals, and water and sewage treatment. QUESTION Name or identify each of the following carboxylic acids: (a) gives rancid butter its foul odor; (b) toxic, it is found in small concentrations in raw spinach and rhubarb; (c) forms in our muscles as the result of metabolic activity; (d) produces the flavor of Swiss cheese; (e) used as its sodium salt to preserve canned and bottled fruit drinks; (f) responsible for the taste of sour milk; (g) produces the acidity of citrus fruit; (h) generates the sting of red ant bites; (i) the major organic acid of vinegar. 10.9 Antacids: Bases That Fight Cannibalism Carbon dioxide is released when an Alka-Seltzer tablet is dropped into water. As the sodium bicarbonate and citric acid of the tablet react in water, they form carbonic acid. With increasing concentration the carbonic acid decomposes to carbon dioxide and water. antacids such as Alka-Seltzer, Milk of Magnesia, Rolaids, Titralac, and or simply some baking soda in water. Each year Americans buy a quarter of a billion dollars worth of these and other antacid products simply for the relief of pain brought on by maverick hydronium ions of the stomach. (Baking soda is the commercial term for sodium hydrogen carbonate, NaHC03, which is also known by an older name, sodium bicarbonate. The anion HC03- can be called the hydrogen carbonate or the bicarbonate ion. 246 • Chapter 10 Acids and Bases In terms of commercial production, sulfuric acid (H2S04) is by far our lead-ing industrial chemical. In raw tonnage produced, about 44 million tons in the United States in 2000, it swamps any of its rivals. Most of it ends up as a reactant or a catalyst (Sec. 7.7) in the manufacture of various consumer products, including pharmaceuticals, plastics, synthetic fibers, and synthetic detergents. More calcium oxide (CaO, or lime; roughly 22 million tons in 2000) is produced than any other base. Much of it goes into the production of building materials, the generation of still other industrial chemicals, and water and sewage treatment. Q U E S T I O N Name or identify each of the following carboxylic acids: (a) gives rancid butter its foul odor; (b) toxic, it is found in small concentrations in raw spinach and rhubarb; (c) forms in our muscles as the result of metabolic activity; (d) produces the flavor of Swiss cheese; (e) used as its sodium salt to preserve canned and bottled fruit drinks; (f) responsible for the taste of sour milk; (g) produces the acidity of citrus fruit; (h) generates the sting of red ant bites; (i) the major organic acid of vinegar. Aluminum hydroxide, Al(OH)3 Magnesium hydroxide, Mg(OH)Z Calcium carbonate, CaC03 Sodium bicarbonate, NaHC03 Magnesium carbonate, MgC03 Potassium bicarbonate, KHC03 Magnesium oxide, MgO, is also used as an antacid ingredient since it reacts with water to form magnesium hydroxide: Mg0 + H20 -> Mg(OH)2 Table 10.5 Common Antiacids Principal Active Representative Ingredient Antiacid Neutralization Reaction  Sodium bicarbonate Alka-Seltzer NaHC03 + HCl -~ NaCI + H2C03 1 Potassium bicarbonate (HZC03 --j HZO + COZ) Magnesium hydroxide Phillips' Milk Mg(OH)2 + 2HC1 -~ MgCIZ + 2H20 of Magnesia Dihydroxyaluminum Rolaids Al(OH)ZNaC03 + 4HC1 -~ A1C13 + sodium carbonate NaCI + 2 H20 + HZC03 Calcium carbonate Titralac CaC03 + 2HC1 ~ CaC12 + HZC03 Tums Aluminum hydroxide Di-Gel Magnesium carbonate Magnesium hydroxide Al(OH)3 + 3 HCl ~ A1C13 + 3 H20 MgC03 + 2 HCl -~ MgC12 + HZC03 Mg(OH)Z + 2HC1 ~ MgC12 + 2H20 248 • Chapter 10 Acids and Bases • QUESTION Some commercial antacids claim only to neutralize "excess" stomach acidity. Why is it undesirable to neutralize completely all stomach acidity? What would result from bringing the pH of stomach fluids all the way up to 7? 10.10 Red Cabbage, Antacid Fizz, and Le Chatelier's Principle We're now in a position to understand why the cabbage breath test works and how the color change of the cabbage extract is connected to the fizz that an Alka-Seltzer tablet produces. In addition we'll also see how breathing helps maintain a stable pH for your blood. In the opening demonstration, the ammonia that's added to the deep blue so-lution of cabbage extract makes the solution slightly basic and turns the color of the indicator solution to an emerald green. As someone blows into the basic test solution of the opening demonstration, the carbon dioxide of the exhaled breath dissolves in the water to form carbonic acid, which immediately reacts with the dissolved ammonia, neutralizing it. Formation of carbonic acid as carbon dioxide dissolves in water: 11 COZ + H20 ' HO-C-011 carbon carbonic dioxide acid Neutralization of ammonia by carbonic acid to form a salt, ammonium carbonate 11 11 HO-C-OH + 2NH3 - NH4+-O-C-O-+NH4 carbonic ammonium carbonate acid Then, after all the ammonia has been converted to ammonium carbonate, the excess carbonic acid ionizes and produces hydronium cations and bicarbonate anions, and the indicator turns to a light blue color as the test solution becomes slightly acidic. Ionization of excess carbonic acid, with water acting as a base as it accepts the proton released by the carbonic acid and forms the hydronium ion:  II II HO-C-OH + H20 H30+ + -O-C-OH carbonic hydronium bicarbonate acid ion anion Adding the vinegar at the end of the demonstration introduces acetic acid into the solution. The acetic acid is a much stronger acid than carbonic acid; it makes the test solution far more acidic than the carbon dioxide of breath does. With the marked increase in acidity, the indicator turns a vivid pink or red. Ionization of acetic acid to form a hydronium ion and an acetate anion:  11 11 CH3-C-OH + H20 CH3-C-O- + H30+  acetic acid anion acetate 11.10 Why Batteries Work • 269 Again in the opening demonstration we saw that adding a chlorine bleaeh to the nearly colorless solution causes the color of the iodine to return. To see why-and knowing that the oxidizing agent in the bleach is C10-, as we saw in the discussion of the opening demonstration-we'll now ask: Will the C10-oxidize the iodide ion to molecular iodine and therefore restore the color? For the oxidation of iodide ion to molecular iodine, the oxidation half-ce11 is: oxidation: 2I- ' I2 + 2e (-0.54 volt) With C10- as the oxidizing agent, the reduction half-cell is: reduction: C10- + Hz0 + 2e- ~ Cl- + 2 OH- (+0.84 volxj Thus the redox reaction is: redox: 2I- + C10- + FIzO ~ IZ + Cl- + 20H- (+(1.30volt) With a positive redox potential, the C10- of the bleach oxidizes the iodide ion spontaneously; regenerating the IZ as the deep color oI the molecular io-dine returns. Now for another question. Why don't the sodium cations and the chloride anions of table salt react with eaeh other to form sodium metal and chlorine gas? In this case, we're asking why the following redax reaction doesn't occur spontaneously in a salt-shaker: 2hTa+ + 2C1- ~ 2Na~ + ClZ Once again we add an oxidation potential and a reduction potential to get a redox potential. (Notice that although it's necessary to double all the chemi-cal species in the reduction reaction so that the number of electrons matches the number used in the oxidation, the reduction voltage remains unchanged.) oxidation: reduction: 2 Cl- ~~ C12 + 2e (-1:36 volts) E X A IYi I' L E The Color Returns table Salt 2Na+ + 2e ---~ 2NaQ (-2.71 voltsj 2 Na} + 2 Cl- ~ 2 : -+~ Cl~ (-4.07 voltsj'' re negative redox potential explains why the sodium cations and the chloride anions don't react with each other spontaneously. If they did, all the table salt in our kitchens and restaurants would burning away right now, with sodium cations and chloride anions interreacting with each other, producing very dangerous sodium metal and poison-gas (Sec 3.2). Section 10.2 we saw that acids liberate hydrogen gas when in contact with certain metals, such as iron and zinc. Using the data ofTable 11.1, show that the reactions of iron and zinc with an acid spontaneously generate hydrogen gas by redox reactions. Identify three other metals that will spontaneously liberate hydrogen gas from an acid. iron and zinc Identify three metals that will not. 270 • Chapter 11 Oxidation and Reduction 11.11 Galvanized Tacks, Drugstore lodine, and Househoid Bleach Revisited the de-colorization of iodine by galvanized nails and the regeneration of the purple-violet color of the iodine by household bleach take place by redox reactions. In reduc-ing the iodine molecules to iodide ions, the zinc metal acts as a reducing agent and transfers its electrons to iodine molecules. The purple-violet iodine molecules are reduced to colorless iodide ions. In restoring the color, the solution of bleach, which contains a reserve of CIO-, oxidizes the colorless iodide ions back to purple-violet iodine molecules. As for why, the answer is that the redox potential of each of these reactions is positive. Each one proceeds spontaneously by the transfer of electrons from a reducing agent to an oxidizing agent. • QUESTION Which, if any, of the following metals will decolorize tincture of iodine: (a) nickel, (b) copper, (c) silver, (d) magnesium, (e) calcium? Explain your answer for each. copper decolorize 11.12 Energy versus Rate We've seen that the sum of the two half-cell voltages- the redox potential-represents the measured voltage of the entire cell. Standard reduction potentials not only provide the voltages of batteries, whether real or proposed, but they also tell us something about the energies of chemical reactions. Sodium and chlorine, for example, react explosively when they come into contact with each other under ordinary conditions. The sum of the oxidation potential of sodium and the reduc-tion potential of chlorine is over 4 volts, a sizable value compared with the voltages generated by the Daniell cell (1.10 volts), by a common flashlight battery (1.5 volts), or by one of the cells of the lead-acid storage battery (about 2 volts, as we'll see shortly). We should note, though, that the vigor of the reaction between sodium and chlorine, or between any other substances for that matter, depends not only on the amount of energy released, which is indicated by the electrochemical poten ~ tial, but also on the rate at which the energy is liberated. Some reactions that r lease plenry of energy take place so slowly that not only are they rcot explosive they're too slow even to be observed under ordinary conditions. That isn't the c; with sodium and chlorine. • Q U E S T 1 O N Using the half-cell reactions ofTable 11.1, write the redox reaction that would lease the greatest amount of energy.That is, write the redox reaction that produ the greatest redox voltage. 11.13 Ideal Batteries and Real Batteries At the other end of the table from fluorine lies lithium. With its reduction poten tial of -3.04 volts, the lithium cation shows very little tendency to pick up an elea tron and be reduced. On the other hand, reversing the half-cell reaction and changing the algebraic sign of the potential to +3.04 volts reveals that lithium metal has a very strong tendency to lose an electron and to be oxidized to the lithi-cation: Lie - Li+ + e (+3.04 volts) Lithium metal, then, is a powerful reducing agent. In its redox reaction with fluo-rine, lithium produces a potential of +5.91 volts, as you can see in the following example. 11.14 Chemistry That Starts Cars • 271 E X A M! P L. E e Daniell cell itself isn't used as a commercial battery. Suggest at least one rea- • QUESTION n why it isn't. 11.14 Chemistry That Starts Cars We turn now to a battery that's more practical than the Daniell cell and that produces electricity by a simpler set of chemical reactions than the batteries of the preceding section. It's the lead-acid battery that starts our cars (Fig. 11.9). The Show that the redox reaction of lithium and fluorine produces a potential of +5:91 volts. ฎ For the redox reaction we have . oxidation: 2 Lio ) 2 Li+ + 2e (+3.04 volts) reduction: F2 + 2e ' 2F- (+2.89 volts) (redox): 2Li + F2 ) 2Li+ + F- (+5.91 volts) Although the cell's high voltage might make it an ideal battery for many uses, fluorine gas is far too reactive and far too hazardous to be used in any consumer product 1.5-volt flashlight batteries head-to-tail in flashlights. For a two-battery flashlight this alignment gives a total, combined voltage of about 3.0 volts. Another of the more common, popular, practical, commercial batteries is the alkaline battery, built much like the carbon-zinc battery but containing potassium hydroxide in addition to the other substances described in Section 11.1. Like the carbon-zinc battery, the alkaline battery delivers about 1.5 volts, but over a much longer lifetime. Other more specialized batteries include the lightweight lithium battery, in which lithium rather than zinc is oxidized and which provides over 3 volts; the mercury battery, which delivers a very constant 1.3 volts from a redox re-ction of zinc and an oxide of mercury, HgO; and the small and long-lived silver dde battery, which provides about 1.5 volts from a reaction of zinc and silver tide, A920. The rechargeable nickel-cadmium battery, consisting principally of ,Imium and an oxide of nickel, and the rechargeable lead-acid battery. High Voltage Aluminum hydroxide, Al(OH)3 Magnesium hydroxide, Mg(OH)2 Calcium carbonate, CaC03 Sodium bicarbonate, NaHC03 Magnesium carbonate, MgC03 Potassium bicarbonate, KHC03 Magnesium oxide, MgO, is also used as an antacid ingredient since it reacts with water to form magnesium hydroxide: Mg0 + H20 -> Mg(OH)2 The active ingredients of several of the more popular antacid preparations appear in Table 10.5. On reaction with HCI, the sodium bicarbonate of Alka-Seltzer and other commercial antacids forms carbonic acid, which is a much weaker acid than HCl and which decomposes readily (and reversibly) to carbon dioxide and water: NaHC03 + HCl -~ NaCI + H2CO3 carbonic acid H2C03 C02 + H20 274 • Chapter 11 Oxidation and Reduction anode (from oxidation of the chloride ions in the solution) and hydrogen at the cathode. At the cathode a net reduction of water's protons to HZ leaves the hy-droxide anion, OH-, in the remaining solution. The combination of this anion with Na+ left over from the oxidation of the chloride anions results in the formation of NaOH, sodium hydroxide, within the remaining solution: Na+ + OH- ~ NaOH sodium hydroxide Sodium hydroxide is an important industrial chemical, useful in the production of a va-riety of commercial products. As a direct consumer chemical itself, though, its appli-cation is limited to use as highly caustic lye for opening clogged sinks and drains. It is an extremely corrosive and hazardous substance that must be used with great care. Electrolysis on a commercial scale consumes enormous quantities of electric-ity and can be carried out economically only in regions where electric power is cheap and plentiful. In one of these locations, Niagara Falls, the power of falling water is harnessed to provide the needed energy. The chlorine produced in the electrolysis reaction is a valuable industrial raw material for manufacturing a large number of consumer products ranging from simple, rugged plastic plumbing fix-tures to pharmaceuticals with intricate and complex molecular structures. As a strong oxidizing agent, chlorine also provides an important tool for safe-guarding the public health. Its oxidizing power makes it deadly to bacteria, in-cluding those that cause typhoid fever. The large-scale chlorination of public water supplies, swimming pools, and sewage, made possible by the commercial produc-tion of inexpensive chlorine, has played a major role in eliminating epidemics of typhoid fever and other public health threats in developed nations. Chlorine gas can be deadly to humans, too. It was one of the poison gases used in the trench war-fare of World War I, as we saw in Section 3.2.) • Q U E S T I O N What three chemicals are produced through the electrolysis of sodium chloride so-lutions? chlorine What three chemicals would you expect to be produced by the electrolysis of a solution of sodium bromide? 11.16 Redox in Everyday Life Our contact with redox and electrolysis in our everyday lives isn't limited to b teries, or the benefits of disinfection through chlorination. Many of our metals, example, come to us through one of these processes. Commercial quantities of r minum are produced through the electrolysis of hot solutions of aluminum ox A1203, dissolved in cryolite, Na3A1F6: 2 A1 O electrolysis , 4 A1 + 3 O 2 3 2 The aluminum oxide is obtained through the processing of bauxite, an alumi: containing ore. The highly purified form of silicon needed for the production of silicon cl. used in computers and calculators comes from a redox reaction of highly purifi~ silicon chloride, SiC14, with hydrogen: SiC14 + 2H2 ~ Si + 4HCl Even the copper plating of baby shoes and similar objects depends on the kinds of electron transfers we've examined in this chapter. Copper plating-the 11.16 Redox in Everyday Life • 275 transfer of copper atoms from a copper strip to another object-takes place when metallic copper and the object to be plated are placed in a solution of an elec-trolyte and are connected to the poles of a battery. The copper is connected to the anode; the plating takes place at the cathode. To facilitate the plating, objects that aren't good conductors of electricity are often coated with a thin layer of graphite, a form of carbon much like the central core of a flashlight battery. Up to this point we've examined some of the more useful aspects of oxidation and reduction: storing and obtaining electrical energy from batteries, and useful as pects of electrolysis. There's another, undesirable side of redox though: corrosion. Corrosion is the erosion and Although we normally think of corrosion as affecting metals, it's defined more disintegration of a material re- generally as the erosion and disintegration of any material as the result of chem- sulting from chemical reac- ical reactions. The term rust applies specifically to the corrosion of iron that pro- tions. Rust is the corrosion of duces various scaly, reddish-brown oxides of iron. iron to form various reddish- Corrosion of all kinds does billions of dollars of damage each year in the brown oxides of iron. United States alone. The redox reaction of metals, of which rusting is only one ex-ample, is accelerated by moisture, the presence of acids or bases, and various pol-lutants of the air and water. Because of the variety and complexity of the chemical reactions that lead to corrosion. One results from the direct oxidation of metals that are exposed to air and water. The direct oxidation of metals in the presence of air or water results from a se-ries of redox reactions involving a combination of the metal itself, oxygen, and water. Iron, for example, rusts more rapidly in humid air than in dry air. These re actions result in the formation of metal oxides, chemical combinations of the metal and oxygen. Perhaps surprisingly, the formation of these oxides can either accel-erate the corrosion or retard it, depending on the nature of the metal and the oxide it forms. Iron rusts rapidly because its oxides are granular and flaky. Once formed, the oxides fall or rub off the metal easily and expose fresh surfaces to additional corrosion. Aluminum, too, reacts quickly with oxygen to form aluminum oxide, A1Z03. This aluminum oxide, unlike the oxides of iron, forms a thin, tough, protective coating on aluminum that retards further oxidation. although alu-minum metal oxidizes easily, it is highly resistant to corrosion. The largest commercial use for metallic zinc isn't in manufacturing batteries, but in galvanizing other metals, especially iron and steel products, to provide them Galvanizing is a process that ,ith a thin surface film of zinc metal that protects them from corrosion (chapter- provides a protective zinc coat -)ening demonstration). Galvanizing is usually carried out in any of three ways: to metals. by dipping the metal into hot, molten zinc; ly spraying molten zinc onto the metal's surface; or y reducing zinc cations directly onto the metal surface through an electro-aemical redox reaction. zinc protects iron products by reacting with components of the atmosphere to - a a protective film, much as aluminum does, and also by oxidizing more read-aan the iron it's protecting. If the coating of zinc should crack in spots so that .e iron's surface becomes exposed to the atmosphere, the zinc metal corrodes ,efore the iron does. In essence, the zinc is used as a sacrificial metal to protect the nore valuable iron. Since galvanizing a large metal object presents practical dif-ficulties, metal tanks used for underground storage of gasoline and other haz-ardous liquids are often protected from oxidation by attaching a sacrificial block of aluminum, magnesium, or zinc. Because these three metals are more readily oxidized than the iron of the tanks, they protect it from corrosion. 11.15 Niagara Falls FightsTyphoid through Electrolysis • 273 produced by the generator or the alternator restores the electrochemical energy of the battery by reversing the redox reaction. The current enters the battery and reconverts the lead sulfate and water into sulfuric acid, spongy lead metal, and lead dioxide: charge: 2PbS04 + 2H20 ~ Pb + Pb02 + 2HZS04 (-2.04 volts, which we again round off to -2 volts) The negative potential of the redox reaction tells us that a battery won't recharge itself spontaneously. Common sense tells us the same thing. To carry out this redox reaction electrical energy must be put into the battery, as we saw in Section 11.10. Notice that the electrical potential produced by the discharge redox reaction is 2 volts. The case of the standard 12-volt automobile battery actually encloses six of these 2-volt cells in series, head-to-tail as in a flashlight. What change takes place in the composition of the battery fluid-the liquid that • QUESTION bathes the battery's plates-as the battery is recharged by the generator or alternator? 11.15 Niagara Falls FightsTyphoid through Electrolysis With one exception, all the reactions we've seen in this chapter produce an electric current or a voltage by means of a chemical change occurring in a battery. In that single exception, the recharging of a lead-acid storage battery, electrical energy supplied to the battery produces a chemical change within it. Lead sulfate and water are transformed into lead, lead dioxide, and sulfuric acid. Electrical energy can also be used to generate a variety of other chemical changes that don't occur spontaneously, including the electrolysis of water into hy-drogen and oxygen. The suffix -lysis implies a cleavage, rupture, or decomposition; electrolysis produces the decomposition of a substance into its component parts Electrolysis is the decompo- by means of electricity. sition of a substance by In 1800 William Nicholson, an English writer, lecturer, and experimenter in means of electricity. -.,~..:-~- what was then known as "natural philosophy," read Volta's newly published de- ~;ription of his Volta pile (Sec.11.7) and built one of his own. Nicholson attached o platinum wires and used them to pass an electric current from the pile through ontainer of water. The resulting electrolysis of the water produced bubbles of at proved to be hydrogen gas at one wire and oxygen at the other, always in a ~tant ratio of two volumes of hydrogen to one of oxygen (Fig. 11.10). The con vncy of this ratio provided early evidence that a water molecule contains twice any hydrogen atoms as oxygen atoms. The reasoning behind this conclusion ~ecome evident in Sec. 12.10.  2 H O electrolysis 2 H + 2 z two molecules of water  two molecules one molecule of of hydrogen, each oxygen containing containing two two oxygen atoms hydrogen atoms Figure 11.10 The electrolysis of water. Twice as much gas Today electrolysis represents a valuable process in the chemical industry, use- (hydrogen) is being produced in ful for generating a variety of commercially important chemicals. The electrolysis the tube on the left as in the ; of a solution of sodium chloride in water, for example, produces chlorine gas at the one on the right (oxygen). OZ 274 • Chapter 11 Oxidation and Reduction anode (from oxidation of the chloride ions in the solution) and hydrogen at the cathode. At the cathode a net reduction of water's protons to HZ leaves the hy-droxide anion, OH-, in the remaining solution. The combination of this anion with Na+ left over from the oxidation of the chloride anions results in the formation of NaOH, sodium hydroxide, within the remaining solution: Na+ + OH- ) NaOH sodium hydroxide Sodium hydroxide is an important industrial chemical, useful in the production of a variety of commercial products. As a direct consumer chemical itself, though, its application is limited to use as highly caustic lye for opening clogged sinks and drains. It is an extremely corrosive and hazardous substance that must be used with great care. Electrolysis on a commercial scale consumes enormous quantities of electric-ity and can be carried out economically only in regions where electric power is cheap and plentiful. In one of these locations, Niagara Falls, the power of falling water is harnessed to provide the needed energy. The chlorine produced in the electrolysis reaction is a valuable industrial raw material for manufacturing a large number of consumer products ranging from simple, rugged plastic plumbing fix-tures to pharmaceuticals with intricate and complex molecular structures. As a strong oxidizing agent, chlorine also provides an important tool for safe-guarding the public health. Its oxidizing power makes it deadly to bacteria, in-cluding those that cause typhoid fever. The large-scale chlorination of public water supplies, swimming pools, and sewage, made possible by the commercial produc-tion of inexpensive chlorine, has played a major role in eliminating epidemics of typhoid fever and other public health threats in developed nations. Chlorine gas can be deadly to humans, too. It was one of the poison gases used in the trench war-fare of World War I, • Q U E S T I O N What three chemicals are produced through the electrolysis of sodium chloride so-lutions? What three chemicals would you expect to be produced by the electrolysis of a solution of sodium bromide?  11.16 Redox in Everyday Life Our contact with redox and electrolysis in our everyday lives isn't limited to b teries, or the benefits of disinfection through chlorination. Many of our metals, example, come to us through one of these processes. Commercial quantities of r minum are produced through the electrolysis of hot solutions of aluminum ox A1203, dissolved in cryolite, Na3A1F6: electrolysis 2A1203 , 4 A1 + 3 O 2 3 2 The aluminum oxide is obtained through the processing of bauxite, an alumi: containing ore. The highly purified form of silicon needed for the production of silicon cl. used in computers and calculators comes from a redox reaction of highly puriff silicon chloride, SiC14, with hydrogen: SiC14 + 2H2 ) Si + 4HCl Even the copper plating of baby shoes and similar objects depends on the kinds of electron transfers we've examined in this chapter. Copper plating-the 11.16 Redox in Everyday Life • 275 transfer of copper atoms from a copper strip to another object-takes place when metallic copper and the object to be plated are placed in a solution of an electrolyte and are connected to the poles of a battery. The copper is connected to the anode; the plating takes place at the cathode. To facilitate the plating, objects that aren't good conductors of electricity are often coated with a thin layer of graphite, a form of carbon much like the central core of a flashlight battery. Up to this point we've examined some of the more useful aspects of oxidation and reduction: storing and obtaining electrical energy from batteries, and useful as pects of electrolysis.There's another, undesirable side of redox though: corrosion. Corrosion is the erosion and Although we normally think of corrosion as affecting metals, it's defined more disintegration of a material re- generally as the erosion and disintegration of any material as the result of chem- sulting from chemical reac- ical reactions. The term rust applies specifically to the corrosion of iron that pro- tions. Rust is the corrosion of duces various scaly, reddish-brown oxides of iron. iron to form various reddish- Corrosion of all kinds does billions of dollars of damage each year in the brown oxides of iron. United States alone. The redox reaction of metals, of which rusting is only one ex-ample, is accelerated by moisture, the presence of acids or bases, and various pol-lutants of the air and water. Because of the variety and complexity of the chemical reactions that lead to corrosion, we'll consider here only a few that affect us most directly One results from the direct oxidation of metals that are exposed to air and water. Here we're using oxidation in a more conventional sense, as the com-bination of something with oxygen. The direct oxidation of metals in the presence of air or water results from a se-ries of redox reactions involving a combination of the metal itself, oxygen, and water. Iron, for example, rusts more rapidly in humid air than in dry air. These re actions result in the formation of metal oxides, chemical combinations of the metal and oxygen. Perhaps surprisingly the formation of these oxides can either accel-erate the corrosion or retard it, depending on the nature of the metal and the oxide it forms. Iron rusts rapidly because its oxides are granular and flaky. Once formed, the oxides fall or rub off the metal easily and expose fresh surfaces to additional corrosion. Aluminum, too, reacts quickly with oxygen to form aluminum oxide, A1Z03. This aluminum oxide, unlike the oxides of iron, forms a thin, tough, protective coating on aluminum that retards further oxidation. although alu-minum metal oxidizes easily, it is highly resistant to corrosion. The largest commercial use for metallic zinc isn't in manufacturing batteries, but in galvanizing other metals, especially iron and steel products, to provide them Galvanizing is a process that ~ith a thin surface film of zinc metal that protects them from corrosion (chapter- provides a protective zinc coat ~ening demonstration). Galvanizing is usually carried out in any of three ways: to metals. by dipping the metal into hot, molten zinc; ~y spraying molten zinc onto the metal's surface; or y reducing zinc cations directly onto the metal surface through an electro-aemical redox reaction. zinc protects iron products by reacting with components of the atmosphere to - a a protective film, much as aluminum does, and also by oxidizing more read-:~ an the iron it's protecting. If the coating of zinc should crack in spots so that .e iron's surface becomes exposed to the atmosphere, the zinc metal corrodes ~efore the iron does. In essence, the zinc is used as a sacrificial metal to protect the nore valuable iron. Since galvanizing a large metal object presents practical dif-ficulties, metal tanks used for underground storage of gasoline and other haz-ardous liquids are often protected from oxidation by attaching a sacrificial block of aluminum, magnesium, or zinc. Because these three metals are more readily oxidized than the iron of the tanks, they protect it from corrosion.  276 • Chapter 11 Oxidation and Reduction Galvanic or bimetallic corro-sion result from the contact of two different metals separat-ed by a thin layer of electrolyte. Of course, some metals are simply inherently resistant to any form of corro-sion. Gold's high resistance to oxidation (and other forms of corrosion as well), coupled with its ability to conduct electricity well, makes it useful as a coating for electrical connections. Since the ability of the gold coating to conduct a current is high to begin with and doesn't deteriorate through corrosion, many of the more expensive units of stereo and other electronic equipment, for example, use gold-coated parts and connectors. Another form of corrosion results from the contact of two different metals separated by a thin layer of electrolyte. Because it results from the generation of an elec-tric current between the two metal parts, it's sometimes called galvanic or bimetallic corrosion. This type of corrosion is produced by the same sort of redox reaction we saw in the Daniell cell. Anyone who has teeth containing metallic fillings and has in-advertently bitten a piece of metal foil has felt the jolt of the electric current gener-ated in galvanic corrosion. This kind of corrosion is most severe in metallic objects, such as boating equipment, that are in constant contact with salt water. What is galvanized metal? Describe two ways galvanizing helps keep iron from rusting. 11.17 Vitamin C, Drugstore Iodine, and Household Bleach ... A Final Visit With our knowledge of redox we can now understand why the opening demon-stration works as it does. The zinc reduces the deeply colored 12 to colorless I-, and the C12 of the bleach oxidizes the I- back to I2. Although these redox reactions illustrate a nice piece of chemistry, they probably don't do much for us in our daily lives. Here's one that does. Place a drop or two of drugstore iodine on a piece of cotton cloth. Use a worthless scrap that won't be missed if something goes wrong. If this were an article of clothing or a valuable piece of fabric, you might consider the fabric ruined by the iodine stain. But you can remove the stain by rubbing it with a moist tablet of vitamin C. Dampen the tablet and rub it over the spot. You'll find that the color of the iodine vanishes. It might seem to be magic, but it's simply redox in operation once again. Vit-amin C is an organic compound we'll examine in more detail in Chapter 19. It's nc only needed in our diets for good health, but since it happens to be oxidized ver easily it's also a good reducing agent. The structure of vitamin C and the chemist of its oxidation are too complex to be examined here, the redox reaction cc verts the 12 into colorless I- just as in the opening demonstration. This example of everyday chemistry works well for removing iodine sta from clothing and similar articles. But be careful not to bleach the fabric until rinse out the residual I-. The bleach can reoxidize any remaining I- to IZ and th by cause the stain to reappear, just as in the opening demonstration. It's best to r the area thoroughly, immediately after you remove the stain, to wash out the res_ ual I- and the vitamin C. (In a related bit of redox chemistry, the reaction of C12 and I- has been useL to reveal the illegal trapping of egg-bearing lobsters. To escape detection, lobstei harvesters sometimes use a C12 solution to help remove the eggs from the lob ster's shell. The illegal harvesting comes to light when parts of the lobsters' shells are dipped into a solution of KI and the residual C12 on the shell oxidizes the I-to the telltale color of 12 .) 298 • Chapter 12 Solids, Liquids, and Especially Gases Figure 12.16 'The gas laws and a carbonated drink. • Q U E S T 1 O N Fish, which consume oxygen just as all other animals do, survive on atmospheric oxygen that dissolves in water. Name a gas present in water in a greater concen-tration than oxygen. Explain. Henry's Law Boyle's Law Henry's Law High pressure When cap is With drop in of COz in sealed removed the partial pressure of container causes pressure drops COZ above liquid, COz to dissolve to atmospheric, the solubility of in carbonated causing the gases COZ in the drink drink. to expand and also drops. With escape. continued loss of CO2 , the drink Dalton's Law eventually gces flat. Partial pressure of CO2 above the liquid drops as well. As the drink stands unstoppered, the very low partial pressure of the atmospheric CO2 (0.2 mm-Hg, Table 12.3) allows almost all the CO2 to escape from its liquid solution, causing the soda to go flat (Fig. 12.16) 12.12 Don't Shake a Warm Bottle of Soda; Also Some Advice About an Aquarium Henryฐs Law tells us all we need to know about the actual solubility of a gas in a liquid, but it says nothing about how fast the gas dissolves or how fast it comes out of solution. It doesn't tell us anything about the rates of the two processes or how to change them. We know from experience that a carbonated beverage loses its C02 slowly. We can watch the bubbles form on the sides and bottom of a glass and rise to the top slowly, over a reasonably long period, before the drink goes flat and the entire process stops. But shaking a bottle or a can of soda, especially a warm one in which the solubility of the CO2 is low, often causes the drink to foam up and spill out of !f-~''~'~- ;~ the container when we open it. A combination of the laws of '~is foaming results from a proeess called nucleation. Shaking the soda caus- gases, including their low solubility es microscopic bubbles of the gas in the space above the drink to become trapped in a warm liquid, causes this to , inside the liquid. These serve as nuclei around which dissolved C02 can come out happen when you shake a bottle ~ of solution to form gas bubbles quickly as we open the can or bottle and the ex- of warm soda before you open it. ternal pressure drops sharply. With the sudden drop in the external pressure and  12.13 The Art and Science of Breathing • 299  the rapid formation of a large number of COZ bubbles around the gaseous nuclei, the drink foams up and gushes out. ,. N ucleation can also occur on the surface of a solid. Try adding a few crystals of tabl sugar to a freshly poured soft drink. As soon as the sugar granules enter the liquid, they provide a surface for nucleation and result in a rush of gas bubbles. The reverse process, dissolving a gas, requires a high pressure or a large sur-face area, preferably both. At atmospheric pressure a large area of contact be-tween the gas and the liquid helps speed the flow of the gas into solution. Like other animals, fish need oxygen for life; they depend on the atmospheric oxygen that dissolves at a partial pressure of 159 mm-Hg (for dry air; Table 12.3) through the surface of the waters of lakes, streams, oceans, and home aquaria. To provide plenty of oxygen for an aquarium containing several fish, it's usually necessary to pump air into the aquarium water as a stream of small bubbles. The smaller the bub- bles the better, because as a sphere shrinks its volume decreases more rapidly than its surface area. Plenty of small air bubbles present a larger surface area, per vol- ume of gas, than a few large ones. This high ratio of surface area to the volume of gas permits an effective transfer of the oxygen into the water. Because of their higher ratio of surface area to volume, small bubbles of gas transfer their oxygen to water more effectively than large bubbles.  Aside from temperature, what is one factor that determines how much N2 can dis- •QUESTION solve in a given quantity of water? What is one factor that determines how fast the N2 dissolves? , 12.13 The Art and Science of Breathing The simple act of breathing provides us with the most common and the most im-portant application of the gas laws to our everyday lives. We breathe simply to ex-change the oxygen of the air for the carbon dioxide produced by the body's cells as they metabolize macronutrients (Sec. 8.12). As an illustration, the cellular oxi-dation of glucose produces carbon dioxide, water, and energy: C61-11206 + 602 ) 61-120 + 6 C02 + energy glucose oxygen water carbon dioxide Our cells use or store the energy that's generated, and the water becomes part of our general physical inventory. But the carbon dioxide, a waste product, has to be transported by the blood from the cells to the lungs so that it can be eliminated in exhaled breath. In a normal, healthy adult, the blood reaches the lungs carrying its cargo of CO2 at a concentration equivalent to what we'd find in a solution that's under a partial pressure of 45 mm-Hg of carbon dioxide at normal body temperature. Henry's Law tells us that at any specific temperature the concentration of a gas in a solution is directly related to its partial pressure above the fluid. Knowing this we can use PCo2 = 45 mm-Hg (or simply "45 mm-Hg") to define the concentra-tion of carbon dioxide in the blood reaching the lungs. Here, PCo2 represents the partial pressure of CO2 SOO • Chapter 12 Solids, Liquids, and Especially Gases A tank of compressed gas furnishes oxygen at a partial pressure high enough to allow normal breathing underwater. As we inhale, the pressure inside our expanding lungs drops slightly and the outside air, traveling from a region of higher external atmospheric pressure to a slightly lower internal pressure, enters the lungs. Once inside, the air's oxygen moves continuously to regions of ever lower partial pressure until it comes, final-ly, to the interior of the alveoli. Here the gaseous oxygen's partial pressure is at its lowest, about 100 mm-Hg. Within the sac itself, and still moving from a region of higher partial pressure to one of lower pressure, the oxygen passes through the thin membrane of the capillary wall and enters the fluid (blood) that's moving within the blood vessel (Fig. 12.17). With the passage of oxygen across the wall and into the capillary, the concentration of oxygen within the blood increases from the 40 to 45 mm-Hg of venous blood to arterial blood's 100 mm-Hg. Air enters the lungs and oxygen passes through the bronchial network to the alveoli. Alveolar duct Blood within the network of capillaries crossing the alveoli exchanges its carbon dioxide for the oxygen within the alveolar sac. C02 leaves blood / Figure 12.17 The lungs and the alveoli. Here's another piece of chemical magic. Unlike the cabbage breath test of Chapter 10, this demonstration requires a little ad vance preparation.You begin by "floating" a thumbtack on the surface of a glass of cold water. We know, of course, that thumb-tacks don't actually float on water, but there's an old parlor stunt in which you place a thumbtack, or some other small metal object like a needle or a paper clip, very gently on the surface of a glass of water. Instead of sinking, the metal seems to float. Actually it isn't floating at all; it's resting on the water's surface, supported by a phenomenon known as surface ten-sion. We'll have more to say about surface tension later, but for now the key to this feat lies in placing the thumbtack gently onto the surface. If you have trouble with this step you can use a loop of fine wire shaped as shown in Figure 13.1. Now challenge someone to duplicate what you're about to do next. Announce that you are about to poke the end of a toothpick into the water so very carefully-with nerves as steady as a chemical bond-that the thumbtack will remain undisturbed on the surface. The challenge is to push the toothpick into the water repeatedly, but so gently that the tack doesn't plummet to the bottom. Push the toothpick ever so gently through the surface about midway between the tack and the edge of the glass. With a little practice you'll be able to do this easily with-out sinking the tack. A cylindrical toothpick, tapered to a point at each end, is better for this stunt than one of those flat toothpicks, broad at one end and narrow at the other. Now give the toothpick to your friend. With the first stab into the water, no matter how gentle, the tack drops to the bottom of the glass. The secret of the stunt lies in a r twist of chemistry. Better yet, it lies in a twist of the toothpick. To make the magic work, secretly coat one end of the toothpick with a drop of a colorless liquid detergent just before you begin the proceedings. You poke the dry end of the toothpick into the water, but as you hand it to your challenger you invert the tooth pick (unobserved) so that your friend sticks the detergent-coated end into the water. Rotating the toothpick as you pass it over takes a little sleight of hand and a bit of practice, but it's really the chemistry that does the job. Just as soon as the detergent touch- " es the water, the tack drops sharply to the bottom of the glass. Figure 13.2 describes it all. (Using a toothpick whose ends have identical shapes decreases very slightly the likeli-hood of discovery.That's why the symmetrical toothpicks are a bit better for this stunt.) In this chapter we'll examine surface tension and its origin. We'll see how detergents affect surface tension and how they help us clean clothes and other household goods. We'll look at some of the similarities and differences between soaps and detergents, and we'll see why synthetic detergents are more efficient than soaps in regions with hard water. In doing all this, we'll use the examination of soaps and detergents to reveal some Figure 13.1 "Floating" a tack of the extraordinary chemistry brought to us by a box of ordinary detergent. = , on water. With Nerves as Steady as a Chemical Bond 308 • Chapter 13 Surfactants Figure 13.2 Place a tack on the surface of a glass of water. The tack remains on the water's surface as you gently push a toothpick into the water. The tack drops as soon as someone else pushes the toothpick through the water's surface, no matter how gently. The secret lies in the chemistry of liquids, surfaces, and detergents. 13.1 Density, and How Insects Walk on Water The density of a substance is its mass per unit volume. Den-sity is stated in units of grams per milliliter or grams per cubic centimeter. The real magic of the opening demonstration lies in the chemistry of surface ten-sion and of soaps and detergents. If you've ever seen an insect skimming across the surface of a puddle or pond, you've seen surface tension in action. To understand the effects of surface tension-how it allows insects to walk over water and tacks to rest on its surface-we'll look at one of the fundamental properties of matter: density. The density of any substance is simply its mass per unit of volume. In scientific work, the accepted units of density are grams per milliliter (g/mL) and grams per cubic centimeter (g/cm3). Since a milliliter is the same as a cubic centimeter, the two measures of density are equivalent and interchangeable. We calculate densi-ties by the formula mass density = volume (An easy way to determine the volume of an object is to immerse it in water and determine the volume of water it displaces. Naturally, if the object can be dam-aged by water some other technique must be used.) A I~s P L E Statuesque Density small statue has a mass of 99 g and a volume of 45 cm3. What is the densi of the statue? To find density, we divide mass by volume. In this case density = mass volume 99 g density = 3 = 2.2 g/em3 45 cm The density of the statue is 2.2 g/cm3. 13.1 Density, and How Insects Walk on Water • 309 Be sure that you recognize the difference between the weight of an object and its density. We sometimes think of lead, for example, as a heavy metal. But what we really mean is that it's dense. A single lead fishing sinker weighs only a few grams and is small enough to be held in your hand. A huge tree, though, can be heavy enough to crush a house if the tree falls in a storm. While the single tree is certainly much heavier than the sinker, the tree is nonetheless far less dense than the sinker. The key here is that 1 cm3 of the sinker (lead) is heavier than the same volume-1 cm3-of the tree (wood). Lead is more dense than wood, but small things made of lead can weigh less than large things made of wood. Densities of some typical solid substances appear in Table 13.1. Table 13.1 Average Densities of Typical Solids  Density Substance (g/mL or g/cm3) Aluminum - 2.7 Cork 0.2 Diamond 3.5 Glass (common) 2.6 Gold 19.3 Ice 0.9 Lead 11.4 Pyrite (a worthless mineral called "fool's gold" and easily mistaken for gold) 5.0 Quartz 2.6 Sodium chloride (as rock salt) 2.2 Sucrose 1.6 Wax (candles, paraffin) 0.9 Wood (average values) Balsa 0.1 Birch 0.6 Maple _ . ~ , 0.7 Oak 0.8 Teak 0.9 Our standard for density is water, which has a density of 1.0 g/mL. Anything that's less dense than water-wood for example-floats; anything that's more dense-lead-sinks. That's why trees float in water but lead weights sink. Drop a nickel into a glass of water or a concrete block into Lake Erie and it sinks to k the bottom. Metals and concrete are more dense than water-they have a greater mass than the volume of water they displace-so they sink. Anything a with a smaller mass than its equivalent volume of water floats. Fats and oils float because they're intrinsically less dense than water. Boats float because the air trapped inside their hulls gives them an average density less than water's. Empty buckets float for the same reason. Some brands of bar soap, Ivory for example, float because of an enormous number of microscopic bubbles of air whipped into them as they're manufactured. Ducks float because a film of oil on the surface of their feathers traps plenty of air next to their bodies (Fig. 13.3). 310 • Chapter 13 Surfactants Figure 13.3 Ducks float on water, supported by the buoyancy of air trapped by their feathers. Water's surface tension prevents it from penetrating the oily layer of their feathers and displacing the air.  But the tack you've been using doesn't float. The metal tack is denser than water and there's no trapped air to give it buoyancy. The tack is supported in a small dent on the water's surface, held up by the same phenomenon that supports an insect's feet as it walks across a pond: surface tension. • Q U E S T I O N Which is heavier, a block of aluminum with a volume of 10 cm3 or a block of lead with a volume of 2 cm 3? Which is more dense, the block of aluminum or the block of lead? 13.2 Surface Tension Surface tension supports both the insect and the tack, and keeps them from dropping into the water even though they're both more dense than water, ;-' because water's surface-the surface of any liquid for that matter-behaves a little differently from the bulk of its interior. As your friend pokes the toothpick into the water, the small bit of detergent on its tip lowers the surface tension sharply and the tack drops to the bottom. Now we'll examine the connection between the detergent's molecular structure and its effect on surface tension. : 13.3 Soap, a Detergent • 311 Surface molecules exert particularly strong _ attractive forces to their sides, front and back, and below. Interior molecules exert weaker forces in all directions. Describe a simple way to lower water's surface tension. • QUESTION 13.3 Soap, a Detergent Detergent comes from the Latin detergere, meaning to wipe off or to clean. A de-tergent is anything that cleans, especially if it removes oily or greasy dirt. To see how • detergents work, we'll look first at one particular kind of detergent, a soap. Each time you use a bar of soap you go back a long way, chemically, into an un-certain history. There's reason to believe the Babylonians knew how to make soap al-most 5000 years ago. While the Phoenicians and ancient Egyptians may have manufactured it, too, most historians give the Romans the real credit for discovering soap, or at least for writing down the secrets of its preparation and passing them along. The Romans knew that heating goat fat with extracts of wood ashes, which contain bases, produces soap. They also used lye (sodium hydroxide, NaOH), a stronger base than the ash extracts and more effective in converting fat into soap. The word lye it-self is connected to soap and soapmaking through an intricate linguistic path that in-cludes a long list of words from Latin, Greek, Old English, Old Irish, and other languages, with meanings such as lather, wash, bathe, and even ashes. Sodium palmi-tate, the sodium salt of palmitic acid, is a typical soap. (It's a salt in the same sense that NaCl, KI, MgS04, and CaC03 are salts; see Sec. 10.2.) Figure 13.4 The origin of surface tension. 312 • Chapter 13 Surfactants CH3-CH2-CHz-CHZ-CHZ-CH2-CHZ-CHZ-CH2-CHZ-CHZ-CH2-CHZ-CH2-CHZ Hydrophillic or headshuns hydrocarbon-like CHg-(CH2)lq-C02H substances but is attracted to palmitic acid water molecules CH3-(CH~)lq-C02-Na+ Na+ sodium palmitate, a soap Anionic portion of ( molecul `e Hydrophobic tail shuns water but is attracted to oily, greasy,hydrocarbon-like substances With sodium palmitate serving as a specific illustration, we ean generalize th lecular structure of a soap molecule as CH3-(CH2)n-COZ-Na+ where the subscript n represents an even number, usually ranging from 8 to 16. ~ entire carbon chain, including both the methyl carbon and the earboxylate bon, runs from 10 to 18 carbons.) With this structure a soap moleeule possesses opposing chemical tendeneies. On the one hand, the long chain of methylene groups that ends in the met group CH3-(CH2)~ resembles quite closely the long chains of the hydrocarbon molecules of Chapter 6. Like the molecules of gasoline and mineral oil, this part of the soap mol cule tends to dissolve readily in materials that are or that resemble hydrocarbor but not in water. All these long chains of -CHZ- groups of soaps and of h drocarbons and hydrocarbon-like materials intermingle easily, but they don't m readily with the H20 molecules of water. The other end of the molecule, though, is ionic: O - C -O-Na+ Like sodium chloride and other ionic compounds, that ionic end tends to dissolve in water, but not in hydrocarbon solvents. As a result we have here one molecule with two opposite and contradictory tendencies. Part of the molecule eontains hydrophilic structure; the ionic end is attracted toward water molecules but shw hydrocarbons and other oily and greasy substances. The other part, the long h drocarbon chain, is a hydrophobic structure; it shuns water but mixes easily wi those very oily, greasy substances that repel the hydrophilic part (Fig. 13.5). Wi its long chain of -CH2- groups, this hydrophobic portion of the soap molecu follows the old adage that oil and water don't mix. (Both hydrophilic and hydrophobic start with hydro-, which is taken from Greek word for water. The endings -philic and -phobic come from Greek worv meaning loving and fearing, respectively. In this sense, the hydrophilic end of tl soap molecules loves or seeks out water; the hydrophobic end fears or shuns wate~ • Q U E S T 1 O N What structure forms the hydrophobic portion of a soap molecule? What structure forms the hydrophilic portion? Figure 13.5 A typical soap molecule. 13.4 Surfactants 13.5 Micelles, Colloids, and John Tyndall • 313 Soap, detergents, and any other substances that accumulate at surfaces and change their properties sharply, especially by lowering the surface tension, are p ~ ~ 4 surface-active agents or, more briefly, surfactants. Substances other than surfac- tants can also change surface tension, but not nearly as effectively as surfactants. Figure 13.6 Surface effect of Even a small amount of a surface-active agent can produce dramatic effects. At a detergent molecules. concentration of 0.1 %, for example, soap lowers water's surface tension by almost 70%. In contrast, sodium hydroxide, which is not a surfactant and which diffuses Surfactant ( homogeneously throughout its water solutions rather than concentrating at the surface, actually raises water's surface tension very slightly. At a 5% concentra- \ tion, Some detergents, the soaps, are sodium or potassium salts \ ~ Soap of long-chain carboxylic acids. Other detergent molecules have different structures, yet all detergents have a typical molecular structure in common: a long, hydropho-bic carbon chain that resembles a molecular "tail," which is connected to a hydrophilic "head." In Section 13.11 we'll examine some detergents that aren't soaps. Figure 13.7 All soaps are detergents; all detergents are surfactants. •QUEST1ON What do all surfactants, detergents, and soaps have in common? What do all detergents have in common? Identify a substance that is a surfactant but not a detergent. All detergent molecules, like those of soaps, consist of a hydrophilic portion and Detergent molecules disrupt a hydrophobic portion. When they enter water, detergent molecules head for the surface forces and single location where both tendencies can be accommodated: the surface. There the lower~ surface tension hydrophilic end of the molecule becomes comfortably embedded among the water , molecules that make up the surface while the hydrophobic tail sticks up, away from the water molecules. As shown in Figure 13.6, the detergent molecules become interspersed among the molecules at the water's surface. In disrupting this tightly knit layer of molecules, the detergent interferes with the strong attractive forces that the surface water molecules normally exert on each other and thereby low ers the surface tension. This is why the tack drops when the toothpick introduces q the detergent into the water. for example, sodium hydroxide increases water's surface tension by about 6%. Detergent Figure 13.7 illustrates the relationship among the three terms: surfactant, deter- gent, and soap. All surfactants act at surfaces. Some surfactants, the detergents, are also good cleaning agents. 13.5 Micelles, Colloids, and John Tyndall As the water's surface becomes filled with surfactant molecules and even more detergent is added, the additional detergent molecules soon become crowded out of the surface. They begin shielding their hydrophobic tails from water molecules in a different way. They begin clustering into micelles within the bulk of the water. Micelles are submicroscopic globules or spheres of one substance distributed Micelles are submicroscopic ;throughout another, usually a liquid. As detergent molecules accumulate into mi- globules or spheres of one sub- 1celles in the interior bulk of the water, their hydrophilic heads form the spheres' stance distributed throughout surfaces and their hydrophobic tails point inward, shielded from the water mole- another, usually a liquid. tcules in an accommodating environment made up of other, similar, hydrophobic hydrocarbon chains (Fig. 13.8). Although these detergent micelles are well dispersed in the water, they aren't actually dissolved. They're present as a colloid rather than as the solute of a solution (Sec. 9.5). A colloidal dispersion differs from a true solution largely in the size of the  314 • Chapter 13 Surfactants A colloid is made up of parti- dispersed particles. In a colloid the particles run from about 10-~ to 10-4 cm in di- cles of one substance dis- ameter. In contrast, the diameter of a chloride ion is 3.6 X 10-s cm; for a sodium ion persed throughout another.The it's barely 2 x 10-$ cm. As we've seen in earlier chapters, sodium chloride dissolves particles of the dispersed sub- in water to form a true solution of Na+ cations and Cl- anions. stance ra7 ge in diameter from '~ere's no sharp, well-defined division between the size of a particle dispersed about 10- to 10- cm. as a colloid and one that's dissolved in a true solution. As with acids and bases, we Hydrophilic heads have to rely on observable phenomena to determine which we're dealing with. form the surface 'I'he easiest way to see the difference between a solution and a colloidal dispersion of the micelle is to shine a light through each of them. Shining a flashlight beam through a solu-tion of sodium chloride in water doesn't show much. The beam passes through the clear solution without producing any observable effect. But shine the beam through a mixture of soap and water, even one containing very little soap, and you can see the beam's path clearly illuminated, especially if you view the mixture against a dark background. This Tyndall effect, produced as the colloidal particles scatter ,„„„ the light to all sides, was discovered by John Tyndall, a British physicist born in Ireland in 1820. It's one of the more easily observed properties of a colloidal dis-persion, one that readily distinguishes it from a true solution (Fig. 13.9). The Tyndall effect isn't limited to detergents. A few drops of milk in a glass of water also show the path of the light. Milk is essentially an aqueous mixture of colloidal fats and proteins along with dissolved lactose (milk sugar) and minerals. You can even see the Tyndall effect outdoors on a foggy night as the fog-a col-Hydrophobic tails loidal dispersion of water in air-scatters the headlight beams of automobiles. compose the With one exception, colloids can form when each of the three states of matter- micelle's interior solids, liquids, and gases (Chapter 12)-disperse in each of the others. Since all gases Figure 13.8 Cross section of a are infinitely soluble in each other, no gas forms a colloidal dispersion in any other spherical detergent micelle. gas. Examples of the various kinds of dispersions appear in Table 13.2.  John Tyndall, discoverer of the Tyndall effect, delivering a popular lecture on science.  13.6 How Soap Cleans • 315 Table 13.2 Colloidal Dispersions Common Name Example Solid dispersed in Solid Ruby glass-glass colored red by a colloidal dispersion of solid gold particles Liquid Clay, paint, putty, toothpaste Gas Aerosol Smoke Liquid dispersed in Solid Gel Gelatin, jelly Liquid Emulsion Milk, salad dressing Gas Aerosol Fog Gas dispersed in Solid Popcorn Liquid Foam Whipped cream Gas (Does not exist) What's the simplest way to determine whether a liquid mixture represents a solution •QUESTION or a colloidal dispersion? 13.6 How Soap Cleans , Now we can begin to understand why soap acts as a detergent. Soap cleans by:  l. decreasing water's surface tension, making it a better wetting agent; 2. converting greasy and oily dirt into micelles that become dispersed in the soapy water, and 3. keeping the grease micelles in suspension, thereby preventing them from coalesc-ing back to large globules of grease that could be redeposited on a clean surface. Each of these functions has its basis in the structure of the soap molecule. Our common sense tells us that water wets whatever it touches, but if we look closely we find that water isn't a particularly effective wetting agent after all. Figure 13.9 The Tyndall effect is evident as a beam of light passes through a colloidal dispersion of water droplets in the atmosphere. Surface tension holds water in the form of small beads on the leaves of the Japanese Root Iris. 316 • Chapter 13 Surfactants Figure 13.10 Detergents Water's surface tension causes enable water to penetrate it to bead on the surface of fabrics. rapidly into fabrics. Adding detergent lowers water's surface tension and allows it to ... pentrate into the fabric. Water Fabric being washed h Figure 13.11 Water, grease, and soap. Soap molecules Grease environment for the hydrophobic tails as the water provides for the hydrophilic heads, the tails are just as much at home in the grease as the heads are in the water. With their heads embedded in the water and their tails in the grease, the soap mol-ecules effectively nail these two phases together (Fig. 13.11). Agitation now breaks the grease into micelles whose surfaces are covered by the negatively charged carboxylate groups, the hydrophilic -CO2- groups of the embedded soap molecules (Fig. 13.12). With a coating of negative electrical charges enveloping the entire surface of each micelle, the grease droplets repel each other and remain suspended in the wash water instead of coalescing and redepositing on the material being cleaned. In the end, the suspended droplets go down the drain with the wash water. (While all this is going on, the sodium ions move about freely and independently in the wash water, just as they did in the electrolyte solution of the light bulb demonstration that began Chapter 1.) Figure 13.12 Grease micelles with embedded soap molecules. 13.7 Esters and the Manufacture of Soap • 317 Since the anionic carboxylate groups of the soap molecules place a cover of negative electrical charge on the micelles' surfaces, soap falls into the class of anionic detergents. All surfactants lower surface tension, but only some surfactants are detergents. • Q U E S T I O N What functions does a chemical perform in addition to lowering surface tension that allows us to classify it as a detergent? 13.7 Esters and the Manufacture of Soap However soap is made, whether by boiling goat fat and wood ashes in ancient kettles (Sec. 13.3) or through the modern methods of 20th-century factories, it's all the same chemically. Soap comes from the hydrolysis of naturally occurring fats and oils, which are themselves members of a class of organic compounds known as esters. [An ester is a compound whose molecules contain the functional group (Sec. 6.12) O -C-O-C- while hydrolysis is the decomposition of a substance, or its conversion to other Hydrolysis is the decomposi- substances, through the action of water.] tion of a substance, or its con- All naturally occurring fats and oils are esters of fairly complex molecular version to other substances, structures. We'll start instead with a simpler ester, ethyl acetate, which is used as a through the action of water. food flavoring and as a common, commercial solvent found in many brands of nail polish and paint remover. (Ethyl acetate doesn't occur in fats, though.) O 11 CH3-C-O-CH2-CH3 ethyl acetate Ethyl acetate results from the reaction of acetic acid and ethyl alcohol in the presence of a small, catalytic amount of a strong acid. As the acetic acid and the ethyl alcohol react, the oxygen atom of the alcohol becomes bonded to the carbonyl carbon of the acid (Sec. 10.8), while the H of the alcohol's -OH group and the entire -OH of the acid leave as a molecule of water, a by-product of this esteri-fication reaction (Fig. 13.13). Although the carboxylic acid that takes part in this esterification is itself an acid, it's a relatively weak one: The reaction requires the presence of a much stronger acid, such as HCl or H2SOq, as a catalyst. Catalysts, which affect the rate of a reaction but are not themselves reagents (Sec. 7.7), are ` usually written above the reaction arrow along with required conditions, such as heat and pressure. Figure 13.13 An acid-catalyzed esterification. O Acid catalyst O New covalent bond II H+ ~ II / CH3-C- OH + H O-CH2-CH3 ~ CH3-C-O-CHZ-CH3 + H -OH Acetic acid Ethyl alcohol Ethyl acetate (an ester) Water To make the magic work, secretly coat one end of the toothpick with a drop of a colorless liquid detergent just before you begin the proceedings. You poke the dry end of the toothpick into the water, but as you hand it to your challenger you invert the tooth pick (unobserved) so that your friend sticks the detergent-coated end into the water. Rotating the toothpick as you pass it over takes a little sleight of hand and a bit of practice, but it's really the chemistry that does the job. Just as soon as the detergent touch- " es the water, the tack drops sharply to the bottom of the glass. Figure 13.2 describes it all. (Using a toothpick whose ends have identical shapes decreases very slightly the likeli-hood of discovery.That's why the symmetrical toothpicks are a bit better for this stunt.) In this chapter we'll examine surface tension and its origin. We'll see how detergents affect surface tension and how they help us clean clothes and other household goods. We'll look at some of the similarities and differences between soaps and detergents, and we'll see why synthetic detergents are more efficient than soaps in regions with hard water. In doing all this, we'll use the examination of soaps and detergents to reveal some Figure 13.1 "Floating" a tack of the extraordinary chemistry brought to us by a box of ordinary detergent. = , on water. With Nerves as Steady as a Chemical Bond 308 • Chapter 13 Surfactants  Figure 13.2 Place a tack on the surface of a glass of water. Th tack remains on the water's surface as you gently push a toothpick into the water. The tack drops as soon as someone else pushes the toothpick through the water's surface, no matter how gently. The secret lies in the chemistry of liquids, surfaces, and detergents. 13.1 Density, and How Insects Walk on Water The density of a substance is its mass per unit volume. Den-sity is stated in units of grams per milliliter or grams per cubic centimeter. The real magic of the opening demonstration lies in the chemistry of surface ten-sion and of soaps and detergents. If you've ever seen an insect skimming across the surface of a puddle or pond, you've seen surface tension in action. To understand the effects of surface tension-how it allows insects to walk over water and tacks to rest on its surface-we'll look at one of the fundamental properties of matter: density. The density of any substance is simply its mass per unit of volume. In scientific work, the accepted units of density are grams per milliliter (g/mL) and grams per cubic centimeter (g/cm3). Since a milliliter is the same as a cubic centimeter, the two measures of density are equivalent and interchangeable. We calculate densi-ties by the formula density = mass volume (An easy way to determine the volume of an object is to immerse it in water and determine the volume of water it displaces. Naturally, if the object can be dam-aged by water some other technique must be used.) A IV P L E Statuesque Density small statue has a mass of 99 g and a volume of 45 cm3. What is the densi of the statue? To find density, we divide mass by volume. In this case density = mass volume  density = 99 g 3 = 2.2 g/em3 45 cm  The density of the statue is 2.2 g/cm3. 13.7 Esters and the Manufacture of Soap • 317 Since the anionic carboxylate groups of the soap molecules place a cover of negative electrical charge on the micelles' surfaces, soap falls into the class of anionic detergents. All surfactants lower surface tension, but only some surfactants are detergents. • Q U E S T I O N What functions does a chemical perform in addition to lowering surface tension that allows us to classify it as a detergent? 13.7 Esters and the Manufacture of Soap However soap is made, whether by boiling goat fat and wood ashes in ancient kettles (Sec.13.3) or through the modern methods of 20th-century factories, it's all the same chemically. Soap comes from the hydrolysis of naturally occurring fats and oils, which are themselves members of a class of organic compounds known as esters. [An ester is a compound whose molecules contain the functional group (Sec. 6.12) O -C-O-C- while hydrolysis is the decomposition of a substance, or its conversion to other Hydrolysis is the decomposi- substances, through the action of water.] tion of a substance, or its con- All naturally occurring fats and oils are esters of fairly complex molecular version to other substances, structures. We'll start instead with a simpler ester, ethyl acetate, which is used as a through the action of water. food flavoring and as a common, commercial solvent found in many brands of nail polish ~nd paint remover. (Ethyl acetate doesn't occur in fats, though.) O ~I CH3-C-O-CH2-CH3 ethyl acetate Ethyl acetate results from the reaction of acetic acid and ethyl alcohol in the presence of a small, catalytic amount of a strong acid. As the acetic acid and the ethyl alcohol react, the oxygen atom of the alcohol becomes bonded to the carbonyl carbon of the acid (Sec. 10.8), while the H of the alcohol's -OH group and the entire -OH of the acid leave as a molecule of water, a by-product of this esteri-fication reaction (Fig. 13.13). Although the carboxylic acid that takes part in this esterification is itself an acid, it's a relatively weak one: The reaction requires the presence of a much stronger acid, such as HCl or H2SOq, as a catalyst. Catalysts, which affect the rate of a reaction but are not themselves reagents (Sec. 7.7), are ` usually written above the reaction arrow along with required conditions, such as heat and pressure. Figure 13.13 An acid-catalyzed esterification. O Acid catalyst O New covalent bond II H+ ~ II ,~ CH3-C- OH + H O-CH2-CH3 ~ CH3-C-O-CHZ-CH3 + H-OH Acetic acid Ethyl alcohol Ethyl acetate (an ester) Water 318 • Chapter 13 Surfactants The name ethyl acetate reveals that the compound has structural connections to both ethyl alcohol and acetic acid. The suffix -ate tells us we're dealing either with an ester or with a salt of a carboxylic acid, such as sodium acetate: In naming esters we give the name of the alcohol first, then the acid, with the suf-fix -ate replacing the acid's -ic. For example, the ester formed by the reaction of iso-propyl alcohol (Sec. 6.8) with benzoic acid (Sec. 10.8), in the presence of a strong acid, is isopropyl benzoate (Fig. 13.14). Heating an ester with water in the presence of either an acid or a base produces a hydrolysis, with water adding to the ester in a reversal of the esterification reac-tion. As shown in Figure 13.15, when the hydrolysis is carried out in the presence of an acid, the reaction becomes precisely the reverse of the esterification. Here an ester reacts with water, forming an alcohol and a carboxylic acid. Carrying out the hydrolysis in the presence of a base, such as sodium hydroxide, produces the salt of the carboxylic acid rather than the acid itself. In this case the carboxylic acid and the base react with each other in a neutralization reaction (Sec. 10.2). In A saponification is a hydrol- the presence of a base, and with the formation of the salt of the acid rather than ysis of an ester carried out in the acid itself, the hydrolysis is called a saponification (Fig. 13.16), a term that the presence of a base. brings us to the chemistry of soapmaking. Figure 13.14 Isopropyl benzoate. Figure 13.15 An acid-catalyzed hydrolysis. An ester reacts with water, producing an acid and an alcohol. O Acid catalyst O II H+ II CH3-C-O-CHZ-CH3 + H + OH CH3-C- OH+H O-CHZ-CH3 Ethyl acetate (an ester) Water Acetic acid Ethyl alcohol Figure 13.16 A basic hydrolysis; a saponification. O 11 CH3 - C - O - CHZ - CH3 + NaOH Ethyl acetate < Sodium (an ester) - hydroxide (a base) CH3- C-O-Na+ sodium acetate O O 11 H+ 11 CH3-CH-OH+HO-C CH3-CH-O-C Isopropyl Benzoic + H20 Isopropyl benzoate alcohol acid HZO O 11 CH3 - C - O-Na+ + HO - CHZ - CH3 Sodium acetate Ethyl alcohol What is the name of the molecule formed by reversing the orientation of the ester • QUESTION functional group of ethyl acetate (switching the positions of the -CO- group and the -O- group)? Section 10.8 contains information that might prove useful. Ethyl acetate, as we've seen, is a simple ester formed from an alcohol (ethyl alcohol) that bears a single -OH group. The fats and oils are more complex esters, formed from glycerol, a triol (or trihydroxy alcohol) bearing three -OH groups. Glycerol is also known more commonly as glycerin, sometimes spelled with an added e, glycer-ine. Glycerol is used in many hand and body lotions to soften the skin. Each of glycerol's three -OH groups constitutes the hydroxyl functional group of an alcohol, so each one can enter into ester formation with a carboxylic acid. The result is a triester (Fig. 13.17) in which the three organic groups of the acids (R, R', and R" of Fig. 13.17) can be identical or can differ from each other. The generalized triester of Figure 13.17 bears a variety of generic names. Most ' commonly, it's described as a glyceride or a triglyceride. While the structures of Triglycerides are the principal the three acids that combine with glycerin can vary, almost all of the acids organic compounds of animal formed by saponifying fats and oils show certain structural similarities. Sodium salts of the fatty acids containing from 10 to 18 carbons make ate through hydrolysis. the best soaps (Table 13.3). Triglycerides are the principal organic compounds of animal fats and vegetable oils, and fatty acids are the acids they generate through hydrolysis. we can produce a soap by heating a triglyceride-an animal fat or a vegetable oil-in an aqueous solution of sodium hydroxide (Fig. 13.18). Hy-drolysis of the triglyceride generates both glycerol, which remains dissolved in the water, and the sodium salts of the various acids that make up the triglyceride. These salts of the fatty acids congeal at the surface as the mixture cools and we scoop ` them up as soap. Figure 13.17 A triester of glycerol. O 11 CH2 - OH 3 different acids CH- O- C - R' 13.8 From Fats to Soap • 319 R, R', and R"' represent carbon chains of different lengths CH2-OH HO -C-RI CH2-0=C-R" The generalized structure of a triglyceride Glycerol glycerol, also known as glycerin or glycerine CHZ-CH-CHZ OH OH OH 320 • Chapter 13 Surfactants Table 13.3 Common Fatty Acids of Soap Structure and Name Capric acid CH3-CHz-CHz-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-COZH Lauric acid CH3-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHZ-CH2-CHZ-CHZ-COZH Myristic acid CH,-CHZ-CH,-CHZ-CHZ-CHZ-CHz-CHZ-CHz-CHz-CH2-CHZ-CHz-CHZ-CHz-COZH Palmitic acid CH3-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CH2-CH2-CHZ-COZH Stearic acid CH3-(C.H2)7_CH=CH-(CHZ)7-COzH Oleic acid CH3-(CH2)4-CH=CH-CH2-Cli=cx-(CHz)7-co2x Linoleic acid CH2-O-C-R CHZ-OH R-C-O-Na+ II H O I II CH-O-CO-R' + 3 NaOH Heat CH-OH + R'-CO-O-Na+ 101 II+ - CHZ-OH R„-C-0 Na Glycerol Soaps CHZ-O-C-R" A triglyceride Figure 13.18 The saponification of a triglyceride. n of CH,-(CH2)„-C02H 6 10 12 14 16 • Q U E S T 1 O N What part of their chemical structures is common to all triglycerides? How do the chemical structures of the various triglycerides differ from each other?  13.9 A Problem: Hard Water As we saw in Section 9.11, the drinking water of many regions contains various min-erals, dissolved in slightly acidic rainwater as it filters through the soil. Water that's rich in the salts of calcium, magnesium, and/or iron is called hard water. (Soft water, on the other hand, is virtually free of these minerals.) The mineral cations of hard water combine with fatty acid anions and remove them from water as waxy, in-soluble salts. In regions where the water is particularly hard, you can actually see these precipitates deposited as gray rings, known as curd, or soap curd, around bathtubs and sinks after washing with soap. This curd is made up of the calcium, magnesium, and/or iron salts of the fatty acids of soap: 320 • Chapterl3 Surfactants Table 13.3 Common Fatty Acids of Soap Structure and Name CH3-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-COZH Caprylic acid CH3-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHz-CHz-COZH Capric acid CH3-CHz-CHz-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-COZH Lauric acid CH3-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHZ-CH2-CHZ-CHZ-COZH Myristic acid CH~-CHZ-CH,-CHZ-CHZ-CHZ-CHz-CHZ-CHz-CHz-CH2-CHZ-CHz-CHZ-CHz-COZH Palmitic acid CH3-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CH2-CH2-CHZ-COZH Stearic acid ~3-(~2)~ ~=~-(~Zh-~zH Oleic acid ~3-(~2>4-~=~-~2-~=cx-(~z)~-co2x Linoleic acid CH2-O-C-R CHZ-OH R-C-O-Na+ II H O I II CH-O-CO-R' + 3 NaOH Heat ~ CH-OH + R'-CO-O-Na+ I I „- II - - + CHZ-OH R C O Na Glycerol Soaps CHZ-O-C-R" A triglyceride    Figure 13.18 The saponification of a triglyceride. n of CH3-(CH2)„-C02H 6 10 12 14 16 • Q U E S T 1 O N What part of their chemical structures is common to all triglycerides? How do the chemical structures of the various triglycerides differ from each other?  13.9 A Problem: Hard Water As we saw in Section 9.11, the drinking water of many regions contains various min-erals, dissolved in slightly acidic rainwater as it filters through the soil. Water that's rich in the salts of calcium, magnesium, and/or iron is called hard water. (Soft water, on the other hand, is virtually free of these minerals.) The mineral cations of hard water combine with fatty acid anions and remove them from water as waxy, in-soluble salts. In regions where the water is particularly hard, you can actually see these precipitates deposited as gray rings, known as curd, or soap curd, around bathtubs and sinks after washing with soap. This curd is made up of the calcium, magnesium, and/or iron salts of the fatty acids of soap: 13.10 One Solution: Water Softeners • 321 2CH3-(CHZ)n-COZ-+Na + Ca 2+ -~ CH3-(CHZ)n-COZ-Ca2+-02C-(CHZ)n-CH3 + 2Na+ curd, or calcium soap (the ring that forms around the bathtub in regions with hard water) Hard water wastes soap because much of the soap that would otherwise be used in cleaning is consumed in curd formation as it reacts with the mineral ions of hard water. In hard water, a certain amount of soap has to be used up initially in combining with the mineral cations and removing all of them from solution be-fore additional soap can act effectively as a detergent. What's more, this curd de-posits on the surface of laundered clothes, dulling the cloth and giving washed goods a slightly gray appearance. You can see the effect of hard water on soap by first shaking up some soap in distilled water. A piece of common bar soap will do nicely for this demonstration, but laundry detergent won't work for reasons we'll come to soon. Distilled water, which you can get in a supermarket or convenience store, is free of the mineral ions of hard water and generates a good deal of suds with the soap. Now add some hard tapwater to the sudsy mixture or, if you live in an area of soft water, add about a tablespoon of milk, which contains considerable calcium. (Skim milk also works well, as does a solution of an antacid that contains calcium.) The suds van-ish as you stir the hard water or the milk into the soapy water because the fatty acid anions are converted into their insoluble calcium salts. You'll probably be able to see the curd swirling in the water.  Soap forms rich suds in soft water. In hard water soap is less efficient. The mineral cations of hard water combine with the soap, forming curds and reducing the soap's effectiveness The demonstration described in this Section asks you to shake a piece of common bar soap in distilled water, then add some hard tapwater to the mixture. What would you expect to see if you reversed the procedure by shaking the soap first in some hard tapwater, then adding some distilled water to the mixture? • Q U E S T 1 O N 13.10 One Solution: Water Softeners One solution to the problem caused by hard water is to remove the cations that produce the hardness. Commercial water softeners do this by trading sodium ions for the water-hardening cations-the calcium, magnesium, and iron ions-and thereby converting hard water to soft water. The typical water softener installed in a home consists of a tank contain-ing a specially prepared polymer, a storage bin for sodium chloride, and regu-lators to control the flow of water (Fig. 13.19). (Polymers are materials made of extraordinarily large molecules; Chapter 21). The polymers used in these water softeners have large numbers of anionic functional groups, which allow the polymeric molecules to hold large numbers of cations. You activate or charge the water softener by running concentrated salt water through it. The sodium ions of the salt water displace whatever cations might be on the poly-mer and stick to the polymer in the tank. Then, when hard water passes through the tank, the cations of the hard water take their turn at displacing the sodium cations from the polymer. With the exchange of calcium, magnesium, and iron ions of the hard water for the sodium ions held by the polymer, the water passing through becomes softened and the polymer eventually becomes saturated with the ions of the hard water.  From water Valve controls From recharge supply; input reservoir contains Ca 2+ FeZ+ Mgz ...-~. ~.-cations Sodium ~ chloride pellets O O D LF--iJ ~ D O O ~ ~ SOdium chloride Ion exchange ~~ solution resin I Reservoir of sodium chloride solution for recharging Valve controls To household output outlets II Softened water containing I\ a+ cations Waste water generated I ~ ~ ~ I for household use during recharge cycle, contains Ca2+, Fe~+, MgZ+ cations Because of this gradual accumulation of the ions of the hard water, the water sof-tener must be recharged with sodium ions periodically by passing salt water (formed from the sodium chloride pellets in the storage bin) through it. With the offending ions removed from the water, the sodium carboxylates-the soaps-now remain dispersed in the water and can act as effective detergents. (Resinous polymers of the kind used to replace one ion for another as a fluid passes through them are known as ion exchange resins.) What happens to the calcium, iron, and other ions of hard water that have accumu-lated on the ion exchange resin as they are replaced by sodium ions during the recharging process? Where do these cation of hard water go? 13.11 Another Solution: Synthetic Detergents  As an alternative to softening hard water, we can use a detergent that remains dis-persed even in the presence of cations that would inactivate a soap. In the 1940s chemical science and technology solved the problem of using hard water for wash-ing by devising economical, commercially useful synthetic detergents. In the most suc-cessful of these, the alkylbenzenesulfonates, a sulfonate functional group, -S03-, rather than a carboxylate group, -COZ-, acts as the hydrophilic structure: -COZ -503 a carboxylate group a sulfonate group The advantage of the sulfonate anion is the great water solubility of virtually every one of its mineral salts. Unlike soaps, alkylbenzenesulfonates remain dispersed and effective in hard water. [The term alkyl refers to the group produced by re-moval of a hydrogen atom from an alkane (Sec. 6.3). Alkyl groups we've already seen include the methyl group, CH3-, the ethyl group, CH3-CH2-, the propyl group, CH3-CHZ-CHz-, and the isopropyl group.] Since there's no simple, economical way to place a sulfonate group direct-ly onto a long hydrocarbon chain in large-scale production, commercially suc-cessful synthetic detergents don't mimic exactly the structure of a soap molecule. Some commercially feasible reactions do exist, though, that allow chemists to place both a hydrocarbon chain and a sulfonate group onto the same benzene ring (Sec. 6.11). Figure 13.20 Typical detergents. Anionic: Cationic: Nonionic: R - COZ Na+ A sodium R - N+- CH3 Cl-alkylcarboxylate (a soap) CH3 R ~~ ~~ S03-Na+ A sodium alkylbenezenesulfonate R-O-S03 Na  CH3-CH- CH3 CH3 An alkyl trimethylammonium chloride  13.11 Another Solution: Synthetic Detergents • 323 R-(CHZ-CHZ-O-)nH An alkyl polyethoxylate In all these structures, R represents a long carbon chain  A variety of synthetic laundry detergents.     A sodium An alkylpyridinium alkylsulfate chloride 324 • Chapter 13 Surfactants Anionic detergents, which make up the great bulk of all synthetic detergents, are particularly effective at cleaning fabrics that absorb water readily, such as those made of natural fibers of cotton, silk, and wool. Nonionic detergents, many of which have large numbers of covalently bonded oxygens in their hydrophilic structures, are es-pecially useful in cleaning synthetic fabrics, such as polyesters (Chapter 21). Most nonionic detergents are liquids that produce little foam. They are used, along with an-ionic detergents, in formulating dishwashing liquids and liquid laundry detergents. Most cationic detergents are ammonium salts (Sec. 10.3) that also happen to be effective germicides. They're used in antiseptic soaps and mouthwashes, and also in fabric softeners since their positive charges adhere to many fabrics that normally carry negative electrical charges. Molecular structures of some typical nonionic and cationic detergents appear in Figure 13.20.  • Q U E S T 1 O N What would you expect to see if you repeated the demonstration described at the end of Section 13.9, but used a synthetic detergent rather than a piece of bar soap? Explain.  13.12 What's in a Box of Detergent? Now, with our understanding of what detergents are and how they work, we can ask: What's actually in a box of laundry detergent, the kind we get off a store shelf? The answer is: A mixture of chemistry and consumerism, and of fact and fantasy. We'll observe this intermingling as we take a detailed look at its contents. Naturally, the most important ingredient of a detergent formulation is the sur-factant itself (Table 13.4). In the decades since synthetic detergents were intro-duced, the anionic alkylbenzenesulfonates have been the principal surfactants in detergent formulations. Today, though, this dominance may be shifting toward non- Table 13.4 Components of a Typical Detergent Formulation Component Example Function The ingredients in a box of Enzymes detergent. Surfactants Sodium alkylbenzenesulfonates Detergency Builders Phosphates, zeolites Soften water and increase surfactant's efficiency Fillers Sodium sulfate: Na2S04 Add to bulk of detergent and keep detergent pouring freely Corrosion Sodium silicates: Coat washer parts to inhibit inhibitors NazSi03, Na2Si205, rust Na4Si04 Suspension agents Carboxymethylcellulose Help keep dirt from (CMC) redepositing on fabric - Remove protein stains, such as grass and blood Bleaches Perborates Remove stains Optical whiteners Fluorescent dyes Add brightness to white fabrics Add fragrance to both the detergent and fabrics Coloring agents - Add blueing effect Fragrances 13.12 What's in a Box of Detergent? • 325 ionic surfactants, such as the alkyl polyethoxylates of Figure 13.20, as the result of a growing concern for the environment. Among the environmental advantages of the nonionic detergents is their smaller need for builders, which are essentially water-softening agents. (The term builders reflects the ability of these added agents to "build up" the detergent power of the surfactant.) Although all classes of syn-thetic detergents are superior to soaps in hard water, the nonionic detergents are even more effective than the anionic detergents. With less builder needed for the nonionic detergents, their formulations can be more concentrated and their pack-ages smaller. Compact packaging decreases the amount of discarded packing ma-terial in our trash and garbage; concentration results in smaller amounts of detergents passed into the environment with the waste wash water. For many years phosphates, such as sodium tripolyphosphate, Na5P301o, seemed to be the perfect builders. Their low cost, very low toxicity, and general absence of hazard, coupled with their ability to bind firmly to the ions of hard water and thereby reduce their chemical activity, made them the leading builders. Yet phosphates suffer from one overwhelming defect: They are superb nutrients for the algae and other small plants that grow on the surfaces of lakes and streams. Algae, nourished by a steady supply of phosphates, can cover the surface of a body of water and prevent atmospheric oxygen from reaching the marine life below. The resulting death of fish and other aquatic animals, sometimes occurring on a large scale in lakes and rivers covered by algae, led many states to ban the use of phosphates as detergent builders. The most promising substitute is a class of com-pounds of aluminum, silicon, and oxygen, known as zeolites. When added to hard water as part of a commercial detergent, the sodium salts of zeolites act like ion exchange resins, exchanging their sodium ions for the ions that produce the hard-i4ess and thereby softening the water. One of the major functions of fillers, primarily sodium sulfate, NaZSOq, was to give consumers a sense that they were getting their money's worth. At one time a bulky box of detergent was seen as giving the consumer a lot of detergent for the cost. The bulk was provided principally by the added sodium sulfate (which also made the granular detergent a bit easier to pour). With increasing consumer awareness and a growing concern for the environment, the amount of filler used in a box of detergent has dropped from about 35% to 10% or, in some cases, none at all. Other ingredients include corrosion inhibitors to protect the machinery that agitates the wash; suspension agents to help keep the grease, dirt, and grime in suspension so they don't redeposit on the fabrics; enzymes to help decompose pro teins of blood, grass, and other difficult stains; and oxygen-containing bleaches to help remove stains. All of these contribute to the surfactant's ability to produce a clean product. Some of the remaining ingredients may add more to the appearance of a clean wash than to its reality. Optical whiteners are organic compounds that coat the fabrics and convert the invisible ultraviolet component of sunlight (Secs.14.8 and 22.13) into an almost imperceptible blue tint. The effect of this blue tint, which can also be produced by blue coloring agents added to the detergent, is to add a bit of brilliance to white fabrics and give them the appearance of extra cleanli-ness. Finally, added perfumes and fragrances produce what many regard as a pleas-ant odor in the finished wash. Why were phosphates originally added to detergent formulations? Why were they • Q U E S T I O N subsequently removed? 320 • Chapterl3 Surfactants Table 13.3 Common Fatty Acids of Soap Structure and Name CH3-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-COZH Caprylic acid CH3-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHz-CHz-COZH Capric acid CH3-CHz-CHz-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-COZH Lauric acid CH3-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHZ-CH2-CHZ-CHZ-COZH Myristic acid CH~-CHZ-CH,-CHZ-CHZ-CHZ-CHz-CHZ-CHz-CHz-CH2-CHZ-CHz-CHZ-CHz-COZH Palmitic acid CH3-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CH2-CH2-CHZ-COZH Stearic acid ~3-(~2)~ ~=~-(~Zh-~zH Oleic acid ~3-(~2>4-~=~-~2-~=cx-(~z)~-co2x Linoleic acid CH2-O-C-R CHZ-OH R-C-O-Na+ II H O I II CH-O-CO-R' + 3 NaOH Heat ~ CH-OH + R'-CO-O-Na+ I I „- II - - + CHZ-OH R C O Na Glycerol Soaps CHZ-O-C-R" A triglyceride    Figure 13.18 The saponification of a triglyceride. n of CH3-(CH2)„-C02H 6 10 12 14 16 • Q U E S T 1 O N What part of their chemical structures is common to all triglycerides? How do the chemical structures of the various triglycerides differ from each other?  13.9 A Problem: Hard Water the drinking water of many regions contains various min-erals, dissolved in slightly acidic rainwater as it filters through the soil. Water that's rich in the salts of calcium, magnesium, and/or iron is called hard water. (Soft water, on the other hand, is virtually free of these minerals.) The mineral cations of hard water combine with fatty acid anions and remove them from water as waxy, in-soluble salts. In regions where the water is particularly hard, you can actually see these precipitates deposited as gray rings, known as curd, or soap curd, around bathtubs and sinks after washing with soap. This curd is made up of the calcium, magnesium, and/or iron salts of the fatty acids of soap: 13.10 One Solution: Water Softeners • 321 2CH3-(CHZ)n-COZ-+Na + Ca2+ -~ CH3-(CHZ)n-COZ-Ca2+-OZC-(CHZ)n-CH3 + 2Na+ curd, or calcitam soap (the ring that forms around the bathtub in regions with hard water) Hard water wastes soap because much of the soap that would otherwise be used in cleaning is consumed in curd formation as it reacts with the mineral ions of hard water. In hard water, a certain amount of soap has to be used up initially in combining with the mineral cations and removing all of them from solution be-fore additional soap can act effectively as a detergent. What's more, this curd de-posits on the surface of laundered clothes, dulling the cloth and giving washed goods a slightly gray appearance. You can see the effect of hard water on soap by first shaking up some soap in distilled water. A piece of common bar soap will do nicely for this demonstration, but laundry detergent won't work for reasons we'll come to soon. Distilled water, which you can get in a supermarket or convenience store, is free of the mineral ions of hard water and generates a good deal of suds with the soap. Now add some hard tapwater to the sudsy mixture or, if you live in an area of soft water, add about a tablespoon of milk, which contains considerable calcium. (Skim milk also works well, as does a solution of an antacid that contains calcium.) The suds van-ish as you stir the hard water or the milk into the soapy water because the fatty acid anions are converted into their insoluble calcium salts. You'll probably be able to see the curd swirling in the water.  Soap forms rich suds in soft water. In hard water soap is less efficient. The mineral cations of hard water combine with the soap, forming curds and reducing the soap's effectiveness The demonstration described in this Section asks you to shake a piece of common bar soap in distilled water, then add some hard tapwater to the mixture. What would you expect to see if you reversed the procedure by shaking the soap first in some hard tapwater, then adding some distilled water to the mixture? • Q U E S T 1 O N 13.10 One Solution: Water Softeners One solution to the problem caused by hard water is to remove the cations that produce the hardness. Commercial water softeners do this by trading sodium ions for the water-hardening cations-the calcium, magnesium, and iron ions-and thereby converting hard water to soft water. The typical water softener installed in a home consists of a tank contain-ing a specially prepared polymer, a storage bin for sodium chloride, and regu-lators to control the flow of water (Fig. 13.19). (Polymers are materials made of extraordinarily large molecules; Chapter 21). The polymers used in these water softeners have large numbers of anionic functional groups, which allow the polymeric molecules to hold large numbers of cations. You activate or charge the water softener by running concentrated salt water through it. The sodium ions of the salt water displace whatever cations might be on the poly-mer and stick to the polymer in the tank. Then, when hard water passes through the tank, the cations of the hard water take their turn at displacing the sodium cations from the polymer. With the exchange of calcium, magnesium, and iron ions of the hard water for the sodium ions held by the polymer, the water passing through becomes softened and the polymer eventually becomes saturated with the ions of the hard water.  From water Valve controls From recharge supply; input reservoir contains Ca 2+ FeZ+ Mgz ...-~. ~.-cations Sodium ~ chloride pellets O O D LF--iJ ~ D O O ~ ~ SOdium chloride Ion exchange ~~ solution resin I Reservoir of sodium chloride solution for recharging Valve controls To household output outlets II Softened water containing I\ a+ cations Waste water generated I ~ ~ ~ I for household use during recharge cycle, contains Ca2+, Fe~+, MgZ+ cations Because of this gradual accumulation of the ions of the hard water, the water sof-tener must be recharged with sodium ions periodically by passing salt water (formed from the sodium chloride pellets in the storage bin) through it. With the offending ions removed from the water, the sodium carboxylates-the soaps-now remain dispersed in the water and can act as effective detergents. (Resinous polymers of the kind used to replace one ion for another as a fluid passes through them are known as ion exchange resins.) What happens to the calcium, iron, and other ions of hard water that have accumu-lated on the ion exchange resin as they are replaced by sodium ions during the recharging process? Where do these cation of hard water go? 13.11 Another Solution: Synthetic Detergents  As an alternative to softening hard water, we can use a detergent that remains dis-persed even in the presence of cations that would inactivate a soap. In the 1940s chemical science and technology solved the problem of using hard water for wash-ing by devising economical, commercially useful synthetic detergents. In the most suc-cessful of these, the alkylbenzenesulfonates, a sulfonate functional group, -S03-, rather than a carboxylate group, -COZ-, acts as the hydrophilic structure: -COZ -503 a carboxylate group a sulfonate group The advantage of the sulfonate anion is the great water solubility of virtually every one of its mineral salts. Unlike soaps, alkylbenzenesulfonates remain dispersed and effective in hard water. [The term alkyl refers to the group produced by re-moval of a hydrogen atom from an alkane (Sec. 6.3). Alkyl groups we've already seen include the methyl group, CH3-, the ethyl group, CH3-CH2-, the propyl group, CH3-CHZ-CHz-, and the isopropyl group.] Since there's no simple, economical way to place a sulfonate group direct-ly onto a long hydrocarbon chain in large-scale production, commercially suc-cessful synthetic detergents don't mimic exactly the structure of a soap molecule. Some commercially feasible reactions do exist, though, that allow chemists to place both a hydrocarbon chain and a sulfonate group onto the same benzene ring (Sec. 6.11). Combining these reactions in successive steps, which lie beyond the scope of our examination, produces the synthetic alkyl-benzenesulfonate detergents. With a variety of synthetic reactions at hand, the chemist can tailor the struc-ture of a detergent molecule to specific needs. Sodium lauryl sulfate, for example, is an anionic detergent particularly suitable to toothpastes and other toiletries (Chapter 22). an alkylbenzenesulfonate anion (R represents an alkyl group in the form of a long hydrocarbon chain.) (In a sulfate an oxygen atom lies between the sulfur of the hydrophilic group and the carbon of the hydrophobic group; in a sulfonate the sulfur is bonded directly to the carbon; Fig. 13.20). Figure 13.20 Typical detergents. Anionic: Cationic: Nonionic: R - COZ Na+ A sodium R - N+- CH3 Cl-alkylcarboxylate (a soap) CH3 R ~~ ~~ S03-Na+ A sodium alkylbenezenesulfonate R-O-S03 Na  CH3-CH- CH3 CH3 An alkyl trimethylammonium chloride  13.11 Another Solution: Synthetic Detergents • 323 R-(CHZ-CHZ-O-)nH An alkyl polyethoxylate In all these structures, R represents a long carbon chain A variety of synthetic laundry detergents. A sodium An alkylpyridinium alkylsulfate chloride 324 • Chapter 13 Surfactants Anionic detergents, which make up the great bulk of all synthetic detergents, are particularly effective at cleaning fabrics that absorb water readily such as those made of natural fibers of cotton, silk, and wool. Nonionic detergents, many of which have large numbers of covalently bonded oxygens in their hydrophilic structures, are es-pecially useful in cleaning synthetic fabrics, such as polyesters (Chapter 21). Most nonionic detergents are liquids that produce little foam.They are used, along with an-ionic detergents, in formulating dishwashing liquids and liquid laundry detergents. Most cationic detergents are ammonium salts (Sec. 10.3) that also happen to be effective germicides. They're used in antiseptic soaps and mouthwashes, and also in fabric softeners since their positive charges adhere to many fabrics that normally carry negative electrical charges. Molecular structures of some typical nonionic and cationic detergents appear in Figure 13.20. • Q U E S T 1 O N What would you expect to see if you repeated the demonstration described at the end of Section 13.9, but used a synthetic detergent rather than a piece of bar soap? Explain.  13.12 What's in a Box of Detergent? Now, with our understanding of what detergents are and how they work, we can ask: What's actually in a box of laundry detergent, the kind we get off a store shelf? The answer is: A mixture of chemistry and consumerism, and of fact and fantasy. We'll observe this intermingling as we take a detailed look at its contents. Naturally, the most important ingredient of a detergent formulation is the sur-factant itself (Table 13.4). In the decades since synthetic detergents were intro-duced, the anionic alkylbenzenesulfonates have been the principal surfactants in detergent formulations. Today, though, this dominance may be shifting toward non- Table 13.4 Components of a Typical Detergent Formulation Component Example Function The ingredients in a box of Enzymes detergent. Surfactants Sodium alkylbenzenesulfonates Detergency Builders Phosphates, zeolites Soften water and increase surfactant's efficiency Fillers Sodium sulfate: Na2S04 Add to bulk of detergent and keep detergent pouring freely Corrosion Sodium silicates: Coat washer parts to inhibit inhibitors NazSi03, Na2Si205, rust Na4Si04 Suspension agents Carboxymethylcellulose Help keep dirt from (CMC) redepositing on fabrie - Remove protein stains, such as grass and blood Bleaches Perborates Remove stains Optical whiteners Fluorescent dyes Add brightness to white fabrics Add fragrance to both the detergent and fabrics Coloring agents - Add blueing effect Fragrances 13.12 What's in a Box of Detergent? • 325 ionic surfactants, such as the alkyl polyethoxylates of Figure 13.20, as the result of a growing concern for the environment. Among the environmental advantages of the nonionic detergents is their smaller need for builders, which are essentially water-softening agents. (The term builders reflects the ability of these added agents to "build up" the detergent power of the surfactant.) Although all classes of syn-thetic detergents are superior to soaps in hard water, the nonionic detergents are even more effective than the anionic detergents. With less builder needed for the nonionic detergents, their formulations can be more concentrated and their pack-ages smaller. Compact packaging decreases the amount of discarded packing ma-terial in our trash and garbage; concentration results in smaller amounts of detergents passed into the environment with the waste wash water. For many years phosphates, such as sodium tripolyphosphate, Na5P301o, seemed to be the perfect builders. Their low cost, very low toxicity, and general absence of hazard, coupled with their ability to bind firmly to the ions of hard water and thereby reduce their chemical activity, made them the leading builders. Yet phosphates suffer from one overwhelming defect: They are superb nutrients for the algae and other small plants that grow on the surfaces of lakes and streams. Algae, nourished by a steady supply of phosphates, can cover the surface of a body of water and prevent atmospheric oxygen from reaching the marine life below. The resulting death of fish and other aquatic animals, sometimes occurring on a large scale in lakes and rivers covered by algae, led many states to ban the use of phosphates as detergent builders. The most promising substitute is a class of com-pounds of aluminum, silicon, and oxygen, known as zeolites. When added to hard water as part of a commercial detergent, the sodium salts of zeolites act like ion exchange resins, exchanging their sodium ions for the ions that produce the hard-i4ess and thereby softening the water. One of the major functions of fillers, primarily sodium sulfate, NaZSOq, was to give consumers a sense that they were getting their money's worth. At one time a bulky box of detergent was seen as giving the consumer a lot of detergent for the cost. The bulk was provided principally by the added sodium sulfate (which also made the granular detergent a bit easier to pour). With increasing consumer awareness and a growing concern for the environment, the amount of filler used in a box of detergent has dropped from about 35% to 10% or, in some cases, none at all. Other ingredients include corrosion inhibitors to protect the machinery that agitates the wash; suspension agents to help keep the grease, dirt, and grime in suspension so they don't redeposit on the fabrics; enzymes to help decompose pro teins of blood, grass, and other difficult stains; and oxygen-containing bleaches to help remove stains. All of these contribute to the surfactant's ability to produce a clean product. Some of the remaining ingredients may add more to the appearance of a clean wash than to its reality. Optical whiteners are organic compounds that coat the fabrics and convert the invisible ultraviolet component of sunlight (Secs.14.8 and 22.13) into an almost imperceptible blue tint. The effect of this blue tint, which can also be produced by blue coloring agents added to the detergent, is to add a bit of brilliance to white fabrics and give them the appearance of extra cleanli-ness. Finally, added perfumes and fragrances produce what many regard as a pleas-ant odor in the finished wash. Why were phosphates originally added to detergent formulations? Why were they • Q U E S T I O N subsequently removed? 320 • Chapterl3 Surfactants Table 13.3 Common Fatty Acids of Soap Structure and Name CH3-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-COZH Caprylic acid CH3-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHz-CHz-COZH Capric acid CH3-CHz-CHz-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-COZH Lauric acid CH3-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHZ-CH2-CHZ-CHZ-COZH Myristic acid CH~-CHZ-CH,-CHZ-CHZ-CHZ-CHz-CHZ-CHz-CHz-CH2-CHZ-CHz-CHZ-CHz-COZH Palmitic acid CH3-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CH2-CH2-CHZ-COZH Stearic acid ~3-(~2)~ ~=~-(~Zh-~zH Oleic acid ~3-(~2>4-~=~-~2-~=cx-(~z)~-co2x Linoleic acid CH2-O-C-R CHZ-OH R-C-O-Na+ II H O I II CH-O-CO-R' + 3 NaOH Heat ~ CH-OH + R'-CO-O-Na+ I I „- II - - + CHZ-OH R C O Na Glycerol Soaps CHZ-O-C-R" A triglyceride    Figure 13.18 The saponification of a triglyceride. n of CH3-(CH2)„-C02H 6 10 12 14 16 • Q U E S T 1 O N What part of their chemical structures is common to all triglycerides? How do the chemical structures of the various triglycerides differ from each other?  13.9 A Problem: Hard Water As we saw in Section 9.11, the drinking water of many regions contains various min-erals, dissolved in slightly acidic rainwater as it filters through the soil. Water that's rich in the salts of calcium, magnesium, and/or iron is called hard water. (Soft water, on the other hand, is virtually free of these minerals.) The mineral cations of hard water combine with fatty acid anions and remove them from water as waxy, in-soluble salts. In regions where the water is particularly hard, you can actually see these precipitates deposited as gray rings, known as curd, or soap curd, around bathtubs and sinks after washing with soap. This curd is made up of the calcium, magnesium, and/or iron salts of the fatty acids of soap: 13.10 One Solution: Water Softeners • 321 2CH3-(CHZ)n-COZ-+Na + Ca2+ -~ CH3-(CHZ)n-COZ-Ca2+-OZC-(CHZ)n-CH3 + 2Na+ curd, or calcitam soap (the ring that forms around the bathtub in regions with hard water) Hard water wastes soap because much of the soap that would otherwise be used in cleaning is consumed in curd formation as it reacts with the mineral ions of hard water. In hard water, a certain amount of soap has to be used up initially in combining with the mineral cations and removing all of them from solution be-fore additional soap can act effectively as a detergent. What's more, this curd de-posits on the surface of laundered clothes, dulling the cloth and giving washed goods a slightly gray appearance. You can see the effect of hard water on soap by first shaking up some soap in distilled water. A piece of common bar soap will do nicely for this demonstration, but laundry detergent won't work for reasons we'll come to soon. Distilled water, which you can get in a supermarket or convenience store, is free of the mineral ions of hard water and generates a good deal of suds with the soap. Now add some hard tapwater to the sudsy mixture or, if you live in an area of soft water, add about a tablespoon of milk, which contains considerable calcium. (Skim milk also works well, as does a solution of an antacid that contains calcium.) The suds van-ish as you stir the hard water or the milk into the soapy water because the fatty acid anions are converted into their insoluble calcium salts. You'll probably be able to see the curd swirling in the water.  Soap forms rich suds in soft water. In hard water soap is less efficient. The mineral cations of hard water combine with the soap, forming curds and reducing the soap's effectiveness The demonstration described in this Section asks you to shake a piece of common bar soap in distilled water, then add some hard tapwater to the mixture. What would you expect to see if you reversed the procedure by shaking the soap first in some hard tapwater, then adding some distilled water to the mixture? • Q U E S T 1 O N 13.10 One Solution: Water Softeners One solution to the problem caused by hard water is to remove the cations that produce the hardness. Commercial water softeners do this by trading sodium ions for the water-hardening cations-the calcium, magnesium, and iron ions-and thereby converting hard water to soft water. The typical water softener installed in a home consists of a tank contain-ing a specially prepared polymer, a storage bin for sodium chloride, and regu-lators to control the flow of water (Fig. 13.19). (Polymers are materials made of extraordinarily large molecules; Chapter 21). The polymers used in these water softeners have large numbers of anionic functional groups, which allow the polymeric molecules to hold large numbers of cations. You activate or charge the water softener by running concentrated salt water through it. The sodium ions of the salt water displace whatever cations might be on the poly-mer and stick to the polymer in the tank. Then, when hard water passes through the tank, the cations of the hard water take their turn at displacing the sodium cations from the polymer. With the exchange of calcium, magnesium, and iron ions of the hard water for the sodium ions held by the polymer, the water passing through becomes softened and the polymer eventually becomes saturated with the ions of the hard water.  From water Valve controls From recharge supply; input reservoir contains Ca 2+ FeZ+ Mgz ...-~. ~.-cations Sodium ~ chloride pellets O O D LF--iJ ~ D O O ~ ~ SOdium chloride Ion exchange ~~ solution resin I Reservoir of sodium chloride solution for recharging Valve controls To household output outlets II Softened water containing I\ a+ cations Waste water generated I ~ ~ ~ I for household use during recharge cycle, contains Ca2+, Fe~+, MgZ+ cations Because of this gradual accumulation of the ions of the hard water, the water sof-tener must be recharged with sodium ions periodically by passing salt water (formed from the sodium chloride pellets in the storage bin) through it. With the offending ions removed from the water, the sodium carboxylates-the soaps-now remain dispersed in the water and can act as effective detergents. (Resinous polymers of the kind used to replace one ion for another as a fluid passes through them are known as ion exchange resins.) What happens to the calcium, iron, and other ions of hard water that have accumu-lated on the ion exchange resin as they are replaced by sodium ions during the recharging process? Where do these cation of hard water go? 13.11 Another Solution: Synthetic Detergents  As an alternative to softening hard water, we can use a detergent that remains dis-persed even in the presence of cations that would inactivate a soap. In the 1940s chemical science and technology solved the problem of using hard water for wash-ing by devising economical, commercially useful synthetic detergents. In the most suc-cessful of these, the alkylbenzenesulfonates, a sulfonate functional group, -S03-, rather than a carboxylate group, -COZ-, acts as the hydrophilic structure: -COZ -503 a carboxylate group a sulfonate group The advantage of the sulfonate anion is the great water solubility of virtually every one of its mineral salts. Unlike soaps, alkylbenzenesulfonates remain dispersed and effective in hard water. [The term alkyl refers to the group produced by re-moval of a hydrogen atom from an alkane (Sec. 6.3). Alkyl groups we've already seen include the methyl group, CH3-, the ethyl group, CH3-CH2-, the propyl group, CH3-CHZ-CHz-, and the isopropyl group.] Since there's no simple, economical way to place a sulfonate group direct-ly onto a long hydrocarbon chain in large-scale production, commercially suc-cessful synthetic detergents don't mimic exactly the structure of a soap molecule. Some commercially feasible reactions do exist, though, that allow chemists to place both a hydrocarbon chain and a sulfonate group onto the same benzene ring (Sec. 6.11). Combining these reactions in successive steps, which lie beyond the scope of our examination, produces the synthetic alkyl-benzenesulfonate detergents. With a variety of synthetic reactions at hand, the chemist can tailor the struc-ture of a detergent molecule to specific needs. Sodium lauryl sulfate, for example, is an anionic detergent particularly suitable to toothpastes and other toiletries (Chapter 22). an alkylbenzenesulfonate anion (R represents an alkyl group in the form of a long hydrocarbon chain.) (In a sulfate an oxygen atom lies between the sulfur of the hydrophilic group and the carbon of the hydrophobic group; in a sulfonate the sulfur is bonded directly to the carbon; Fig. 13.20). Figure 13.20 Typical detergents. Anionic: Cationic: Nonionic: R - COZ Na+ A sodium R - N+- CH3 Cl-alkylcarboxylate (a soap) CH3 R ~~ ~~ S03-Na+ A sodium alkylbenezenesulfonate R-O-S03 Na  CH3-CH- CH3 CH3 An alkyl trimethylammonium chloride 13.11 Another Solution: Synthetic Detergents • 323 R-(CHZ-CHZ-O-)nH An alkyl polyethoxylate In all these structures, R represents a long carbon chain A variety of synthetic laundry detergents. A sodium An alkylpyridinium alkylsulfate chloride 324 • Chapter 13 Surfactants Anionic detergents, which make up the great bulk of all synthetic detergents, are particularly effective at cleaning fabrics that absorb water readily, such as those made of natural fibers of cotton, silk, and wool. Nonionic detergents, many of which have large numbers of covalently bonded oxygens in their hydrophilic structures, are es-pecially useful in cleaning synthetic fabrics, such as polyesters (Chapter 21). Most nonionic detergents are liquids that produce little foam. They are used, along with an-ionic detergents, in formulating dishwashing liquids and liquid laundry detergents. Most cationic detergents are ammonium salts (Sec. 10.3) that also happen to be effective germicides. They're used in antiseptic soaps and mouthwashes, and also in fabric softeners since their positive charges adhere to many fabrics that normally carry negative electrical charges. Molecular structures of some typical nonionic and cationic detergents appear in Figure 13.20.  • Q U E S T 1 O N What would you expect to see if you repeated the demonstration described at the end of Section 13.9, but used a synthetic detergent rather than a piece of bar soap? Explain.  13.12 What's in a Box of Detergent? Now, with our understanding of what detergents are and how they work, we can ask: What's actually in a box of laundry detergent, the kind we get off a store shelf? The answer is: A mixture of chemistry and consumerism, and of fact and fantasy. We'll observe this intermingling as we take a detailed look at its contents. Naturally, the most important ingredient of a detergent formulation is the sur-factant itself (Table 13.4). In the decades since synthetic detergents were intro-duced, the anionic alkylbenzenesulfonates have been the principal surfactants in detergent formulations. Today, though, this dominance may be shifting toward non- Table 13.4 Components of a Typical Detergent Formulation Component Example Function The ingredients in a box of Enzymes detergent. Surfactants Sodium alkylbenzenesulfonates Detergency Builders Phosphates, zeolites Soften water and increase surfactant's efficiency Fillers Sodium sulfate: Na2S04 Add to bulk of detergent and keep detergent pouring freely Corrosion Sodium silicates: Coat washer parts to inhibit inhibitors NazSi03, Na2Si205, rust Na4Si04 Suspension agents Carboxymethylcellulose Help keep dirt from (CMC) redepositing on fabric - Remove protein stains, such as grass and blood Bleaches Perborates Remove stains Optical whiteners Fluorescent dyes Add brightness to white fabrics Add fragrance to both the detergent and fabrics Coloring agents - Add blueing effect Fragrances 13.12 What's in a Box of Detergent? • 325 ionic surfactants, such as the alkyl polyethoxylates of Figure 13.20, as the result of a growing concern for the environment. Among the environmental advantages of the nonionic detergents is their smaller need for builders, which are essentially water-softening agents. (The term builders reflects the ability of these added agents to "build up" the detergent power of the surfactant.) Although all classes of syn-thetic detergents are superior to soaps in hard water, the nonionic detergents are even more effective than the anionic detergents. With less builder needed for the nonionic detergents, their formulations can be more concentrated and their pack-ages smaller. Compact packaging decreases the amount of discarded packing ma-terial in our trash and garbage; concentration results in smaller amounts of detergents passed into the environment with the waste wash water. For many years phosphates, such as sodium tripolyphosphate, Na5P301o, seemed to be the perfect builders. Their low cost, very low toxicity, and general absence of hazard, coupled with their ability to bind firmly to the ions of hard water and thereby reduce their chemical activity, made them the leading builders. Yet phosphates suffer from one overwhelming defect: They are superb nutrients for the algae and other small plants that grow on the surfaces of lakes and streams. Algae, nourished by a steady supply of phosphates, can cover the surface of a body of water and prevent atmospheric oxygen from reaching the marine life below. The resulting death of fish and other aquatic animals, sometimes occurring on a large scale in lakes and rivers covered by algae, led many states to ban the use of phosphates as detergent builders. The most promising substitute is a class of com-pounds of aluminum, silicon, and oxygen, known as zeolites. When added to hard water as part of a commercial detergent, the sodium salts of zeolites act like ion exchange resins, exchanging their sodium ions for the ions that produce the hard-i4ess and thereby softening the water. One of the major functions of fillers, primarily sodium sulfate, NaZSOq, was to give consumers a sense that they were getting their money's worth. At one time a bulky box of detergent was seen as giving the consumer a lot of detergent for the cost. The bulk was provided principally by the added sodium sulfate (which also made the granular detergent a bit easier to pour). With increasing consumer awareness and a growing concern for the environment, the amount of filler used in a box of detergent has dropped from about 35% to 10% or, in some cases, none at all. Other ingredients include corrosion inhibitors to protect the machinery that agitates the wash; suspension agents to help keep the grease, dirt, and grime in suspension so they don't redeposit on the fabrics; enzymes to help decompose pro teins of blood, grass, and other difficult stains; and oxygen-containing bleaches to help remove stains. All of these contribute to the surfactant's ability to produce a clean product. Some of the remaining ingredients may add more to the appearance of a clean wash than to its reality. Optical whiteners are organic compounds that coat the fabrics and convert the invisible ultraviolet component of sunlight (Secs.14.8 and 22.13) into an almost imperceptible blue tint. The effect of this blue tint, which can also be produced by blue coloring agents added to the detergent, is to add a bit of brilliance to white fabrics and give them the appearance of extra cleanli-ness. Finally, added perfumes and fragrances produce what many regard as a pleas-ant odor in the finished wash. Why were phosphates originally added to detergent formulations? Why were they • Q U E S T I O N subsequently removed? 320 • Chapterl3 Surfactants Table 13.3 Common Fatty Acids of Soap Structure and Name CH3-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-COZH Caprylic acid CH3-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHz-CHz-COZH Capric acid CH3-CHz-CHz-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-COZH Lauric acid CH3-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHZ-CH2-CHZ-CHZ-COZH Myristic acid CH~-CHZ-CH,-CHZ-CHZ-CHZ-CHz-CHZ-CHz-CHz-CH2-CHZ-CHz-CHZ-CHz-COZH Palmitic acid CH3-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CH2-CH2-CHZ-COZH Stearic acid ~3-(~2)~ ~=~-(~Zh-~zH Oleic acid ~3-(~2>4-~=~-~2-~=cx-(~z)~-co2x Linoleic acid CH2-O-C-R CHZ-OH R-C-O-Na+ II H O I II CH-O-CO-R' + 3 NaOH Heat ~ CH-OH + R'-CO-O-Na+ I I „- II - - + CHZ-OH R C O Na Glycerol Soaps CHZ-O-C-R" A triglyceride    Figure 13.18 The saponification of a triglyceride. n of CH3-(CH2)„-C02H 6 10 12 14 16 • Q U E S T 1 O N What part of their chemical structures is common to all triglycerides? How do the chemical structures of the various triglycerides differ from each other?  13.9 A Problem: Hard Water As we saw in Section 9.11, the drinking water of many regions contains various min-erals, dissolved in slightly acidic rainwater as it filters through the soil. Water that's rich in the salts of calcium, magnesium, and/or iron is called hard water. (Soft water, on the other hand, is virtually free of these minerals.) The mineral cations of hard water combine with fatty acid anions and remove them from water as waxy, in-soluble salts. In regions where the water is particularly hard, you can actually see these precipitates deposited as gray rings, known as curd, or soap curd, around bathtubs and sinks after washing with soap. This curd is made up of the calcium, magnesium, and/or iron salts of the fatty acids of soap: 13.10 One Solution: Water Softeners • 321 2CH3-(CHZ)n-COZ-+Na + Ca 2+ -~ CH3-(CHZ)n-COZ-Ca2+-02C-(CHZ)n-CH3 + 2Na+ curd, or calcium soap (the ring that forms around the bathtub in regions with hard water) Hard water wastes soap because much of the soap that would otherwise be used in cleaning is consumed in curd formation as it reacts with the mineral ions of hard water. In hard water, a certain amount of soap has to be used up initially in combining with the mineral cations and removing all of them from solution be-fore additional soap can act effectively as a detergent. What's more, this curd de-posits on the surface of laundered clothes, dulling the cloth and giving washed goods a slightly gray appearance. You can see the effect of hard water on soap by first shaking up some soap in distilled water. A piece of common bar soap will do nicely for this demonstration, but laundry detergent won't work for reasons we'll come to soon. Distilled water, which you can get in a supermarket or convenience store, is free of the mineral ions of hard water and generates a good deal of suds with the soap. Now add some hard tapwater to the sudsy mixture or, if you live in an area of soft water, add about a tablespoon of milk, which contains considerable calcium. (Skim milk also works well, as does a solution of an antacid that contains calcium.) The suds van-ish as you stir the hard water or the milk into the soapy water because the fatty acid anions are converted into their insoluble calcium salts. You'll probably be able to see the curd swirling in the water.  Soap forms rich suds in soft water. In hard water soap is less efficient. The mineral cations of hard water combine with the soap, forming curds and reducing the soap's effectiveness The demonstration described in this Section asks you to shake a piece of common bar soap in distilled water, then add some hard tapwater to the mixture. What would you expect to see if you reversed the procedure by shaking the soap first in some hard tapwater, then adding some distilled water to the mixture? • Q U E S T 1 O N 13.10 One Solution: Water Softeners One solution to the problem caused by hard water is to remove the cations that produce the hardness. Commercial water softeners do this by trading sodium ions for the water-hardening cations-the calcium, magnesium, and iron ions-and thereby converting hard water to soft water. The typical water softener installed in a home consists of a tank containing a specially prepared polymer, a storage bin for sodium chloride, and regu-lators to control the flow of water (Fig. 13.19). (Polymers are materials made of extraordinarily large molecules; Chapter 21). The polymers used in these water softeners have large numbers of anionic functional groups, which allow the polymeric molecules to hold large numbers of cations. You activate or charge the water softener by running concentrated salt water through it. From water Valve controls From recharge supply; input reservoir contains Ca 2+ FeZ+ Mgz ...-~. ~.-cations Sodium ~ chloride pellets O O D LF--iJ ~ D O O ~ ~ SOdium chloride Ion exchange ~~ solution resin I Reservoir of sodium chloride solution for recharging Valve controls To household output outlets II Softened water containing I\ a+ cations Waste water generated I ~ ~ ~ I for household use during recharge cycle, contains Ca2+, Fe~+, MgZ+ cations Because of this gradual accumulation of the ions of the hard water, the water sof-tener must be recharged with sodium ions periodically by passing salt water (formed from the sodium chloride pellets in the storage bin) through it. With the offending ions removed from the water, the sodium carboxylates-the soaps-now remain dispersed in the water and can act as effective detergents. (Resinous polymers of the kind used to replace one ion for another as a fluid passes through them are known as ion exchange resins.) What happens to the calcium, iron, and other ions of hard water that have accumu-lated on the ion exchange resin as they are replaced by sodium ions during the recharging process? Where do these cation of hard water go? 13.11 Another Solution: Synthetic Detergents  As an alternative to softening hard water, we can use a detergent that remains dis-persed even in the presence of cations that would inactivate a soap. In the 1940s chemical science and technology solved the problem of using hard water for wash-ing by devising economical, commercially useful synthetic detergents. In the most suc-cessful of these, the alkylbenzenesulfonates, a sulfonate functional group, -S03-, rather than a carboxylate group, -COZ-, acts as the hydrophilic structure: -COZ -503 a carboxylate group a sulfonate group The advantage of the sulfonate anion is the great water solubility of virtually every one of its mineral salts. Unlike soaps, alkylbenzenesulfonates remain dispersed and effective in hard water. [The term alkyl refers to the group produced by re-moval of a hydrogen atom from an alkane (Sec. 6.3). Alkyl groups we've already seen include the methyl group, CH3-, the ethyl group, CH3-CH2-, the propyl group, CH3-CHZ-CHz-, and the isopropyl group.] Since there's no simple, economical way to place a sulfonate group direct-ly onto a long hydrocarbon chain in large-scale production, commercially suc-cessful synthetic detergents don't mimic exactly the structure of a soap molecule. Some commercially feasible reactions do exist, though, that allow chemists to place both a hydrocarbon chain and a sulfonate group onto the same benzene ring (Sec. 6.11). Combining these reactions in successive steps, which lie beyond the scope of our examination, produces the synthetic alkyl-benzenesulfonate detergents. With a variety of synthetic reactions at hand, the chemist can tailor the struc-ture of a detergent molecule to specific needs. Sodium lauryl sulfate, for example, is an anionic detergent particularly suitable to toothpastes and other toiletries (Chapter 22). an alkylbenzenesulfonate anion R represents an alkyl group in the form of a long hydrocarbon chain. (In a sulfate an oxygen atom lies between the sulfur of the hydrophilic group and the carbon of the hydrophobic group; in a sulfonate the sulfur is bonded directly to the carbon; Fig. 13.20). Figure 13.20 Typical detergents. Anionic: Cationic: Nonionic: R - C02- Na+ A sodium R - N+- CH3 Cl-alkylcarboxylate (a soap) CH3 R -(I '\~_ S03-Na+ A sodium alkylbenezenesulfonate R-O-S03 Na R_/\_S03_ CH3-CH- CH3 CH3 An alkyl trimethylammonium chloride  13.11 Another Solution: Synthetic Detergents • 323 R-(CHZ-CHZ-O-),H An alkyl polyethoxylate In all these structures, R represents a long carbon chain  A variety of synthetic laundry detergents.     A sodium An alkylpyridinium alkylsulfate chloride 324 • Chapter 13 Surfactants Anionic detergents, which make up the great bulk of all synthetic detergents, are particularly effective at cleaning fabrics that absorb water readily, such as those made of natural fibers of cotton, silk, and wool. Nonionic detergents, many of which have large numbers of covalently bonded oxygens in their hydrophilic structures, are es-pecially useful in cleaning synthetic fabrics, such as polyesters (Chapter 21). Most nonionic detergents are liquids that produce little foam. They are used, along with an-ionic detergents, in formulating dishwashing liquids and liquid laundry detergents. Most cationic detergents are ammonium salts (Sec. 10.3) that also happen to be effective germicides. They're used in antiseptic soaps and mouthwashes, and also in fabric softeners since their positive charges adhere to many fabrics that normally carry negative electrical charges. Molecular structures of some typical nonionic and cationic detergents appear in Figure 13.20.  • Q U E S T 1 O N What would you expect to see if you repeated the demonstration described at the end of Section 13.9, but used a synthetic detergent rather than a piece of bar soap? Explain.  13.12 What's in a Box of Detergent? Now, with our understanding of what detergents are and how they work, we can ask: What's actually in a box of laundry detergent, the kind we get off a store shelf? The answer is: A mixture of chemistry and consumerism, and of fact and fantasy. We'll observe this intermingling as we take a detailed look at its contents. Naturally, the most important ingredient of a detergent formulation is the sur-factant itself (Table 13.4). In the decades since synthetic detergents were intro-duced, the anionic alkylbenzenesulfonates have been the principal surfactants in detergent formulations. Today, though, this dominance may be shifting toward non- Table 13.4 Components of a Typical Detergent Formulation Component Example Function The ingredients in a box of Enzymes detergent. Surfactants Sodium alkylbenzenesulfonates Detergency Builders Phosphates, zeolites Soften water and increase surfactant's efficiency Fillers Sodium sulfate: Na2S04 Add to bulk of detergent and keep detergent pouring freely Corrosion Sodium silicates: Coat washer parts to inhibit inhibitors NazSi03, Na2Si205, rust Na4Si04 Suspension agents Carboxymethylcellulose Help keep dirt from (CMC) redepositing on fabric - Remove protein stains, such as grass and blood Bleaches Perborates Remove stains Optical whiteners Fluorescent dyes Add brightness to white fabrics Add fragrance to both the detergent and fabrics Coloring agents - Add blueing effect Fragrances 13.12 What's in a Box of Detergent? • 325 ionic surfactants, such as the alkyl polyethoxylates of Figure 13.20, as the result of a growing concern for the environment. Among the environmental advantages of the nonionic detergents is their smaller need for builders, which are essentially water-softening agents. (The term builders reflects the ability of these added agents to "build up" the detergent power of the surfactant.) Although all classes of syn-thetic detergents are superior to soaps in hard water, the nonionic detergents are even more effective than the anionic detergents. With less builder needed for the nonionic detergents, their formulations can be more concentrated and their pack-ages smaller. Compact packaging decreases the amount of discarded packing ma-terial in our trash and garbage; concentration results in smaller amounts of detergents passed into the environment with the waste wash water. For many years phosphates, such as sodium tripolyphosphate, Na5P301o, seemed to be the perfect builders. Their low cost, very low toxicity, and general absence of hazard, coupled with their ability to bind firmly to the ions of hard water and thereby reduce their chemical activity, made them the leading builders. Yet phosphates suffer from one overwhelming defect: They are superb nutrients for the algae and other small plants that grow on the surfaces of lakes and streams. Algae, nourished by a steady supply of phosphates, can cover the surface of a body of water and prevent atmospheric oxygen from reaching the marine life below. The resulting death of fish and other aquatic animals, sometimes occurring on a large scale in lakes and rivers covered by algae, led many states to ban the use of phosphates as detergent builders. The most promising substitute is a class of com-pounds of aluminum, silicon, and oxygen, known as zeolites. When added to hard water as part of a commercial detergent, the sodium salts of zeolites act like ion exchange resins, exchanging their sodium ions for the ions that produce the hard-i4ess and thereby softening the water. One of the major functions of fillers, primarily sodium sulfate, NaZSOq, was to give consumers a sense that they were getting their money's worth. At one time a bulky box of detergent was seen as giving the consumer a lot of detergent for the cost. The bulk was provided principally by the added sodium sulfate (which also made the granular detergent a bit easier to pour). With increasing consumer awareness and a growing concern for the environment, the amount of filler used in a box of detergent has dropped from about 35% to 10% or, in some cases, none at all. Other ingredients include corrosion inhibitors to protect the machinery that agitates the wash; suspension agents to help keep the grease, dirt, and grime in suspension so they don't redeposit on the fabrics; enzymes to help decompose pro teins of blood, grass, and other difficult stains; and oxygen-containing bleaches to help remove stains. All of these contribute to the surfactant's ability to produce a clean product. Some of the remaining ingredients may add more to the appearance of a clean wash than to its reality. Optical whiteners are organic compounds that coat the fabrics and convert the invisible ultraviolet component of sunlight (Secs.14.8 and 22.13) into an almost imperceptible blue tint. The effect of this blue tint, which can also be produced by blue coloring agents added to the detergent, is to add a bit of brilliance to white fabrics and give them the appearance of extra cleanli-ness. Finally, added perfumes and fragrances produce what many regard as a pleas-ant odor in the finished wash. Why were phosphates originally added to detergent formulations? Why were they • Q U E S T I O N subsequently removed? 320 • Chapterl3 Surfactants Table 13.3 Common Fatty Acids of Soap Structure and Name CH3-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-COZH Caprylic acid CH3-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHz-CHz-COZH Capric acid CH3 Myristic acid Palmitic acid COZH Stearic acid ~3-(~2)~ ~=~-(~Zh-~zH Oleic acid ~3-(~2>4-~=~-~2-~=cx-(~z)~-co2x Linoleic acid CH2-O-C-R CHZ-OH R-C-O-Na+ II H O I II CH-O-CO-R' + 3 NaOH Heat ~ CH-OH + R'-CO-O-Na+ I I „- II - - + CHZ-OH R C O Na Glycerol Soaps CHZ-O-C-R" A triglyceride    Figure 13.18 The saponification of a triglyceride. n of CH3-(CH2)„-C02H 6 10 12 14 16 •QUESTION What part of their chemical structures is common to all triglycerides? How do the chemical structures of the various triglycerides differ from each other? 13.9 A Problem: Hard Water The drinking water of many regions contains various min-erals, dissolved in slightly acidic rainwater as it filters through the soil. Water that's rich in the salts of calcium, magnesium, and/or iron is called hard water. (Soft water, on the other hand, is virtually free of these minerals.) The mineral cations of hard water combine with fatty acid anions and remove them from water as waxy, in-soluble salts. In regions where the water is particularly hard, you can actually see these precipitates deposited as gray rings, known as curd, or soap curd, around bathtubs and sinks after washing with soap. This curd is made up of the calcium, magnesium, and/or iron salts of the fatty acids of soap: 13.10 One Solution: Water Softeners • 321 2CH3-(CHZ)n-COZ-+Na + Ca 2+ -~ CH3-(CHZ)n-COZ-Ca2+-02C-(CHZ)n-CH3 + 2Na+ curd, or calcium soap (the ring that forms around the bathtub in regions with hard water) Hard water wastes soap because much of the soap that would otherwise be used in cleaning is consumed in curd formation as it reacts with the mineral ions of hard water. In hard water, a certain amount of soap has to be used up initially in combining with the mineral cations and removing all of them from solution be-fore additional soap can act effectively as a detergent. What's more, this curd de-posits on the surface of laundered clothes, dulling the cloth and giving washed goods a slightly gray appearance. You can see the effect of hard water on soap by first shaking up some soap in distilled water. A piece of common bar soap will do nicely for this demonstration, but laundry detergent won't work for reasons we'll come to soon. Distilled water, which you can get in a supermarket or convenience store, is free of the mineral ions of hard water and generates a good deal of suds with the soap. Now add some hard tapwater to the sudsy mixture or, if you live in an area of soft water, add about a tablespoon of milk, which contains considerable calcium. (Skim milk also works well, as does a solution of an antacid that contains calcium.) The suds van-ish as you stir the hard water or the milk into the soapy water because the fatty acid anions are converted into their insoluble calcium salts. You'll probably be able to see the curd swirling in the water. Soap forms rich suds in soft water. In hard water soap is less efficient. The mineral cations of hard water combine with the soap, forming curds and reducing the soap's effectiveness The demonstration described in this Section asks you to shake a piece of common bar soap in distilled water, then add some hard tapwater to the mixture. What would you expect to see if you reversed the procedure by shaking the soap first in some hard tapwater, then adding some distilled water to the mixture? • Q U E S T 1 O N 13.10 One Solution: Water Softeners One solution to the problem caused by hard water is to remove the cations that produce the hardness. Commercial water softeners do this by trading sodium ions for the water-hardening cations-the calcium, magnesium, and iron ions-and thereby converting hard water to soft water. The typical water softener installed in a home consists of a tank contain-ing a specially prepared polymer, a storage bin for sodium chloride, and regu-lators to control the flow of water (Fig. 13.19). (Polymers are materials made of extraordinarily large molecules; Chapter 21). The polymers used in these water softeners have large numbers of anionic functional groups, which allow the polymeric molecules to hold large numbers of cations. You activate or charge the water softener by running concentrated salt water through it. The sodium ions of the salt water displace whatever cations might be on the poly-mer and stick to the polymer in the tank. Then, when hard water passes through the tank, the cations of the hard water take their turn at displacing the sodium cations from the polymer. With the exchange of calcium, magnesium, and iron ions of the hard water for the sodium ions held by the polymer, the water passing through becomes softened and the polymer eventually becomes saturated with the ions of the hard water.  From water Valve controls From recharge supply; input reservoir contains Ca 2+ FeZ+ Mgz ...-~. ~.-cations Sodium ~ chloride pellets O O D LF--iJ ~ D O O ~ ~ SOdium chloride Ion exchange ~~ solution resin I Reservoir of sodium chloride solution for recharging Valve controls To household output outlets II Softened water containing I\ a+ cations Waste water generated I ~ ~ ~ I for household use during recharge cycle, contains Ca2+, Fe~+, MgZ+ cations Because of this gradual accumulation of the ions of the hard water, the water sof-tener must be recharged with sodium ions periodically by passing salt water (formed from the sodium chloride pellets in the storage bin) through it. With the offending ions removed from the water, the sodium carboxylates-the soaps-now remain dispersed in the water and can act as effective detergents. (Resinous polymers of the kind used to replace one ion for another as a fluid passes through them are known as ion exchange resins.) What happens to the calcium, iron, and other ions of hard water that have accumu-lated on the ion exchange resin as they are replaced by sodium ions during the recharging process? Where do these cation of hard water go? 13.11 Another Solution: Synthetic Detergents  As an alternative to softening hard water, we can use a detergent that remains dis-persed even in the presence of cations that would inactivate a soap. In the 1940s chemical science and technology solved the problem of using hard water for wash-ing by devising economical, commercially useful synthetic detergents. In the most suc-cessful of these, the alkylbenzenesulfonates, a sulfonate functional group, -S03-, rather than a carboxylate group, -COZ-, acts as the hydrophilic structure: -COZ -503 a carboxylate group a sulfonate group The advantage of the sulfonate anion is the great water solubility of virtually every one of its mineral salts. Unlike soaps, alkylbenzenesulfonates remain dispersed and effective in hard water. [The term alkyl refers to the group produced by re-moval of a hydrogen atom from an alkane (Sec. 6.3). Alkyl groups we've already seen include the methyl group, CH3-, the ethyl group, CH3-CH2-, the propyl group, CH3-CHZ-CHz-, and the isopropyl group.] Since there's no simple, economical way to place a sulfonate group direct-ly onto a long hydrocarbon chain in large-scale production, commercially suc-cessful synthetic detergents don't mimic exactly the structure of a soap molecule. Some commercially feasible reactions do exist, though, that allow chemists to place both a hydrocarbon chain and a sulfonate group onto the same benzene ring (Sec. 6.11). Combining these reactions in successive steps, which lie beyond the scope of our examination, produces the synthetic alkyl-benzenesulfonate detergents. With a variety of synthetic reactions at hand, the chemist can tailor the struc-ture of a detergent molecule to specific needs. Sodium lauryl sulfate, for example, is an anionic detergent particularly suitable to toothpastes and other toiletries (Chapter 22). an alkylbenzenesulfonate anion (R represents an alkyl group in the form of a long hydrocarbon chain.) (In a sulfate an oxygen atom lies between the sulfur of the hydrophilic group and the carbon of the hydrophobic group; in a sulfonate the sulfur is bonded directly to the carbon; Fig. 13.20). Figure 13.20 Typical detergents. Anionic: Cationic: Nonionic: R - COZ Na+ A sodium R - N+- CH3 Cl-alkylcarboxylate (a soap) CH3 R ~~ ~~ S03-Na+ A sodium alkylbenezenesulfonate R-O-S03 Na  CH3-CH- CH3 CH3 An alkyl trimethylammonium chloride  13.11 Another Solution: Synthetic Detergents • 323 R-(CHZ-CHZ-O-)nH An alkyl polyethoxylate In all these structures, R represents a long carbon chain  A variety of synthetic laundry detergents.     A sodium An alkylpyridinium alkylsulfate chloride 324 • Chapter 13 Surfactants Anionic detergents, which make up the great bulk of all synthetic detergents, are particularly effective at cleaning fabrics that absorb water readily such as those made of natural fibers of cotton, silk, and wool. Nonionic detergents, many of which have large numbers of covalently bonded oxygens in their hydrophilic structures, are es-pecially useful in cleaning synthetic fabrics, such as polyesters (Chapter 21). Most nonionic detergents are liquids that produce little foam.They are used, along with an-ionic detergents, in formulating dishwashing liquids and liquid laundry detergents. Most cationic detergents are ammonium salts (Sec. 10.3) that also happen to be effective germicides. They're used in antiseptic soaps and mouthwashes, and also in fabric softeners since their positive charges adhere to many fabrics that normally carry negative electrical charges. Molecular structures of some typical nonionic and cationic detergents appear in Figure 13.20.  • Q U E S T 1 O N What would you expect to see if you repeated the demonstration described at the end of Section 13.9, but used a synthetic detergent rather than a piece of bar soap? Explain.  13.12 What's in a Box of Detergent? Now, with our understanding of what detergents are and how they work, we can ask: What's actually in a box of laundry detergent, the kind we get off a store shelf? The answer is: A mixture of chemistry and consumerism, and of fact and fantasy. We'll observe this intermingling as we take a detailed look at its contents. Naturally, the most important ingredient of a detergent formulation is the sur-factant itself (Table 13.4). In the decades since synthetic detergents were intro-duced, the anionic alkylbenzenesulfonates have been the principal surfactants in detergent formulations. Today, though, this dominance may be shifting toward non- Table 13.4 Components of a Typical Detergent Formulation Component Example Function The ingredients in a box of Enzymes detergent. Surfactants Sodium alkylbenzenesulfonates Detergency Builders Phosphates, zeolites Soften water and increase surfactant's efficiency Fillers Sodium sulfate: Na2S04 Add to bulk of detergent and keep detergent pouring freely Corrosion Sodium silicates: Coat washer parts to inhibit inhibitors NazSi03, Na2Si205, rust Na4Si04 Suspension agents Carboxymethylcellulose Help keep dirt from (CMC) redepositing on fabrie - Remove protein stains, such as grass and blood Bleaches Perborates Remove stains Optical whiteners Fluorescent dyes Add brightness to white fabrics Add fragrance to both the detergent and fabrics Coloring agents - Add blueing effect Fragrances 13.12 What's in a Box of Detergent? • 325 ionic surfactants, such as the alkyl polyethoxylates of Figure 13.20, as the result of a growing concern for the environment. Among the environmental advantages of the nonionic detergents is their smaller need for builders, which are essentially water-softening agents. (The term builders reflects the ability of these added agents to "build up" the detergent power of the surfactant.) Although all classes of syn-thetic detergents are superior to soaps in hard water, the nonionic detergents are even more effective than the anionic detergents. With less builder needed for the nonionic detergents, their formulations can be more concentrated and their pack-ages smaller. Compact packaging decreases the amount of discarded packing ma-terial in our trash and garbage; concentration results in smaller amounts of detergents passed into the environment with the waste wash water. For many years phosphates, such as sodium tripolyphosphate, Na5P301o, seemed to be the perfect builders. Their low cost, very low toxicity, and general absence of hazard, coupled with their ability to bind firmly to the ions of hard water and thereby reduce their chemical activity, made them the leading builders. Yet phosphates suffer from one overwhelming defect: They are superb nutrients for the algae and other small plants that grow on the surfaces of lakes and streams. Algae, nourished by a steady supply of phosphates, can cover the surface of a body of water and prevent atmospheric oxygen from reaching the marine life below. The resulting death of fish and other aquatic animals, sometimes occurring on a large scale in lakes and rivers covered by algae, led many states to ban the use of phosphates as detergent builders. The most promising substitute is a class of com-pounds of aluminum, silicon, and oxygen, known as zeolites. When added to hard water as part of a commercial detergent, the sodium salts of zeolites act like ion exchange resins, exchanging their sodium ions for the ions that produce the hard-i4ess and thereby softening the water. One of the major functions of fillers, primarily sodium sulfate, NaZSOq, was to give consumers a sense that they were getting their money's worth. At one time a bulky box of detergent was seen as giving the consumer a lot of detergent for the cost. The bulk was provided principally by the added sodium sulfate (which also made the granular detergent a bit easier to pour). With increasing consumer awareness and a growing concern for the environment, the amount of filler used in a box of detergent has dropped from about 35% to 10% or, in some cases, none at all. Other ingredients include corrosion inhibitors to protect the machinery that agitates the wash; suspension agents to help keep the grease, dirt, and grime in suspension so they don't redeposit on the fabrics; enzymes to help decompose pro teins of blood, grass, and other difficult stains; and oxygen-containing bleaches to help remove stains. All of these contribute to the surfactant's ability to produce a clean product. Some of the remaining ingredients may add more to the appearance of a clean wash than to its reality. Optical whiteners are organic compounds that coat the fabrics and convert the invisible ultraviolet component of sunlight (Secs.14.8 and 22.13) into an almost imperceptible blue tint. The effect of this blue tint, which can also be produced by blue coloring agents added to the detergent, is to add a bit of brilliance to white fabrics and give them the appearance of extra cleanli-ness. Finally, added perfumes and fragrances produce what many regard as a pleas-ant odor in the finished wash. Why were phosphates originally added to detergent formulations? Why were they • Q U E S T I O N subsequently removed? 320 • Chapterl3 Surfactants Table 13.3 Common Fatty Acids of Soap Structure and Name CH3-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-COZH Caprylic acid CH3-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHz-CHz-COZH Capric acid CH3-CHz-CHz-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-COZH Lauric acid CH3-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHZ-CH2-CHZ-CHZ-COZH Myristic acid CH~-CHZ-CH,-CHZ-CHZ-CHZ-CHz-CHZ-CHz-CHz-CH2-CHZ-CHz-CHZ-CHz-COZH Palmitic acid CH3-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-CHz-CH2-CH2-CHZ-COZH Stearic acid ~3-(~2)~ ~=~-(~Zh-~zH Oleic acid ~3-(~2>4-~=~-~2-~=cx-(~z)~-co2x Linoleic acid CH2-O-C-R CHZ-OH R-C-O-Na+ II H O I II CH-O-CO-R' + 3 NaOH Heat ~ CH-OH + R'-CO-O-Na+ I I „- II - - + CHZ-OH R C O Na Glycerol Soaps CHZ-O-C-R" A triglyceride    Figure 13.18 The saponification of a triglyceride. n of CH3-(CH2)„-C02H 6 10 12 14 16 • Q U E S T 1 O N What part of their chemical structures is common to all triglycerides? How do the chemical structures of the various triglycerides differ from each other?  13.9 A Problem: Hard Water As we saw in Section 9.11, the drinking water of many regions contains various min-erals, dissolved in slightly acidic rainwater as it filters through the soil. Water that's rich in the salts of calcium, magnesium, and/or iron is called hard water. (Soft water, on the other hand, is virtually free of these minerals.) The mineral cations of hard water combine with fatty acid anions and remove them from water as waxy, in-soluble salts. In regions where the water is particularly hard, you can actually see these precipitates deposited as gray rings, known as curd, or soap curd, around bathtubs and sinks after washing with soap. This curd is made up of the calcium, magnesium, and/or iron salts of the fatty acids of soap: 13.10 One Solution: Water Softeners • 321 2CH3-(CHZ)n-COZ-+Na + Ca 2+ -~ CH3-(CHZ)n-COZ-Ca2+-02C-(CHZ)n-CH3 + 2Na+ curd, or calcium soap (the ring that forms around the bathtub in regions with hard water) Hard water wastes soap because much of the soap that would otherwise be used in cleaning is consumed in curd formation as it reacts with the mineral ions of hard water. In hard water, a certain amount of soap has to be used up initially in combining with the mineral cations and removing all of them from solution be-fore additional soap can act effectively as a detergent. What's more, this curd de-posits on the surface of laundered clothes, dulling the cloth and giving washed goods a slightly gray appearance. You can see the effect of hard water on soap by first shaking up some soap in distilled water. A piece of common bar soap will do nicely for this demonstration, but laundry detergent won't work for reasons we'll come to soon. Distilled water, which you can get in a supermarket or convenience store, is free of the mineral ions of hard water and generates a good deal of suds with the soap. Now add some hard tapwater to the sudsy mixture or, if you live in an area of soft water, add about a tablespoon of milk, which contains considerable calcium. (Skim milk also works well, as does a solution of an antacid that contains calcium.) The suds van-ish as you stir the hard water or the milk into the soapy water because the fatty acid anions are converted into their insoluble calcium salts. You'll probably be able to see the curd swirling in the water.  Soap forms rich suds in soft water. In hard water soap is less efficient. The mineral cations of hard water combine with the soap, forming curds and reducing the soap's effectiveness The demonstration described in this Section asks you to shake a piece of common bar soap in distilled water, then add some hard tapwater to the mixture. What would you expect to see if you reversed the procedure by shaking the soap first in some hard tapwater, then adding some distilled water to the mixture? • Q U E S T 1 O N 13.10 One Solution: Water Softeners One solution to the problem caused by hard water is to remove the cations that produce the hardness. Commercial water softeners do this by trading sodium ions for the water-hardening cations-the calcium, magnesium, and iron ions-and thereby converting hard water to soft water. The typical water softener installed in a home consists of a tank contain-ing a specially prepared polymer, a storage bin for sodium chloride, and regu-lators to control the flow of water (Fig. 13.19). (Polymers are materials made of extraordinarily large molecules; Chapter 21). The polymers used in these water softeners have large numbers of anionic functional groups, which allow the polymeric molecules to hold large numbers of cations. You activate or charge the water softener by running concentrated salt water through it. The sodium ions of the salt water displace whatever cations might be on the poly-mer and stick to the polymer in the tank. Then, when hard water passes through the tank, the cations of the hard water take their turn at displacing the sodium cations from the polymer. With the exchange of calcium, magnesium, and iron ions of the hard water for the sodium ions held by the polymer, the water passing through becomes softened and the polymer eventually becomes saturated with the ions of the hard water.  From water Valve controls From recharge supply; input reservoir contains Ca 2+ FeZ+ Mgz ...-~. ~.-cations Sodium ~ chloride pellets O O D LF--iJ ~ D O O ~ ~ SOdium chloride Ion exchange ~~ solution resin I Reservoir of sodium chloride solution for recharging Valve controls To household output outlets II Softened water containing I\ a+ cations Waste water generated I ~ ~ ~ I for household use during recharge cycle, contains Ca2+, Fe~+, MgZ+ cations Because of this gradual accumulation of the ions of the hard water, the water sof-tener must be recharged with sodium ions periodically by passing salt water (formed from the sodium chloride pellets in the storage bin) through it. With the offending ions removed from the water, the sodium carboxylates-the soaps-now remain dispersed in the water and can act as effective detergents. (Resinous polymers of the kind used to replace one ion for another as a fluid passes through them are known as ion exchange resins.) What happens to the calcium, iron, and other ions of hard water that have accumu-lated on the ion exchange resin as they are replaced by sodium ions during the recharging process? Where do these cation of hard water go? 13.11 Another Solution: Synthetic Detergents  As an alternative to softening hard water, we can use a detergent that remains dis-persed even in the presence of cations that would inactivate a soap. In the 1940s chemical science and technology solved the problem of using hard water for wash-ing by devising economical, commercially useful synthetic detergents. In the most suc-cessful of these, the alkylbenzenesulfonates, a sulfonate functional group, -S03-, rather than a carboxylate group, -COZ-, acts as the hydrophilic structure: -CO2 -503 a carboxylate group a sulfonate group The advantage of the sulfonate anion is the great water solubility of virtually every one of its mineral salts. Unlike soaps, alkylbenzenesulfonates remain dispersed and effective in hard water. [The term alkyl refers to the group produced by re-moval of a hydrogen atom from an alkane (Sec. 6.3). Alkyl groups we've already seen include the methyl group, CH3-, the ethyl group, CH3-CH2-, the propyl group, CH3-CHZ-CHz-, and the isopropyl group.] Since there's no simple, economical way to place a sulfonate group direct-ly onto a long hydrocarbon chain in large-scale production, commercially successful synthetic detergents don't mimic exactly the structure of a soap molecule. an alkylbenzenesulfonate anion (R represents an alkyl group in the form of a long hydrocarbon chain.) (In a sulfate an oxygen atom lies between the sulfur of the hydrophilic group and the carbon of the hydrophobic group; in a sulfonate the sulfur is bonded directly to the carbon; Fig. 13.20). Figure 13.20 Typical detergents. Anionic: Cationic: Nonionic: R - COZ Na+ A sodium R - N+- CH3 Cl-alkylcarboxylate (a soap) CH3 R ~~ ~~ S03-Na+ A sodium alkylbenezenesulfonate R-O-S03 Na CH3-CH- CH3 CH3 An alkyl trimethylammonium chloride 13.11 Another Solution: Synthetic Detergents • 323 R-(CHZ-CHZ-O-)nH An alkyl polyethoxylate In all these structures, R represents a long carbon chain A variety of synthetic laundry detergents. A sodium An alkylpyridinium alkylsulfate chloride 324 • Chapter 13 Surfactants Anionic detergents, which make up the great bulk of all synthetic detergents, are particularly effective at cleaning fabrics that absorb water readily, such as those made of natural fibers of cotton, silk, and wool. Nonionic detergents, many of which have large numbers of covalently bonded oxygens in their hydrophilic structures, are es-pecially useful in cleaning synthetic fabrics, such as polyesters (Chapter 21). Most nonionic detergents are liquids that produce little foam. They are used, along with an-ionic detergents, in formulating dishwashing liquids and liquid laundry detergents. Most cationic detergents are ammonium salts (Sec. 10.3) that also happen to be effective germicides. They're used in antiseptic soaps and mouthwashes, and also in fabric softeners since their positive charges adhere to many fabrics that normally carry negative electrical charges. Molecular structures of some typical nonionic and cationic detergents appear in Figure 13.20. •QUEST1ON What would you expect to see if you repeated the demonstration described at the end of Section 13.9, but used a synthetic detergent rather than a piece of bar soap? Explain. 13.12 What's in a Box of Detergent? Now, with our understanding of what detergents are and how they work, we can ask: What's actually in a box of laundry detergent, the kind we get off a store shelf? The answer is: A mixture of chemistry and consumerism, and of fact and fantasy. We'll observe this intermingling as we take a detailed look at its contents. Naturally, the most important ingredient of a detergent formulation is the sur-factant itself (Table 13.4). In the decades since synthetic detergents were intro-duced, the anionic alkylbenzenesulfonates have been the principal surfactants in detergent formulations. Today, though, this dominance may be shifting toward non- Table 13.4 Components of a Typical Detergent Formulation Component Example Function The ingredients in a box of Enzymes detergent. Surfactants Sodium alkylbenzenesulfonates Detergency Builders Phosphates, zeolites Soften water and increase surfactant's efficiency Fillers Sodium sulfate: Na2S04 Add to bulk of detergent and keep detergent pouring freely Corrosion Sodium silicates: Coat washer parts to inhibit inhibitors NazSi03, Na2Si205, rust Na4Si04 Suspension agents Carboxymethylcellulose Help keep dirt from (CMC) redepositing on fabric - Remove protein stains, such as grass and blood Bleaches Perborates Remove stains Optical whiteners Fluorescent dyes Add brightness to white fabrics Add fragrance to both the detergent and fabrics Coloring agents - Add blueing effect Fragrances 13.12 What's in a Box of Detergent? • 325 ionic surfactants, such as the alkyl polyethoxylates of Figure 13.20, as the result of a growing concern for the environment. Among the environmental advantages of the nonionic detergents is their smaller need for builders, which are essentially water-softening agents. (The term builders reflects the ability of these added agents to "build up" the detergent power of the surfactant.) Although all classes of syn-thetic detergents are superior to soaps in hard water, the nonionic detergents are even more effective than the anionic detergents. With less builder needed for the nonionic detergents, their formulations can be more concentrated and their pack-ages smaller. Compact packaging decreases the amount of discarded packing ma-terial in our trash and garbage; concentration results in smaller amounts of detergents passed into the environment with the waste wash water. For many years phosphates, such as sodium tripolyphosphate, Na5P301o, seemed to be the perfect builders. Their low cost, very low toxicity, and general absence of hazard, coupled with their ability to bind firmly to the ions of hard water and thereby reduce their chemical activity, made them the leading builders. Yet phosphates suffer from one overwhelming defect: They are superb nutrients for the algae and other small plants that grow on the surfaces of lakes and streams. Algae, nourished by a steady supply of phosphates, can cover the surface of a body of water and prevent atmospheric oxygen from reaching the marine life below. The resulting death of fish and other aquatic animals, sometimes occurring on a large scale in lakes and rivers covered by algae, led many states to ban the use of phosphates as detergent builders. The most promising substitute i s a class of com-pounds of aluminum, silicon, and oxygen, known as zeolites. When added to hard water as part of a commercial detergent, the sodium salts of zeolites act like ion exchange resins, exchanging their sodium ions for the ions that produce the hard-i4ess and thereby softening the water. One of the major functions of fillers, primarily sodium sulfate, NaZSOq, was to give consumers a sense that they were getting their money's worth. At one time a bulky box of detergent was seen as giving the consumer a lot of detergent for the cost. The bulk was provided principally by the added sodium sulfate (which also made the granular detergent a bit easier to pour). With increasing consumer awareness and a growing concern for the environment, the amount of filler used in a box of detergent has dropped from about 35% to 10% or, in some cases, none at all. Other ingredients include corrosion inhibitors to protect the machinery that agitates the wash; suspension agents to help keep the grease, dirt, and grime in suspension so they don't redeposit on the fabrics; enzymes to help decompose pro teins of blood, grass, and other difficult stains; and oxygen-containing bleaches to help remove stains. All of these contribute to the surfactant's ability to produce a clean product. Some of the remaining ingredients may add more to the appearance of a clean wash than to its reality. Optical whiteners are organic compounds that coat the fabrics and convert the invisible ultraviolet component of sunlight (Secs.14.8 and 22.13) into an almost imperceptible blue tint. The effect of this blue tint, which can also be produced by blue coloring agents added to the detergent, is to add a bit of brilliance to white fabrics and give them the appearance of extra cleanli-ness. Finally, added perfumes and fragrances produce what many regard as a pleas-ant odor in the finished wash. Why were phosphates originally added to detergent formulations? Why were they • QUESTION subsequently removed? 324 • Chapter 13 Surfactants Anionic detergents, which make up the great bulk of all synthetic detergents, are particularly effective at cleaning fabrics that absorb water readily such as those made of natural fibers of cotton, silk, and wool. Nonionic detergents, many of which have large numbers of covalently bonded oxygens in their hydrophilic structures, are es-pecially useful in cleaning synthetic fabrics, such as polyesters (Chapter 21). Most nonionic detergents are liquids that produce little foam.They are used, along with an-ionic detergents, in formulating dishwashing liquids and liquid laundry detergents. Most cationic detergents are ammonium salts (Sec. 10.3) that also happen to be effective germicides. They're used in antiseptic soaps and mouthwashes, and also in fabric softeners since their positive charges adhere to many fabrics that normally carry negative electrical charges. Molecular structures of some typical nonionic and cationic detergents appear in Figure 13.20.  • Q U E S T 1 O N What would you expect to see if you repeated the demonstration described at the end of Section 13.9, but used a synthetic detergent rather than a piece of bar soap? Explain.  13.12 What's in a Box of Detergent? Now, with our understanding of what detergents are and how they work, we can ask: What's actually in a box of laundry detergent, the kind we get off a store shelf? The answer is: A mixture of chemistry and consumerism, and of fact and fantasy. We'll observe this intermingling as we take a detailed look at its contents. Naturally, the most important ingredient of a detergent formulation is the sur-factant itself (Table 13.4). In the decades since synthetic detergents were intro-duced, the anionic alkylbenzenesulfonates have been the principal surfactants in detergent formulations. Today, though, this dominance may be shifting toward non- Table 13.4 Components of a Typical Detergent Formulation Component Example Function The ingredients in a box of Enzymes detergent. Surfactants Sodium alkylbenzenesulfonates Detergency Builders Phosphates, zeolites Soften water and increase surfactant's efficiency Fillers Sodium sulfate: Na2S04 Add to bulk of detergent and keep detergent pouring freely Corrosion Sodium silicates: Coat washer parts to inhibit inhibitors NazSi03, Na2Si205, rust Na4Si04 Suspension agents Carboxymethylcellulose Help keep dirt from (CMC) redepositing on fabrie - Remove protein stains, such as grass and blood Bleaches Perborates Remove stains Optical whiteners Fluorescent dyes Add brightness to white fabrics Add fragrance to both the detergent and fabrics Coloring agents - Add blueing effect Fragrances 13.12 What's in a Box of Detergent? • 325 ionic surfactants, such as the alkyl polyethoxylates of Figure 13.20, as the result of a growing concern for the environment. Among the environmental advantages of the nonionic detergents is their smaller need for builders, which are essentially water-softening agents. (The term builders reflects the ability of these added agents to "build up" the detergent power of the surfactant.) Although all classes of syn-thetic detergents are superior to soaps in hard water, the nonionic detergents are even more effective than the anionic detergents. With less builder needed for the nonionic detergents, their formulations can be more concentrated and their packages smaller. Compact packaging decreases the amount of discarded packing ma-terial in our trash and garbage; concentration results in smaller amounts of detergents passed into the environment with the waste wash water. For many years phosphates, such as sodium tripolyphosphate, Na5P301o, seemed to be the perfect builders. Their low cost, very low toxicity, and general absence of hazard, coupled with their ability to bind firmly to the ions of hard water and thereby reduce their chemical activity, made them the leading builders. Yet phosphates suffer from one overwhelming defect: They are superb nutrients for the algae and other small plants that grow on the surfaces of lakes and streams. Algae, nourished by a steady supply of phosphates, can cover the surface of a body of water and prevent atmospheric oxygen from reaching the marine life below. The resulting death of fish and other aquatic animals, sometimes occurring on a large scale in lakes and rivers covered by algae, led many states to ban the use of phosphates as detergent builders. The most promising substitute is a class of com-pounds of aluminum, silicon, and oxygen, known as zeolites. When added to hard water as part of a commercial detergent, the sodium salts of zeolites act like ion exchange resins, exchanging their sodium ions for the ions that produce the hard-i4ess and thereby softening the water. One of the major functions of fillers, primarily sodium sulfate, NaZSOq, was to give consumers a sense that they were getting their money's worth. At one time a bulky box of detergent was seen as giving the consumer a lot of detergent for the cost. The bulk was provided principally by the added sodium sulfate (which also made the granular detergent a bit easier to pour). With increasing consumer awareness and a growing concern for the environment, the amount of filler used in a box of detergent has dropped from about 35% to 10% or, in some cases, none at all. Other ingredients include corrosion inhibitors to protect the machinery that agitates the wash; suspension agents to help keep the grease, dirt, and grime in suspension so they don't redeposit on the fabrics; enzymes to help decompose pro teins of blood, grass, and other difficult stains; and oxygen-containing bleaches to help remove stains. All of these contribute to the surfactant's ability to produce a clean product. Some of the remaining ingredients may add more to the appearance of a clean wash than to its reality. Optical whiteners are organic compounds that coat the fabrics and convert the invisible ultraviolet component of sunlight (Secs.14.8 and 22.13) into an almost imperceptible blue tint. The effect of this blue tint, which can also be produced by blue coloring agents added to the detergent, is to add a bit of brilliance to white fabrics and give them the appearance of extra cleanliness. Finally, added perfumes and fragrances produce what many regard as a pleas-ant odor in the finished wash. QUESTION Why were phosphates originally added to detergent formulations? Why were they • subsequently removed? 326 • Chapter 13 Surfactants 13.13 A Return to the Dropping Tack We can see now that the opening demonstration summarizes much of the chemistry of this chapter. Even though the tack is more dense than water, it remains on the surface, held up by the surface tension that results from the strong at-tractive forces among the water molecules at the surface. When you add the de-tergent, its molecules gather at the surface, with their hydrophilic heads among the water molecules and their hydrophobic tails pointed upward, away from the water. As the detergent disperses among the water molecules at the surface, its molecules disrupt the attractive forces among them, producing a sharp drop in the surface tension. With decreasing surface tension, the density of the tack becomes the controlling factor and the tack drops. We've also seen that this same surfactant effect enhances the cleaning action of soaps and synthetic detergents. R S P E C T Where Do Detergents Belong?  Although this chapter focuses on soaps and detergents and the chemistry that makes them work, you can find an-other, more subtle theme as well. As you progress through the discussion of surface tension, surfactants, micelles, and the like, and into their applications in com-mercial detergents, you may find that the borders be-tween pure chemistry and applied chemistry (Chapter 12, Perspective) occasionally grow dim and perhaps vanish in places. The same holds true for the sometimes arbitrary divisions among the various branches of chemistry, such as organic and inorganic chemistry, and even be-tween chemistry itself and other sciences, including bi-ology, geology, and physics. For example, it's usually reasonable to define chem-istry as the science that examines the composition and properties of matter and the changes it can undergo, as we did in Section 1.2. In a similar vein, we might also hold that the science of physics deals (in part) with studies of the forces of attraction and repulsion between bodies. According to this view, then, a discussion of the forces that hold molecules close to each other in a liquid, and that cause them to interact more strongly at a liquid's surface than in its interior-and that produce the phenomenon of surface tension-belongs more properly to physics than to chemistry. Yet without an appreciation of how these forces act, the chemistry of a detergent doesn't make much sense. The border between these two areas of science grows less distinct in the study of detergents. • , Again, it's possible to maintain that since detergent molecules contain such large numbers of carbon atoms, their study rests more appropriately within an examina tion of organic compounds.Yet without understanding the effects of such inorganic cations as Ca2+, Mg2+, Fe2+, and Na+ on both soaps and anionic detergents, it's difficult to understand the effects of hard water on soaps and de-tergents. Moreover, organic detergents act within the confines of water, a fully inorganic solvent. Here again, the border drawn between two regions of chemistry seems to vanish. Finally, it might seem that a study of commercial soaps and synthetic detergents, a set of widely used consumer products, certainly involves an examination of applied chemistry.Yet without an understanding of the fundamental science behind the properties of surfaces and micelles, the reactions of esters, the process of ion exchange, and a host of other structures, reactions, and phenomena, the box of detergent you find on your grocer's shelf might not even exist. One of the themes of this chapter, then, is that while it's often convenient and sometimes necessary to divide science into a variety of arbitrary categories, our com prehension of the universe we live in cannot be limited by the boundaries we draw. They are borders and divi-sions that we ourselves construct and that we ourselves can and must remove when they obstruct our larger view of our universe. • 380 • Chapter 15 Fats and Oils sodium chloride and sucrose. Nevertheless, short-range intermolecular attractive forces within the solid and semisolid triglycerides do hold their molecules together tightly, in a compact, somewhat orderly arrangement. These are the same sort of forces that bind together, for example, the large alkane molecules of candle wax, and they depend on the ability of the hydrocarbon chains to pack snugly against each other. All this gives us liquid triglycerides, the oils (Fig. 15.9). 15.8 The Omega Acids • 381 Glyceryl tristearate; chains are packed closely Figure 15.9 Molecular packing in glyceryl tristearate and glyceryl trioleate. Polyunsaturation increases the space occupied by fatty acid side chains, causing polyunsaturated triglyceride molecules to lie farther from each other than molecules with more fully saturated side chains. This increased distance of separation decreases the attractive forces the polyunsaturated molecules exert on each other and lowers the melting points of polyunsaturated triglycerides. Glyceryl trioleate; double bonds prevent close packing For clarity, only the center chain is shown fully form of serum cholesterol, the LDL, which we'll examine in Section 17.10. In the next section we'll find that, in addition to its geometry, the location of the double bond within the chain also has implications for human health.  CH CH CH Why does the hydrogenation of a polyunsaturated triglyceride raise its melting point? • QUESTION 15.8 The Omega Acids We use the fatty acids of triglycerides not only as a source of biochemical energy, but also as raw material for many of our bodies' physical structures and biochemical catalysts, including cellular membranes and the hormones that regulate a host of bodily functions. In generating these substances from our food chemicals, we can produce almost all of the necessary modifications ourselves, converting one molecular structure into another or joining several into larger, more complex forms. We're often flexible in our approach. If we find a needed molecular structure among our food's nutrients, we use it. If not, we generate it from other compo-nents of our foods. But there are some chemicals our bodies simply don't have the ability to create, including the molecular structures of linoleic acid and linolenic acid (Table 15.1), the essential fatty acids of human nutrition. We can't generate either linoleic acid or linqlenic acid by modifying the molecular structures of other fatty $83 • Chapter 15 Fats and Oils The essential fatty acids are the fatty acids our bodies can-not synthesize from other chemicals and that we must obtain from our foods. acids. Both linoleic and linolenic acid must be present in the foods we eat. Because we can't produce either of them by our own bodily processes, not even from close-ly related acids, we label these two critical acids as essential fatty acids-essential because they must be part of our diets. Linoleic and linolenic acids are members of two more general categories of fatty acids critical to human well-being, the omega-3 and the omega-6 fatty acids. The defining characteristic of these categories is the location of the C=C double bond most remote from the carbonyl carbon (Sec. 10.8). In dealing with these groups of acids, it's particularly convenient to label the carbons of the fatty acid chain with Greek letters. We identify the first carbon beyond the carbonyl group with the first letter of the Greek alphabet. It becomes the ซ (alpha) carbon. The second is the R (beta) carbon, the third is the y (gamma), etc. If we're considering a set of acids with long chains of various lengths and we're inter-ested in a structural feature near the most remote carbon- the one farthest from the carbonyl group-we can label that most remote carbon with the letter that's in a parallel location in the Greek alphabet, at the end: (o. That methyl group at the end of the chain becomes the omega carbon, regardless of the length of the chain: O CH3-CHZ-CHZ-CHZ- -CHZ-CHZ-CH2-C-OH W Y R ซ Working backward from the methyl group at the end of the chain, with its omega carbon, the C=C double bond of linolenic acid begins at the third carbon from the end. Reflecting this, linolenic acid is a member of the omega-3 group of fatty acids. Similarly linoleic acid is an omega-6 fatty acid: CH3-CHZ-CH=CH-- - --CHZ-COZH the two ends of linolenic acid, an omega-3 fatty acid CH3-CHZ-CHZ-CHZ-CHZ-CH=CH-- - --CHZ-COZH the two ends of linoleic acid, an omega-6 fatty acid In the same sense that the Perspective of each chapter is the terminal, or omega, section, regardless of the chapter's length, the methyl group of each fatty acid con-tains its omega carbon, regardless of the chain's length. • Q U E S T 1 O N Considering the Perspective as the terminal section of this chapter, what omega designation would you give to this current section? 15.9 Storing Energy: Adipose Tissue In Chapter 8 we saw that the sun serves as the ultimate source of our bodily en-ergy. Photosynthetic reactions convert the sun's radiant energy into the chemical energy of plant nutrients. When we eat these plants, or products of the animals that feed on them, we convert this nutrient, chemical energy into our own biolog-ical energy. Yet although we expend biological energy constantly, we don't replenish it constantly. In the Energy Equation of Section 8.8,  Energy In = Energy Out + Energy Stored 384 • Chapter 15 Fats and Oils Converting an excess of a macronutrient into body fat and then converting this fat into energy later, when we need it, is a particularly effective means of long-term en-ergy storage. With a gram of carbohydrate or protein providing only about 44 % (four ninths; Sec. 8.10) of the amount of energy of a gram of fat, storing excess energy in the form of either carbohydrates or proteins would raise our bulk and weight considerably and make us far less mobile. The high energy density of fat-its ability to store energy compactly in relatively little space and with relatively little weight compared with car-bohydrates and proteins-allows us to carry our stores of energy with us. It gives us and other animals the mobility and freedom necessary for survival in a world that was, and can still be, unforgiving to those poorly equipped for survival. • Q U E S T 1 O N Suppose you're 15 pounds overweight. That is, you are carrying around, at all times, an excess of 15 pounds of adipose tissue. Translate this into the equivalent number of excess stored Calories you are carrying with you at all times. PERSPECTIVE - Fats and OiIs:The Perfect Examples carbon-carbon double bonds. Obesity is linked to both high blood pressure vide the raw materials for major industries. and diabetes. Dietary fat is implicated in heart disease Fats and oils are also substances that work both for and some forms of cancer. The connection among dietary andagainst life and good health.We'vealready seen, forex- fat, cholesterol, and atherosclerosis is well established ample, that body fat stores energy for us so that if we fast, (Sec. 15.4). Although several health and scientific or- miss a meal, or even sleep through a particularly long night, ganizations recommend that we obtain a maximum of 30% : we still have the energy to breathe and to keep our hearts of our dietary calories from fats and oils, an average of beating. Our adipose tissue also forms cushioning shields about 37% of our calories now come from these triglyc- . around our major organs, protecting them against damage erides. This tissue also provides thermal cancer don't provide proof of a cause-and-effect rela- insulation to our bodies, guarding against a rapid loss of tionship, cutting fatty calories to well below 30% of our body heat to the external environment. total caloric intake seems desirable. Fats also carry the flavors and vitamins of many of our Fats and oils provide us with almost perfect examples foods. Although fats have no flavors of their own, many of of the chemical basis of our everyday world; of the risks, the substances that do add flavor and enjoyment to eating hazards, and benefits in chemicals; of the contrast between are far more soluble in fats than in the more watery sub- the benefits that can be derived from moderate amounts of stances of food. The fat in meat, for example, carries the a particular chemical and the damage that can be done by 15.9 Storing Energy: Adipose Tissue • 383 'The body stores energy as the triglycerides of fat or adipose tissue. our Energy Out is continuous-through basal metabolism even while we're sleeping and virtuously continuous exercise of various intensities throughout our waking hours-but Energy In is far from continuous. Several hours normally elapse between meals, sometimes with vigorous exercise. In fact, it's possible to fast for many days yet still have the energy to do most of the things we normally do. Very little of the energy we expend as exercise comes immediately from the food we eat, and what does often goes largely toward specific dynamic action and a portion of our basal metabolism. If we didn't store the unused chemical energy of our food-if the only meta-bolic energy available to us and to our ancestors were the energy immediately available from the macronutrients of a recent meal none of us would be alive today. The human race would have vanished eons ago as a result of mass starva-tion. Without some means for storing energy in the body, a temporary and minor shortage of the animals hunted by our cave-dwelling ancestors or a brief scarcity of the grains, fruits, or vegetables they ate would have been catastrophic; it would have wiped out the human race. Even now, with food in plentiful supply and continuously available in many regions of the world, energy storage within our bodies is literally a matter of life and death. Our hearts, lungs, and other vital organs would run out of energy between meals, even as we sleep, if it were not for our body's ability to store the excess fuel of each meal and then use that stored fuel to provide a continuous supply of ener-gy between meals. The principal mode of long-term energy storage available to our ancestors and to us operates through the formation, storage, and metabolism of body fat. (Short-term energy storage, usually from one meal to another, occurs through a starchlike substance called glycogen, which we'll examine in Chapter 16.) We can think of body fat as stored energy. The body converts much of the unused carbohydrates, proteins, and triglycerides that make up our macronutrients into small globules of fat that end up in the specialized cells of adipose tissue, the fatty tissue of the body. One pound of adipose tissue stores (and provides when needed) roughly 3500 Cal of energy. Adipose tissue is the fatty tissue of the body. It stores chemical energy at about 3500 Cal/pound. How to Tell a Potato from an Apple, the Hard Way Figure 16.1 The color produced by an iodine solution distinguishes the starch of a potato from the cellulose of an apple. The iodine turns blue-black with starch but remains reddish brown with cellulose. You can tell a potato from an apple by smelling or tasting them. Of course, you could just look at them. But there's a harder way to do it. It's more fun, too. The interior pulp of an apple looks very much like the interior pulp of a potato. They're both pale and appear to have the same consistency. If you slice out a piece of the interior of a raw potato and an apple it's hard to see any difference between them. But announce that you can tell which is the section of an apple and which is the section of a potato with-out smelling, tasting, or touching either one. Leave the room while a friend cuts out a piece of a raw potato and a similar piece of an apple a ripe Delicious apple works well and places them on a small dish, side by side, without any skin or other identifying characteristics on either one. ,'  Now return to the room with a small bottle of tincture of iodine, the kind used for demonstrations in earlier chapters. Put a few drops of iodine on each. When the iodine contacts the potato it turns a very dark purple, nearly black, as you can see in Figure 16.1. While the apple might show a few small, dark spots too, for the most part the iodine on the apple retains the same reddish-brown color it produces on skin when it's used on a cut. The piece that turns almost black is the potato; the one that's mostly reddish brown is the apple. Why? We'll soon learn the secret. In this chapter we'll examine carbohydrates, the second of the three classes of macronutrients. carbohydrates form the digestible sugars and starches of our food and an indigestible component of our diet we call fiber. We'll also learn of two new classes of organic compounds-aldehydes and ketones-and we'll find a new , form of isomerism that produces the same kind of differences in the shapes of molecules that we see in our right and left hands. • Glucose also supplies the energy that keeps 16.4 Glucose:AnAldohexose • 391 Table 16.1 Common Carbohydrates Monosaccharide(s) Molecular Source or Produced on Carbohydrate Formula Origin Hydrolysis Monosaccharide Glucose (also known as blood sugar, Blood, plant sap, fruit, honey grape sugar, and dextrose) C6H12O6 Fructose (also known as levulose) C6H12O6 Plants, fruit, honey Galactose C6H12O6 From the hydrolysis of lactose Disaccharide Sucrose (also known as table sugar, beet sugar, and cane sugar) Maltose (also known as malt sugar) Cellobiose Lactose (also known as milk sugar) Sugar cane, sugar beets, maple syrup, Glucose and and various fruits and vegetables fructose Partial hydrolysis of starch Glucose Partial hydrolysis of cellulose Glucose Makes up about 5 % of milk Glucose and galactose Polysaccharide Starch Potatoes, corn, various grains Glucose Cellulose Cell walls of plants Glucose skeletons, the more complex carbohydrate chains of polysaccharides can be clipped easily by breaking the carbon-oxygen bonds that hold them together. Water does the job nicely through hydrolysis, especially if there's a little acid and perhaps a spe-cific enzyme present. We'll have more to say about the catalytic action of enzymes in Section 16.12. Table 16.1 presents some of the more common carbohydrates, their common names, and some of their chemical characteristics. Give the chemical names of two: (a) monosaccharides; (b) disaccharides; • Q U E S T I O N (c) polysaccharides. t 16.4 Glucose: An Aldohexose It's useful to classify the monosaccharides themselves according to • the lengths of their carbon chains, and • which one of two important functional groups they contain. We'll take the matter of chain lengths first. A monosaccharide with a molecular skeleton three carbons long is a triose. The suffix -ose tells us that we are dealing with a carbohydrate, while the prefix tri- indicates the number of carbons, three in this case. A tetrose is a four-carbon monosaccharide, a pentose contains five carbons, a hexose has six. The -ose ending of these names comes from the word glucose, which was itself adopted as a chemical term in 1838, by a committee of French sci-entists, from a Greek word for fermenting fruit juice or sweet wine, or simply for the quality of sweetness. 392 • Chapter 16 Carbohydrates As for their functional groups, all common monosaccharides consist of a chain of carbons in which all but one are bonded to a hydroxyl group (C-OH). The single exception is a carbon doubly bonded to an oxygen, thereby forming a carbonyl group (Sec.10.8). O  carbonyl group The two atoms (other than the oxygen) that are bonded directly to the car-bonyl carbon determine whether it is part of an aldehyde or a ketone. In An aldehyde contains a caraldehydes, at least one of the substituents on the carbonyl carbon is a hydrogen. bonyl group bonded to at least Glucose contains just such a functional group. Among the simpler aldehydes one hydrogen. are formaldehyde (in which both substituents are hydrogens), acetaldehyde, and benzaldehyde. O O O H-C-H CH3-C-H C-H formaldehyde acetaldehyde benzaldehyde Formaldehyde is a water-soluble gas. A 37 % solution in water, known as for-" ~ ""'""ฐ malin, is an effective biological preservative and is used in preparing embalming fluids. Benzaldehyde, also known as oil of bitter almond, is useful as a food fla-voring and is a ingredient of many perfumes. A ketone contains a carbonyl In a ketone, both of the atoms bonded to the carbonyl carbon are carbons. group bonded to two carbon Typical simple ketones include the solvents acetone and methyl ethyl ketone. atoms. (Methyl ethyl ketone, which is known commercially as MEK, also has the more for-mal, chemical name, 2-butanone.) Both acetone and methyl ethyl ketone are liq-uids at room temperature. Acetone serves as the major solvent in some nail polish removers. (You can usually find it listed among the ingredients on the label.) Methyl ethyl ketone is a common component of nail polish, nail polish removers, and commercial paint thinners and removers. O CH3-C-CH3 CH3-C-CHZ-CH3 The solvent acetone is a major component of nail polish remover. acetone methyl ethyl ketone or 2-butanone All common monosaccharides contain one or the other of these two car-bonyl groups. They are either polyhydroxy aldehydes or polyhydroxy ketones, or compounds very closely resembling polyhydroxy aldehydes and ketones. (The poly- of polyhydroxy reflects the presence of many hydroxyl groups on the molecular structure.) Monosaccharides with an aldehydic carbonyl group are the aldoses; those with a ketonic group are the ketoses. The classification of monosaccharides can indicate, simultaneously, both their carbon chain lengths and the kinds of substituents on their carbonyl groups. Glucose, for example, with a six-carbon skeleton topped off by an aldehydic group, is an aldohexose. Here the prefix aldo- tells us that glucose contains the aldehyde carbonyl group (aldehyde, because there's a hydrogen bonded to the carbonyl group's carbon), the stem -hex- refers to the six carbons present, and the suffix -ose places the compound in the carbohydrate family. 16.4 Glucose: AnAldohexose • 393    O the II carbonyl CH ~ group CH-OH CH-OH glucose, an aldohexose CH-OH CH-OH "12-OH In Chapter 18 we'll learn about ribonucleic acid (RNA), a molecule that uses the genetic information carried in all our cells to guide protein formation with-cells. An important part of the molecular structure of RNA is the mono-accharide ribose, an aldopentose of molecular formula CSHip05. Draw a molecular structure for ribose.  The prefix aldo- tells us that ribose contains an aldehyde functional group,;' .o we can begin by writing the structure: O The next portion of the name, -pent-, indicates the presence of five carbons in the molecule. We'll add four more carbons to produce a total of five: C ( C C The suffix -ose emphasizes that ribose is a carbohydrate, so we'll add hydro-gens and hydroxyl groups to produce a structure in which each carbon (except the carbonyl carbon) is bonded to one -OH group: O 11 C-H CH-OH CH-OH CH-OH CHZ-OH  This structure now represents a molecule of ribose. E X A M P L E Sweet Heredity 394 • Chapter 16 Carbohydrates • Q U E S T I O N As we've just seen, glucose is an example of an aldohexose and ribose is an aldopentose. What would you call the category of monosaccharides that includes fructose? CH2-OH I c=o I CH-OH fructose CH-OH I CH-OH I U12-UN .. 16.5 Chirality:Your Right Hand, Your Left Hand, and a Mirror Two structural characteristics dominate the properties and behavior of monosac-charides that are important to human health and nutrition. All of them • contain at least one carbon that's bonded to four different groups and • form five- and six-membered rings with extraordinary ease.  After we examine each of these two characteristics individually, we'll see how they interact to produce remarkable differences in the properties of, for example, the starch of a potato and the cellulose of an apple. Carbons bonded to four different groups are capable of a new kind of iso-merism (Sec. 6.6), one that depends on the particular arrangement of these four groups around the carbon atom. As we saw much earlier, in Section 6.2, a carbon of an alkane or, more generally, any carbon bonded to four groups lies at the cen-ter of a tetrahedron, a symmetrical, four-sided structure. With the carbon at its center, each of the four substituents lies at one of the four corners or apexes of the tetrahedron. If we have before us a carbon bonded to four different groups, such as the generalized molecule CWXYZ, W Y we can represent the shape of the carbon and its four bonded groups as a tetra-hedron, with C at the center of the three-dimensional figure and the substituents W X, Y, and Z occupying the apexes (Fig. 16.2). (This isn't to suggest that a carbon Figure 16.2 A tetrahedral atom actually exists as a tetrahedron. Rather, if we imagine the carbon nucleus at carbon bonded to four different the center of a tetrahedron, the four substituents would lie at the apexes of the groups: W X, Y, and Z. imaginary, symmetrical geometric figure.) We'll examine the unusual behavior of the CWXYZ carbon through the al-dotriose glyceraldehyde, an aldehyde that contains three carbons and is a member _ `~`- - - of the carbohydrate family. This compound has no direct consumer applications whatever; its significance to us lies in its small size and its simplicity. It's a very good place to start: 16.5 Chirality:Your Right Hand,Your Left Hand,and a Mirror • 395 With its central, tetrahedral carbon bonded to four different groups, CHZOH glyceraldehyde clearly represents a CWXYZ molecule. The specific orientation in space of the four groups surrounding the central carbon represents the carbon's stereochemistry (Sec. 6.2; Fig.16.3). This stereochemistry represents an important Figure 16.3 Glyceraldehyde characteristic of a CWXYZ molecule since any tetrahedral carbon bonded to four stereochemistry. different groups takes on a peculiar property also found in your right and left hands: it is not superposable on its mirror image. We consider two structures to be superposable if we can merge them in space so that each and every point on one of the structures coincides exactly with its equivalent point on the other structure. If such point-for-point merging in space is not possible, the two are not superpos-able. The glyceraldehyde molecule of Figure 16.3 is not superposable on its mirror image. Molecules with this property of handedness are called chiral molecules (pronounced KI-rul), from a Greek word for Chiral molecules have the a hand. Chiral molecules exist as two different, isomeric structures that are alike in characteristic "handedness" every way except for their stereochemistry and its consequences. Each of these two of right and left hands. Enan- isomers, the "right-handed" and the "left-handed" molecule, is an enantiomer of the tiomers are nonsuperposable other. Together they form an enantiomeric pair. The two enantiomers of glyceralde- mirror images. HO hyde appear in Figure 16.4. Notice that they are mirror images of each other, like your right and left hands. Notice also that they are not superposable on each other, again like your right and left hands. It's important to recognize that the two different mol-ecules of Figure 16.4 represent different compounds, with different properties and different names, just as the two geometric isomers of 2-butene represent two dif-ferent compounds (the cis-2-butene and trans-2-butene of Sec.15.6). The most striking 0 HC 0 CH O CH2-CH-CH glyceraldehyde Figure 16.4 The two enantiomers of glyceraldehyde.The two molecules are nonsuperposable mirror images of each other. O -CHZOH -H -OH -CH 396 • Chapter 16 Carbohydrates difference in the properties of two enantiomers lies in their effect on light, as we'll see in Section 16.8. This effect allows us to give each a unique name. We'll close here with a comment on an important structural requirement for chirality. We've seen that every carbon bonded to four different groups, as in CWXYZ, is chiral. Notice, though, that if two or more of the four substituents are identical, as in CWXYY, then the molecule is superposable on its mirror image and cannot be chiral. Remember that when we look at the substituents to deter-mine whether any two are identical, we have to look at each substituent group as a whole, not simply at the four individual atoms bonded directly to the carbon. •QUESTION Suppose that the carbon of CWXYZ were square planar rather than tetrahedral That is, suppose all five of the atoms lay in the same plane, with the carbon at the center and each of the substituent atoms at one of the corners of the square. Would a mol-ecule with this stereochemistry be chiral? Explain. 16.6 The Fischer Projection Drawing the structure of a chiral molecule in as much detail as in Figure 16.3 is time consuming and requires a bit of artistic skill. A simpler and much more con-A Fischer projection is used venient approach to showing stereochemistry, the Fischer projection, appears in to show the stereochemistry Figure 16.5. Emil Fischer, a German chemist, received the Nobel Prize in 1902 part-of a chiral carbon. ly for his studies of the chemistry of sugars. To represent the three-dimensional stere-ochemistry of a chiral carbon on a two-dimensional surface, such as the pages of a book or a periodical, in as simple a way as possible, Fischer proposed that each chi-ral carbon be represented by a cross, following a few simple rules. To illustrate Fischer's procedure we'll use the enantiomer of glyceraldehyde that's 11 CH held in the right hand of Figure 16.4. In Figure 16.Sa you see this same enantiomer, but with the hand removed for clarity. Next, in Figure 16.Sb, you see this enantiomer rotated slightly so that the top and bottom carbons appear to lie behind (or below) H the paper and the H- and HO- substituents on the chiral carbon appear to lie in V;- CHZoH front of (or above) the paper. With the vertical substituents behind (or below) the plane HO of the paper and with the horizontal substituents in front of (or above) the plane, draw Figure 16.5a This is lines connecting the two vertical and the two horizontal substituents (Fig. 16.5c). The enantiomer held in the right result is the Fischer projection of this particular enantiomer of glyceraldehyde, with hand of Figure 16.4. the chiral carbon at the intersection of the two lines you've just drawn. You now have the Fischer projection of one of the two enantiomers of glycer-aldehyde. To generate the Fischer projection of the other enantiomer you can apply O the same procedure to the model held in the left hand of Figure 16.4, or you can sim CH - ply draw the mirror image of the Fischer projection of the right-hand model (Fig. 16.5d). Because of the way the Fischer projections are generated, we are not permitted H OH to (mentally) remove them from the paper on which they're printed, nor are we per-mitted to rotate them except for a rotation of 180ฐ, wholly within the plane of the CHZoH paper. But we can slide them about on the paper to determine whether they represent Figure 16.5b Here the structures that can or cannot be superposed. 16.6 The Fischer Projection • 397 H OH HO H CHZOH CHZOH Figure 16.5c The Fischer projection Figure 16.5d The Fischer projection of the enantiomer of glyceraldehyde of the enantiomer of glyceraldehyde held in the right hand of Figure 16.4. held in the left hand of Figure 16.4. CH3  CH3 Figure 16.6 Superposition and nonsuperposition of Fischer projections.  CHZ CHZ I I CH3 CH3 Cl CH3 CH3 CH3 CH3 ~ H H H C1 Cl H " ฐ-.,~H; CHzCH3 CHzCH3 CHZCH3 Cl These two Fischer projections represent different enantiomers of 2-chlorobutane and therefore cannotbesuperposed.  : ~~ i ~~ : ~>_ i 9 CHZ CH3 CHz CH3   CH3 H H   e'Ti~CH~ CH2CH3  CH2CH3 CHzCH3 H These two Fischer projections represent the same enantiomer of 2-bromobutane, so they can be superposed.  398 • Chapter 16 Carbohydrates E X A M P L E Fischer Projection Do the following two Fischer projections of 1,2-dibromopropane represent enantiomers? CHZBr CH3 Br Br CH3 CH,Br If we keep the first of these two Fischer projections fixed as shown above but-' rotate the second by 180ฐ, as we are permitted by the rules described above, we get H CH3  CH3  Clearly, if we slide one structure onto the other, all the groups will correspond. These are superposable and are therefore identical structures rather than enantiomers.   • Q U E S T 1 O N Draw the Fischer projections of both enantiomers of CH3-CH-CH2-CH3 OH and show that they cannot be superposed on each other. 16.7 Polarized Light, Glare, and Sunglasses The most remarkable property that chirality confers on a molecule lies in its effect on polarized light. To understand what polarized light is and how chiral molecules affect it, we'll start by examining the phenomenon of light itself. We'll treat radi-ant light as if it consisted of waves with crests and troughs, much like those we see on large bodies of water (Fig. 16.7). Figure 16.7 An apple bobbing in water.  The apple oscillates up ... ... and down as the waves pass from left to right. 16.7 Polarized Light, Glare, and Sunglasses • 399  Figure 16.8 Unpolarized light. In water waves any molecule of water, or any object floating on the water, moves largely up and down-from trough to crest and back down again-in a di-rection perpendicular to the direction in which the wave is traveling. While the wave itself appears to travel horizontally, the water itself oscillates vertically. We can think of light in much the same way. According to one useful physical model, a light beam moves along with its waves undulating, like water's waves, in a direction perpendicular to the direction of the light's travel. Unlike water waves, though, the undulations of light oscillate in all directions perpendicular to the di-rection of the beam. If we could place a sheet of some special material into a light beam's path so that we could watch these vibrations, we'd see something that looks like Figure 16.8. This represents ordinary or unpolarized light. Polarized light differs from unpolarized light in one critical respect. While un-polarized light is made up of oscillations in all planes that include the beam's line of travel, the oscillations of polarized light are limited to only one, single plane, the plane of polarization. For emphasis, this form of light is sometimes called plane-polarized light (Fig. 16.9). Polarized light is light con-sisting of oscillations in only one plane, which is known as the plane of polarization.  Figure 16.9 Plane-polarized light. 400 • Chapter 16 Carbohydrates Figure 16.10 Reflected glare is plane-polarized light. Glare Water, sand, snow, ice, glass, or the surface of a road Li Several devices and some physical phenomena and processes can convert un-polarized light into plane-polarized light by blocking or removing all of the vibrations except those occurring in what becomes the plane of polarization. Light reflected as glare from water, sand, snow, ice, roads, or other surfaces becomes po-larized, with the plane of polarization parallel to the reflecting surface. Glare, then, is an example of plane-polarized light (Fig. 16.10). Polarizing sunglasses reduce glare because their lenses are made of polarizing filters that block out all planes of vibration except one. Setting the lenses into the frames so that their polarizing planes are vertical orients them perpendicular to the horizontal surfaces that cause glare. The lenses now block out all the horizontally polarized light that forms the glare. Hold a pair of these sunglasses in front of you, look through the lenses at surface glare, and rotate the glasses. You'll see the glare alternately brighten and grow dim as the lenses rotate (Fig.16.11). That's because the lenses of the sunglasses let all the polarized light of the glare through only when the plane of polarization of the lenses matches the direction of the light's os-cillations. When the two planes are crossed, none of the glare gets through. As you rotate the lenses their plane of polarization also rotates, alternately perpendicular to the plane of the glare and parallel to it. In fact, you can block out virtually all light from any source of relatively low intensity by crossing the lenses of two pairs of polarizing sunglasses as shown in Figure 16.12. The first lens effectively converts ordinary, unpolarized light into     Figure 16.11 Polarizing sunglasses versus glare. Figure 16.12 The effect of polarizing lenses on unpolarized light. 16.8 Optical Activity • 401 Y  plane-polarized light; the second lens, with its plane of polarization perpendicular to that of the first lens, blocks out almost all the plane-polarized light coming through the first lens. The result is a dark spot. Suppose you had a pair of polarizing sunglasses with perfectly circular lenses. One • Q U E S T 1 O N of the circular lenses suddenly popped out and rolled a bit on the ground.You want to repair the glasses by snapping the lens back into the frame but you're not sure what orientation to use. How would you go about determining the proper orientation of the lens before reinserting it into the frame? 16.8 Optical Activity We can use polarized light and an instrument that operates much like the two po-larizing lenses of Section 16.7 to distinguish between enantiomers and to examine an important property of carbohydrates. The instrument, a polarimeter, consists of a hollow tube placed between two sheets of polarizing material called polarizing filters. The filter you look through, the nearer filter, has a pointer attached to it and can be rotated clockwise and counterclockwise. An angular scale allows you to measure the degree of rotation. The filter at the far end of the tube is fixed in position; it can't be rotated. Behind the fixed filter is a light source (Fig.16.13). If you set the nearby, movable analyzing filter so that its plane of polarization is exactly perpendicular to that of the fixed, polarizing filter at the other end, you see only a dark or very dim field as you look through the empty polarimeter tube. But fill the polarimeter tube with any substance made up of chiral molecules of a single stereochemistry, either of the pure enantiomers of glyceraldehyde for ex-ample, and the image brightens. Chiral molecules have the remarkable property of rotating the plane of polarized light. To return to the darkest possible image you have to readjust the analyzing filter by rotating it through a measurable angle. The actual, quantitative angle through which you have to rotate the filter to return to the darkest setting depends on several factors, including the molecular structure of the chiral compound, its concentration (if you were using a solution), the tempera ture, and the length of the polarimeter tube. But under any specific set of conditions, the direction of rotation depends only on which one of the two enantiomers you were examining. Under identical conditions, the two enantiomers of a chiral compound ro-tate the plane of polarized light to exactly the same degree, but in opposite directions. We call the enantiomer that requires the analyzing filter to be rotated clockwise dex-trorotatory, from the Latin dextra for "to the right" (or, in a related sense, clockwise). Light source Empty polarimeter Fixed tube polarizing filter Movable analyzing filter with degree scale • ~w ~ . . .. . .0~1 _   402 • Chapterl6 Carbohydrates An optically active sub-stance is capable of rotating the plane of polarized light. The other enantiomer, the one that generates a counterclockwise rotation, is levoro-tatory from the Latin laevus, for "to the left" (counterclockwise). Anything capable of rotating the plane of polarized light (in either direction) is optically active; substances that don't or can't produce such rotation are optically inactive. On examining each of the two enantiomers of glyceraldehyde we'd find that one of them is dextrorotatory and the other is levorotatory. While we could use these two terms to distinguish the two enantiomeric glyceraldehydes from each other, it's much simpler to use an algebraic "+" to indicate dextrorotation and a "-" to indicate levorotation. Encasing the sign in parentheses, we write the name of the dextrorotatory glyceraldehyde as (+)-glyceraldehyde; the levorotatory enan-tiomer is (-)-glyceraldehyde. Q U E S T 1 O N Knowing that the two enantiomers of a chiral compound rotate polarized light to ex-actly the same extent, but in opposite directions, what effect do you think a mixture of equal amounts of the two enantiomers of a chiral compound would have on plane-polarized light? Mixtures of this kind are called racemates. Is a racemate optically ac-tive? What term used in Section 16.8 can be applied to a racemate to describe its effect on polarized light? 16.9 Dextrose, Levulose, Honey, and Invert Sugar We'll move now from the relatively simple glyceraldehyde, with its single chiral car-bon, to the monosaccharides glucose and fructose, which contain several such car-bons.The Fischer projections of Figures 16.14 and 16.15 reveal that glucose contains four chiral carbons and fructose three. As we might expect, each of these mono-saccharides exists as enantiomers that are optically active. Virtually all naturally oc-curring glucose exists as the dextrorotatory enantiomer, (+)-glucose, shown in Figure 16.14. Another frequently used name for this monosaccharide, dextrose, emphasizes its dextrorotatory character. In contrast to glucose, naturally occur-ring fructose is levorotatory. It's often referred to as (-) fructose or, emphasizing its levorotation, levulose. p CH CH20H H OH C=0 HO H HO -~- H OH ~OH H~OH CH20H CHZOH H OH Figure 16.14 The Fischer projection of the naturally occurring enantiomer of glucose. Figure 16.15 The Fscher projection of the naturally occurring enantiomer of fruct~e. 16.10 Cyclic Monosaccharides • 403  The difference in the direction of rotation caused by glucose and fructose pro-duces a curious result in the hydrolysis of sucrose, a disaccharide. All naturally occur-ring sucrose is dextrorotatory and is composed of a chemically bonded combination of one unit of glucose and one unit of fructose. Hydrolysis of (+)-sucrose thus produces equal amounts of (+)-glucose and (-)-fructose. Since (-)-fructose rotates plane-polarized light through a larger angle, counterclockwise, than (+)-glucose does in a clockwise direction, a mixture of equal amounts of the two monosaccharides is lev-orotatory. As a result, the hydrolysis of sucrose proceeds with an inversion of the di-rection of rotation, from clockwise [because initially only (+)-sucrose is present] to counterclockwise [because at the end of the hydrolysis only a levorotatory mixture of equal amounts of (+)-glucose and (-)-fructose is present]. Because of this inversion in the direction of rotation, a mixture of equal amounts of glucose and fructose is known as invert sugar. Invert sugar is the principal compo-nent of honey. It's formed as bees, using an enzyme generated in their bodies, hydrolyze the sucrose of the nectar they gather from flowers and convert it into its two compo-nent monosaccharides. Because of the ability of invert sugar to decrease the volatili-ty of water and slow its rate of evaporation (Sec. 7.1), this mixture of glucose and fructose is sometimes added to foods and candies to help keep them moist. You want to convert a portion of invert sugar into an optically inactive substance by in- • Q U E S T I O N creasing the amount of one of its monosaccharide components. Would you add naturally occurring glucose or fructose to the invert sugar? If you added just the right amount of the selected monosaccharide to achieve optical inactivity, would the resulting mixture be a racemate? Explain. (See the Question following Sec. 16.8for additional information.) 16.10 Cyclic Monosaccharides Now, with an understanding of the consequences of chirality, we'll turn to the cyclic structures of our most important monosaccharides, particularly the pentoses (five-carbon monosaccharides) and the hexoses (six-carbon monosaccharides). These monosaccharides form rings through the addition of an -OH group of one of their chiral carbons to the carbonyl group of the aldose or ketose. The reaction is much like the addition of water to the double bond of an alkene, which generates an alcohol (Sec. 6.10, Fig. 6.16). Ring formation in ketoses occurs in a manner sim-ilar to that shown for the aldose of Figure 16.16. Ring formation of this kind occurs simply because it transforms the molecule into a more stable form. Chemically, these six-membered rings (and, in some cases, five-membered rings) are more stable than the straight chains of the monosaccharides. [The cyclic representations of monosaccharide rings shown in Figure 16.17 are called Haworth structures, in honor of Walter Norman Haworth, a British chemist who shared the Nobel Prize in 1937 for his research on carbohydrates and vitamin C. Ha worth devised methods for determining the size and stereochemistry of carbohydrate rings and played a major role in determining the chemical structure of vitamin C. Much of the chemistry described in this chapter was discovered by either Haworth or Emil Fischer (Sec. 16.6).]  Honey is largely invert sugar, a mixture of glucose and fructose. Invert sugar is a mixture of equal quantities of glucose and fructose. 404 • Chapter 16 Carbohydrates Figure 16.16 Formation of the cyclist structure of glucose. H H OH A side view of a glucose molecule, showing the arc of the carbon skeleton. Notice that the -OH groups alternate above and below the ring in the same order as in the Fischer projection. Rotation around the bond, as shown, produces the structure below. Addition of the O and the H to the carbonyl group produces the cyclic structure below. The cyclic structure of glucose. Planar, and with only three groups bonded to its carbon, the carbonyl group of glucose can't be chiral as long as the molecule remains in the form of an alde-hyde. (Anything that's two-dimensional or planar is always superposable on its own mirror image.) But with the addition of the -OH group in ring formation, the carbonyl carbon not only becomes tetrahedral, but it now bears four different substituents: 1. an -OH group, 3. the oxygen of the ring, and 2. -H, 4. a carbon of the ring. Figure 16.17 The two glucose rings. 16.11 Starch and Cellulose: You Eat Both, You Digest One • 405 This carbon is now chiral and can hold its new -OH group pointing either up or down in the Haworth projection. If the new -OH group points down, we have an alpha (a) ring; if it's up, the ring is beta (R). There are, then, two cyclic forms of glu-cose: a-glucose and (3-glucose (Fig. 16.17). Although the two isomers rotate the plane of polarized light to different extents, each one is dextrorotatory. They are, therefore, (+)-a-glucose and (+)-R-glucose. How many chiral carbons are therein a molecule of the noncyclic form of glucose? How • Q U E S T I O N many are in a molecule of the cyclic form? What's the reason for this difference? 16.11 Starch and Cellulose: You Eat Both, You Digest One The existence of these two forms of glucose, a and R, explains nicely the dif-ference between the two polysaccharides that make up an important part of our diet: • the starch of the seeds and roots of plants (such as wheat, corn, and potatoes), and • the cellulose of their more fibrous structures (such as bran or seed husks of oats, rye, and wheat; celery stalks; lettuce leaves). In their molecular structures, starch and cellulose resemble each other closely. Each consists of very long polysaccharide molecules that give only glucose on com-plete hydrolysis. Each is made up exclusively of glucose rings joined to each other to form long molecular strings. Yet while we digest and absorb the starch of our foods easily, their cellulose passes through our bodies largely unchanged and un-absorbed. Starch serves as a macronutrient; cellulose provides us with dietary fiber, sometimes called roughage or indigestible carbohydrate (Sec. 16.12). This differ-ence between the two polysaccharides originates in their molecular structures: Starch is made up exclusively of rings of a-glucose; cellulose is composed exclu-sively of rings of R-glucose. In forming any of the larger carbohydrates, ranging from the simple disac-charides of sucrose and lactose to the polysaccharides of starch and cellulose, individual cyclic molecules of monosaccharides combine and join together through the loss of water molecules. We'll now see how this combination occurs and how it produces the important difference between starch and cellulose. We'll look first at cellulose since it provides us with the simpler example. There's probably more cellulose on this planet than any other single organic compound. By one estimate, growing plants produce something like 100 bil-lion tons of cellulose worldwide each year. This polysaccharide, which doesn't occur at all in animals, is the principal component of plant cells. Cellulose gives plants their structural strength. The molecular chain of cellulose consists of molecules of (3-glucose, joined together through oxygens that link carbon 1 of one of the rings with carbon 4 of another. As the rings join they lose a mole-cule of water. ; - Figure 16.18 illustrates a combination of this sort as two glucose rings join to 1 form the disaccharide cellobiose. The ring carbons are numbered in the figure for : easy reference. Notice that the ring on the left is R-glucose since the oxygen on car-bon 1 lies above the ring. As a result the two glucose rings of cellobiose are joined. The rings lie one ! H O H above the other, in OH • • different horizontal H OH planes CHZOH   H OH Figure 16.19 Beta-glucose and the chain of the cellulose molecule. called amylose. These amylose molecules are strings of a-glucose rings aver-aging several hundred rings each. The chains of another type of starch, amylopectin, run several hundred thousand glucose rings long, with branches occurring from carbon 6 at about every 25th glucose ring. These branches lead to still other a-glucose chains of varying lengths. The amylose molecule looks like a long string with plenty of twists and turns; the amylopectin resembles the branches of a tree. The relative proportions of amylose and amylopectin in 16.11 Starch and Cellulose: You Eat Both, You Digest One • 407   . ~ ~ OH Figure 16.20 Two glucose molecules (one of them a-glucose) combine to form maltose and water. CHZOH  HOH 408 • Chapter 16 Carbohydrates  ' ~CHZOH ~CHZOH CH20H CH20H O. __ tr ~r O. __ H /_'_ O\ H H ~'~-O The rings all lie in the same plane. Figure 16.21 Alpha-glucose and the chain of the starch molecule. Two polysaccharides of food: the starch of potatoes and the cellulose of cabbage. food starches vary; the starches of corn and cereal grains run about three parts amylopectin to one part amylose. One more polysaccharide is of interest to us here: glycogen. This carbohydrate resembles amylopectin in molecular structure except that its molecules are more highly branched and smaller, with fewer glucose rings in each. Animals manufacture and store glycogen to serve as a reservoir of readily available glucose. Deposited largely in the liver and muscles, the glycogen molecule can be cleaved quickly to individual glucose molecules, thus providing the body with a ready supply of en-ergy. Because of its storage in the animal body as a reserve of glucose, glycogen is sometimes called animal starch. We don't store much glycogen, though. We use up the liver's supply each night as we sleep and must replenish it the next day. A longer fast causes us to eat into our stores of fat. Neither starch nor cellulose has any significant taste, although many natural-ly occurring mono- and disaccharides are distinctly sweet. Tabte 16.21ists the rel-ative sweetness of several mono- and disaccharides, with table sugar (sucrose) assigned a rating of 100 for comparison. Table 16.2 Relative Sweetness of Sugars Sweetness Sugar (Relative to Sucrose) Fructose 173 Invert sugar (mixture of equal parts glucose and fructose) 130 Sucrose - 100 Glucose 74 Maltose 32 Lactose 16 16.12 How We Digest Carbohydrates • 409 In what single way does the molecular structure of maltose differ from the molecu- • Q U E S T I O N lar structure of cellobiose? 16.12 How We Digest Carbohydrates While any of the monosaccharides-glucose or fructose for example-easily penetrates the intestinal wall to enter the bloodstream, neither disaccharides nor the larger carbohydrates normally get through the intestinal barrier. They are simply too large. To assimilate these larger carbohydrates, ranging from maltose and sucrose to starch, we must first clip them down to their component monosaccharides, which are able to pass through the intestinal wall and into the bloodstream. As we've seen, in forming the larger carbohydrate molecules the individual monosaccharide rings connect to each other with loss of a molecule of water. To reverse this process, to cleave the disaccharides and the polysac- , charides to their component monosaccharides, we must return the water to the molecules through hydrolysis. Our bodies carry out this hydrolysis through the catalytic action of our diges-tive enzymes. Enzymes, you'll recall, act as biological catalysts that allow chemical reactions to take place more rapidly or under milder conditions than they might otherwise, but without being consumed themselves. In cleaving the nutrient poly-saccharides quickly and efficiently in the relatively mild chemical environment of our digestive systems, these molecular catalysts act very much like the platinum and The fiber, bulk, or roughage palladium catalysts that help remove unburned hydrocarbons from automobile of our foods is largely cellu- exhausts (Sec. 7.7). lose, a carbohydrate we find An enzyme that enables us to digest both maltose and starch is maltase, which indigestible because of our lack of the enzyme cellobiase. our bodies produce in sufficient quantities to allow us to digest the starch we eat. As you might infer from this example, an enzyme's name usually resembles the name of the substance it acts on. For the simple disaccharides, just replace the -ose ending of the sugar with -ase to get the name of the enzyme that hydrolyzes the disaccharide. Maltase helps us hydrolyze the links of maltose and starch. We've seen that the combination of two glucose units through a (31ink produces cellobiose, which resembles two links of the cellulose chain. Since we don't produce cellobiase, the digestive enzyme that hydrolyzes the link, we can't digest either cellobiose or cellulose. For humans, starch constitutes a digestible carbohydrate, while cellulose is one of the indigestible carbohydrates that form a large part of the fiber, bulk, or roughage of our diets. Grass, leaves, and other plant material, all of which are indigestible in our own intestines, provide metabolic energy to cows, goats, sheep, and other ruminants, and to termites and similar insects, simply because the di-gestive systems of these animals harbor microorganisms that produce the needed cellobiase. We don't have the required enzyme, so we can't live on grass and wood. Fruits and vegetables provide us For humans, fiber-rich foods include fruits, vegetables, bran, and nuts. with plenty of fiber.  What monosaccharide is produced by the action of both cellobiase and maltase on • Q U E S T 1 O N polysaccharides?   410 • Chapter 16 Carbohydrates 16.13 Lactose Intolerance: Why Large Quantities of Dairy Products Can Cause Digestive Problems in Two Adults Out of Three Lactose (from the Latin lac, for milk), the principal carbohydrate of milk (Table 16.1), offers a good example of the problems we can encounter through de-fects in our enzyme-catalyzed digestive processes. Lactose is a disaccharide that consists of a galactose ring joined to a glucose ring through a R link. The mono-saccharide galactose differs only subtly from glucose, through the stereochemistry of carbon 4. If the -OH on carbon 4 of the monosaccharide ring points down, we have glucose; if it points up, we have galactose (Fig. 16.22). Since virtually no dis-accharide of any kind gets through the intestinal wall and into the bloodstream, we need the enzyme lactase to hydrolyze lactose into its components, galactose and glu-cose. The more milk and milk products we consume, the more lactase we need. Normally, there's plenty of lactase in the digestive systems of infants and chil-dren. That's fortunate, since nursing babies get about 40% of their calories from the lactose of their mother's milk. as adults. In this condition we produce very small amounts of lactase, too little to handle more than a glass or two of milk at a time. Figure 16.22 Galatose, glucose, and lactose. H OH H OH HOH ,6-Galactose Glucose The rings lie one above the other, in different horizontal planes.  CHZOH OH In this chapter we'll examine proteins in detail. We'll learn what they are made of, how they behave, what foods provide them, and why they are important to us. In Chap-ter 18 we'll examine the role proteins play in the chemical transfer of genetic informa-tion from one generation to the next. 17.1 Proteins: More Than Macronutrients  Proteins themselves form the third of the three classes of macronutrients. Like the polysaccharides starch and cellulose, proteins exist as long, threadlike molecules formed by linked sequences of smaller units. But while each unit of starch and cellulose is a cyclic glucose molecule, protein molecules consist of long sequences of nitrogen-' containing units known as amino acids, which we'll examine in the next section. The word protein comes to us from a 19th-century Dutch chemist and physician, Gerardus Mulder. In 1838 Mulder wrote of discovering a substance he believed to be the chemical essence of all life and that (he thought) permeates all parts of every liv- ing thing. To reflect what he imagined to be this new substance's fundamental impor-` tance, he chose its name from the Greek word proteios, meaning primary or first. Although proteins do, indeed, occur in every living cell, Mulder's enthusiasm and the limits of chemical science in the early 19th century overstated the case for proteins as the fundamental chemical substances of all life. Yet proteins are, indeed, vital to our lives and furnish us with virtually every atom of nitrogen that's found in our tissues. While our brain, nerves, and muscles depend on the carbohydrate glucose for energy, and although we might be as immobile as plants if it weren't for the com-pact storehouse of energy that fat provides, it's protein that gives the very shape to our bodies. Proteins form our hair and our nails. Along with water, they are the principal substances of our muscles, organs, blood, and skin. Proteins form the col-lagen of the connective tissue that holds our bones together in a cohesive skele-ton and wraps our bodies in flesh. They are the molecules of our enzymes, those catalysts so effective in promoting the chemical reactions that digest our food, pro-vide us with energy, and manufacture the tissue of our bodies. Even the secret of life itself seems to be sealed in protein molecules. In human nutrition, proteins stand along with carbohydrates and fats and oils as one of our three macronutrients. Yet in a broader sense, as we consider their im-portance in the physical structures of our bodies, in the formation and operation of our enzymes, and in the transmission of genetic information, proteins surely stand as the first among equals. Fats and oils are chemical combinations of long-chain fatty acids and glycerol. Poly-saccharides consist of chemically iinked chains of monosaccharides. What chemi-cal units form the chains of proteins? 17.2 Amines and Amino Acids 'The long chains of protein molecules range in molecular weight from about 10,000 to well over 1,000,000 amu. For comparison, the molecular weight of a typical fat mol-ecule runs between 500 and 1000 amu. Unlike the more common carbohydrates, though, whose individual links consist of one or another of only three different mono-saccharides (glucose, fructose, and galactose), the protein molecules-at least those important to human life-are formed from an assortment of some 20 different amino As we're all aware, it's possible to turn an egg white white by heating it. Actually, the clear, gelatinous part of a raw egg, the part we call the "white" (as distinct from the yolk), isn't white at all. It's colorless. But you can make it turn white by heating it or by doing a few other simple things we'll describe here. An egg white is a combination of about 90% water and 10% proteins. Within the raw egg, the pro-teins of this mixture are distributed in small globules throughout the water. As they occur naturally, both in the egg white and more generally throughout the tis-sues and fluids of plants and animals, proteins are in their native state. That is, their molecules take the particular shapes and forms suited to each protein's function within the organism. In the egg white each long protein molecule folds and wraps around itself to form a small sphere. As denaturation progresses, the proteins of the egg white begin assembling into combinations with each other.The clear, transparent "white" actually turns white and becomes opaque and firm.The longer you cook an egg, the greater the change in the proteins.The white becomes more opaque and more firm as it progresses from soft boiled to poached to fried and as its native proteins become increasingly denatured. You can denature some of the white's proteins even without heat. Break open a raw egg and separate the white from the yolk. (We'll use only the white here.) Put the white into a small glass and sprinkle a little table salt on it. Within a few minutes you'll see the egg white turn opaque and coagulate around the salt grains. The salt is dena-turing the protein.You can do the same thing with some baking soda, which is the com-mon name of sodium bicarbonate, NaHC03. It's a basic substance and it raises the pH of the protein just enough to denature it. An even more dramatic effect involves use of the scientific method. Divide an egg white between two different glasses. Put about a tablespoon of rubbing alcohol into one of the glasses and swirl it slightly.The egg soon begins to turn white and coagu late, as if it were being heated. rubbing alcohol is a solution of 70% isopropyl alcohol and 30% water. Is it the isopropyl alcohol or the water that's denaturing the egg protein? We can answer this question with the portion of the white in the other glass. Since we can't easily obtain pure isopropyl alcohol to determine its effect on the protein, we're left with an examination of water's effect. Add about a teaspoon of water, rough- ly the amount of water that's in a tablespoon of rubbing alcohol, to the white in the other glass.This may produce a little coagulation, but not nearly on the scale produced by the rubbing alcohol. We conclude that it was the isopropyl alcohol, not the water, that denatured the protein of the egg white (Fig. 17.1). • CHZOH ~,y H •H O\OH O I • ,• i H • •I \ OH CH20H H O H / ~_ O\ OH • The rings lie one ! H O H above the other, in ~~T ~--0 OH • • different horizont ~al H OH planes. ~ ~ OH CH2OH H OH Figure 16.19 Beta-glucose and the chain of the cellulose molecule. called amylose. These amylose molecules are strings of a-glucose rings aver-aging several hundred rings each. The chains of another type of starch, amylopectin, run several hundred thousand glucose rings long, with branches occurring from carbon 6 at about every 25th glucose ring. These branches lead to still other a-glucose chains of varying lengths. The amylose molecule looks like a long string with plenty of twists and turns; the amylopectin resembles the branches of a tree. The relative proportions of amylose and amylopectin in 16.11 Starch and Cellulose:You Eat Both,You Digest One • 407   Figure 16.20 Two glucose molecules (one of them a-glucose) combine to form maltose and water. CHZOH  HOH 408 • Chapter 16 Carbohydrates  ' ~CHZOH ~CHZOH CH20H CH20H O. __ tr r O. __ -O H O\ H H The rings all lie in the same plane. Figure 16.21 Alpha-glucose and the chain of the starch molecule. Two polysaccharides of food: the starch of potatoes and the cellulose of cabbage. food starches vary; the starches of corn and cereal grains run about three parts amylopectin to one part amylose. One more polysaccharide is of interest to us here: glycogen. This carbohydrate resembles amylopectin in molecular structure except that its molecules are more highly branched and smaller, with fewer glucose rings in each. Animals manufacture and store glycogen to serve as a reservoir of readily available glucose. Deposited largely in the liver and muscles, the glycogen molecule can be cleaved quickly to individual glucose molecules, providing the body with a ready supply of en-ergy. Because of its storage in the animal body as a reserve of glucose, glycogen is sometimes called animal starch. We don't store much glycogen. We use up the liver's supply each night as we sleep and must replenish it the next day. A longer fast causes us to eat into our stores of fat. Neither starch nor cellulose has any significant taste, although many natural-ly occurring mono- and disaccharides are distinctly sweet. Table 16.2 lists the rel-ative sweetness of several mono- and disaccharides, with table sugar (sucrose) assigned a rating of 100 for comparison. Table 16.2 Relative Sweetness of Sugars Sweetness Sugar (Relative to Sucrose) Fructose 173 Invert sugar (mixture of equal parts glucose and fructose) 130 Sucrose - 100 Glucose 74 Maltose 32 Lactose 16 16.12 How We Digest Carbohydrates • 409 •QUESTION In what single way does the molecular structure of maltose differ from the molecular structure of cellobiose? 16.12 How We Digest Carbohydrates While any of the monosaccharides-glucose or fructose for example-easily penetrates the intestinal wall to enter the bloodstream, neither disaccharides nor the larger carbohydrates normally get through the intestinal barrier. They are simply too large. To assimilate these larger carbohydrates, ranging from maltose and sucrose to starch, we must first clip them down to their component monosaccharides, which are able to pass through the intestinal wall and into the bloodstream. As we've seen, in forming the larger carbohydrate molecules the individual monosaccharide rings connect to each other with loss of a molecule of water. To reverse this process, to cleave the disaccharides and the polysac- , charides to their component monosaccharides, we must return the water to the molecules through hydrolysis. Our bodies carry out this hydrolysis through the catalytic action of our diges-tive enzymes. Enzymes, you'll recall, act as biological catalysts that allow chemical reactions to take place more rapidly or under milder conditions than they might otherwise, but without being consumed themselves. In cleaving the nutrient poly-saccharides quickly and efficiently in the relatively mild chemical environment of our digestive systems, these molecular catalysts act very much like the platinum and The fiber, bulk, or roughage palladium catalysts that help remove unburned hydrocarbons from automobile of our foods is largely cellu- exhausts (Sec. 7.7). lose, a carbohydrate we find An enzyme that enables us to digest both maltose and starch is maltase, which indigestible because of our lack of the enzyme cellobiase. our bodies produce in sufficient quantities to allow us to digest the starch we eat. an enzyme's name usually resembles the name of the substance it acts on. For the simple disaccharides, just replace the -ose ending of the sugar with -ase to get the name of the enzyme that hydrolyzes the disaccharide. Maltase helps us hydrolyze the links of maltose and starch. We've seen that the combination of two glucose units through a (31ink produces cellobiose, which resembles two links of the cellulose chain. Since we don't produce cellobiase, the digestive enzyme that hydrolyzes the link, we can't digest either cellobiose or cellulose. For humans, starch constitutes a digestible carbohydrate, while cellulose is one of the indigestible carbohydrates that form a large part of the fiber, bulk, or roughage of our diets. Grass, leaves, and other plant material, all of which are indigestible in our own intestines, provide metabolic energy to cows, goats, sheep, and other ruminants, and to termites and similar insects, simply because the di-gestive systems of these animals harbor microorganisms that produce the needed cellobiase. We don't have the required enzyme, so we can't live on grass and wood. Fruits and vegetables provide us For humans, fiber-rich foods include fruits, vegetables, bran, and nuts. with plenty of fiber.  What monosaccharide is produced by the action of both cellobiase and maltase on • Q U E S T 1 O N polysaccharides? NH2 Isoleucine Ile Essential CH3-CH-CHZ CH3 -CH-COzH Leucine Leu Essential NH2 IHZN-CHZ-CHz-CHz-CHZ CH-COZH Lysine Lys Essential NH2 CH3-S-CHZ-CH2 CH-COZH Methionine Met Essential NH2 CHZ CH -COZH Phenylalanine Phe Essential NHZ H2 C.  HZC ---fNH HO-CHZ CH-COZH Serine Ser Nonessential NH2 . CH3-CH-OH -CH-COZH Threonine Thr Essential NHZ CHZ CH-COZH NHZ Tryptophan Trp Essential   CH3 -CH-COZH NHZ CH2~- i H-COZH, NH2 Tyrosine Tyr Nonessential Valine Val Essential HZC/ -CH-COZH Proline Pro Nonessential The essential amino acids are those that our bodies cannot synthesize from other chemicals and that we must obtain from our foods. The nonessential amino acids are those that our bodies can produce from other chemicals. 424 • Chapter 17 Proteins •QUEST1ON Is the following statement true or false? "A nonessential amino acid is one that is not essential for the formation of human protein:" Explain. The essential amino acids are the amino acids that our bodies cannot synthesize from other chemicals and that we must obtain from our foods. The nonessential amino acids are the amino acids our bodies can synthesize from other chemicals. part of our diets. The question of whether any one of these amino acids must be part of the foods we eat, or whether we can form it within our own bodies (from other nu-trients) as we need it, is important in assessing the quality of the proteins in our diet. Of these 20 amino acids, our bodies lack the ability to synthesize about half, all of which are known as the essential amino acids. We must get these essential amino acids from the proteins of our foods so that we can use them in forming our own bodily protein. The remainder, those that our own bodies can produce as needed, are the nonessential amino acids. 17.5 The Quality of Our Protein The quantities of total protein contained in various foods appear in Table 17.2. But total protein isn't enough. The essential amino acids must be there in the protein of the food we eat. They must all be there, simultaneously, in sufficient amounts and in the right ratios if our bodies are to use them in our own protein formation. Table 17.2 Protein Content of Foods Food Percent Protein (average or range) Cheese Peanuts Chicken Fish Beef Eggs Wheat flour White flour Cornmeal Lima beans Milk Rice Peas Corn Dates Potatoes Bananas Carrots Orange juice  Cream cheese 9 H 36 Parmesan 27 21 Flounder 15 H 21 Sardines Hamburger 16 H 20 Round 13 13 11 9 , 8 Whole 4 H 8 Condensed 8 7 4 2 2 1 1 1 410 • Chapter 16 Carbohydrates 16.13 Lactose Intolerance: Why Large Quantities of Dairy Products Can Cause Digestive Problems in Two Adults Out of Three Lactose (from the Latin lac, for milk), the principal carbohydrate of milk (Table 16.1), offers a good example of the problems we can encounter through de-fects in our enzyme-catalyzed digestive processes. Lactose is a disaccharide that consists of a galactose ring joined to a glucose ring through a R link. The mono-saccharide galactose differs only subtly from glucose, through the stereochemistry of carbon 4. If the -OH on carbon 4 of the monosaccharide ring points down, we have glucose; if it points up, we have galactose (Fig. 16.22). Since virtually no dis-accharide of any kind gets through the intestinal wall and into the bloodstream, we need the enzyme lactase to hydrolyze lactose into its components, galactose and glu-cose. The more milk and milk products we consume, the more lactase we need. Normally, there's plenty of lactase in the digestive systems of infants and chil-dren. That's fortunate, since nursing babies get about 40% of their calories from the lactose of their mother's milk. By and large, older children have more than enough lactase to digest all the lactose of the milk, cheese, ice cream, and other dairy products they eat. But gradually, as we grow from infancy to adolescence, most of us lose the ability to produce lactase in large quantities, so we're largely lactase-deficient as adults. In this condition we produce very small amounts of lac-tase, too little to handle more than a glass or two of milk at a time. It's been esti-mated that about 70% of the world's adult population, or about two out of three adults throughout the world, have very low levels of lactase in their digestive sys-tems. More specifically, estimates for the percentage of lactase-deficient adults range from about 3% for Scandinavians and northern Europeans to 80 to 100% for some Asians. In North America the estimates for adults run from 5 to 20% for the white population to 70% for the nonwhite population. Figure 16.22 Galatose, glucose, and lactose. H OH H OH HOH ,6-Galactose Glucose The rings lie one above the other, in different horizontal planes. CHZOH OH Dates, lima beans, cornmeal, and peanuts represent plant foods that are deficient in one or more essential amino acids and that furnish low-quality protein. 17.6 The Vegetarian Diet Finding the actual content of the essential amino acids in various foods and com-paring their ratios with those found in eggs can be laborious and tricky. The ap-proach used in Figure 17.3 makes the comparisons easier. Each bar in this figure reflects the amount of the amino acid (in a particular food protein) as a percent-age of that amino acid's contribution to egg protein. A bar that reaches 100% rep-resents an amino acid that's present in the same ratio to the others as it is in eggs. For any particular foodstuff that contains all the essential amino acids in exactly the same ratio as egg protein (or human protein) and is therefore of the same nu-tritional quality as egg protein, all the bars representing the amino acids would extend uniformly to the 100% mark. Bars that rise above the 100% mark repre-sent amino acids present in excess. Like the leucine of cornmeal, they would be con-verted to energy instead of being incorporated into a protein. Bars falling below 100% represent amino acids present in smaller ratios than in egg protein. In Figure 17.3a we see clearly the deficiencies of lysine, methionine, and tryp-tophan in cornmeal. Because of these and similar deficiencies in other essential  Figure 17.3 Essential amino acids of the typical plant (a) and animal (b) proteins as compared with egg protein. Amino acids: I I Amino acids: Isoleucine Leucine Lysine  Methionine Tryptophan Valine  Tryptophan   . v~e I ,.,~:..,a. 0 40 80 100 120 160 0 40 80 100 120 160 Percent Percent 17.6 The Vegetarian Diet • 427  amino acids, the common food grains, fruits, and most vegetables and other plant products are poor sources of complete dietary protein. Of the common plant foods only peanuts provide substantial amounts of almost all the essential amino acids (with methionine the principal exception). It shouldn't surprise us that animal foods in general-beef, poultry, seafood, dairy products, and, of course, eggs- 3b) while plants serve as poorer ' provide plenty of high-quality protein (Fig. 17. sources. The bodies of animals and the materials they produce to nourish their young are all chemically and biologically more nearly akin to our own physical bodies than are the products of the plant kingdom. While the high-quality proteins of meat, milk, and eggs provide us with our most efficient sources of the essential amino acids, they are by no means absolutely necessary to a healthful and perfectly satisfactory diet. After all, we're looking for Animal products such as milk, only 8 to 10 essential amino acids, regardless of what sort of dietary proteins or fish, beef, and chicken typically combination of proteins furnish them. Consuming a combination of proteins from provide more high-quality protein than do plant products. two or more different foods at the same meal can make up for a marked lack of protein quality in any one of the foods. Different low-quality proteins that complement each other to mimic high- quality protein are known as complementary proteins and are found in many of Complementary proteins the traditional dishes of various cultures. The breakfast of cereal and milk pro- are combinations of incom- vides a good illustration. The plentiful lysine of the milk provides a nice comple- plete or low-quality proteins ment to the lysine deficiencies of our cereals. Other sets of complementary proteins that, taken together, provide come in the combinations of peanut butter and bread, beans with rice or corn, and about tha same ratio of essen- rice with peanuts or soybean curds. Generally, combinations of legumes (includ- qualityfial amino proteins acids . as do high-ing peas and beans) with grains provide complementary proteins . Beef, veal, pork, and other meats are among our best sources of high-quality protein. Those of us who abstain from them (whether because of their potentially hazardous saturated fats and cholesterol or because of ethical, religious, or other dietary restrictions) can find good sources of protein in fish and poultry, as we see in Figure 17.3b. Eggs and dairy products provide rich protein for diets from which all forms of meat have been banished. Vegetarians who refuse to eat any animal products at all have a much harder time of it, but they can still obtain all the essential amino acids by careful dietary choices that include complementary plant proteins. Failure to secure a good dietary supply of the essential amino acids, in the prop-er proportions, can produce devastating results, especially among the young. Kwash-iorkor (kwash-e-OR-kor), a potentially fatal condition, develops from a protein deficiency due to the virtually complete absence of essential amino acids from the diet. The word kwashiorkor comes from the language of Ghana, a country on the west coast of Africa. There, nursing infants normally receive sufficient protein from , their mother's milk. With the coming of a second child, though, the first is com-monly weaned and placed on a diet consisting almost exclusively of readily avail-able fresh fruits, potatoes, and other plants that may be rich in many nutrients but are poor in protein. This new diet contains only small quantities of protein, and , low-quality protein at that. The first born soon suffers from a severe protein defi- ciency and develops a variety of symptoms including a swollen abdomen loss of ,, rr,e loss of hair coloring and a color from the hair, patchy and cracked skin, loss of appetite, and general listless- swollen abdomen are typical ness. Death often follows. The word kwashiorkor originated as the name of an evil symptoms of the protein spirit that, tradition held, afflicted the first child after the second was born. While deficiency known as kwashiorkor occurs principally in the tropics, its effects can be found worldwide. kwashiorkor.    What is the limiting essential amino acid of both peanuts and lima beans? • Q U E S T 1 0 N 428 • Chapter 17 Proteins  17.7 Amides, Peptides, and Proteins how we use these amino acids to construct the complex protein molecules that compose and regulate our bod-ies. In fashioning their various protein molecules, our bodies Iink the individual a -amino acids, both the essential and nonessential, into enormously long sequences, much as individual monosaccharides join with each other to form polysaccharides. As a simple illustration of this combination, we can imagine two molecules of glycine joining together to form a new (and very short) molecule, glycylglycine. In this process, the -OH of the carboxyl group of one glycine molecule and one of the amino hydrogens of the other glycine molecule combine and leave as a water molecule (Fig. 17.4). The two glycines join through a covalent bond connecting the carbonyl carbon of one of them with the nitrogen of the other, thereby form-The amide functional group ing an amide functional group, consists of a carbonyl group co-valently bonded to a nitrogen.  This amide group isn't limited to organic compounds related to amino acids. Sim-ple examples include acetamide and benzamide. More important to us as con-sumers are the more complex amides such as acetaminophen, which is the analgesic or painkiller of several over-the-counter medications, including Datril and Tylenol. In acetaminophen, which is an amide despite the "amino" of acetaminophen, we see an example of an N-substituted amide, a compound in which one of the hy-drogens of the amide nitrogen has been replaced by an organic group: O CH3-C-NHZ O acetamide NH - C - CH3 O C-NHZ   OH acetaminophen A peptide bond or a peptide link is a carbon-nitrogen bond that links two amino acids.The benzamide resulting compound is a Although this amide link or functional group occurs in a variety of organic dipeptide, a tripeptide, a compounds, it's particularly important in connecting amino acids to each other. tetrapeptide, and so on, de- When it serves this function the carbon-nitrogen bond of the amide is called a pending on the total number of amino acids jointed by peptide PePtide bond or a peptide link. The resulting compound, glycylglycine in the case links. Polypeptides consist of ~'~'e've just examined, is a peptide. A sequence of two amino acids joined through chains of 10 or more amino a peptide link forms a dipeptide. (Glycylglycine, then, is a dipeptide.) Three amino acids. acids, joined by two peptide links, make up a tripeptide; four, joined by three pep- Proteins are polypeptides tide links, form a tetrapeptide; and so on. Chains of 10 or more amino acids are with molecular weight greater polypeptides. It's only when the molecular weight of a polypeptide exceeds about than about 10,000 amu. 10,000 amu that it becomes a protein. In peptides and in proteins, the peptide link or the peptide bond HZN - CHZ - CO - NH - CHZ - COZH Ala Asp Gly Ser Met Val Thr Ala Lys Figure 17.5 A typical segment of the chain of a polypeptide or a protein. •QUESTION What name would you give to the following compound? (Refer toTable 17.1.) H2N-CH-C-NH-CH-C02H CH3 CH3 17.8 Primary Structures To understand how the set of 20 amino acids of Table 17.1 can generate the enor-mous variety of peptides and proteins found in the human body, we'll begin by ex-amining how many dipeptides we can construct from just two amino acids, alanine and glycine. We've seen two of the dipeptides already, glycylglycine in Section 17.7 and alanylalanine in the question at the end of that section. Two additional The amide functional group + H20 17.8 Primary Structures • 429 Glycylglycine, or Gly-Gly 430 • Chapter 17 Proteins dipeptides are glycylalanine and alanylglycine or, using the abbreviations in Table 17.1, Gly-Ala and Ala-Gly: 11 11 H2N-CH2-C-NH-CH-COZH HZN-CH-C-NH-CH2-COZH CH3 CH3 glycylalanine, Gly-Ala alanylglycine, Ala-Gly These are, indeed, two different compounds. Notice that the part of the struc-ture bearing the carboxyl functional group (-COZH) comes from an alanine mol-ecule in Gly-Ala but from a glycine molecule in Ala-Gly. (In writing the molecular structures of the peptides, it's customary to place the amino acid with the free amino group on the left and the one with the free carboxyl group on the right and to name the various amino acids from left to right.) With just two amino acids, then, we can devise four different dipeptide chains: Ala-Ala, Ala-Gly, Gly-Gly, and Gly-Ala. As we increase the number of amino acids available for use and as we lengthen the chain we construct, the number of peptides that result grows almost beyond comprehension. anagrams, determine how many words can be formed by rearranging the sequence of letters. With N, for example, representing alanine, and O representing glycine (and limiting ourselves to using each letter once and only once in each word), we can form the two words NO (for alanylglycine) and ON (for glycylalanine): NO ON In the next step, let the three letters A, E, and T represent three different amino acids. With these we can generate the four words ATE, EAT, TEA, and ETA (the seventh letter of the Greek alphabet), and two nonsense words, AET and TAE, for a total of six three-letter combinations: AET EAT TAE ATE ETA TEA Adding an M to our supply gives us a total of 24 four-letter words, including such English words as MEAT, TEAM, MATE, and TAME and a long list of non-sense combinations, such as AEMT and EMTA: AEMT EAMT MAET TAEM AETM EATM MATE TAME AMET EMAT MEAT TEAM AMTE EMTA META TEMA ATEM ETAM MTAE TMAE ATME ETMA MTEA TMEA The primary structure of the peptide is the sequence in which the amino acids are bonded to each other in the peptide chain. The sequence of amino acids indicated by the letters of each of these words rep-resents the primary structure of the peptide, which is simply the sequence in which the amino acids are bonded to each other in the peptide chain. By using each of four different amino acids once and only once in the chain, we can generate 24 different tetrapeptides, each with its own, unique primary structure. Of course, we're limiting ourselves here by using each amino acid just once in the sequence. We could form far more by omit-ting one or more of the amino acids and using any of the others more than once. 17.9 Oxytocin, Vasopressin, and Insulin • 431 Our exercise with the letters A, E, and T demonstrates that three different amino •QUESTION acids can form six different tripeptides, with each amino acid represented once and only once. If we remove this restriction of once and only once-if we permit any of the three amino acids to be used more than once, and if we don't require that all three amino acids be represented in the tripeptide-what's the total number of tripep-tides that can be formed from three different amino acids? 17.9 Oxytocin, Vasopressin, and Insulin Now we can leap ahead to the entire assortment of 20 amino acids of human pro-tein. If we were to assign a letter to each of these 20 amino acids and limit ourselves to constructing as many 20-letter words as possible, with each letter appearing once and only once in every sequence, much as we did in Section 17.8, we'd have more than 2,430,000,000,000,000,000 (or 2.43 x 1018) different words, each rep-resenting a different protein. We've limited ourselves to 20 amino acids in the primary structure, with each acid used once and only once. Our bodies don't have any such limitations. Peptides and proteins of any length can be formed, and any of the 20 amino acids can be dropped from any particular primary structure, or repeated here and there anywhere within the sequence. Each is a hor-mone that regulates specific activities of the body. (The italicized amino acids in the following structures represent amino acids that differ in the two structures.) Ile -Gln Tyr~ Asn Pro-Leu-G1yNH2 oxytocin Oxytocin plays a vital role in the release of milk during lactation. Notice that the sulfur atoms of two cysteine units of the peptide are joined, forming a ring. Also note that an amide functional group of a glycine terminates the short chain: Figure tT.6 The primary structure of human insulin. Note the sulfur-sulfur bonds that connect pairs of cysteine groups. phenylalanine and arginine, respectively, replace the isoleucine and leucine of oxytocin. As a result of this change in the primary structure of the peptide, vaso-pressin's principal function is to regulate the amount of water retained by the body. 17.10 Higher Structures, More Complex Functions In earlier examinations of triglycerides and carbohydrates we found that rel-atively small changes in molecular structure can produce major effects in prop- Val 1 Asn-Tyr - Cys -Asn \Glu ~ Ala - Leu - Tyr - Leu - V al - Cys - Gly~ Glu Lys Thr ~ Pro Thr ~Tyr Phe i Phe Converting carbon-carbon double bonds of triglyceride side chains from cis to trans, for example, can raise the melting point of a triglyceride, transforming an oil to a fat (Sec. 15.7). In carbohydrates, the geo-metric difference between an a link and a R link affects the three-dimension-al shapes of polysaccharide chains, causing starch and cellulose to interact differently with molecular iodine. As we saw in Section 16.15, the long, a-linked carbohydrate chains of starch bend into helices that accommodate diatomic iodine molecules and that are thereby responsible for the dark blue color pro-duced on starch by iodine. In protein chemistry, these effects on molecular structure are magnified. The bending, twisting, and folding of the long molecular strands of primary protein structures result in the formation of increasingly complex shapes known as the higher structures of proteins, their secondary, tertiary, and quaternary structures. Among the forces that hold these higher structures in place are hydrogen bonds, weak bonds formed by the attraction of a nitrogen, oxygen, or fluorine atom for a nearby hydrogen that's bonded to a different nitrogen, oxygen, or fluorine (Fig. 17.7). Since protein molecules don't contain fluorine, only hydrogen bonds to nitrogen and oxygen are important in proteins. Hemoglobin, the complex protein of the red blood cells that transport oxy-gen from the lungs to tissues throughout the body, provides an illustration of the consequences of a change in even a single amino acid in a primary struc ture. The disease occurs principally in people of West African ancestry. It gets its name from its distortion of the red blood cells from their normal disklike form into the shape of a sickle (Fig. 17.9). Normally, the hemoglobin molecule consists of two pairs of polypeptide chains, with 141 amino acids units on each chain of one pair and 146 on each chain of the other pair, for a total of 574 individual amino acid units in all four chains. During hemoglobin's synthesis within the body, each amino acid is placed at a specific point within these chains, producing a primary structure that gives rise to normal secondary and higher structures, and normal red blood cells. 17.10 Higher Structures, More Complex Functions • 433 A hydrogen bond is a weak bond formed by the attraction of a nitrogen, oxygen, or fluo-rine atom for a nearby hydrogen bonded to a different nitrogen, oxygen, or fluorine atom. tertiary and quaternary structures of the proteins of hemoglobin. Amino acid The lipoproteins are classified by their density: the HDLs are high-density, •QUESTION What is the chemical basis for sickle cell anemia? Quartenary structure Hemoglobin Small spheres and rectangles (in red) represent iron atoms held by small organic rings imbedded within the folds of hemoglobin. Sickle cell anemia results from a genetic error that places valine rather than the required glutamic acid at a precise point within one of the pairs of hemoglo-bin's polypeptide chains. As a result of this small change in primary structure, the hydrogen bonds that form the higher structures of hemoglobin produce an ab-normal molecule. The hemoglobin protein becomes distorted, forcing the red blood cells into a characteristic sickle shape and impairing their ability to carry oxygen. Although often fatal, the disease can be treated with bone marrow transplants and with various forms of medication. In addition to their roles as hormones and in giving shape and substance to var-Figure 17.9 Normal red blood ious structures of the body, proteins perform other functions as well. They play a cells and sickle cells. part, for example, in the control of serum cholesterol (Sec.15.4). Cholesterol is a hydrophobic molecule (Sec. 13.3) that has very little tendency to dissolve in water. To transport it through the blood, our bodies wrap packets of cholesterol in a sheath of proteins and varying amounts of triglycerides that present a more hy-drophilic surface to the water of the blood. cholesterol 17.11 Egg White Revisited 436 • Chapter 17 Proteins in contact with other protein molecules, which have also lost their globular shapes. These denatured proteins now gather into shapes more like those of fibrous pro-teins and form the familiar tough white of the cooked egg. Adding salt or the iso-propyl alcohol of rubbing alcohol to the protein, as we did in our opening demonstration, also disrupts the sequence of hydrogen bonds in the native protein and denatures it. Cooking an egg, then, is one way to denature the native proteins of an egg white. The heat breaks the hydrogen bonds holding the protein molecules in their native secondary and higher structures. The proteins then regroup in other ways that produce the texture and appearance of the cooked egg. •QUEST1ON What is the advantage of a globular rather than a fibrous structure for the enzymes of the blood? the primary structure of a protein determines what protein it is and how it functions. We've also seen that hydrogen bonds can hold the primary struc-ture in specific shapes of secondary, tertiary, and higher structures. The shape of a protein's higher structures determines how well the protein can do its job. Two types of proteins, fibrous and globular, have shapes that suit them particularly to several of the functions they perform. Our hair and nails, and the claws of animals, for example, are tough and strong because of their fibrous proteins. Their strength comes from the organization of their protein molecules into parallel strands that entwine much like strands of fiber twisted into strong rope. P E S P E C T 1 - Protein and Health Our first contact with proteins might lead us to believe- How much protein do we need? As a general recom- along with Gerardus Mulder (Sec. 17.1)-that they are, in- mendation, only about 10 to 15% of our calories should come deed, the foremost chemicals of life. Proteins build the from protein. (Estimates for the remainder of our calories tissues of our organs and our muscles. All our enzymes are - vary, but 20 to 25% has been recommended as a healthful proteins. We rely on proteins for maximum from fats and oils. For good health, most of our • digesting food; calories ought to come from the large carbohydrate mole- • carrying oxygen to our tissues; cules of starches.) For now we can say that, as a rough rule • growing hair and nails; of thumb, most Americans consume at least twice as much • healing cuts, wounds, and broken bones; and protein as they need. Of course, the term most isn't the • fighting off the invading microorganisms of disease. same as a//. There are special demands and stresses brought on by illness, on the one hand, and pregnancy and "Surely," we might think, "the more protein we eat, lactation, on the other. Because of the need to repair and the better our lives." Not quite. Remember that in many create tissue, these stresses require extra quantities of pro- ways proteins are just another macronutrient, furnishing tein. Other groups who may not be getting enough protein the same 4 Cal/g as carbohydrates. We don't use them as include dieters with severely restricted food intake and brain fuel, as we do glucose, nor store them as readily those who simply can't obtain sufficient protein because of portable supplies of energy, as we do fats. While protein poverty or disability. is being processed by our digestive systems, our bodies While both plants and animals can supply us with pro- look at it as a collection of amino acids, to be used as tein, each source provides its own advantages. Animal needed. protein is high-quality protein, rich in the essential amino If there's no demand for the special talents of the pro- acids.Yet animal protein brings with it cholesterol and sat- tein molecules we can make from amino acids-if we aren't urated fatty acids. Vegetable protein spares us these, but by ill, generating body tissue, recovering from an injury, run- and large it's poor in some vital minerals, notably calcium, ning short of insulin or some other enzyme, or under some iron, and zinc. On the other hand, plant protein is less ex- sort of physical stress-we use them for energy or convert pensive than animal protein and supplies us with fiber as a them to body fat as we do our other macronutrients. We bonus. For most of us, fortunately, the answer is simple: A can't simply decide thatthis morning's fried eggs are going varied diet including our major sources of protein-meat, into muscle tissue, or antibodies, or hair. If there's no de- fish, poultry, vegetables, and legumes, along with milk, milk mand for muscle tissue, generated by exercise, or for anti- products, and some eggs-supplies us with adequate bodies, generated by an invasion of microorganisms, or for , amounts of the nutrient. some other specialized molecules that only theamino acids In the chemical and biological mechanics of how we can form, we either use them for energy or store them by disassemble the molecules of our foods and recombine their converting them to fat. . components into the proteins and other substances Pineapple Gelatin If you want to make some pineapple gelatin for dessert, not simply pineapple-flavored gelatin but gelatin holding suspended chunks of the fruit itself, you have to use canned pineapple. Fresh pineapple won't work. Here's proof. ' Get a package of a simple gelatin dessert mix. Jell-O, Knox, or a similar powdered mix will do. It can be any flavor or no flavor at all, either with sugar or sugar-free. Also pick up a can of pineapple, crushed or in small chunks, and a piece of fresh pineapple as well. In addition you'll need five small bowls or containers, roughly half a cup or about 100 mL each. Before beginning work on the gelatin, cut or crush both the canned pineapple chunks and the fresh pineapple into very small pieces. But keep the two samples sep-arate from each other. Use different utensils tor each set. Don't allow the two pineap-ple samples to contaminate each other in any way. Now follow the directions on the gelatin package. Add the specified amount of boiling water, stir until the gelatin powder dissolves, add cold water (and perhaps ice cubes) as directed. Pour equal amounts of the liquid mixture into each of the five containers. For the scientific analysis, stir a teaspoon of the canned pineapple into one bowl of liquid gelatin and a teaspoon of the fresh pineapple into another. In the same way add a teaspoon of table sugar to the third and a teaspoon of table salt to the fourth. Add nothing at all to the fifth.The four bowls that receive the pineapple, sugar, and salt should get nearly equal amounts of each. Label or mark the containers so you know what each contains.The bowls with the sugar, the salt, and with no additive at all rep-resent applications of the scientific method of Chapter 1. Examine the bowls after you have refrigerated them as directed or overnight. You're likely to find that all have gelled nicely except the one containing the fresh pineapple. The mixture in the bowl containing canned pineapple does form a gel, but we find only a cold, watery pineapple soup in the bowl with the fresh fruit (Fig. 18.1). The explanation for this difference involves both the chemistry of proteins and the biology of survival.  Figure 18.1 (1) Preparing the elahn. (2) Addm canned g ~g pineapple to the liquid gelatin. (3) Adding fresh pineapple to the liquid gelatin. (4) The gelatin mixture does not solidify in the presence of fresh pineapple. 441 442 • Chapter 18 The Chemistry of Heredity 18.1 Pineapple's Enzymes vs. Gelatin's Proteins Examining the effect of pineapple on the gelatin begins with the protein chem-istry of Chapter 17. Gelatin is a protein derived from collagen, a component of connective tissue found in the bodies of animals. Meat processors remove colla-gen from the hooves, skins, bones, and other parts of slaughtered animals and convert the raw collagen to the purified form of collagen protein we know as gelatin. The powder we pour out of a box of commercial gelatin consists of a mixture of fibrous protein filaments associated with each other in the form of triple helices. [A helix is a three-dimensional structure resembling the thread on a screw. A double helix forms when a pair of parallel strands assume the shape of a helix. The triple helix of gelatin proteins forms from a set of three parallel strands (Fig. 18.2). We'll examine the double helix of DNA in Sec. 18.10.] These helical proteins separate from each other and become disorganized, in-dividual protein strands when they dissolve in hot water and are denatured by the high temperature. 18.2 Biochemistry • 443 The cold gel is essentially a network of water molecules trapped within a framework of associated, organized, helical protein molecules. This cold, semisol-id gelatinous network holds fruit, nuts, and other small pieces of food nicely including even the canned bits of pineapple-as the protein molecules and trapped water molecules wrap around the suspended food particles and suspend them in the semisolid protein-water network. This gives us our pineapple gelatin dessert when we use the canned fruit. But as we've seen, something very different happens if we use fresh pineap-ple instead. Here the failure of gel formation reflects the ability of the fresh pineap-ple to destroy the protein network. The culprit here is the bromelin of the fresh pineapple. Many plants, including pineapple, produce within their leaves, stems, fruit and other structures various substances that serve as poisons, toxins, irritants, or other kinds of chemical deterrents to attack by predators. Among these is the bromelin of the pineapple plant. Bromelin is a set of closely related proteolytic enzymes, bi-ological catalysts that promote the degradation, cleavage, or destruction of proteins. Both the sap and the fruit of the pineapple plant contain these enzymes, which ef-fectively inactivate or destroy many of the proteins they contact. They have been used for a variety of purposes, including tenderizing meat (by destroying the pro-tein of the collagen and other connective tissue that strengthen the physical struc-ture of the meat) and reducing some forms of pain and swelling (by removing or inhibiting the formation of proteins that produce these effects). They can also de-grade structural and enzymatic proteins of insect predators, thus providing some protection against attack by insects. The ability to produce bromelin enzymes, then, can be viewed as a survival trait of the pineapple plant. Extended exposure to the high temperatures of the canning process denatures and deactivates the bromelin enzymes of the canned pineapple. Under these con-ditions the bromelin loses its ability to decompose the helical proteins of the gel atin. The gelatin proteins, then, survive in the environment of the canned pineapple but are destroyed by the active enzymes of the fresh pineapple. Classify as reversible or irreversible the effects of (a) hot water on the proteins of • Q U E S T 1 O N gelatin, (b) the high temperature canning process on the proteins of bromelin, and (c) the high temperatures of frying on the proteins of egg white. 18.2 Biochemistry The proteins of gelatin and bromelin are chemicals produced by living organisms. Although-given enough time, chemicals, and other resources-we could repli-cate their molecular structures in the laboratory, their actual generation through the chemical processes of life is an illustration of biochemistry, the chemical re- Biochemistry is the branch actions that take place within a living organism. As we saw in Section 6.1, scientists of science devoted to the at one time believed that compounds generated by life processes could be pro- study of the chemical reac- duced only through the operation of a "vital force," a mysterious power that (it was tions taking place within a thought) operates in living organisms but is unavailable to scientists working with living organism. the apparatus of a chemical laboratory. Friedrich Wohler's chemical synthesis of urea helped dispel this idea. Nonetheless, a complete understanding of how biochemical reactions produce the extraordinarily complex molecules of the organisms that generate them 444 • Chapter t8 The Chemistry of Heredity r presents science with one of its greatest challenges. In this chapter we'll examine a closely related question: How do plants and animals transmit their own ability to create these chemicals, such as the bromelin of pineapples and the collagen of animals, from generation to generation? We'll examine this and related questions as we consider the biochemistry of heredity. • Q U E S T 1 O N Identify a polypeptide produced by the human body that helps ensure the effective nourishment of newly born children. (See Sec. 17.9.) 18.3 Apples and Oranges; Pineapples and Potatoes; Cows and Humans As the common saying points out, "You can't mix apples and oranges." They're clearly different fruits. But beyond their obvious differences-appearance, taste, odor, texture, and so on-lie more fundamental, chemical differences. Oranges, for example, contain far more vitamin C than apples; pineapples contain far more bromelin than either apples or oranges. These represent only two chemical illus-trations of the often complex and extensive chemical differences that exist among all species of plants and animals. Oranges produce vitamin C, apples produce cellulose, potatoes produce starch, humans produce maltase, and cows produce cellobiase, all because of the genetic programming of their biochemical reactions. The chemical behavior of each living organism is a function of the organism itself and helps define the organism. And the origin of that chemical behavior lies in the progenitors of each plant and ani-mal. It comes to them through the process of heredity. •QUEST1ON Name another chemical, in addition to vitamin C, that is found in much higher con centrations in oranges (and lemons, as well as other citrus fruit) than in apples. (See ` Chapter 10.) 18.5 Mitosis and Meiosis: Information TransferThrough Cell Division • 445 18.4 Gregor Mendel Observations that offspring of plants and of animals resemble their parents go back to the beginnings of civilizations. They formed the basis for agricultural and farming methods that sought to reproduce the best characteristics of domesticated plants and animals by encouraging the reproduction of the most desirable spec-imens, and they supported royal lines of succession in which the descendants of great rulers were themselves believed destined to be great rulers as well. Mendel (1822-1884), an Austrian monk, studied the effects of cross-breeding on the traits of garden peas and other plants. He carefully recorded and analyzed con-nections between the characteristics of parents and their offspring. Although he published his observations and conclusions in 1866, his writings remained dormant Figure 18.3 Gregor Mendel and unknown to the rest of the scientific world until they were discovered inde- laid the foundation for our pendently by three European botanists in 1900,16 years after Mendel's death. QUESTION Is red hair classified as a phenotype or a genotype? What term do we give to the • carrier of the genetic information that transmits the characteristic of red hair from parent to child? phenotype 18.5 Mitosis and Meiosis: Information Transfer Through Cell Division The cell is the fundamental structural unit of all living things. With a few excep-tions, such as red blood cells (Sec. 17.10) and single-celled bacteria, each cell x consists of a well-defined nucleus embedded in cytoplasm, and a surrounding membrane (Fig.18.4). The membrane encloses and protects the cellular materi-al. Structures within the cytoplasm do most of the work of the cell, including photosynthesis (in plants) and the conversion of nutrient chemicals into biolog-ical energy (in animals). Our interest lies in the nucleus, which contains the or-ganism's genetic information. (; Within the nucleus are the chromosomes, long strands of material that (as we'll see) serve as the carriers of this information. The term chromosome reflects f the ability of these bodies to accept biological dyes and show distinctive colors. Chromosomes are structures within a cell's nucleus that carry the organism's genetic information. 446 • Chapter 18 The Chemistry of Heredity Figure 18.4 A typical animal Cytoplasm cell.  Nucleus, site of chromosomes, which contain DNA As long as the cell is not in the process of dividing, the material of the chromosomes lies diffused within the nucleus in threadlike filaments. 18.5 Mitosis and Meiosis: Information Transfer Through Cell Division • 447 from one species to another. Each cell of a fruit fly holds 8; for horses, 64; for both potatoes and red ants, 48; dogs, 78; sugar cane, 80; carp, 104. Each human cell con-tains 46. In most species, including humans but excluding the cells involved in re-production, the chromosomes form pairs. Human cells, then, except for the single-celled sperm and eggs, contain 23 pairs of chromosomes. As the cells of the body divide, the chromosomes divide as well, with their genetic information transferred equally to the newly produced cells. In mitosis, a cell divides to produce two identical copies of itself. The chromosomes of the cell duplicate them selves, with one copy going into each of the new cells. Figure 18.6 Stages in the mitosis of a human cell. The product will be two cells, each with replicas of the chromosomes of the original cell. 448 • Chapter 18 The Chemistry of Heredity had a single cell, we now have two cells, identical to each other and to the original cell. Since the chromosomes of the original cell have simply replicated themselves in the formation of the new cells, each new cell holds the same genetic information as the original cell. This form of cellular reproduction is sometimes known as asexual re-production. It's the mode by which most body cells, those of the skin, for example, di-vide. In effect, cellular division by mitosis simply leads to more of the same. Meiosis, the kind of division important in sexual reproduction, represents a more complex process. Here half the chromosomes (one from each pair) move to one of the new cells, half (the other member of each pair) go to the other. This kind of division occurs in the formation of sperm and egg cells. To produce a cell containing the full complement of chromosomes, 46 in the case of humans, two of these cells-one sperm cell and one egg, each containing half the required num-ber of chromosomes-must unite. In human reproduction this produces again the characteristic 23 pairs of chromosomes. Half the new set of 46 chromosomes (and half the genetic information) comes from one parent, half from the other. Unlike mitosis, meiosis, with its resultant mixture of the genetic properties of two parents, produces something new rather than more of the same. Meiosis produces a new combination of chromosomes and a new set of genetic information, with half of each coming from each parent. • QUEST1ON Based on the limited data of this section, what correlation, if any, appears to exist between the number of chromosomes in the cells of mammals and nonmammals? Of plants and animals? 18.6 The Gene Fl~ure 18.7 An carly (1953) model of a portion of a DNA molecule, designed and built by James Watson, left, and Francis Crick, right (Sec.18.10). A gene is a segment of a chromosome that carries in-formation necessary for the creation of a specific protein or polypeptide. This combination of biological loeation (the nucleus) and chemieal eharacteristic (acid) accounts for the -nucleic acid portion of the term. • QUEST1ON What is the full chemical term represented by the letters of DNA? Chemically, the structures characterized as chromosomes consist of long, tightly coiled molecules known as DNA, an abbreviation for deoxyr~ibonucleic acid, an acid found almost exclusively in the nuclei of our eells Each gene coincides with a specific, short seetion of DNA that (generally) determines the amino acid sequence of a specific polypeptide. Each gene represents a chemical blueprint for the formation of the globular and fibrous polypeptides and proteins that serve as enzymes, hormones, and structural and regulatory proteins that determine the form, appearance, and functions of an organism. the DNA chain is simply a set of alternating 2-deoxyribose and phos- OH phate units, with four amines-adenine, cytosine, guanine, and thymine-strung out as substituents along the chain. HO - P = O The sequence of these amine bases determines the sequence of the amino acids that make up the primary structures of the body's proteins. Phosphoric acid passed from generation to generation through the sequence of bases on the DNA Figure 18.8 Ribose, molecule. A gene is simply a portion of the DNA chain with a large number of 2-deoxyribose, and phosphoric bases arranged in the right order to direct the formation of a specific polypeptide. 18.8 RNA:Transforming Genetic Information into Biochemical Action • 451 •QUESTION How would you define a gene in biological terms? In chemical terms? 18.8 RNA: Transforming Genetic Information into Biochemical Action Protein synthesis itself takes place outside the nucleus, in the cytoplasm (Sec.18.5). As a result, the information contained in the DNA molecule, which remains con-fined to the nucleus, must be transferred out of the nucleus into the cytoplasm. • RNA molecules can pass from the nucleus into the cytoplasm. • Ribose (rather than 2-deoxyribose) forms the carbohydrate ring of the RNA chain. • In RNA the amine uracil replaces the thymine of DNA (Fig.18.12). • RNA molecules are much shorter than DNA; each RNA carries only a small segment of the genetic information stored on the entire strand of DNA. RNA occurs in several different forms, each with a specific function. One form, called mRNA (for messenger RNA), carries information stored in DNA (the message) to the cytoplasm, where the protein synthesis occurs. For the protein synthesis itself, still another kind of RNA, tRNA (transfer RNA), finds and transports (transfers) each required amino acid to the site where the peptide bonds are formed under the direc-tion of the mRNA. This peptide synthesis takes place within the cytoplasm, in bodies known as ribosomes. With biochemical efficiency, one mRNA molecule can simulta-neously guide polypeptide synthesis in several different, associated ribosomes. To summarize the entire process, genetic information is stored as a sequence of four different amine bases in molecules of DNA, which lie within the nucleus of the cell. The information is transcribed, in portions, into a sequence of bases of newly formed mRNA molecules.Three of these bases on the mRNA are identical with those on DNA; one is different. This mRNA leaves the nucleus for the ribo-somes of the cytoplasm and there serves as a guide for joining individual amino acids, brought to it by tRNA, into useful polypeptides. O O Figure 18.12 Thymine and uracil. Thymine Uracil occws in DNA occurs in RNA In what way(s) are mRNA and tRNA similar? How do they differ? • Q U E S T I O N 452 • Chapter 18 The Chemistry of Heredity 18.9 The Genetic Code The sequence of the amines strung out along the RNA molecule determines the pri-mary structure of the polypeptide it forms. Each set of three sequential amines on RNA either identifies one particular amino acid that fits into the polypeptide chain or acts as signal for the chain-forming process itself, such as "start" or "stop". To reflect this coding function, sets of three successive amine bases are called codons. The cor-respondence between any particular sequence of three RNA bases and the specific amino acid or function it represents is known as the genetic code. Table 18.1 presents the correlation between RNA codons and amino acids or synthetic functions. Table 18.1 Codons of mRNA Amino Acid Codona I Amino Acid Codona Ala GCA Lys AAA GCC AAG GCG Met AUG GCU Phe UUU Arg AGA UUC AGG Pro CCA CGA CCC CGC CCG CGG CCU CGU Ser AGC Asn AAC AGU AAU UCA Asp GAC UCC GAU UCG Cys UGC UCU UGU Thr ACA Gin CAA ACC CAG ACG Glu GAA ACU GAG Trp UGG Gly GGA Tyr UAC - GGC UAU GGG Val GUA GGU GUG His ` v CAC GUC CAU GUU Ile AUA Initiate AUG AUC peptide GUG AUU chain Leu CUA Terminate UAA CUC peptide UAG CUG chain UGA CUU UUA UUG a A adenine; C = cytosine; G guanine; U uracil. 18.5 Mitosis and Meiosis: Information Transfer Through Cell Division • 447 from one species to another. Each cell of a fruit fly holds 8; for horses, 64; for both potatoes and red ants, 48; dogs, 78; sugar cane, 80; carp, 104. Each human cell con-tains 46. In most species, including humans but excluding the cells involved in re-production, the chromosomes form pairs. Human cells, then, except for the single-celled sperm and eggs, contain 23 pairs of chromosomes. As the cells of the body divide, the chromosomes divide as well, with their genetic information transferred equally to the newly produced cells. In mitosis, a cell divides to produce two identical copies of itself. The chromosomes of the cell duplicate them selves, with one copy going into each of the new cells (Fig. 18.6). Where we previously Figure 18.6 Stages in the mitosis of a human cell. The product will be two cells, each with replicas of the chromosomes of the original cell. 448 • Chapter 18 The Chemistry of Heredity had a single cell, we now have two cells, identical to each other and to the original cell. Since the chromosomes of the original cell have simply replicated themselves in the formation of the new cells, each new cell holds the same genetic information as the original cell. This form of cellular reproduction is sometimes known as asexual re-production. It's the mode by which most body cells, those of the skin, for example, di-vide. In effect, cellular division by mitosis simply leads to more of the same. Meiosis, the kind of division important in sexual reproduction, represents a more complex process. Here half the chromosomes (one from each pair) move to one of the new cells, half (the other member of each pair) go to the other. This kind of division occurs in the formation of sperm and egg cells. To produce a cell containing the full complement of chromosomes, 46 in the case of humans, two of these cells-one sperm cell and one egg, each containing half the required num-ber of chromosomes-must unite. In human reproduction this produces again the characteristic 23 pairs of chromosomes. Half the new set of 46 chromosomes (and half the genetic information) comes from one parent, half from the other. Unlike mitosis, meiosis, with its resultant mixture of the genetic properties of two parents, produces something new rather than more of the same. Meiosis produces a new combination of chromosomes and a new set of genetic information, with half of each coming from each parent. : • Q U E S T 1 O N Based on the limited data of this section, what correlation, if any, appears to exist between the number of chromosomes in the cells of mammals and nonmammals? Of plants and animals? 18.6 The Gene Fl~ure 18.7 An carly (1953) model of a portion of a DNA molecule, designed and built by James Watson, left, and Francis Crick, right (Sec.18.10). A gene is a segment of a chromosome that carries in-formation necessary for the creation of a specific protein or polypeptide. Chemically, the structures characterized as chromosomes consist of long, tightly coiled molecules known as DNA, an abbreviation for deoxyr~ibonucleic acid, an acid found almost exclusively in the nuclei of our eells (Fig.18.7). This combination of biological loeation (the nucleus) and chemieal eharacteristic (acid) accounts for the -nucleic acid portion of the term. We'll examine the significance of the first part of the name. deoxyribo-, in the next section. These DNA molecules carry all the genetic informa-tion of every living organism. Moreover, the DNA in virtually every cell of any indi-vidual organism is identical with the DNA in every other cell of that same organism. With very few exceptions, then, each cell of every organism carries within its DNA the complete genetic blueprint of the entire organism. An organism's genetic information resides in the DNA molecule, within se-quences of genes strung out along the length of the DNA. Each gene coincides with a specific, short seetion of DNA that (generally) determines the amino acid sequence of a specific polypeptide. Each gene represents a chemical blueprint for the formation of the globular and fibrous polypeptides and proteins that serve as enzymes, hormones, and structural and regulatory proteins that determine the form, appearance, and functions of an organism. They hold (and transmit from generation to generation) the directions for the formation of the bromelin, colla-gen, insulin, oxytocin, vasopressin, hemoglobin, and all other polypeptide struc-tures that define the organism. In summary, gene is the term used to describe a segment of a chromosome that carries the information needed to create a specif-ic protein. With this, genes hold the keys to the biochemistry of life.   • Q U E S T 1 O N What is the full chemical term represented by the letters of DNA?  18.7 DNA: The Storehouse of Genetic Information The deoxyribonucleic acid molecule that coils into a chromosome consists of three chemical segments: • HO `CH2 /O~O: • a series of four cyclic amine bases (Sec. 17.2), adenine, cytosine, guanine, an ~d • 2-deoxyribose and H ~f i • phosphoric acid, H3P04. OH OH  In its chemical structure, 2-deoxyribose resembles the cyclic form of the aldopen- /3-Ribose tose ribose (Exercise "Sweet Heredity," Sec.16.4). The 2-deoxy- portion indicates • that it's identical with ribose except for the absence of an oxygen at the number 2 carbon. The structures of (3-ribose, (3-2-deoxyribose, and phosphoric acid appear in HO-CH O OH Figure 18.8; adenine, cytosine, guanine, and thymine are shown in Figure 18.9. • ~ Combining 2-deoxyribose, phosphoric acid, and any one of the four organic H H~ H H bases of Figure 18.9 produces a nucleotide (Fig. 18.10), the repeating structural • unit of DNA. A long sequence of one nucleotide unit after another, each bearing OH H one of the bases of Figure 18.9, produces the primary structure of a DNA mole- p_2_Deoxyribose cule. Figure 18.11 represents a typical segment of the primary structure of DNA. To sum up, the DNA chain is simply a set of alternating 2-deoxyribose and phos- OH phate units, with four amines-adenine, cytosine, guanine, and thymine-strung out as substituents along the chain. HO - P = O The sequence of these amine bases determines the sequence of the amino acids that make up the primary structures of the body's proteins. That is, the primary OH structure of each of the body's proteins is determined by the genetic information Phosphoric acid passed from generation to generation through the sequence of bases on the DNA Figure 18.8 Ribose, molecule. A gene is simply a portion of the DNA chain with a large number of 2-deoxyribose, and phosphoric bases arranged in the right order to direct the formation of a specific polypeptide. acid. 18.8 RNA: Transforming Genetic Information into Biochemical Action • 451 •QUESTION How would you define a gene in biological terms? In chemical terms? 18.8 RNA: Transforming Genetic Information into Biochemical Action Protein synthesis itself takes place outside the nucleus, in the cytoplasm (Sec. 18.5). As a result, the information contained in the DNA molecule, which remains con-fined to the nucleus, must be transferred out of the nucleus into the cytoplasm. The transfer begins within the nucleus as the information contained on the DNA molecule is transcribed, in portions, onto another kind of molecule, RNA (an abbreviation for ribonucleic acid). RNA, formed by biochemical reactions within the nucleus, differs from DNA in four important ways: • RNA molecules can pass from the nucleus into the cytoplasm. • Ribose (rather than 2-deoxyribose) forms the carbohydrate ring of the RNA chain. • In RNA the amine uracil replaces the thymine of DNA (Fig. 18.12). • RNA molecules are much shorter than DNA; each RNA carries only a small segment of the genetic information stored on the entire strand of DNA. RNA occurs in several different forms, each with a specific function. One form, called mRNA (for messenger RNA), carries information stored in DNA (the message) to the cytoplasm, where the protein synthesis occurs. For the protein synthesis itself, still another kind of RNA, tRNA (transfer RNA), finds and transports (transfers) each required amino acid to the site where the peptide bonds are formed under the direc-tion of the mRNA. This peptide synthesis takes place within the cytoplasm, in bodies known as ribosomes. With biochemical efficiency, one mRNA molecule can simulta-neously guide polypeptide synthesis in several different, associated ribosomes. To summarize the entire process, genetic information is stored as a sequence of four different amine bases in molecules of DNA, which lie within the nucleus of the cell. The information is transcribed, in portions, into a sequence of bases of newly formed mRNA molecules. Three of these bases on the mRNA are identical with those on DNA; one is different. This mRNA leaves the nucleus for the ribo-somes of the cytoplasm and there serves as a guide for joining individual amino acids, brought to it by tRNA, into useful polypeptides. O O Figure 18.12 Thymine and uracil.  Thymine Uracil occurs in DNA occurs in RNA In what way(s) are mRNA and tRNA similar? How do they differ? • Q U E S T 1 0 N 452 • Chapter 18 The Chemistry of Heredity 18.9 The Genetic Code The sequence of the amines strung out along the RNA molecule determines the pri-mary structure of the polypeptide it forms. Each set of three sequential amines on RNA either identifies one particular amino acid that fits into the polypeptide chain or acts as signal for the chain-forming process itself, such as "start" or "stop". To reflect this coding function, sets of three successive amine bases are called codons. The cor-respondence between any particular sequence of three RNA bases and the specific amino acid or function it represents is known as the genetic code. Table 18.1 presents the correlation between RNA codons and amino acids or synthetic functions. Table 18.1 Codons of mRNA Amino Acid Codona I Amino Acid Codona Ala GCA Lys AAA GCC AAG GCG Met AUG GCU Phe UUU Arg AGA UUC AGG Pro CCA CGA CCC CGC CCG CGG CCU CGU Ser AGC Asn AAC AGU AAU UCA Asp GAC UCC GAU UCG Cys UGC UCU UGU Thr ACA Gin CAA ACC CAG ACG Glu GAA ACU GAG Trp UGG Gly GGA Tyr UAC - GGC UAU GGG Val GUA GGU GUG His ` v CAC GUC CAU GUU Ile AUA Initiate AUG AUC peptide GUG AUU chain Leu CUA Terminate UAA CUC peptide UAG CUG chain UGA CUU UUA UUG a A adenine; C = cytosine; G guanine; U uracil. 450 • Chapter 18 The Chemistry of Heredity Figure 18.10 The combination NHZ of 2-deoxyribose, cytosine, and phosphoric acid produces a ~ r ' ` " typical nucleotide. \ N Figure 18.11 A typical segment of the DNA chain. Cytosine N N~NHZ Guanine NH2 18.8 RNA: Transforming Genetic Information into Biochemical Action • 451 How would you define a gene in biological terms? In chemical terms? •QUESTION 18.8 •QUEST10N In what way(s) are mRNA and tRNA similar? How do they differ? RNA: Transforming Genetic Information into Biochemical Action Protein synthesis itself takes place outside the nucleus, in the cytoplasm (Sec. 18.5). As a result, the information contained in the DNA molecule, which remains con-fined to the nucleus, must be transferred out of the nucleus into the cytoplasm. The transfer begins within the nucleus as the information contained on the DNA molecule is transcribed, in portions, onto another kind of molecule, RNA (an abbreviation for ribonucleic acid). RNA, formed by biochemical reactions within the nucleus, differs from DNA in four important ways: • RNA molecules can pass from the nucleus into the cytoplasm. • Ribose (rather than 2-deoxyribose) forms the carbohydrate ring of the RNA chain. • In RNA the amine uracil replaces the thymine of DNA (Fig. 18.12). • RNA molecules are much shorter than DNA; each RNA carries only a small segment of the genetic information stored on the entire strand of DNA. RNA occurs in several different forms, each with a specific function. One form, called mRNA (for messenger RNA), carries information stored in DNA (the message) to the cytoplasm, where the protein synthesis occurs. For the protein synthesis itself, still another kind of RNA, tRNA (transfer RNA), finds and transports (transfers) each required amino acid to the site where the peptide bonds are formed under the direc-tion of the mRNA. This peptide synthesis takes place within the cytoplasm, in bodies known as ribosomes. With biochemical efficiency, one mRNA molecule can simulta-neously guide polypeptide synthesis in several different, associated ribosomes. To summarize the entire process, genetic information is stored as a sequence of four different amine bases in molecules of DNA, which lie within the nucleus of the cell. The information is transcribed, in portions, into a sequence of bases of newly formed mRNA molecules. Three of these bases on the mRNA are identical with those on DNA; one is different. This mRNA leaves the nucleus for the ribo-somes of the cytoplasm and there serves as a guide for joining individual amino acids, brought to it by tRNA, into useful polypeptides. O O Figure 18.12 Thymine and uracil. Thymine Uracil occurs in DNA occurs in RNA 452 • Chapter 18 The Chemistry of Heredity 18.9 The Genetic Code The sequence of the amines strung out along the RNA molecule determines the pri-mary structure of the polypeptide it forms. Each set of three sequential amines on RNA either identifies one particular amino acid that fits into the polypeptide chain or acts as signal for the chain-forming process itself, such as "start" or "stop". To reflect this coding function, sets of three successive amine bases are called codons. The cor-respondence between any particular sequence of three RNA bases and the specific amino acid or function it represents is known as the genetic code. Table 18.1 presents the correlation between RNA codons and amino acids or synthetic functions. Table 18.1 Codons of mRNA Amino Acid Codona I Amino Acid Codona Ala GCA Lys AAA GCC AAG GCG Met AUG GCU Phe UUU Arg AGA UUC AGG Pro CCA CGA CCC CGC CCG CGG CCU CGU Ser AGC Asn AAC AGU AAU UCA Asp GAC UCC GAU UCG Cys UGC UCU UGU Thr ACA Gin CAA ACC CAG ACG Glu GAA ACU GAG Trp UGG Gly GGA Tyr UAC - GGC UAU GGG Val GUA GGU GUG His ` v CAC GUC CAU GUU Ile AUA Initiate AUG AUC peptide GUG AUU chain Leu CUA Terminate UAA CUC peptide UAG CUG chain UGA CUU UUA UUG a A adenine; C = cytosine; G guanine; U uracil. 18.10 The Double Helix of Watson and Crick (and Wilkins and Franklin) • 453 •QUESTION What amino acid does the codon GGC correspond to? With four different bases arranged in codons of three bases each, a total of 64 different sequences (codons) is available. This allows for plenty of redundancy. For example, with adenine, cytosine, guanine, and uracil represented by A, C, G, and U, respectively, each of the following four codons represents the amino acid ala-nine: GCA, GCC GCG, and GCU. The signal to terminate the protein chain is given by each of the codons UAA, UAG, and UGA. 18.10 The Double Helix of Watson and Crick , (and Wilkins and Franklin) As we saw for proteins in Chapter 17, the primary structures of long molecular chains-the sequence of the individual units that form them-tell only part of the chemical story. And as with proteins, the shape taken by the primary structure of DNA influences its behavior and biochemical effects. The discovery in 1953 that DNA exists as a double helix led to rapid ad-vances in understanding the chemical basis of biological heredity. Working in Cambridge, England, the biologists James D. Watson (born 1928) and Francis Crick (born 1916), American and English respectively, elucidated the structure of DNA largely through the construction of models based on X-ray studies carried out in London by Rosalind E. Franklin, an English biophysicist (1920-1958). In 1962 Watson and Crick shared the Nobel Prize in medicine with Maurice H. E Wilkins (born 1916, New Zealand), who had been a co-worker of Franklin. Because Rosalind Franklin died before the award of the Nobel Prize, her name does not appear on it. Nobel Prizes may not be award-ed posthumously. Watson and Crick found that the DNA molecule consists of two nucleotide strands held together in a double helix by hydrogen bonds (Sec.17.10) formed be-tween the amine bases of the adjacent strands. Although the hydrogen bond is a weak bond, the huge numbers of these bonds that can form between the two strands hold them together effectively in the double helix (Fig.18.13). The two deoxyribonucleic acid strands that form the double helix are not iden-tical. They are complementary strands, which means that every cytosine of one strand lies opposite a guanine of the other strand; every adenine of one strand lies opposite a thymine of the other strand. The hydrogen bonds that hold the strands together form between these base pairs, which occupy the central portion or core of the helix, as shown in Figure 18.13. An estimated 6 billion of these base pairs exist in the DNA of each human cell. (In contrast, RNA consists of only a single strand of nucleotides, with genetic information copied selectively from only one of the two DNA strands.) When a cell divides, replicas of its DNA form as the double helix uncoils and a complementary strand forms adjacent to each one of the original strands (Fig.18.14). Each of the two new cells receives one of the newly formed double he-lixes. This accounts for the identity of the DNA in each cell of an organism. 454 • Chapter 18 The Chemistry of Heredity  Adenine pairs with thymine and guanine pairs with cytosine H p;_.... 3H=N N~ N _g._...;p N~ \ `N-H.....N ~ N~ ~ j,J.....H_ N N~ ~ - N . H Adenine I Cytosine Guanine  The double helix of DNA A = adenine C = cytosine G = guanine T = thymine P and S represent the phosphate and sugar (deoxyribose) units of the chain Figure 18.13 Hydrogen bonding and the double helix of DNA. Figure 18.14 DNA replication. •QUEST1ON Why are the two DNA strands of a double helix regarded as complementary rather than identical? 18.11 The Human Genome Given the importance of our genetic information-it's all that distinguishes you from a yeast cell or an earthworm-an enormous amount of time and effort have gone into determining the precise sequence of genes and their bases in our DNA. _ 19.5 Vitamin D ... Or Is It? • 469 Carrots are considered to be excellent sources of vitamin A, yet they contain no vitamin A. •QUEsTION How do you explain this apparent contradiction? 19.5 Vitamin D ... Or Is It? Vitamin D promotes the absorption of calcium and phosphorus from our foods through the intestinal wall and into the bloodstream, thereby providing the raw ma-terials for forming and maintaining healthy bones Without vitamin D, children's bones develop poorly, resulting in the severely bowed legs and other skeletal deformations that characterize the physical condition known as rickets. Fortifying milk with added vitamin D makes sense since milk is a major food of young children, it's rich in calci-um, and the fat-soluble vitamin dissolves readily in the milk fats. But vitamin D, like A, has its own story. Both rickets and the vitamin itself may be largely the products of the way civilization has developed in the northern and southern latitudes. For some of us the chemical may not be a vitamin after all. Part of the reason for questioning whether it's really a vitamin is that, unlike other vita-mins, D forms in our own bodies. Under the right conditions we don't need it in our foods; instead, it forms in our skin, under the action of the sun's ultraviolet rays. CH3 HO 7-dehydrocholesterol, occurs in the skin CH3 CH3 I I Cholecalciferol, Vitamin D  18.10 The Double Helix of Watson and Crick (and Wilkins and Franklin) • 453 With four different bases arranged in codons of three bases each, a total of 64 different sequences (codons) is available. This allows for plenty of redundancy. For example, with adenine, cytosine, guanine, and uracil represented by A, C, G, and U, respectively, each of the following four codons represents the amino acid ala-nine: GCA, GCC GCG, and GCU. The signal to terminate the protein chain is given by each of the codons UAA, UAG, and UGA. What amino acid does the codon GGC correspond to? •QUESTION 18.10 The Double Helix of Watson and Crick , (and Wilkins and Franklin) The discovery in 1953 that DNA exists as a double helix led to rapid ad-vances in understanding the chemical basis of biological heredity. Working in Cambridge, England, the biologists James D. Watson (born 1928) and Francis Crick (born 1916), American and English respectively, elucidated the structure of DNA largely through the construction of models based on X-ray studies carried out in London by Rosalind E. Franklin, an English biophysicist (1920-1958). In 1962 Watson and Crick shared the Nobel Prize in medicine with Maurice H. E Wilkins (born 1916, New Zealand), who had been a co-worker of Franklin. Because Rosalind Franklin died before the award of the Nobel Prize, her name does not appear on it. Nobel Prizes may not be award-ed posthumously. Watson and Crick found that the DNA molecule consists of two nucleotide strands held together in a double helix by hydrogen bonds (Sec. 17.10) formed be-tween the amine bases of the adjacent strands. Although the hydrogen bond is a weak bond, the huge numbers of these bonds that can form between the two strands hold them together effectively in the double helix (Fig. 18.13). The two deoxyribonucleic acid strands that form the double helix are not iden-tical. They are complementary strands, which means that every cytosine of one strand lies opposite a guanine of the other strand; every adenine of one strand lies opposite a thymine of the other strand. The hydrogen bonds that hold the strands together form between these base pairs, which occupy the central portion or core of the helix, as shown in Figure 18.13. An estimated 6 billion of these base pairs exist in the DNA of each human cell. (In contrast, RNA consists of only a single strand of nucleotides, with genetic information copied selectively from only one of the two DNA strands.) When a cell divides, replicas of its DNA form as the double helix uncoils and a complementary strand forms adjacent to each one of the original strands (Fig. 18.14). Each of the two new cells receives one of the newly formed double he-lixes. This accounts for the identity of the DNA in each cell of an organism. 454 • Chapter 18 The Chemistry of Heredity Adenine pairs with thymine and guanine pairs with cytosine H Adenine I Cytosine Guanine The double helix of DNA A = adenine C = cytosine G = guanine T = thymine P and S represent the phosphate and sugar (deoxyribose) units of the chain Figure 18.13 Hydrogen bonding and the double helix of DNA. Figure 18.14 DNA replication. Web Questions • 459 26. A rabbit can run from a hungry tiger, but a plant can't run from a hungry locust. Describe what defense(s) a plant might have against a predatory insect. Some plants contain poisons. Castor Bean plants contain poisons. aab 27. The bromelin of pineapple is a set of proteolytic en- zymes capable of inactivating and/or destroying the proteins of a variety of organisms. Yet although the bromelin enzymes are themselves proteins, they do not inactivate or destroy themselves. What conclusion(s) do you draw from this . observation? 28. What function does cell division by meiosis serve in the reproduction of the organisms of a species? In this form of reproduction, why can meiosis be considered superior to mitosis? 29. What are some possible reasons that might have led the scientists who first cloned a sheep to wait approximately half a year before announcing their success? 30. Human cloning is a controversial topic. Suggest some ethical considerations in favor of human cloning. Suggest some in opposition to human cloning. activate an ultraviolet light underneath the micromanipulator, briefly illuminating the DNA inside the egg. It's the only way he can see the genetic material without hurting the egg. If the UV is on for more than a few seconds, the egg could be damaged. Human eggs can sell for $4,000 each. steps on a second pedal to control the second pipette, called a piezo, which acts like a tiny drill. The micromanipulator click-click-clicks like a minuscule jackhammer as Chung begins enucleation, the delicate task of puncturing the egg's protective membrane and sucking out its nucleus. He must be certain to retrieve all of the chromosomes inside the egg - 2 meters' worth, if they were unraveled and stretched end to end - without collapsing the membrane. no exposure of the eggs to fluorescent light, and no deviation from a room temperature of 85 degrees Fahrenheit. Lanza is especially concerned with CO2 levels inside the incubator; he keeps an eye on the digital display, believing that an experiment conducted in September implanted the sheep embryo to grow a cloned animal; Lanza will keep the resulting embryos in a petri dish to grow stem cells. can't get stem cells until he grows an embryo that has divided into at least 16 cells 31. Give your own answers to the following questions and ex- plain your reason for each. a. Would you wish to have a pet of yours cloned? No. b. Would you wish to have yourself cloned? No. c. Are there circumstances under which a human might be cloned? d. Should governments control animal and/or human cloning or should cloning be left to the judgments of in- dividuals, physicians, and scientists. Yes Web Questions Use the Web to answer or accomplish each of the following. Report your Web source for each response 1. Find two other edible plants or plant products, in addition to pineapples, that produce proteolytic enzymes. Identify the plants and the enzymes. Blueberries 2. Write a brief description of the life and work of Gregor Mendel? 3. Describe the contributions to our understanding of genet- ics and cellular division made by Walther Flemming and by Eduard Strasburger. 4. What are purines and pyrimidines? Which of the compounds discussed in this chapter are purines? Which are pyrimidines? 5. How many genes are there in the DNA of a fruit fly? How does this compare with the number of genes in human DNA? 6. Explain why the cloning of cats is easier to accomplish than the cloning of dogs. 7, Describe in detail the difference between the reproductive processes of cloning and twinning. 8. Identify Francis Collins and Craig Venter and describe their connection to the topics of this chapter. Chapter 19 Vitamins, Minerals, Additives. Food Chemicals •QUEST1ON Why are the two DNA strands of a double helix regarded as complementary rather than identical? 18.11 The Human Genome Given the importance of our genetic information-it's all that distinguishes you from a yeast cell or an earthworman enormous amount of time and effort have gone into determining the precise sequence of genes and their bases in our DNA. _ 19.5 Vitamin D ... Or Is It? • 469 Carrots are considered to be excellent sources of vitamin A, yet they contain no vitamin A. •QUEsTION How do you explain this apparent contradiction? 19.5 Vitamin D ... Or Is It? Vitamin D promotes the absorption of calcium and phosphorus from our foods through the intestinal wall and into the bloodstream, thereby providing the raw ma-terials for forming and maintaining healthy bones Without vitamin D, children's bones develop poorly, resulting in the severely bowed legs and other skeletal deformations that characterize the physical condition known as rickets. Fortifying milk with added vitamin D makes sense since milk is a major food of young children, it's rich in calci-um, and the fat-soluble vitamin dissolves readily in the milk fats. But vitamin D, like A, has its own story. Actually, vitamin D isn't even a single organic compound. The term applies to a set of very closely related molecular structures, differentiated from each other by subscripts. There are vitamins D1, D2, D3 , and so on, all with the same physiological function. As ultraviolet radiation strikes our skin, it converts a bodily substance named 7-dehydrocholesterol into the form of the vitamin known as vitamin D3 or, by its chemical name, cholecalciferol (Fig. 19.3). With plenty of sunshine, lots of exposed skin, and long hours in the outdoors, cholecalciferol would be in plentiful supply in all our bodies, rickets would be virtually unknown, and vitamin D wouldn't be a vi-tamin at all. But with the limited sunshine, copious clothing, and indoor living and working conditions of the more extreme northern and southern latitudes, the chemical becomes scarce. This could be especially tragic for children, whose bones are still growing. Under these conditions rickets would be common. CH3 HO 7-dehydrocholesterol, occurs in the skin CH3 CH3 I I Cholecalciferol, Vitamin D3 470 • Chapter 19 Vitamins, Minerals, and Additives •QUEST1ON What are the name and the symptoms of the physical condition brought about by a deficiency of vitamin D? It's probably impossible to produce dangerously high levels of vitamin D in the body through exposure to the sun, since the natural tanning of the skin blocks out the rays and stops the chemical conversion. Unfortunately the same can't be said about the excessive use of vitamin supplements. Overzealous use of vitamin D supplements has led to excessive absorption of calcium and phosphorus and the formation of calcium deposits in the soft body tissues, including the major organs such as the heart and the kidneys. Extreme cases have resulted in death. 19.6 Vitamin C: Bleeding Gums and the Bulbul Bird i H20H Water-soluble vitamin C, the best known of all the vitamins, is taken as a dietary supplement by more Americans than any other. As ascorbic acid (Fig. 19.4), its HCOH chemical name represents two properties of the substance, one chemical, the other \ /O~ biological. First, it's an acid, although it clearly doesn't belong to the class of car- /C C=0 boxylic acids (Sec. 10.8). Moreover, the word ascorbic reflects its biological value H \ _ ~ in protecting against the disease scurvy. (The words scurvy and ascorbic come from /C-C\OH the Latin word for the symptoms of the disease, scorbutus, described below.) HO Humans require vitamin C for formation of the collagen of our connective Figure 79.4 Vitamin issues (Sec. 18.1). Tough fibers of this protein are important components of our C, ascorbic acid. skin, muscles, blood vessels, scar tissue, and similar bodily structures. Since the gums are rich in blood vessels and are subject to wear and abrasion through eat-ing and by brushing the teeth, the bleeding of gum tissue weakened by deteriora-tion of its collagen becomes the first visible symptom of scurvy. As the disease progresses, the gums weaken and decay, the teeth fall out, and the body bruises eas-ily. Scurvy itself isn't fatal, but as it progresses it leads to a decline in the body's re-sistance to other, lethal diseases. the fresh fruits and vegetables that could supply them with vitamin C. Chiral carbons The hydrogen lies below the plane of the ring Like all atoms of one isotope of any particular element, all molecules of any particular compound are mutually identical. For example, it takes exactly 20 pro-tons, 20 electrons, and 20 neutrons, arranged so that all the protons and neutrons form the nucleus and all the electrons are organized into shells surrounding the nu-cleus, to make up the most common isotope of a calcium atom. Similarly, it takes exactly 6 carbon atoms, 6 oxygen atoms, and 8 hydrogen atoms to make up a mol-ecule of vitamin C. Moreover, the atoms must all be organized into a precise arrangement, even to the exact arrangement of the atoms bonded to the chiral carbons (Sec. 16.5; Fig. 19.5). With this specific molecular structure, including the necessary chirality, we have vitamin C; without it we don't. Figure 19.6 Vitamin C and molecular structure. i HZOH i HZOH i H20H H-C-OH H-C-OH H-C-OH 19.8 Natural versus Synthetic • 473 Figure 19.5 The stereochemistry of vitamin C. All molecules of vitamin C have this structure and stereochemistry, regardless of their source. CH20H H-C-OH II Z 0 ~ \ "1 0 1-1 \ 1-1 0 1-1 C C=OC C=0 C C=0 H~ \ / . H/ \ / H~ \ / /C=C1\ /C=C~ /C=C\\ /C=C\ HO OH HO OH HO OH HO OH A molecule of vitamin C from A molecule of vitamin C of A molecule of a substance that from an orange, lemon, or lime a kilogram batch synthesized unknown origin, found in an may or may not have useful in large vats by a major ancient bottle, in an old attic properties, but that is definitely pharmaceutical firm not vitamin C A molecule of vitamin C isolated  What is the single factor that determines whether or not a given molecule is •QUESTION vitamin C? 474 • Chapter 19 Vitamins, Minerals, and Additives 19.9 Foods versus Pills The discussion of "natural" versus "synthetic" vitamins brings us to a related ques-tion: If all molecules of any particular vitamin are mutually identical, regardless of their source, does it matter whether we get our vitamins from a well-balanced diet. or can we eat what we please and rely on vitamin and mineral supplements for our micronutrients? The answer seems to be that it matters very much whether we get our vitamins from food or pills, that a well-balanced diet is far superior to re-liance on vitamin a nd mineral supplements. The following explains why. While there's no solid evidence that vitamins can cure any disease (other than de-ficiency diseases), there is circumstantial evidence that some vitamins, particularly C and E, and the (3-carotene that forms vitamin A, might prevent certain diseases, es pecially heart disease and some forms of cancer. The problem with this kind of evi-dence is that it comes largely from two different kinds of studies, involving people • whose diets are rich in fresh fruits and vegetables, and • others who report taking high doses of vitamin supplements. The correlation between diets containing plentiful amounts of vitamin-containing foods- especially fresh fruits and vegetables-and a low incidence of cancer and other diseases is well established. Based on evidence of this sort, gov ernment agencies and health organizations have been urging us for many years to increase the proportions of fresh fruits and vegetables in our diets as protection against heart disease, cancer, and perhaps other illnesses. Yet even an established connection between consumption of foods that con-tain plenty of vitamins and low cancer rates doesn't prove that the vitamins are the active agents in disease prevention. There are many uncertainties. Perhaps specific, as-yet-unidentified components of these foods, other than vitamins, guard against the disease. Or maybe there are other, as-yet-unrecognized pro-tective characteristics common to people who eat lots of fresh fruits and veg-etables. The same sort of reasoning also clouds any conclusions about those who take vitamin supplements. Several double-blind studies (Perspective, Chapter 23) have been carried out to clarify these ambiguities and to pinpoint the effects of the vitamins themselves. One, which ended in 1996, examined a group of about 18,000 men and women who were considered to have a high risk of lung cancer because of their history of smoking or exposure to asbestos. • QUESTION What evidence suggests that plant chemicals other than vitamins may offer pro-tection against cancer, heart disease, and strokes? Those who took large doses of (3-carotene and of vitamin A daily for at least four years showed a 28 % increase in incidence of lung cancer and a 17% increase in overall death rate, compared to those in the group who did not take these large doses of the supplements. These results echo the conclusions of a study of 30,000 male smokers in Finland that ended in 1994. Smok-ers in that study who took supplements of vitamin E over periods of five to eight years were more likely to die of strokes than those who did not take the supple-ments, and those taking (3-carotene were more likely to die of lung cancer or heart disease. (In still another recent study of 22,000 male physicians, taking (3-carotene supplements every other day for 12 years produced no benefits and did no harm.) One possible interpretation of the results of these studies is that plant chem-icals (phytochemicals, from the Greek word phuton, for plants) other than vitamins might produce the protective effects noted in previous studies. We'll have more to say about this in the Perspective of this chapter. 510 • Chapter 20 Poisons,Toxins, Hazards, and Risks Figure 20.7 Aspartame, a From aspartic acid From phenylalanine A dipeptide about 160 times as ~- ` sweet as sucrose. II II Methyl ester HZN-CH-C-NH-CH-C-O-CH3  CHZ CHZ C=0 / OH  Aspartame is the principal ingredient of several non-nutritive sweetners, including NutraSweet. Spurred by public pressure, Congress acted. Through the Saccharin Study and Labeling Act of 1977 it ordered additional studies of saccharin and temporarily pro-hibited the FDA from banning it as a food additive. Congress also required that a label appear on all commercial foods containing the additive, warning that it caus-es cancer in laboratory animals and that "use of this product may be hazardous to your health." The moratorium against FDA action has been extended every few years and continues even now. The public had decided, through its elected representatives, that the benefits accompanying continued use of saccharin outweighed the risk of cancer. The risk was judged to be acceptable and, as a result, saccharin was to be considered safe. Today saccharin stands in the shadow of still another synthetic sweetener, as-partame, a synthetic dipeptide (Sec.17.7) of aspartic acid and the methyl ester of phenylalanine (Fig. 20.7). As a dipeptide, aspartame provides the same 4.0 cal/g as do proteins, yet its intense sweetness, about 160 times that of sucrose, allows it to provide the equivalent sweetness of table sugar with about 1/160 as many calories. Aspartame is the major ingredient of sweeteners such as NutraSweet and Equal. • Q U E S T 1 O N Even though the application of the Delaney Amendment might have ended the use of saccharin as a food additive when the sweetener was shown to cause cancer in laboratory animals, its continued use was not prohibited. Why not? 20.12 An Ingredients Label for the Mango We might speculate briefly on what our attitude would be toward the chemicals of our foods and toward the hazards they present if all foods, both processed and un-processed, bore ingredients labels. Imagine what we might find if an orange grow-ing on a tree or a potato freshly dug up from the ground carried a stamp showing all the chemicals it contained. Certainly one major difference between processed foods and those prepared by nature is that packages of processed foods must carry lists of their ingredients, while foods taken directly from the ground don't. To learn what's in unprocessed foods like oranges freshly off the trees or potatoes freshly out of the ground, or in apples, steaks, tomatoes, and the like, we're forced to turn to the chemists who analyze them and study their components. Without exception, the lists of chemicals isolated from foods grown on the farm and in the orchard and sold with little or no processing far exceed those ap-pearing on the ingredients panels of processed foods. The oil of an orange, for ex ample, contains more than 40 different chemicals, grouped by organic chemists 20.13 The Questionable Joys of Natural Foods • 511 Figure 20.8 A partial ingredients list for a typical mango. a-Terpinolene, ethyl butanoate, 3-carene, ethyl acetate, ethyl 2-butenoate, a-terpinene, a-thujene, dimethyl sulfide, limonene, (3-phellandrene, myrcene, p-cymen-8-ol, (3-caryophyllene, cis-3-hexene-l-ol, hexadecyl acetate, 5-butyldihydro-3H-2-furanone, trans-2-hexenal, ethyl tetradecanoate, a-humulene, sabinene, 2-carene, camphene, ethyl octanoate, 4-isopropenyl-l-methylbenzene, l-hexanol, a-terpinene, hexanal, ethyl hexadecanoate, a-copaene, hexadecanal, ethanol, ethyl propionate, dihydro-5-hexyl-3H-2-furanone, carveol, geranial, ethyl decanoate, furfural, butyl into categories such as alcohols, aldehydes, esters, hydrocarbons, and ketones. A po- acetate, methyl butanoate, tato yields some 150 different compounds, each of which can be synthesized in a dihydro-5-octyl-3H-2-furanone, chemical laboratory or poured from a bottle on the chemist's shelf. Each is a chem- p-cytnene, octadecanal, ical put there by nature, synthesized by the plant itself as it grows. 6-pentyltetrahydro-2H-2- The mango, a particularly tasty tropical fruit, offers an excellent example of what PYranone, 2, 3-pentanedione, l, an ingredients label on a piece of a natural, unprocessed fruit might look like. Man- 1-diethoxyethane, pentadecanal, goes are prized delicacies throughout much of the world, especially in India and the butyl formate, Far East. In terms of total tonnage consumed, the mango is the most popular of all 1-butanol, 5-methylfurfural, ethyl dodecanoate, 2-acetylfuran, fruits. Figure 20.8 presents a partial list of the chemicals responsible for the flavor of 2_methyl-l-butanol, a typical mango. It represents only a small fragment of all the chemicals that make up 4-methylacetophenone, the fruit. Within Figure 20.8 the chemicals appear in decreasing order by their rela- acetaldehyde, cyclohexane. tive abundance in the essential oil, just as they would on an ingredients label. Very few of them have been examined sufficiently for use as food additives. Is the mango safe to eat? By any reasonable standard, and based on the mass-es of people throughout the world who eat mangoes daily without ill effects, the answer must be yes. (Of course, the answer could be no for those individuals who may be allergic to mangoes, for those with diabetes who may have to avoid the mango's sugars, and for others who may be sensitive to individual chemicals with-in the fruit.) Yet since its chemicals have not been tested for safety and have not been approved for use in foods, an identical mango that might somehow be man-ufactured in a food processing plant could not be sold legally as a food. At least one of the major flavor ingredients of the mango (Fig. 20.8) has been ap- • QUESTION proved for use in foods. Which one has this approval? (See Sec. 19.15 for help.) 20.13 The Questionable Joys of Natural Foods The example of mangoes can be repeated with all of our other foods, many times over and sometimes with sinister implications. Many of the compounds that form in plants and that become part of our food supply are very effective insect poi-sons, rivaling commercial insecticides in toxicity (certainly to insects and probably 512 • Chapter 20 Poisons, Toxins, Hazards, and Risks  Examples of foods containing hazardous chemicals. Nutmeg contains myristicin, a chemical that can produce liver damage and hallucinations when taken in very large amounts. Large amounts of the glycyrrhizic acid of licorice can damage the cardiovascular system. The allyl isothiocyanate of horseradish, the symphytine of comfrey, and the estragole of basil can produce tumors. to humans) and overwhelming them in number. For every gram of synthetic pes-ticide that we eat as an unwanted residue of a commercial, agricultural spray, an estimated 10 kg of natural pesticides enter our bodies as natural poisons of natu-ral foods. With some reflection, this shouldn't surprise us. With eons of evolution behind them, it's entirely reasonable that plants should develop powerful toxins as part of their chemical armory against insects and other predators. Unlike animals, plants can't run from their enemies; they can only poison them chemicals that are not only toxic in the more common sense of the word but are carcinogenic as well. Safrole, for example, makes up about 85% of oil of sassafras, which comes from the bark around the root of the sassafras tree and is also a minor component of cocoa, black pepper, and spices and herbs such as mace, nutmeg, and Japanese wild ginger. Safrole produces the taste of sassafras tea and was at one time used as the principal fla-voring ingredient in the manufacture of root beer. Both the oil of sassafras and safrole itself have been banned from use as food additives. Safrole produces liver cancer in mice and has been listed as a carcino-gen by the Environmental Protection Agency. The FDA judges both safrole and the oil to be too dangerous for use in foods and considers any food containing ei-ther one of them to be adulterated. Figure 20.9 shows safrole and several additional plant substances that pro-duce tumors in mice: • allyl isothiocyanate, a pungent, irritating oil that occurs in brown mustard as well as horseradish and garlic and is also known as mustard oil; 20.13 The Questionable Joys of Natural Foods • 513 Table 20.3 Toxic or Carcinogenic Chemicals Occuring Naturally in Foods or Produced through Cooking Food Substance Source Potential Hazard E Y Allyl isothiocyanate Brown mustard, Tumors horseradish, garlic Benzo(a)pyrene Smoked and broiled meat Gastrointestinal cancer Oil of bitter almond General toxicity cashew nuts, lima beans Dimethylnitrosamine Cooked bacon Cancer Estragole Basil, fennel, oil of tarragon Tumors Glycyrrhizic acid Licorice Hypertension and cardiovascular damage Cancer Gastrointestinal distress (Sec.16.13) Black pepper, carrots, celery, Hallucinations dill, mace, nutmeg, parsley Oxalic acid Rhubarb, spinach Kidney damage Saxitoxin Shellfish Paralysis Symphatine Comfrey plant Tumors Tannic acid and related Black teas, coffee, cocoa Cancer of the mouth and tannins throat Tetrodotoxin Pufferfish Paralysis Cyanides Hydrazines Raw mushrooms Lactose Milk Myristicin   This word moderation holds the key to our own defenses against food toxins. For most of our ordinary foods, normal levels of consumption lie far below any-thing that might produce an acute illness. Although the myristicin of nutmeg (Table 20.3), eaten in very large quantities at one sitting, can produce hallucinations and liver damage, the amount of nutmeg ordinarily used in even the most heavily spiced meal runs about 1 or 2% of the quantity needed to produce anything more notable than flavorful food. To suffer cardiovascular damage from the glycyrrhizic acid of licorice seems to require eating perhaps 100 g of the candy each day for several days. Caffeine, with its LDSO of about 130 mg/kg in mice, is the major physiologically active com pound of coffee and a powerful stimulant of the central nervous system. At 100 to 150 mg of caffeine to a cup of coffee, it would take about 70 cups of coffee at one sitting to reach the mouse's LDSO in a 70-kg human. Surely other, urgent problems would arise long before the approach of a lethal dose. (Structures of caffeine, gly-yrrhizic acid, and myristicin appear in Fig. 20.10.) The body's most effective shield against molecular poisons lies in the opera-tion of the liver. This organ can call up a great variety of metabolic reactions to change the chemical structures of poisons, usually rendering them harmless. As long as a healthy liver isn't overpowered by a massive dose of any one toxin, it can effectively protect the rest of the body. By using a variety of metabolic defenses, the liver far more easily disposes of, say, a tenth of a gram of each of 10 different tox-ins than the same total weight, one gram, of a single toxin. While small amounts of the 10 poisons might be metabolized effectively by 10 different enzymatic reac- s, a large dose of a single poison could overwhelm the only biochemical path 514 • Chapter 20 Poisons, Toxins, Hazards, and Risks   CH3 CH3- O O--\\ /r CHZ - CH = CHZ  Myristicin Caffeine Figure 20.10 Caffeine, myristicin, and glycyrrhizic acid. available for its removal. In this sense a varied diet, which implies eating foods containing a variety of natural toxins, each present in exceedingly small amounts, is far less hazardous than a diet that concentrates on large quantities of only one or two foods. • Q U E S T I O N What hazardous chemical occurs in each of the following and what effects or bod-ily harm are associated with it? (a) nutmeg; (b) licorice; (c) rhubarb; (d) black tea; (e) horseradish.  20.14 Some Factors to Be Considered in Spreading Poisons All Around In opening this chapter we demonstrated that an insecticide can be safe enough for use in the human environment even though it's lethal to insects. One factor we examined there is the quantitative difference between the concentration of the active ingredient in the human body and the insect body. Anoth~j important factor, Perspective • 515  t i which we only touched on in that discussion, involves differences in the effects of poisons on different species-insects and humans in the opening demonstration. As the chapter progressed we examined LDsos, which allow us to quantify these differences in toxic effects, and we defined "safety" in terms of our own and soci-ety's judgments about potential hazards. In an earlier discussion of Dr. Wiley's Poison Squad (Sec. 19.12) we saw an example of how poisons were tested near the beginning of the 20th century by feeding them to human volunteers. Ethical standards for testing chemical hazards have changed since then. Humans, even volunteers, no longer form Poison Squads, and the use of animals such as mice and rabbits is coming under critical examina-tion. In the closing Perspective we'll see how technical advances in microbiology have provided a simple technique for testing the mutagenic effects of chemicals using nothing more advanced biologically than bacteria.  P E R S P E C T 1 V E ฎ How Many Dead Mice Is a Bowl of Fresh Cereal Worth? Today laboratory animals, usually mice, replace Dr. Wiley's human Poison Squad volunteers. Even now, though, both a heightened sense of ethics and the costs of large-scale an-imal testing spur the development of other, faster, less ex-pensive, and more humane tests: laboratory studies of a type that would provide accurate information without the sacrifice of large numbers of laboratory animals. New laboratory procedures such as the Ames test, de-veloped by Bruce N. Ames of the University of California, Berkeley, may point the way to better, less expensive, and surer methods of toxicity testing. The Ames test operates on the assumptions that both cancer and mutations begin with genetic damage of some sort and that a chemical mu-tagen stands a very good chance of being a chemical car-cinogen as weILThe test uses a strain of bacteria known as Salmonella typhimurium that is modified biologically to make it very sensitive to genetic damage by chemical means and therefore sensitive to chemically induced mu-tation. What's more, the bacteria are altered further so that the amino acid histidine, which is normally a nonessential di-etary amino acid for the bacteria, becomes an essential amino acid (Sec. 17.4). As a result of its newly acquired de- Bruce N.Ames, developer of the Ames test to determine pendence on histidine as an essential amino acid, a colony whether chemicals produce mutations in certain bacteria. A of the biologically altered bacteria won't grow in the ab- Positive Ames test suggests that the chemical may also cause sence of this amino acid. But exposing it to a mutagen that cancer. switches it back to its more common form allows it to syn- that may not be mutagens themselves but that are convert- thesize its own histidine and to flourish. ed into other, mutagenic substances as the liver enzymes In practice the investigator places the altered bacte- detoxify them. Adding the chemical under examination ria in a medium that contains all the needed nutrients for starts the test. Rapid growth of the bacterial colony, at a growth, except histidine, as well as an extract taken from rate comparable to that of unaltered bacteria under the rat livers. Using the liver extract helps identify chemicals same conditions, indicates that the added chemical (or 616 • Chapter 20 Poisons, Toxins, Hazards, and Risks  whatever it's being metabolized to) is a mutagen and caus-es the bacteria to switch back to the form for which histi-dine is a nonessential amino acid. Because of a very good overlap between the list of chemicals known to produce mutations and those known to cause cancer-about 90% of the chemicals on each list appear on the other-the Ames test and similar tech-niques can serve as useful, rapid, and inexpensive screen-ing tools for identifying chemical carcinogens. Yet laboratory animals, which stand far closer to humans in their genetic makeup than bacteria do, still offer the best and most reliable estimate of chemical dangers to hu-mans. In this respect, questions of ethical and economi-cal values in animal testing must be balanced against the reliability of the animal experiments in protecting humans against chemical harm. In concluding, we return to the questions about safety that began this chapter. We've seen that all chemicals pres-ent hazards. We've seen that there are, indeed, poisons and carcinogens in our foods and that they are to be found in processed foods and in natural, unprocessed foods as well. We've seen that various governmental agencies have the power to protect us from excessive, known chemical risks but that it is our own judgment of the acceptability of risks, both as individuals and as members of society, that ul-timately determines the issue of safety. We've seen, finally, that the idea of absolute safety is a phantasm.To the extent that we are well informed and that our judgments are sound, we can weigh the very real benefits that chemicals provide and balance them against the very real risks of their use. In this way, and only in this way, can we ensure that our world, while never free of hazards, is indeed safe.  E X E R C I S E S  For Review 2, 3, 7, 8-tetrachlorodibenzo- lethal 1. Following are a statement containing a number of blanks P-dioxin mutagens and a list of words and phrases. The number of words equals acceptability oil of sassafras the number of blanks within the statement, and all but two of aspirin risk the words fit correctly into these blanks. Fill in the blanks of the body weight saccharin statement with those words that do fit, then complete the state- botulinum toxin A safrole ment by filling in the two remaining blanks with correct words carcinogens sodium cyanide (not in the list) in place of the two words that don't fit. diphtheria toxin TCDD Since anything can be harmful if we consume it in excessive half teratogens amounts or use it carelessly or improperly, everything we come in contact with presents some risk of . Be- injury tetanus toxin cause of this, we find it useful to define safety as the LDso of . One measure of lethal risk in 2, Describe, define, or identify the following: the chemicals we consume is the , which is the weight of the substance (per unit of ) that is aflatoxin OSHA to of a large population of labora- comfrey parathion tory animals. According to this measure, the deadliest chem- isoflurophate solanine ical known is , produced by a common 3• What contribution did each of the following make to the microorganism. Second and third on the list of deadly chem- subject matter of this chapter: (a) William Lowrance, (b) James icals, respectively, are and . The J. Delaney, (c) Bruce N. Ames, (d) Ira Remsen and Constantine fourth most lethal chemical is one produced by laboratory Fahlberg, (e) Harvey W Wiley? reactions carried out by humans, , which is also known by the simpler term . Other risks, not '`}Name a chemical affected by each of the following acts of immediately lethal, include the risk of severe birth defects, Congress and describe how the law affects our use of the chem- produced by ; the lesser genetic changes in- ical: (a) the Poison Prevention Packaging Act of 1970, (b) the duced by ; and the risk of cancer, generated by Saccharin Study and Labeling Act of 1977. . Among the carcinogens are natural products 6• In what food does each of the following chemicals occur: such as , which is a component of , (a) lactose, (b) glycyrrhizic acid, (c) myristicin, (d) oxalic acid, and the synthetic sweetener . Both of these (e) benzo(a)pyrene, (f) tetrodotoxin? chemicals are banned from use as food additives by provi- 6. What governmental agency is responsible for (a) investi- sions of the , but the sweetener is in continued gating outbreaks of illness caused by food spoilage; (b) the use because of the enormous public demand for it. The reg- chemicals of beer, wine, liquor, and tobacco; (c) chemical pes- ulation of food additives is the responsibility of the ticides; (d) exposure to chemicals in the workplace; (e) chem- , an agency of the federal government. icals used as food additives? What the experiment showed was that the number of through the vacuum of space to the Earth. To test this idea, muon neutrinos coming up through the Earth to the de- scientists are now trying to determine whether the number tector was smaller than the number that reached it when of solar neutrinos arriving at the detector varies with the the Sun was overhead. These data suggest that the muon seasons. Remember that the Earth is about 3 percent neutrinos change to another type of neutrino on their way closer to the Sun in winter than in summer, and this differ- through the Earth. Those that travel only through the ence may be enough to affect our neutrino counts. Earth's atmosphere don't have time to undergo this As you can see, ideas in science really do change as we change. Since neutrinos can change type only if they have are able to do better and better experiments. For decades, mass, this experiment is the first persuasive evidence that students were taught that the neutrino had no mass. When at least some lands of neutrinos do have mass. it was announced at a scientific conference in Japan in 1998 Unfortunately, this experiment does not tell us whether that the muon neutrino apparently does have mass, the au- the electron neutrinos produced by the Sun have mass. dience stood and cheered. New experiments over the next The Japanese detector sees equal numbers of electron decade should help determine whether the other types of neutrinos in all directions. All this really tells us is that the neutrinos also have mass and if so how much. And that, in electron neutrinos do not change from one tvpe to another turn, may help us solve the mystery of the missing solar as they pass through the Earth. They still might change neutrinos and understand even better just how the Sun type on their long journey from the interior of the Sun produces its vast output of energy   Plastics, Water, and Rubbing Alcohol Figure 21.1 Separating plastics of different densities with a mixture of isopropyl alcohol (rubbing alcohol) and water. The more dense plastics sink; the less dense plastics float.  Plastics are remarkably useful materi-als, but one of their greatest advantages over other materials, their durability, is also one of their greatest handicaps. They don't disintegrate. Once we dump them into the environment, they just stay there. Some plastics seem to last forev-er. One way to keep discarded plastics from overwhelming us is to recycle them, to use them over and over again. But there are different kinds of plastics, and one type doesn't mix well with another. To reuse plastics we have to separate one kind from another so that we can combine all compatible plastics into one group and reprocess them as a whole. One way to sort them is by taking advantage of differences in the densities of different kinds of plastics (Sec. 13.1). You can do this yourself by using some rubbing alcohol, water, and a few pieces of different kinds of plastics. For a good start, use the rather hard plastic of a milk bottle. (Be sure to use a plastic bottle, not a waxed paper carton.) Another good plastic to use here is a trash bag. Plastic milk bottles are made of a high-density polyethylene, while trash bags are made of a low-density polyethylene. Made by one process, the polyeth-ylene forms as a hard, rigid, high-density material well suited to bottles and other con-tainers. Made in a different way, the polyethylene forms as a soft, flexible, low-density plastic that gives trash bags their desirable characteristics. A mixture of one part water to two parts rubbing alcohol, by volume, provides a good start for separating the two.The milk bottle plastic should sink in this mixture and the trash bag should float. If both sink, add a little water. If both float, add a bit of rubbing alcohol. Water is more dense than the isopropyl alcohol of the rubbing alcohol (Sec. 9.7). If both plastics sink, adding some water should force the less dense plastic to float. Adding the rubbing al-cohol decreases the density of the liquid mixture, causing the more dense plastic to sink. Either way, by adding water or rubbing alcohol to adjust the density of the liquid, you can separate plastics of different densities. Once you learn how with the polyethyl-enes, try separating pieces of plastic taken from other containers (Fig. 21.1).Tech niques of this sort can help us keep used plastics out of our trash dumps and put them back into consumer products. A ,. 21.1 The Age of Plastics If an era is known by the kinds of materials its people use to manage the world they live in, then the Stone Age, the Bronze Age, and the Iron Age have given way to our own Plastic Age. Plastics form much of our packing and wrapping materials, many of our bottles and containers, textiles, plumbing and building materials, furniture and flooring, paints, glues and adhesives, electrical insulation, automobile parts and bod-ies, television, stereo and computer cabinets, medical equipment, cellular telephones, 520 21.1 The Age of Plastics • 521   compact disks, personal items, including pens, razors, toothbrushes, and hairsprays, and even the plastic bags we use to discard all our plastic trash. Except for our food, air, and water, almost every ordinary thing we come into contact with each day contains some sort of plastic somewhere in, on, or around it. So many of our throwaway goods are made of plastic that, despite its low density, the material makes up roughly 10% of the total weight of all solid municipal wastes, largely as plastic containers and pack-ing materials. What's more, at about a quarter of the entire volume of our trash, plas-tic products form a highly visible part of what we discard. We'll have more to say about the problem of plastic wastes in the Perspective. In 2000 the U.S. chemical industry produced over 37 million tons (roughly 34 billion kilograms) of unprocessed, raw plastics of all kinds. Table 21.1 describes Plastics in everyday trash. some of the more important properties and uses of the most common commercial plastics, in declining order of the quantities manufactured. About half of all man-ufactured plastics goes into packaging and into building and construction materi-als; roughly 10% forms personal consumer products; the remainder is used in a variety of products, including furniture, parts for cars and other vehicles, and elec-trical and electronic equipment. Table 21.1 MajorTypes of Commercial Plastics and Related Materials Plastic Characteristics Typical Applications Low-density polyethylene Low melting; very Bags for trash and consumer products; flexible; soft; squeeze bottles; food wrappers; coatings for low density electrical wires and cables Poly(vinyl chloride), Tough; resistant Garden hoses; inexpensive wallets, purses, ; also known as PVC to oils keyholders; bottles for shampoos and foods; blister packs for various consumer products; plumbing, pipes, and other construction fixtures High-density polyethylene Higher melting, Sturdy bottles and jugs, especially for milk, water, ' more rigid, stronger, liquid detergents, engine oil, antifreeze; shipping and less flexible drums; gasoline tanks; half to two-thirds of all than low-density plastic bottles and jugs are made of this plastic polyethylene Polypropylene Retains shape at Automobile trim; battery temperatures well cases; food bottles and above room caps; carpet filaments temperature and backing; toys Light weight; can be Insulation; packing materials, including converted to plastic "plastic peanuts"; clear drinking glasses; thermal foam cups for coffee, tea, and cold drinks; inexpensive tableware and furniture; appliance cabinets Poly(ethylene terephthalate), Easily drawn into Synthetic fabrics; food packages; backing for also known as PET strong, thin filaments; magnetic tapes; soft drink bottles forms an effective barrier to gases Phenol-formaldehyde Strongly adhesive Plywood; fiberboard; insulating materials ` resins Polystyrene Nylon Easily drawn into Synthetic fabrics; strong, thin filaments; fishing lines; gears and resistant to wear other machine parts 522 • Chapter 21 Polymers and Plastics Durable or fragile, rigid or flexible, sturdy or flimsy, dense or light, strong or weak, plastics provide us with inexpensive materials of virtually unlimited prop-erties. With chemical ingenuity we can transform them into almost whatever shapes we wish with almost whatever properties we desire. And at their root, in the polymeric molecules that make up these extraordinary substances of our every-day world, lies one of the shining achievements of modern chemistry. We'll begin by examining the difference between the plastics of our world and the polymers that form them. • Q U E S T 1 O N Plastic makes up about 10% of the mass of our discarded trash, but about 25% of its volume. What is the likely reason for the difference between these two figures? 21.2 Plastics and Polymers  Plastics, especially the plastics of our most common commercial products, are materials that we can shape into virtually any form we want. The word itself comes from the Greek plastikos, for a substance that's suitable for molding or shaping. We can form plastics into round, hard, resilient bowling balls, draw them out into the thin, flexible threads of synthetic fibers, mold them into in-tricately designed, durable machine parts, or flatten them into flimsy but tough A plastic is a material capa- sheets of clinging kitchen film. Today, the word plastic refers mostly to a prop- ble of being shaped into virtu- erty of a material: its ability to be shaped into the myriad forms of today's com- ally any form. mercial and consumer products. When we speak of a polymer, though, we return to the molecular level. All the plastics of our everyday lives, as well as all the proteins, starch and cellulose of our foods; the cotton, silk, and wool of our textiles; and even the DNA that carries the genetic code within the nucleus of the cell are formed of enormously large polymeric molecules. The combination of the Greek words poly, meaning many, and meros, parts, gives us the word for the molecules that compose these substances, A polymer is a molecule of polymer. A polymer is a molecule of very high molecular weight, formed through very high molecular weight the repeated chemical linking of a great many smaller molecules. formed by the repeated chemi- As the word implies, polymers are extremely large molecules, sometimes called cal linking of a great many macromolecules to emphasize their very large size. The individual parts that com- simpler, smaller molecules. bine to form them, their monomers (from the Greek mono, signifying one or a Monomers are the individual single unit), join to each other in enormously large numbers to produce polymers structures that are linked to with molecular weights ranging from the tens of thousands to millions of atomic each other to form a polymer. mass units. In many polymers the monomers have joined to each other to form enor-mously long, linear molecular threads, very much like long chains we might find in a hardware store (with the individual links representing the monomers). In other polymers the chains may be branched to various degrees, or they may be inter-connected at occasional junctions, or so frequently that they form a web or even a rigid, three-dimensional lattice (Fig. 21.2). In any event, a polymer is a substance composed of huge molecules, sometimes in the form of very long chains, some-times as sheets, sometimes as intricate, three-dimensional lattices. A plastic, on the other hand, is a material that can be molded readily into a va-riety of shapes. All of today's commercial plastics are polymers, even though some .V . . _ . . r. of our most important polymers-the starch and cellulose of our foods (Chap-ter 16), the proteins of our foods and bodies (Chapter 17), and the silicates of our earth (Sec. 21.15), for example-are not at all plastic. 21.3 Modes of Polymerization: Addition Polymers and Condensation Polymers • 523 An unbranched polymeric chain - CHz - CHz - CHz - CHz - CHz - CHz - CHz - CHz - CHz - CHz - CHz - CHz - A branched polymeric chain t ~`.~i I&F S.. ~ ( ~W ~ ,'.~14 - +~ 1~a ~! CHz - CH2 - i Hz - CHz - CHz - CHz - CH2 - CH2 - CHz - CHz - i Hz - CH,) I H2 I Hz - CHz - CH3 I Hz iHz iH2 CHz - CHz - CHz CHz - CH3 CHz - CHz - CHz Figure 21.2 Chains and polymers. We'll begin our review of plastics and polymers by examining their • chemistry of formation, • molecular structures, and • physical properties. Then we'll look briefly at a history of polymers and their discoverers and inventors.  What are three polymers found as major components of our foods? • Q U E S T I O N  21.3 Modes of Polymerization: Addition Polymers and Condensation Polymers  The actual linking of the monomers through covalent bonds occurs through poly- Polymerization is the merization, a chemical process easily divided into two broad categories: addition process whereby individual polymerization (which produces addition polymers) and condensation polymer- monomers link together to ization (which produces condensation polymers). Addition polymers, such as poly- form a polymer. ethylene (Sec. 21.13) and several of its close molecular relatives, dominate today's chemical economy. They account for more than half of all the plastics currently 20.13 The Questionable Joys of Natural Foods • 513 Table 20.3 Toxic or Carcinogenic Chemicals Occuring Naturally in Foods or Produced through Cooking Food Substance Source Potential Hazard E Y Allyl isothiocyanate Brown mustard, Tumors horseradish, garlic Benzo(a)pyrene Smoked and broiled meat Gastrointestinal cancer Oil of bitter almond General toxicity cashew nuts, lima beans Dimethylnitrosamine Cooked bacon Cancer Estragole Basil, fennel, oil of tarragon Tumors Glycyrrhizic acid Licorice Hypertension and cardiovascular damage Cancer Gastrointestinal distress (Sec.16.13) Black pepper, carrots, celery, Hallucinations dill, mace, nutmeg, parsley Oxalic acid Rhubarb, spinach Kidney damage Saxitoxin Shellfish Paralysis Symphatine Comfrey plant Tumors Tannic acid and related Black teas, coffee, cocoa Cancer of the mouth and tannins throat Tetrodotoxin Pufferfish Paralysis Cyanides Hydrazines Raw mushrooms Lactose Milk Myristicin   This word moderation holds the key to our own defenses against food toxins. For most of our ordinary foods, normal levels of consumption lie far below any-thing that might produce an acute illness. Although the myristicin of nutmeg (Table 20.3), eaten in very large quantities at one sitting, can produce hallucinations and liver damage, the amount of nutmeg ordinarily used in even the most heavily spiced meal runs about 1 or 2% of the quantity needed to produce anything more notable than flavorful food. To suffer cardiovascular damage from the glycyrrhizic acid of licorice seems to require eating perhaps 100 g of the candy each day for several days. Caffeine, with its LDSO of about 130 mg/kg in mice, is the major physiologically active com pound of coffee and a powerful stimulant of the central nervous system. At 100 to 150 mg of caffeine to a cup of coffee, it would take about 70 cups of coffee at one sitting to reach the mouse's LDSO in a 70-kg human. Surely other, urgent problems would arise long before the approach of a lethal dose. (Structures of caffeine, gly-yrrhizic acid, and myristicin appear in Fig. 20.10.) The body's most effective shield against molecular poisons lies in the opera-tion of the liver. This organ can call up a great variety of metabolic reactions to change the chemical structures of poisons, usually rendering them harmless. As long as a healthy liver isn't overpowered by a massive dose of any one toxin, it can effectively protect the rest of the body. By using a variety of metabolic defenses, the liver far more easily disposes of, say, a tenth of a gram of each of 10 different tox-ins than the same total weight, one gram, of a single toxin. While small amounts of the 10 poisons might be metabolized effectively by 10 different enzymatic reac- s, a large dose of a single poison could overwhelm the only biochemical path 514 • Chapter 20 Poisons, Toxins, Hazards, and Risks   CH3 CH3- O O--\\ /r CHZ - CH = CHZ  Myristicin Caffeine Figure 20.10 Caffeine, myristicin, and glycyrrhizic acid. available for its removal. In this sense a varied diet, which implies eating foods containing a variety of natural toxins, each present in exceedingly small amounts, is far less hazardous than a diet that concentrates on large quantities of only one or two foods. • Q U E S T I O N What hazardous chemical occurs in each of the following and what effects or bod-ily harm are associated with it? (a) nutmeg; (b) licorice; (c) rhubarb; (d) black tea; (e) horseradish.  20.14 Some Factors to Be Considered in Spreading Poisons All Around In opening this chapter we demonstrated that an insecticide can be safe enough for use in the human environment even though it's lethal to insects. One factor we examined there is the quantitative difference between the concentration of the active ingredient in the human body and the insect body. Anoth~j important factor, Perspective • 515  t i which we only touched on in that discussion, involves differences in the effects of poisons on different species-insects and humans in the opening demonstration. As the chapter progressed we examined LDsos, which allow us to quantify these differences in toxic effects, and we defined "safety" in terms of our own and soci-ety's judgments about potential hazards. In an earlier discussion of Dr. Wiley's Poison Squad (Sec. 19.12) we saw an example of how poisons were tested near the beginning of the 20th century by feeding them to human volunteers. Ethical standards for testing chemical hazards have changed since then. Humans, even volunteers, no longer form Poison Squads, and the use of animals such as mice and rabbits is coming under critical examina-tion. In the closing Perspective we'll see how technical advances in microbiology have provided a simple technique for testing the mutagenic effects of chemicals using nothing more advanced biologically than bacteria.  P E R S P E C T 1 V E How Many Dead Mice Is a Bowl of Fresh Cereal Worth. Today laboratory animals, usually mice, replace Dr. Wiley's human Poison Squad volunteers. Even now, though, both a heightened sense of ethics and the costs of large-scale an-imal testing spur the development of other, faster, less ex-pensive, and more humane tests: laboratory studies of a type that would provide accurate information without the sacrifice of large numbers of laboratory animals. New laboratory procedures such as the Ames test, de-veloped by Bruce N. Ames of the University of California, Berkeley, may point the way to better, less expensive, and surer methods of toxicity testing.The Ames test operates on the assumptions that both cancer and mutations begin with genetic damage of some sort and that a chemical mu-tagen stands a very good chance of being a chemical car-cinogen as weILThe test uses a strain of bacteria known as Salmonella typhimurium that is modified biologically to make it very sensitive to genetic damage by chemical means and therefore sensitive to chemically induced mu-tation. What's more, the bacteria are altered further so that the amino acid histidine, which is normally a nonessential di-etary amino acid for the bacteria, becomes an essential amino acid (Sec. 17.4). As a result of its newly acquired de- Bruce N.Ames, developer of the Ames test to determine pendence on histidine as an essential amino acid, a colony ~'~'hether chemicals produce mutations in certain bacteria.A of the biologically altered bacteria won't grow in the ab- Positive Ames test suggests that the chemical may also cause cancer. sence of this amino acid. But exposing it to a mutagen that switches it back to its more common form allows it to syn- that may not be mutagens themselves but that are convert- thesize its own histidine and to flourish. ed into other, mutagenic substances as the liver enzymes In practice the investigator places the altered bacte- detoxify them. Adding the chemical under examination ria in a medium that contains all the needed nutrients for starts the test. Rapid growth of the bacterial colony, at a growth, except histidine, as well as an extract taken from rate comparable to that of unaltered bacteria under the rat livers. Using the liver extract helps identify chemicals same conditions, indicates that the added chemical (or 474 • Chapter 19 Vitamins, Minerals, and Additives 19.9 Foods versus Pills The discussion of "natural" versus "synthetic" vitamins brings us to a related ques-tion: If all molecules of any particular vitamin are mutually identical, regardless of their source, does it matter whether we get our vitamins from a well-balanced diet. or can we eat what we please and rely on vitamin and mineral supplements for our micronutrients? The answer seems to be that it matters very much whether we get our vitamins from food or pills, that a well-balanced diet is far superior to re-liance on vitamin and mineral supplements. The following explains why. While there's no solid evidence that vitamins can cure any disease (other than de-ficiency diseases), there is circumstantial evidence that some vitamins, particularly C and E, and the (3-carotene that forms vitamin A, might prevent certain diseases, es pecially heart disease and some forms of cancer. The problem with this kind of evi-dence is that it comes largely from two different kinds of studies, involving people • whose diets are rich in fresh fruits and vegetables, and • others who report taking high doses of vitamin supplements. The correlation between diets containing plentiful amounts of vitamin-containing foods-especially fresh fruits and vegetables-and a low incidence of cancer and other diseases is well established. Based on evidence of this sort, gov ernment agencies and health organizations have been urging us for many years to increase the proportions of fresh fruits and vegetables in our diets as protection against heart disease, cancer, and perhaps other illnesses. Yet even an established connection between consumption of foods that con-tain plenty of vitamins and low cancer rates doesn't prove that the vitamins are the active agents in disease prevention. There are many uncertainties. Perhaps specific, as-yet-unidentified components of these foods, other than vitamins, guard against the disease. Or maybe there are other, as-yet-unrecognized pro-tective characteristics common to people who eat lots of fresh fruits and veg-etables. The same sort of reasoning also clouds any conclusions about those who take vitamin supplements. Several double-blind studies (Perspective, Chapter 23) have been carried out to clarify these ambiguities and to pinpoint the effects of the vitamins themselves. One, which ended in 1996, examined a group of about 18,000 men and women who were considered to have a high risk of lung cancer because of their history of smoking or exposure to asbestos. Those who took large doses of (3-carotene and of vitamin A daily for at least four years showed a 28 % increase in incidence of lung cancer and a 17% increase in overall death rate, compared to those in the group who did not take these large doses of the supplements. These results echo the con-clusions of a study of 30,000 male smokers in Finland that ended in 1994. Smok-ers in that study who took supplements of vitamin E over periods of five to eight years were more likely to die of strokes than those who did not take the supple-ments, and those taking (3-carotene were more likely to die of lung cancer or heart disease. (In still another recent study of 22,000 male physicians, taking (3-carotene supplements every other day for 12 years produced no benefits and did no harm.) One possible interpretation of the results of these studies is that plant chem-icals (phytochemicals, from the Greek word phuton, for plants) other than vitamins might produce the protective effects noted in previous studies. We'll have more to say about this in the Perspective of this chapter. • QUESTION What evidence suggests that plant chemicals other than vitamins may offer pro-tection against cancer, heart disease, and strokes? Like humans, guinea pigs need a dietary source of vitamin C. 19.7 Vitamin The mango is a source of vitamin C for the Indian fruit bat. The bulbul bird also requires a dietary source of vitamin C. humans, nor the oldest, including the invertebrates and fishes, can produce ascor-bic acid. The intermediate orders in the chronology of evolution, including am-phibians, reptiles, and the more ancient birds, developed the ability to form ascorbic acid themselves. need to obtain ascorbic acid from food, as do the Indian fruit bat, the guinea pig, and a favorite songbird of the Ori-ent, the bulbul bird. What is the first visible symptom of a severe deficiency of vitamin C? •QUESTION What is the origin of this symptom? The major medical use of the vitamins lies largely in curing the deficiency diseases, those caused by their ab-sences from the diet. Vitamin A certainly alleviates the night blindness caused by a deficiency of vitamin A; vitamin D unquestionably prevents rickets; vitamin C dramatically cures scurvy. , .. ,. 19.10 Health Foods versus Junk Foods • 475 To this point in our examination of the chemicals of our foods, we've considered the chemicals that appear in foods without any human intervention: the macronu-trients and vitamins that plants and animals form through their own biochemical processes and the minerals that plants receive directly from the soil and animals get from the foods they eat. We'll soon look at some of the chemicals we ourselves add to our foods as we prepare, cook, or process them for our tables and that food manufacturers and processors add to foods they package. Before moving to these food additives we'll examine one final pair of categories: health foods and junk foods. We sometimes speak of highly processed foods, sweet foods, snacks, and/or foods served by fast-food restaurants as junk foods. On the other hand, we sometimes think of unprocessed or uncooked fresh fruits and vegetables or foods with little or no sugar, fat, or cholesterol as health foods. Descriptions like these can be a bit vague and hard to apply in specific instances. It's clear that one of the difficulties in discussing health foods and junk foods stems from the lack of a general agreement on what these terms mean. One way of sorting one from the other is by balancing the number of calories in any par ticular food against its content of minerals and vitamins. Since we need energy, in moderate amounts, to maintain life and health and since all foods provide energy, we can differentiate among our foods by focusing on the relative proportions of their calories and their micronutrients. The micronutrients don't supply us directly with energy, we are dealing with two distinct categories here, with no over- lap. Using this approach and applying what we have learned about the chemistry By one definition, a junk food of food, we can describe at least one of the two classes of foods in chemical terms. is a food that supplies a large A junk food, by one popular definition that also makes good chemical sense, is a number of calories but few food that supplies a large number of calories but few micronutrients. A "health food" store, where we can find "organic foods," "natural foods," and foods "without chemicals." 476 • Chapter 18 Vitamins, Minerals, and Additives Sometimes the term empty calories enters into these discussions, often with reference to a food, such as highly refined sugar, that provides calories but few or no micronutrients to accompany them. Highly refined sugar is, as we know, puri fied sucrose, a carbohydrate. As such it's one of the three classes of macronutrients and furnishes us with energy at the rate of 4.0 Cal/g. We saw in Chapters 8 and 16 that sucrose and other carbohydrates provide the energy we need for our basal me-tabolism, physical activities, and specific dynamic action. Consumed in excessive amounts, sugar, or any of the other macronutrients for that matter, also provides the energy we store as fat. Turning now to health foods, we find the label used so loosely and with so little general agreement that it's nearly impossible to define. Nonetheless, using the idea that the relative proportions of calories and micronutrients are impor- By one definition a health tant to good health, we can conclude that, in general, the larger the variety and food is a food that supplies a amount of micronutrients that a food provides and the fewer its calories, the more large number of micronutri- likely we are to consider it a health food. While this doesn't provide a precise def-ents compared with its calo- ries.This definition does not inition or description of a "health food" and doesn't take into consideration cho- take into consideration the lesterol, saturated fats, fiber, and other factors that affect our state of health, it food's content of saturated does give us a basis for examining various foods and assessing their nutritional fats, cholesterol, or other fac- value. In the next section we'll look at some quantitative ways to estimate the lev- tors that can affect our health. els of these components. • Q U E S T 1 O N Is there any processed, packaged food sold in grocery stores or supermarkets that can be considered a health food? If your answer is yes, identify one. If it's no, ex-plain why not. 19.11 Nutrition Facts, Daily Values, and Ingredients Labels Tables 19.1 and 19.2 show us what kinds of foods provide the minerals and vita-mins we need. But this leaves us with questions of how much we need of each and what quantities our foods provide. Table 19.3 presents a representative set of RDAs for minerals and vitamins selected from the 1989 publication. The RDAs serve a valuable role as quantitative standards for recommending daily dietary intakes of our micronutrients, yet they suffer from a few weakness-es. Although establishing RDAs for various categories of gender, age, weight, height, and conditions such as pregnancy and lactation increases the statistical and 19.12 How the Search for Food Additives Led to Marco Polo's Adventures in the Orient • 479 19.12 How the Search for Food Additives Led to Marco Polo's Adventures in the Orient, Columbus's Voyage to America, and Dr. Wiley's Poison Squad Food additives of one sort or another have been with us for a long time. They've been in use since prehistoric cooks began salting and smoking meat to preserve it against decay. Food dyes were used to improve the appearance of food by the Egyptians as early as 3500 years ago. Adding herbs, spices, and sweeteners is also an ancient practice. Another ancient practice, especially among the manufacturers and vendors of food, was the use of additives to make bad food more palatable. Covering the foul tastes and odors of spoiled food was the principal function of spices in the Middle Ages. Indirectly, the lack of good methods for preserving food in those times led to the opening of trade routes to the Orient and to the European discovery of the West-ern Hemisphere. It was at least partly the search for foreign spices that led Marco Polo eastward to the Orient and Columbus westward to the New World. As the centuries passed and people throughout the world moved from the coun-tryside to the cities in more modern times, the distance from the farm and the dairy herd to the dinner table lengthened and so did the time it took to transport food from where a combination of sodium chloride and calcium phosphate designed for use as a food seasoning. As the use of additives grew, the variety of the chemicals used as additives also increased, and so did their hazards. We now have effective governmental regulations to ensure the safety of the chemials added to our foods. That wasn't always the case. In the United States of the late ~OOs, the uninformed and indiscriminate use of chemicals as food additives led to fre-uent and sometimes fatal outbreaks of illness and, eventually, to detailed regulation v the federal government. The first step, taken in 1902, was the formation of a group }thin the U.S. Department of Agriculture to examine the usefulness and the dangers 'food additives. Headed by Dr. Harvey W Wiley, an American chemist who was at , rime the chief of the Department's Bureau of Chemistry, the group became known ~ Wiley's Poison Squad. His group of a dozen healthy young volunteers taken +oke Department actually ate the additives under investigation, along with their ~~arefully supervised meals, while Wiley watched for signs of illness. The FDA is now part of the U.S. Department of Health and Human Services. In 1902, Dr. Harvey W Wiley of the United States Department of Agriculture organized a Poison Squad of volunteers to begin the first tests of the effects of food additives on, humans. What chemicals were used to formulate the first patented food additive? Calcium herbs, spices, and sweeteners QUESTION What was the function of the additive? 480 • Chapter 19 Vitamins, Minerals, and Additives 19.13 The Law of Additives Several amendments and other changes since 1906 have extended and strengthened the Pure Food and Drug Act. • pesticides; • color additives; • substances approved by earlier acts of Congress; and • new animal drugs. To work backward through this list of exemptions, the bottom four are de-fined and regulated either in other laws or in some other section of this Act, Figure 19.8 The legal definition of a food additive as it appears in the current version of the federal Food, Drug, and Cosmetic Act. The term "food additive" means any substance the intended use of which results or may reasonably be expected to result, directly or indirectly, in its becoming , a component or otherwise affecting the characteristics of any food (including any ~ substance intended for use in producing, manufacturing, packing, processing, ' preparing, treating, packaging, transporting, or holding food; and including any source of radiation intended for any such use), except that such term ~ does not include- 1. a pesticide chemical in or on a raw agricultural commodity; or 2. a pesticide chemical to the extent that it is intended for use or is used in the production, storage, or transportation of any raw agricultural commodity; or 3. a color additive; or - 4. any substance used in accordance with a sanction or approval granted prior - to the enactment of this paragraph pursuant to this Act, the Poultry Products Inspection Act (21 U.S,f. 451 and the following) or the Meat Inspection Act 4, of March 4,1907 (s4 Stat.1260), as amended and extended (21 U.S.C. 71 an the following); or ' 5. any new am 19.12 How the Search for Food Additives Led to Marco Polo's Adventures in the Orient • 479 19.12 How the Search for Food Additives Led to Marco Polo's Adventures in the Orient, Columbus's Voyage to America, and Dr. Wiley's Poison Squad Food additives of one sort or another have been with us for a long time. They've been in use since prehistoric cooks began salting and smoking meat to preserve it against decay. Food dyes were used to improve the appearance of food by the Egyptians as early as 3500 years ago. Adding herbs, spices, and sweeteners is also an ancient practice. Another ancient practice, especially among the manufacturers and vendors of food, was the use of additives to make bad food more palatable. Covering the foul tastes and odors of spoiled food was the principal function of spices in the Middle Ages. Indirectly, the lack of good methods for preserving food in those times led to the opening of trade routes to the Orient and to the European discovery of the West-ern Hemisphere. It was at least partly the search for foreign spices that led Marco Polo eastward to the Orient and Columbus westward to the New World. As the centuries passed and people throughout the world moved from the coun-tryside to the cities in more modern times, the distance from the farm and the dairy herd to the dinner table lengthened and so did the time it took to transport food from where it was grown to where it was to be eaten. Because of a lack of effective methods for _ preserving foods~fficient and economical mechanical refrigeration is a product of the 20th century-food spoilage became widespread and so did the use of chemicals to preserve food and to mask the taste and odors of decay, just as in the Middle Ages. With the development of chemical technology and food processing late in the 19th century, the use of chemical additives grew enormously. In 1902, Dr. Harvey W Wiley of the United States Department of Agriculture organized a Poison Squad of volunteers to begin the first tests of the effects of food additives on, humans. What chemicals were used to formulate the first patented food additive? •QUESTION What wasthe function of the additive? To preserve food to keep food from not spoiling. 480 • Chapter 19 Vitamins, Minerals, and Additives 19.13 The Law of Additives Several amendments and other changes since 1906 have extended and strengthened the Pure Food and Drug Act. Currently, the law also covers cosmetics and is known as the Federal Food, Drug, and Cosmetic Act. In effect, this law protects the pub-lic from unsafe food additives by declaring that all substances that might be added to food, in any way, are legally unsafe unless they are specifically exempted from the Act or unless they are used in ways specifically permitted by the Act. As we might expect, the effective operation of the law requires a definition of a food ad-ditive (and of the various exemptions) more attuned to the ears of lawyers, ad-ministrative officials, and judges than to the ears of the general public or scientists. The Act's definition of a food additive has thus been embellished into the legal jar-gon of the single sentence of Figure 19.8. To paraphrase this elaborate, legal definition, a food additive is any substance added to food, directly or indirectly, except for • those shown by scientific studies to be safe, at least under the conditions of their use in foods; • those used as additives before January 1, 1958 (the date this part of the Act be-came effective), and shown to be safe either by scientific studies or by our com-mon experience; • pesticides; • color additives; • substances approved by earlier acts of Congress; and • new animal drugs. To work backward through this list of exemptions, the bottom four are de-fined and regulated either in other laws or in some other section of this Act, 1. a pesticide chemical in or on a raw agricultural commodity; or 2. a pesticide chemical to the extent that it is intended for use or is used in the production, storage, or transportation of any raw agricultural commodity; or 3. a color additive; or - 4. any substance used in accordance with a sanction or approval granted prior - to the enactment of this paragraph pursuant to this Act, the Poultry Products Inspection Act (21 U.S,f. 451 and the following) or the Meat Inspection Act 4, of March 4,1907 s4 Stat.1260 19.13 The Law of dditives • 481 so they aren't actually considered to be food additives by this particular sec-tion of the law. The second category results from a combination of expediency and common sense. By January 1,1958, the date this particular section of the Act went into ef-fect, so many substances had been used as food components regularly and for so long that testing all of them would have been entirely impractical. Instead, panels of scientists were set up to evaluate the safety of these materials that had been in common and long-term use. Those that were generally recognized by the panelists to be safe, on the basis of common experience (but without laboratory testing), were compiled into a list of substances Generally Recognized As Safe, the GRAS The GRAS list is a list of food list. In effect, the GRAS list constitutes the second category of exemptions. (Legal- additives that are generally ly, GRAS substances aren't food additives either.) recognized as safe by a panel This GRAS list is by no means fixed and unchangeable, nor are all the sub- of experts but that have not stances on the list necessarily free of hazard. They are simply generally recog- been subjected to laboratory nized as safe, and they are reviewed periodically to determine their continued testing. suitability for GRAS status. Table 19.4 contains examples of chemicals and other substances currently on the list, together with brief descriptions of their func-tions in food. We'll look at some of their uses in greater detail in the sections that follow. The remaining exemption, the first one of the series, requires that newly de-veloped chemicals, which are by no means GRAS, be shown by scientific studies Table 19.4 Examples of GRAS Substances Substance Structure or Chemical Formula Use or Classification ~ Acetaldehyde O CH3-CH Spices, seasonings, and flavorings Anticaking agents Dietary supplements and nutrients Sequestrants (Sec.19.18)  Plnise O C~nnamon /~"~"'~Ethyl acetate CH3-C-O-CHZ-CH3 Alaminum calcium silicate CaA12(SiOq)Z and CaZA12Si0~ Sodium metabisulfite NaZS205 ~~. Sorbic acid CH3-CH=CH-CH=CH-COZH Ascorbic acid C6H806 Calcium phosphate Ca3(PO4)2 Ferrous sulfate FeS04 Linoleic acid A~ CH3-(CHZ)q-CH=CH-CHZ-CH=CH-(CHZ)~-COZH Zinc oxide Zn0 Dipotassium hydrogen KZHPO4 phosphate CH2-COZNa Trisodium citrate HO-C-COZNa CHZ-COZNa 482 • Chapter 19 Vitamins, Minerals, and Additives By a practical definition, a food additive is anything in-tentionaliy added to a food to produce a specific, beneficial result. QUEST1ON Uder what circumstances is a GRAS substance considered to be a food additive? Under what circumstances is it not considered to be a food additive? to be safe before they can be used in foods. Of course once they are demonstrated to be safe and may legally be added to food, they're no longer legally defined as food additives. There are other good and workable (and certainly simpler) definitions of food additives, aside from the legal one of the Federal Food, Drug, and Cosmetic Act. A more practical definition holds that a food additive is simply anything inten tionally added to a food to produce a specific, beneficial result, regardless of its legal status. Although the extended, legal definition of the Act has the force of U.S. fed-eral law behind it and has the close attention of anyone who processes food for sale to the public, we'll use this simpler definition as we examine what chemical addi-tives are doing in our food and why we use them at all. 19.14 Additives at Work We use additives for a remarkably simple reason: to improve or maintain the quality of our foods. For many of us, adding some combination of salt, sweeteners such as sucrose or corn syrup, and seasonings like mustard, pepper, and other condiments improves the taste of an otherwise bland dish. Food colorings, another class of additives, enhance the appearance of our foods by converting a pallid frosting, for example, into the colorful decorations of a birthday cake. Other additives function in less obvious ways. Adding vitamin D to milk doesn't add any appeal to the milk through taste, odor, or color, but it does improve the ab-sorption of calcium into the body, so it helps protect against rickets, as we saw in Sec - tion 19.5. Similarly, the potassium iodide added to iodized table salt acts to prevent th,e formation of goiter (Sec.19.2). Ascorbic acid (vitamin C), on the other hand, not on?ty improves the nutritional qualities of food but also protects other food componerr.c~' from oxidation by contact with air. The ascorbic acid is itself so easily oxidized that it reacts preferentially with atmospheric oxygen. As a food additive, then, ascorbic acid acts both as a nutrient and as a preservative (specifically, an antioxidant, Sec.19.7 j. Although additives serve a large variety of purposes in foods, we can place them into four major groups, according to their function. Generally, chemicals are introduced into foods in order to   • make them more appealing, • make them more nutritious, • preserve their freshness and keep them unspoiled, and • make them easier to process and keep them stable during storage. These categories aren't exclusive, and they even overlap a bit. For example, we've just seen that through its own preferential oxidation ascorbic acid can act as a preservative as well as a nutrient. In this same sense, any one chemical additive can function in two or more of these categories. Nonetheless, we'll examine the categories individually in the following sections. • Q U E S T I O N What food additive acts both to make foods more nutritious and to preserve their freshness and keep them unspoiled? 19.15 Making Food More Appealing ... with Nail Polish Remover! • 483 19.15 Making Food More Appealing ... with Nail Polish Remover! Among the additives that make our foods more appealing to our sight, smell, and taste are the natural and synthetic sweeteners, colorings, flavor extracts, and flavor enhancers (Table 19.5). Naturally occurring flavorings and fragrances include the essential oils and extracts of plants, such as oil of orange and vanilla extract, all of which contribute a bit of their own tastes and odors to foods. Some of the syn-thetic organic compounds used for these purposes also occur naturally in the plant essences. A particularly simple example is ethyl acetate, a major commercial solvent and a naturally occurring ester (Sec. 13.7) widely distributed in the plant kingdom. Its fruity odor and pleasant taste (when it's considerably diluted) make ethyl ac-etate valuable in the formulation of synthetic fruit flavorings. As with so many other chemicals, ethyl acetate has properties that serve very well in a variety of functions. In addition to its pleasant taste and odor, its fine `s characteristics as a solvent and very low hazard to humans make it an excellent sol-vent for such consumer products as nail polishes and nail polish removers. Its abil-ity to do either one of these jobs-to add its flavor to foods or to remove nail polish-doesn't detract in the least from its value in the other. ,i While these natural and synthetic flavorings and fragrances add their own flavors and aromas to our foods, the flavor enhancers, such as MSG (the monosodium glu-tamate of Table 19.5), sharpen some of the weaker flavors already present in the food without adding any significant taste of their own. MSG is used in preparing some •' processed canned and frozen foods, and it's often used in large amounts in Chinese foods. Some people develop symptoms including lightheadedness, headaches, an un-comfortable sense of warmth, and difficulty in breathing after eating a meal con - taining MSG. Because of the considerable quantities of MSG often used in meals served at Chinese restaurants, the condition has been named the Chinese restaurant syndrome. Many Chinese restaurants will omit MSG from a meal on request. LITTLE EMPIRE 120 2nd AYE. (s.,, m a em sna , ~ ,n„~,.EEx TEL: 673-9464 673•9465 FF97 FREE M~ YERY wyp~Wra We Do Not U+e M.S.G. o A menu from a Chinese restaurant advising that it does not use the flavor enhancer MSG. 41 Table 19.5 Representative Substances Used to Increase the Appeal of Foods Substance Structure or Chemical Formula Function (3-Carotene CaaHs6 Colorant Ethyl acetate Ferric oxide Glucose CH3-C-O-CH2-CH3 Fe203 C6H1206 Flavoring and fragrance Colorant Sweetener NH2 Monosodium glutamate, MSG H02C-CH2-CH2-CH-C02Na Flavor enhancer Paprika Flavoring and colorant Sucrose C12HZ2011 Sweetener Titanium dioxide Ti02 Colorant Monosodium glutamate is a salt of glutamic acid. To what class of compounds, de- • Q U E S T 1 O N scribed in Chapter 17, does glutamic acid belong? 484 • Chapter 19 Vitamins, Minerals, and Additives _ 19.16 Preserving and Protecting Food against Spoilage The added minerals and vitamins that make our foods more nutritious constitute the next category of additives. Adding vitamin D to milk, for example, protects children against rickets. Canned fruit drinks often contain added vitamin C for nu-tritional quality. Some of the chemicals we add to food to increase its nutritional value are illustrated in Table 19.6. Since we've already described the micronutrients in detail earlier in this chapter, we'll move along to the next of the categories of Section 19.14, the preservatives. These keep foods fresh and slow down the process of spoilage and deterioration. Without these preservatives many of our foods would become unpalatable, completely inedible, or even hazardous to our health as they travel from the farm, the dairy, or the processor to our tables. As we saw earlier, chemicals were first added to food as preservatives with the smoking and salting of meat in prehistoric times. Even in those times a rudimentary form of food processing was needed to maintain the stability of the food supply. Today mechanical refrigeration represents our primary nonchemical mode of preservation. To appreciate the important role of food preservation of every sort to our current way of living, imagine the chaos of a modern world without the freezers and refrigerators of our stores and homes. Even though chemical preser-vatives are far less visible to us than these freezers and refrigerators, the aban-donment of chemical preservatives could produce as great a catastrophe as the disappearance of all forms of refrigeration. The preservatives we rely on so heavily make up the group of compounds that protect against • oxidation by air and • spoilage by bacteria and other microorganisms. Table 19.7 shows some of these chemical preservatives. We've already seen that ascorbic acid, by oxidizing preferentially, can slow the reaction between food chemicals and atmospheric oxygen (Sec. 19.14). A pair of widely used antioxidants on the GRAS list are BHA, which is chemically a mix ture of the two isomers (Sec. 6.6) of butylated hydroxyanisole, known as 2-tert-butyl-4-methoxyphenol and 3-tert-butyl-4-methoxyphenol, and BKT, also known as butylated hydroxytoluene or 2,6-di-tert-butyl-4-methylphenol. The additives that guard food against the growth of bacteria and other microorganisms not only preserve the taste and appearance of food but also Table 19.6 Representative Substances Used to Improve Nutrition Function or Substance Chemical Formula Classification Ascorbic acid (3-Carotene Ferrous sulfate Potassium iodide Riboflavin Zinc sulfate C6Hs06 CaoHs6 FeSOa KI C17HzoNa06 ZnSOa Vitamin C Provitamin Aฐ Mineral Prevents goiter Vitamin Bz Mineral ฐA provitamin is a substance that can be converted easily into a vitamin. 482 • Chapter 19 Vitamins, Minerals, and Additives By a practical definition, a food additive is anything in-tentionaliy added to a food to produce a specific, beneficial result. Q U E S T 1 O N Under what circumstances is a GRAS substance considered to be a food additive? Under what circumstances is it not considered to be a food additive? to be safe before they can be used in foods. Of course once they are demonstrat-ed to be safe and may legally be added to food, they're no longer legally defined as food additives. What we mean by "safe" and how chemicals are demonstrated to be safe for addition to our foods are topics we'll examine in Chapter 20, after we take a brief look at the more practical side of additives. There are other good and workable (and certainly simpler) definitions of food additives, aside from the legal one of the Federal Food, Drug, and Cosmetic Act. A more practical definition holds that a food additive is simply anything inten tionally added to a food to produce a specific, beneficial result, regardless of its legal status. Although the extended, legal definition of the Act has the force of U.S. fed-eral law behind it and has the close attention of anyone who processes food for sale to the public, we'll use this simpler definition as we examine what chemical addi-tives are doing in our food and why we use them at all.   19.14 Additives at Work We use additives for a remarkably simple reason: to improve or maintain the qual-ity of our foods. For many of us, adding some combination of salt, sweeteners such as sucrose or corn syrup, and seasonings like mustard, pepper, and other condi-ments improves the taste of an otherwise bland dish. Food colorings, another class of additives, enhance the appearance of our foods by converting a pallid frosting, for example, into the colorful decorations of a birthday cake. Other additives function in less obvious ways. Adding vitamin D to milk doesn't add any appeal to the milk through taste, odor, or color, but it does improve the ab-sorption of calcium into the body, so it helps protect against rickets, as we saw in Sec - tion 19.5. Similarly, the potassium iodide added to iodized table salt acts to prevent th,e formation of goiter (Sec.19.2). Ascorbic acid (vitamin C), on the other hand, not on?ty improves the nutritional qualities of food but also protects other food componerr.c~' from oxidation by contact with air. The ascorbic acid is itself so easily oxidized that it reacts preferentially with atmospheric oxygen. As a food additive, then, ascorbic acid acts both as a nutrient and as a preservative (specifically, an antioxidant, Sec.19.7 j. Although additives serve a large variety of purposes in foods, we can place them into four major groups, according to their function. Generally, chemicals are introduced into foods in order to   • make them more appealing, • make them more nutritious, • preserve their freshness and keep them unspoiled, and • make them easier to process and keep them stable during storage. These categories aren't exclusive, and they even overlap a bit. For example, we've just seen that through its own preferential oxidation ascorbic acid can act as a preservative as well as a nutrient. In this same sense, any one chemical additive can function in two or more of these categories. Nonetheless, we'll examine the categories individually in the following sections. • Q U E S T I O N What food additive acts both to make foods more nutritious and to preserve their freshness and keep them unspoiled? 19.15 Making Food More Appealing ... with Nail Polish Remover! • 483 19.15 Making Food More Appealing ... with Nail Polish Remover! Among the additives that make our foods more appealing to our sight, smell, and taste are the natural and synthetic sweeteners, colorings, flavor extracts, and flavor enhancers (Table 19.5). Naturally occurring flavorings and fragrances include the essential oils and extracts of plants, such as oil of orange and vanilla extract, all of which contribute a bit of their own tastes and odors to foods. Some of the syn-thetic organic compounds used for these purposes also occur naturally in the plant essences. A particularly simple example is ethyl acetate, a major commercial solvent and a naturally occurring ester (Sec.13.7) widely distributed in the plant kingdom. Its fruity odor and pleasant taste (when it's considerably diluted) make ethyl ac-etate valuable in the formulation of synthetic fruit flavorings. As with so many other chemicals, ethyl acetate has properties that serve very well in a variety of functions. In addition to its pleasant taste and odor, its fine `s characteristics as a solvent and very low hazard to humans make it an excellent sol-vent for such consumer products as nail polishes and nail polish removers. Its abil-ity to do either one of these jobs-to add its flavor to foods or to remove nail polish-doesn't detract in the least from its value in the other. ,i While these natural and synthetic flavorings and fragrances add their own flavors and aromas to our foods, the flavor enhancers, such as MSG (the monosodium glu-tamate of Table 19.5), sharpen some of the weaker flavors already present in the food without adding any significant taste of their own. MSG is used in preparing some •' processed canned and frozen foods, and it's often used in large amounts in Chinese foods. Some people develop symptoms including lightheadedness, headaches, an un-comfortable sense of warmth, and difficulty in breathing after eating a meal con - taining MSG. Because of the considerable quantities of MSG often used in meals served at Chinese restaurants, the condition has been named the Chinese restaurant syndrome. Many Chinese restaurants will omit MSG from a meal on request. LITTLE EMPIRE 120 2ad AYE. ~ ~s.,, m a em sna ~~,n„~,.EEx T~:673-9464 673•9465 FF97 FAEE M~ YERY wyp~Wra We po Not U+e M.S.G. o A menu from a Chinese restaurant advising that it does not use the flavor enhancer MSG. Table 19.5 Representative Substances Used to Increase the Appeal of Foods Substance Structure or Chemical Formula Function (3-Carotene CaaHs6 Colorant Ethyl acetate Ferric oxide Glucose O CH3-C-O-CH2-CH3 Fe203 C6H12~6 Flavoring and fragrance Colorant Sweetener NH2 Monosodium glutamate, MSG H02C-CH2-CH2-CH-C02Na Flavor enhancer Paprika Flavoring and colorant Sucrose C12HZ2011 Sweetener Titanium dioxide Ti02 Colorant Monosodium glutamate is a salt of glutamic acid.To what class of compounds, de- • Q U E S T 1 O N scribed in ~hapter 17, does glutamic acid belong? 484 • Chapter 19 Vitamins, Minerals, and Additives _ 19.16 Preserving and Protecting Food against Spoilage  The added minerals and vitamins that make our foods more nutritious constitute the next category of additives. Adding vitamin D to milk, for example, protects children against rickets. Canned fruit drinks often contain added vitamin C for nu-tritional quality. Some of the chemicals we add to food to increase its nutritional value are illustrated in Table 19.6. Since we've already described the micronutrients in detail earlier in this chapter, we'll move along to the next of the categories of Section 19.14, the preservatives. These keep foods fresh and slow down the process of spoilage and deterioration. Without these preservatives many of our foods would become unpalatable, com-pletely inedible, or even hazardous to our health as they travel from the farm, the dairy, or the processor to our tables. As we saw earlier, chemicals were first added to food as preservatives with the smoking and salting of meat in prehistoric times. Even in those times a rudimentary form of food processing was needed to maintain the stability of the food supply. Today mechanical refrigeration represents our primary nonchemical mode of preservation. To appreciate the important role of food preservation of every sort to our current way of living, imagine the chaos of a modern world without the freezers and refrigerators of our stores and homes. Even though chemical preser-vatives are far less visible to us than these freezers and refrigerators, the aban-donment of chemical preservatives could produce as great a catastrophe as the disappearance of all forms of refrigeration. The preservatives we rely on so heavily make up the group of compounds that protect against • oxidation by air and • spoilage by bacteria and other microorganisms. Table 19.7 shows some of these chemical preservatives. We've already seen that ascorbic acid, by oxidizing preferentially, can slow the reaction between food chemicals and atmospheric oxygen (Sec. 19.14). A pair of widely used antioxidants on the GRAS list are BHA, which is chemically a mix ture of the two isomers (Sec. 6.6) of butylated hydroxyanisole, known as 2-tert-butyl-4-methoxyphenol and 3-tert-butyl-4-methoxyphenol, and BKT, also known as butylated hydroxytoluene or 2,6-di-tert-butyl-4-methylphenol. The additives that guard food against the growth of bacteria and other mi-croorganisms not only preserve the taste and appearance of food but also Table 19.6 Representative Substances Used to Improve Nutrition Function or Substance Chemical Formula Classification Ascorbic acid (3-Carotene Ferrous sulfate Potassium iodide Riboflavin Zinc sulfate C6Hs06 CaoHs6 FeSOa KI C17HzoNa06 ZnSOa Vitamin C Provitamin Aฐ Mineral Prevents goiter Vitamin Bz Mineral ฐA provitamin is a substance that can be converted easily into a vitamin. 486 • Chapter 19 Vitamins, Minerals, and Additives protect us against microbiologically generated toxins. Labels on breads and other baked goods usually list calcium propionate (or, less often, sodium pro-pionate or propionic acid itself) among their ingredients. Propionic acid occurs naturally in cheeses and other dairy products, and both the acid and its salts ef-fectively inhibit the growth of mold, a major cause of the spoilage of both dairy products and baked goods. Packaged acidic fruit drinks, especially those that don't have to be refrigerated before being opened, such as canned orange juice and grapefruit juice, usually contain added sodium benzoate, sometimes shown on the ingredients label as 6enzoate of soda. When present in amounts a little less than 0.1%, the sodium benzoate serves as an effective antimicrobial ingredient. • Q U E S T I O N What naturally occurring chemical is used as an additive both to improve nutrition and to add color? 19.17 Chemistry in a Crab's Claw Some additives protect food against spoilage through complex and indirect but nonetheless intriguing chemical actions. One of these, EDTA or ethylenedi-aminetetraacetic acid (sometimes called edetic acid), owes its prowess as an an-tioxidant to a peculiarity of its molecular structure and to a subtle aspect of oxidation chemistry. As shown in Figure 19.9, the intricacy of EDTA's molecular structure rivals the complexity of its name. Behind EDTA's ability to protect foods against oxidation lies a bit of chem-istry involving the catalytic effects of metal ions. Trace quantities of the ions of various metals-aluminum, iron, and zinc, for example-easily enter our processed foods as they go through their many stages of preparation in an assortment of ovens, vats, kettles, and other metal equipment. While these exceedingly small quantities of metal ions don't affect us or our foods directly, they can very effec-tively catalyze the air oxidation of many of the compounds that are present in food and thereby lead to spoilage. It's important to remove even the smallest traces of metal ions from some foods to protect against this catalytic oxidation. That's where EDTA comes in. Figure 19.9 Ethylenediaminetetraacetic acid, or EDTA. II . Ethylene . . . . . . diamine . . . . . tetraacetic acid 19.18 Stabilizers: Moist Coconut, Soft Marshmallows, and Creamy Peanut Butter • 487 In EDTA, a metal ion, two oxygen atoms and two nitrogen ~ atoms comprise a square   What characteristic of the nitrogen and oxygen atoms of EDTA allows the molecule • Q U E S T I O N to act as a chelating agent? 19.18 Stabilizers: Moist Coconut, Soft Marshmallows, and Creamy Peanut Butter  Finally, there's the class of processing aids and stabilizers, which make it easier to prepare and use processed foods and also help prevent undesirable changes in the appearance or physical characteristics of foods while they're being stored. Among these are humectants, such as the glycerine that keeps shredded coconut moist and the glyceryl monostearate that softens marshmallows. Anticaking agents, such as 488 • Chapter 19 Vitamins, Minerals, and Additives Table 19.8 Representative Substances Used in Processing and to Maintain Stability Substance Structure or Chemical Formula Function Acetic acid CH3-COZH Control of pH Calcium silicates CaSi03, Ca2Si04, Ca3Si05 Anticaking agents Glycerine CHZ-CH-CHZ Humectant OH OH OH Glyceryl monostearate CHZ-02C-(CHZ)16-CH3, CHZ-OH Humectant CH-OH CH-02C-(CHZ)I6-CH3 CHZ-OH CHZ-OH Gum arabic (Gummy plant fluid) Thickener, texturizer Mono- and diglycerides CH2-0,C-R CHZ-OZC-R Emulsifiers CH-OH CH-OZC-R CHz-OH CH Z-OH Phosphoric acid and its salts ' H3P04, NaH2P04, Na2HP04, Na3P04 Silicon dioxide Si02 Xanthan gum Complex polysaccharide from corn fermentation Control of pH Anticaking agent Emulsifier, thickener silicon dioxide and the calcium silicates, keep table salt, baking powder, and other finely powdered food substances dry and free-flowing while they're being processed and as they stand on the store shelf or in the kitchen cabinet. Glyceryl monostearate and other mono- and diglycerides also serve as emulsi-fiers that help whip peanut butter into a creamy smoothness and keep it that way until the jar is empty. Xanthan gum helps blend the oils and water that make up salad dressings and stabilizes the product as a smooth, homogeneous mixture. Chemically, emulsifiers are surfactants (Sec. 13.4) that make it possible to mix intimately two phases, oil and water for example, that don't dissolve in each other. Acting very much like the laundry detergents of Chapter 13, the emulsifiers convert one of the phases into micelles, disperse them in the other phase, and stabilize the mixture by keeping the micelles from coming together. If it weren't for its emulsifiers, peanut butter would soon separate into a thick mass of peanut solids topped off by an unappetizing peanut oil. Table 19.8 presents some typical processing aids and stabilizers. • Q U E S T I O N Silicon dioxide is often listed as an additive on boxes of table salt. What function does it serve? wig 19.19 A Return to Vitamin C and Iodine Vitamin C serves as an appropriate focus for this chapter. On the one hand, it's a vitamin that occurs naturally as a micronutrient in many foods and works to pre-serve good health. Because of its important role in protein synthesis, for example, it prevents scurvy. On the other hand, it's a food additive: a chemical deliberately added to processed foods to produce a desirable effect. 504 • Chapter 20 Poisons,Toxins, Hazards, and Risks The toxin solanine accumulates in the green areas of a potato. different species of animals and different methods of administration. For the mice, the LDSO is about 10 mg/kg for aflatoxin injected directly into their abdominal cavity; for the ducklings, oral feeding produces an LDso of 18 x 10-3 mg/kg. The two values differ by more than a factor of 500. Solanine, which occurs in potatoes, especially in or near green areas of the skin and near fresh sprouts projecting from the potato, inhibits the transmis-sion of nerve impulses. In this respect it resembles the synthetic phosphorus containing compounds described earlier. Solanine's potency, like that of the aflatoxins, depends on how it enters the body. Its LDso by direct injection into mice is 42 mg/kg, while oral feeding of 1000 mg/kg produces no ill effects at all. (Direct ingestion can produce ill effects and death in many other species, though, including humans. It's best to cut green areas and fresh sprouts out of potatoes before using them.) • Q U E S T I O N What hazard is associated with moldy peanuts? With potatoes containing many fresh sprouts? 20.7 Safety: Is It Freedom from Hazards or Simply a Matter of Good Judgment? To sum up, we've seen that any chemical can be hazardous to our health and that lethal potencies can be measured as LDsos. We've also seen that these LDSos vary with the species of test animal used and with the method of administration. Nonetheless, it's still possible to estimate the relative toxicities of various chemi-cals by ranking them with respect to each other. Although both botulinum toxin and ordinary table salt can kill, for example, the protein that makes up the toxin is unquestionably more lethal than sodium chloride. Taken as a whole, nature's poisons outrank synthetic chemicals in both number and virulence. Recognizing that there are, indeed, potentially harmful substances in our foods-poisons-we can now turn to the second question we asked at the beginning of this chapter: Are our foods safe? A reasonable answer requires a reasonable definition. Often, when we say that something is "safe" we imply that it is free of danger, hazard, or harm. But no substance is inherently and totally free of danger, hazard, or harm. The harm any substance can do to us, each one of us, depends on • its chemical characteristics, • how much of it we use, • how we use it, • how susceptible to its hazards we are as humans, and • how susceptible we are as individuals. For a more realistic test of safety, we can ask whether, knowing the risks in-volved in using a chemical (or in anything else for that matter), we are willing to By one useful definition, safe- accept those risks. In this sense safety, as defined by William Lowrance, a con ty is the acceptability of risk temporary American organic chemist, is the acceptabiliry of risk. It's a realistic and practical definition of a subtle and sometimes ambiguous term, and it provides us with a convenient way to examine the safety of our food supply and of chemicals in general. With this definition in mind we can look to our own (informed) judg-. .. ~` - ` ment in deciding matters of safety. $~ 20.7 Safety: Is It Freedom from Hazards or Simply a Matter of Good Judgment? • 505 Marked crosswalks, traffic lights, and pedestrian signals help control the risks involved in crossing a busy street and make these risks acceptable. In short, everything in life involves a risk of one sort or another. Those risks we find acceptable are the ones we, ourselves, define as safe. Those we find unac- ceptable we define as unsafe. All of us, collectively, make similar judgments about the risks we are willing to take as a society. '~ Viewing safety as a matter of acceptable risk shines a somewhat clearer light Figure 20.5 Thalidomide. Prescribed as a sleeping pill for pregnant women before its dangers were known, thalidomide acted as a teratogen in women who took it within their first 12 weeks of pregnancy. 606 • Chapter 20 Poisons,Toxins, Hazards, and Risks Q U E S T I O N Under what conditions is thalidomide a hazardous substance? Under what condi-tions does thalidomide provide benefits that outweigh its hazards? no prescription required. (Doubts about the results of the animal testing kept it off the market in the United States.) Within a few years, some 4000 babies in Germany,1000 in Great Britain, and 20 in the United States (to women who had obtained the drug on trips to Europe) had been born with severe birth defects, including severely shortened or absent arms and legs. These defects were traced eventually to thalidomide that the women had taken within the first 12 weeks of pregnancy. Thalidomide is an example of a A teratogen is a substance teratogen, a substance that produces severe birth defects.The word comes from the that produces severe birth Greek teras for a monster or a marvel. defects. More extensive studies of thalidomide, spurred by the birth defects, showed that while it posed no apparent hazards to rats, dogs, cats, chickens, and other species, it did act as a teratogen in monkeys and rabbits, neither of which had been used in the original studies. It was all clearly a case of a 10,OOlst experiment that, tragically, had not been performed. More recently thalidomide, which has a very low inherent toxicity and seems to be hazardous only to a developing fetus, has proven useful in treating severe in-flammations and disorders of the immune system. Thalidomide or compounds closely related to it have shown promise in alleviating a variety of diseases and disorders, including mouth ulcers, rheumatoid arthritis, leprosy, AIDS, tuberculo-sis, and transplant rejection. Once again we see that chemicals, including even thalidomide, are neither good nor evil in themselves but appear to be so only in the ways we choose to use them (Sec.1.2). 20.8 The Laws of Safety the Poison Prevention Packaging Act, Congress placed a larger, societal judgment on free access to aspirin. Aspirin, they said in effect, is safe enough to be handled freely by anyone who can open a sim ple but obstinate twist-and-snap cap, In addition to the FDA, these other agencies include the • Environmental Protection Agency (EPA), which regulates chemical pesticides, among other matters affecting the environment; 20.8 A Factor of 100 0 507 • Occupational Safety and Health Administration (OSHA), which is concerned with exposure to chemicals in the workplace; • Bureau of Alcohol, Tobacco and Firearms (BATF), a division of the Depart-ment of the Treasury that has jurisdiction over the chemicals of beer, wine, liquor, and tobacco; and • U.S. Public Health Service (USPHS), which, among its other activities, investi-gates outbreaks of illness due to food spoilage. Which agency of the federal government has responsibility for; (a) chemicals used • Q U E 8 T 1 O N as food additives; (b) substances that may contaminate the environment; (c) chem- icals that may prove hazardous in the workplace? 20.9 A Factor of 100 Through its rules and regulations, the FDA exercises a societal judgment over the safety of the chemicals that are added to our foods. In practice the agency must first determine that any proposed additive does, indeed, produce a desired, beneficial effect, which is one of the necessary characteristics of any food additive. The FDA then determines the acceptable level of an additive's use in foods through exam-ination of • the LDSp of the proposed additive in at least two (and often more) species of animals, • the chemical's maximum "no-effect" level, and • its long-term hazards, if there are any. Values of LDSO represent the acute or immediate hazard in using a chemical. Nat-urally, a substance must produce a beneficial effect in foods at a level well below its acute toxicity if it's to be used as an additive. How much below, though, is a matter of judgment. In making judgments of this kind the FDA requires that the substance be fed to at least two different species of animals for several months and that the ani-mals be examined thoroughly throughout and at the end of this period for any changes the chemical may have produced. Feeding tests of this sort make it possi-ble to determine the maximum daily amount of the chemical that produces no observable effect on the animals. This is the no-effect level, measured as milligrams of the additive per kilogram of the animal's body weight. With a safety factor of 100, the FDA permits no more than 1/100, or 1%, of this no-effect level in commercially prepared foods, based on estimates of the av erage person's daily consumption. This represents the additive's acceptable daily The acceptable daily intake, or ADI. Any evidence that humans are even more sensitive to the additive intake, or ADI, of a food addi- than the test animals are or that the additive can do its job at less than the 1% tive is 1% of the maximum level can result in even lower ADIs.Then again, if there's evidence of harm detected daily amount of additive that through much longer feeding tests, sometimes lasting several years, the substance produces no observable effect may be prohibited entirely. on laboratory animals. These long-term feeding tests reveal the chronic effects of proposed additives, including some of the more dreaded hazards we sometimes associate with syn-thetic chemicals. Long-term studies uncover the capacity of a chemical to affect an ` animal's ability to reproduce (fertility effects) and to affect offspring either through  the development of severe birth defects (teratogenic effects) or through lesser ge-netic changes (mutagenic effects). Such studies also reveal a chemical's ability to produce cancer (to act as a carcinogen). It's this last hazard-the possibility of chemically induced cancer-that arouses some of our strongest feelings about the chemicals of our foods and our environment. We'll turn now to the question of carcinogens in our foods and to an examination of our search for safety in its strictest form: absolute safety. _ QUEST1ON What is an additive's ADI and how is it determined? •QUESTION Under what condition or circumstance does the Delaney Amendment take effect in regulating the use of a food additive? 20.10 The Legacy of James J. Delaney Through the original Food and Drug Act of 1906 and its many revisions, Congress has generally given federal agencies substantial leeway in setting the standards of safety for chemicals in our food, drugs, and cosmetics and in public areas such as the work-place and municipal drinking water. The matter of safety is, as we have seen, a mat-ter of judgment; our lawmakers have been content, by and large, to delegate the finer, more technical matters of judgment to agency officials and their technical experts. Yet with respect to one particularly fearsome hazard, the risk of cancer from food additives, federal law sets a zero tolerance level. That is, with the notable ex-ception of saccharin, which we'll examine in detail in the next section, our society judges that there is no acceptable level of risk of cancer from a food additive. We'll now see what this zero tolerance implies, how it came about, and why an excep-tion has been made for saccharin. In 1958 Congressman James J. Delaney of New York introduced an amend-ment into a revision of the Food, Drug and Cosmetic Act which provided that no additive shall be deemed to be safe if it is found to induce cancer when ingested by man or animal, or if it is found, after tests which are appropriate for the evaluation of the safety of food additives, to induce cancer in man or animal. In effect this portion of the Act, now known as the Delaney Amendment or the De-laney Clause, prohibits the use of any chemical as a food additive, at any level, if the chemical is found to produce cancer in any way, in any test, at any concentration, in any animal. Although the FDA has established acceptable daily intake levels for var-ious chemical additives of known acute toxicity, including some of those listed in Table 20.1, the Delaney Amendment sets a zero tolerance for the deliberate addi-tion to food of any chemical known to cause cancer in humans or laboratory animals. While this legislative legacy has served as an effective bar against the addi-tion of known carcinogens to our processed foods, it also brings into focus a larg-er need for balancing the potential hazards of any particular food additive against the very real and very desirable benefits that additive may provide. 20.11 The Story of Saccharin • 509 In 1879 Ira Remsen, Professor of Chemistry at the newly founded Johns Hopkins University, and Constantine Fahlberg, a student of Remsen's, were studying some of the more esoteric aspects of the reactions of organic compounds. Remsen was later to become president of the University and one of the major influences on the teaching and practice of chemistry in the United States. One evening at dinner, after having finished his laboratory work and cleaned up, Fahlberg noticed a peculiar sweetness in the bread he was eating. He traced the source of the exceptional taste to his hands and arms. Recognizing that it must have come from residues of chemicals he had been in contact with that day, he returned to his laboratory to find its origin. By using the sensitive but very risky technique of tasting remnants of his work here and there in the laboratory, he traced the un-usual sweetness to his chemical apparatus and to the compounds on which he had been working. He and Remsen immediately published their discovery of the source of the sweetness, the newly prepared chemical saccharin. The name of the sweet compound comes from the Latin and Greek words for sugar itself. Saccharin (Fig. 20.6) provides neither energy nor the materials from which we produce our body tissues, so it has no food value. Yet its intense sweetness, about 500 times that of table sugar, lasts even to incredible dilutions. Dissolve one tea spoon of pure saccharin, about 5 g, in 145,000 liters of water-enough water to fill a cube just over 52.5 m on a side or enough to cover a football field about an inch and a quarter deep-and the sensation of sweetness is still present. Soon after Remsen and Fahlberg's discovery, saccharin was in use as a food preservative and as an antiseptic and then as a replacement for sugar. Around 1907 commercial food canners discovered its popularity among people with dia betes, and it has been with us ever since as a nonnutritive, noncaloric sweetener. With the passage of the 1958 Food, Drug and Cosmetic Act, saccharin, which had been in general use for about half a century, joined the GRAS list of approved food additives (Sec. 19.13). Although sugar-free foods for sufferers of diabetes formed the original mar-ket for the sweetener, the demand for diet soft drinks that sprang up in the early 1960s brought saccharin into much wider use. By 1977 between 50 and 70 million Americans were regular users of saccharin, consuming about six million pounds each year, about three-quarters of it in soft drinks. With this widespread public consumption, doubts arose about saccharin's safe-ty. A few years earlier, in 1972, the FDA had removed it from the GRAS list and placed temporary restrictions on its further use pending the outcome of laboratory tests. Laboratory studies soon indicated that saccharin produces bladder cancer in mice. Even though the sweetener proved to be an extremely weak carcinogen, posing a trivial and perhaps undetectable threat of cancer to the general popula-tion (according to the experts who examined it), the Delaney Amendment came into operation through its zero-tolerance provision and forced the FDA, early in 1977, to announce its intention to ban saccharin as a food additive. Before the FDA's order could take effect, a public outcry against the proposed prohibition overwhelmed Congress. Saccharin was, at the time, the only sweetener available to those who wanted sweetness without calories, taste without the accom panying prospect of weight gain. One physicist published scholarly calculations sug-gesting that for a person 10% overweight the health risk from the saccharin in one diet soft drink was less than the health risk from the calories of the sugar it replaced. O  Figure 20.6 Saccharin.A nonnutritive sweetener about 500 times as sweet as sucrose, saccharin has been shown to be a weak carcinogen. Saccharin has been used as a nonnutritive sweetener since around the beginning of the 20th century. Although it has been shown to cause cancer in mice, saccharin continues to be used as a food additive because of public demand. All products containing saccharin must carry a warning label. 21.15 Silicates, Polymers of the Lithosphere • 545 ~ _+~-_~_~ _~ _~_!~: .~i Syndiotactic (alternating sides) Atactic (random) .„ The terms for the three orientations come from the Greek taktos, meaning ordered, which is modified by the prefixes iso- (same), syndio- (two together), and a- (not). In 1953 Ziegler (Sec. 21.13) and Giulio Natta, Italian-born (1903) professor of industrial chemistry at the Milan Polytechnic, independently prepared the highly ordered polypropylenes, thereby creating the first stereochemically ordered poly-mers. For their pioneering work Ziegler and Natta shared the 1963 Nobel Prize in chemistry. As we might expect from our knowledge of the effects of molecular order on the melting points of triglycerides and on the hardness of the polyethyl-enes, the highly ordered isotactic and syndiotactic polypropylenes are higher melt-ing, more crystalline, and harder than the atactic. Today almost 8 million tons of polypropylene are produced in the United States each year, most of it going into the manufacture of automobile trim and battery cases, carpet filaments and backing, fabrics, small items such as toys and housewares, and the hard plastic caps used on containers made of other materials. Which of the polymers ofTable 21.2 could exist in isotactic and syndiotactic forms? •QUESTION 21.15 Silicates, Polymers of the Lithosphere Not all polymers are organic compounds. Probably the most important and cer-tainly the most abundant of the inorganic polymers are compounds of silicon and oxygen. The clays, rocks, and inorganic soils of the earth's crust are made mostly of these two elements. On average, oxygen constitutes about 46% of the mass of the planet's outer layer of land and ocean bed; silicon, about 28%. Taking into ac-count the difference in their atomic weights, this corresponds to a ratio of almost three atoms of oxygen for every atom of silicon. Figure 21.22 The polypropylenes. 546 • Chapter 21 Polymers and Plastics Figure 21.23 Tetrahedral carbon and tetrahedral silicon. The tetrahedral carbon of methane The tetrahedral silicon of the silicates (the oxygens either are anionic or they are bonded to another silicon.) Most of the solid crust consists of polymers with repeating units of silicon dioxide (Si02) and of ionic aggregates such as Si03, Si04, Si205, Si401~ , and so forth. In these, four oxygens surround each tetracovalent silicon in much the same way as four hydrogens occupy the four corners of a tetrahedral methane molecule (Fig. 21.23). But while methane's hydrogens are monovalent, the oxygen atoms are divalent, so they ei-ther carry a negative ionic charge or bond to a second silicon atom. Bonding of any or all of the oxygens at the corners of the tetrahedra to still other tetrahedral silicons pro-duces threadlike, sheetlike, and three-dimensional, inorganic, silicate polymers. With the other elements of the crust interspersed among them, these inorganic polymers form much of the substance of the earth's rocks and minerals. One form of the mineral asbestos consists of a double strand of the silicate tetrahedra (Fg. 21.24). Asbestos was once used in brake linings and cigarette filters and as insulation in hous-es, schools, and office buildings. Inhaling asbestos fibers has been shown to produce mesothelioma, a cancer of the lungs and the cavity of the chest and the abdomen. Since the mid-1970s the mineral has been abandoned as an insulating material in con-struction. Its use in consumer products is now prohibited by law. Two-dimensional sheets of silicate polymers form micas, clays, and talcs, while quartz is a three-dimensional lattice of silicon dioxide (SiOZ). In the quartz lattice (Fig. 21.25) every oxygen is shared by two different silicon atoms, one at the center of each of two adjacent tetrahedra that are connected through the oxygen. Each sil-icon atom owns, in effect, exactly half of each of the four oxygens bonded to it (with the other half assigned to the other silicon atom bonded to the oxygen). With this arrangement, the molecular formula of quartz becomes Si02. Figure 21.24 A double-stranded asbestos polymer.   548 • Chapter 21 Polymers and Plastics • Q U E S T 1 O N Of PET and polypropylene, which plastic is preferred forth e manufacture oft he bod-ies of soft drink bottles? Why? Which is preferred fort he manufacture of large bot-tles for water, milk, and liquid detergent? Why? E ;;R S P E C T 1 - The Problem with Plastics Unlike metal, discarded plastic boxes and bottles don't corrode and decay. Unlike paper and cloth, ordinary plas-tic bags and wrappings aren't degraded by the weather or by the action of the microorganisms of the soil. Plas-tics, as a rule, simply aren't biodegradable. That is, the microorganisms that inhabit the soil can't degrade plas-tics to the simpler substances that form our natural environment. Plastic litter lies by the side of the road and in our parks and beaches, virtually unchanged by weather or microor-ganisms, until it's gathered up for proper disposal. (An es timated 60% of all the debris collected from our beaches consists of plastics of one sort or another,) Even with prop-er disposal, though, plastic waste presents a growing soci-etal problem as it accumulates, along with other trash, in expensive landfills. These areas, where urban trash of all sorts is dumped and mixed into the land itself, are quickly filling to capacity and closing. About 80% of all our plastic waste ends up in landfills. Incineration, an alternative approach used with about 10% of our plastic trash, is not only expensive but poten-tially hazardous as well. Some plastics, including Teflon, poly(vinyl chloride) and poly(vinylidene chloride), produce irritating or toxic gases when they burn. Added to this is the impact of incineration on the greenhouse effect (Sec. 8.14). Science and technology offer some hope for solving the problem through two possible routes: recycling plastics so that they don't accumulate in the environment as trash, and decomposing the plastics that do become environmental trash. Recycling waste plastics into new products, much as paper, glass, and metal wastes are recovered and recast into new and useful items, would certainly seem to be a promis-ing approach.Yet, as we've seen, plastics come in a variety of molecular structures, with a variety of properties. Each syn-thetic plastic possesses its own particular characteristics that suit it to a set of specific applications. For effective re-cycling, the various plastics of our wastes would have to be sorted into a variety of individual piles, an expensive process, with each pile representing a separate category of proper-ties.Tossing them all together, into a single batch, lowers the cost of the entire operation but produces a low-grade product known informally as "plastic lumber," a satisfactory substi-tute for wood in some of its rougher uses but hardly suitable for more specialized applications. In all, while a little over a quarter of our residential and commercial aluminum wastes and about 40% of similar waste paper are recycled, only about 6% of our plastics are reused. One reason for the low level of recycling plastics is the inherent difficulty and cost of separating different kinds of plastic from each other so that each can be reused effec tively. Another problem is that some plastic products just don't lend themselves to collection for recycling.The plas-tic liners of baby diapers probably offer the best example of this sort of problem. !n another approach plastics can be removed from the • environment by chemically induced degradation. Impregnat- ing the plastic with a substance that promotes its decompo-sition without significantly affecting its properties can cause it to decay much like paper or cloth. 568 • Chapter 22 Cosmetics and Personal Care •QUESTION What is the principal function of a good toothpaste in keeping teeth clean and cavity-free? The dermis is the portion of the skin that contains nerves, blood vessels, sweat glands, and the active portion of the hair follicles, and also sup-ports the upper layer, the epidermis. The stratum corneum is the outermost layer of skin, a pro-tective shield consisting of 25 to 30 layers of dead cells. Table 22.3 Composition of aTypical Dentifrice Weight Ingredient Formula (%) Function Water H~O 39 Solvent and filler Glycerol CHZ-CH-CHZ 32 Humectant,retainsmoisture I I I OH OH OH Dibasic calcium CaHP04 27 Abrasive phosphate Carrageenan A carbohydrate of 1 Thickening agent and seaweed stabilizer Fluorides and other 1 Enamel hardener: additives sweeteners and preservatives also give us the sense of cleanliness. Almost all dentifrices contain a bit of saccha-rin and some flavoring or fragrance to leave us with a sense of sweetness and fresh-ness after brushing. The components of a typical toothpaste appear in Table 22,.3. 22.9 To Make Our Skin Moist, Soft, and . . . On average, about a quarter of every dollar we spend for cosmetics goes toward the care of our skin with moisturizers and emollients (softeners): hand. face. and body soaps; and deodorants and antiperspirants. We've already examined the chem- /' istry of soaps and detergents in Chapter 13; here and in the next section we'll tak~ up the means by which we keep Qur skin-the organ that envelops our bodies~ ' moist, soft, and inoffensive. ' If an organ is a group of tissues that perform one or more specific functiovs. as the heart pumps blood or the kidneys filter it, then our skin is indeed an organ. the largest one of all. Its functions range from the obvious coverina of our bc~dies "~ and protection from damage by foreign matter and microorganisms, to the more subtle tasks of regulating body temperature, sensing the stimuli provided 1-y the outside world, and even synthesizing compounds such as vitamin D (Sec. 19.5). The skin itself is made up of two major layers, the underlying dermis, which contains nerves, blood vessels, sweat glands, and the active portion of the hair fol-licles, and which also supports the upper layer, the epidermis (Fig. 22.5). The epi-dermis consists of several tiers of cells. At its bottom, resting on top of the dermis, " is a single sheet of cells that divide continuously, always pushing upward. As they move toward the outside of the skin, driven along by new cells coming up from be-neath, they lose their ability to divide and eventually die. By the time they become the lifeless, outermost layer of the skin, the stratum corneum, they have been trans-formed into keratin, the same protein that forms the hair. The stratum corneum itself is a layer of 25 to 30 tiers of these dead cells whose sole function is to protect us against the outside world, including the world,Qf our ,  22.10 ...Inoffensive • 569 cosmetics and toiletries. The condition of this layer depends mostly on its water con-tent. Too much moisture nourishes the growth of fungi and other microorganisms; too little dries it out, producing flaking and cracking. A water content of 10% is j ust about right for the stratum corneum. The body supplies protection to the skin with the sebum secreted by the se-baceous glands of hair follicles. This oily substance coats the adjacent skin, lubri-cating and softening its dead keratin (as well as the hair's), and lowering the rate at which water evaporates from its surface. These sebaceous glands occur only at the hair follicles themselves. No sebum coats the skin of the hairless regions of the body, such as the palms of the hands and the soles of the feet. Commercial cosmetic lotions and creams are emulsions, or colloidal dis-persions (Sec. 13.5) of two or more liquids that are insoluble in each other (usu-ally an oil and water). These personal care products act in much the same way as sebum. A contemporary form of cold cream, one of the oldest and most com-mon of the skin moisturizers, consists of an emulsion of about 55 % mineral oil, 19% rose water, 13% spermaceti (a wax obtained from the sperm whale), 12% beeswax, and about 1 % borax (a mineral that combines sodium borate and water). A typical vanishing cream, which fills in wrinkles and appears to make them vanish, incorporates about 70% water, 20% stearic acid (partly as its sodi-um salt; Table 15.1), and 10% glycerol (also known as glycerin; Sec. 13.8), with Skin lotions and creams soften traces of potassium hydroxide, preservatives, and perfumes. In the more freely the lifeless cells of the stratum -,-flowing hand and body lotions, water and oils replace some of the waxes of the corneum. ~, creams. Since the function of these lotions and creams is to keep the outer layer of skin moist, they are most effective when applied after a bath or shower, while the skin is still damp.  The dermis, epidermis, and stratum corneum are layers of the organ known as the • Q U E S T I O N skin. What is their sequence, from top to bottom? What is the composition or struc- ture of each? 22.10 ... Inoffensive We control our body's temperature by perspiring (from Latin words meaning "to breathe through") or sweating (an Anglo-Saxon word that means just what it says). When you're warm or tense, your sweat glands begin their work of cooling you off. One set of these glands, the eccrine glands (sometimes called the "true" sweat glands), covers most of the skin. They're especially dense on the forehead, face, palms, soles, and armpits, and they secrete a slightly acidic, very dilute solution of inorganic ions (largely sodium, potassium, and chloride), lactic acid (CH3-CHOH-C02H), some urea (HzN-CO-NH2; Sec. 6.1), and a little glucose. The cooling effect of sweating comes from the evaporation of the water from this secretion, which ordinarily has no odor. Another set, the apocrine glands (see Fig. 22.5), releases a different kind of substance, one that can easily become disagreeable. Like the sebaceous glands, these apocrine glands secrete their fluids into the hair follicles. But unlike the se baceous glands, which occur wherever hair grows, these apocrine glands lie almost exclusively under the arms, in the groin, and in a few other smaller regions of the body. While their secretions produce little or no odors in themselves, bacteria that Antiperspirants and deodorants accumulate in the nearby strands of hair can degrade the contents of the apocrine help control sweating and fluids into foul-smelling products. associated odors.  570 • Chapter 22 Cosmetics and Personal Care Antiperspirants inhibit sweating and keep the body relatively dry. Deodorants di-rectly attack odors themselves. To control the wetness of perspiration and any of its associated odors we have available two personal care products, antiperspirants and deodorants. The an-tiperspirants inhibit sweating and keep the body relatively dry. Deodorants, on the other hand, directly attack odors themselves. The most widely used of the an-tiperspirants are the aluminum chlorohydrates, A12(OH)4C12 and A12(OH)SCI. These release aluminum cations, which seem to reduce wetness by physically clos-ing the ducts of the eccrine glands for as long as several weeks. They also reduce the odor associated with the apocrine glands, probably by killing the bacteria that decompose the organic portion of the fluid. Deodorants mask odors with fragrant ingredients that cover the offending aroma and also with antibiotics that eliminate the bacteria. In addition to the alu- ` minum salts, these antibacterial agents include various salts of zinc as well as the broad-spectrum antibiotic neomycin. Since the odor itself comes from the action of bacteria on the accumulated residue of perspiration, daily washing alone often solves many of the problems. • Q U E S T 1 O N What's the difference between the action of an antiperspirant and a deodorant? 22.11 Putting a Little Color on Your Skin  The oils, waxes, polymers, and dyes of lipstick protect, soften and brighten the lips. With our hair, teeth, and skin clean and in good shape, we'll focus now on cosmetics that add color: lipsticks, eye colorings, nail polish, and face powder. Lipstick provides a soft-ening and protecting film for the lips, as well as colors ranging from soft and unobtru-sive to dazzling. About half the weight of a tube of modern lipstick is highly purified castor oil (a mixture of triglycerides obtained from plant seeds). This oil serves to dis-solve the dyes and, more importantly, to give the stick the ability to remain a waxy solid in its container yet flow smoothly as it touches the warmer lips. Most of the re-mainder of the stick is a mixture of oils, waxes, hydrocarbons, esters, lanolin (the waxy sebum of sheep), and polymers, all formulated to produce a desirable texture, melting point, ingredient mix, and film flow. In addition, the castor oil and other oils and waxes of lipstick help keep the skin of the lips moist and soft. The remaining ingredients-dyes, perfumes, and preservatives-make up a very small percentage of the weight. Major dyes of modern lipsticks include D&C Orange No. 5, known chemical-ly as a dibromofluorescein, and D&C Red No. 22, a tetrabromofluorescein (Fig. 22.14). The D&C here indicates that the Food and Drug Administration has approved these dyes for use in drugs and cosmetics. Figure 22.14 Lipstick dyes.  HO O OH Na0 O O \ I / \ / Br Br / COZNa \ I  D & C Orange No. 5 , D & C Red No. 22 4',5'-dibromofluorescein 2',4',5',7'-tetrabromofluorescein 570 • Chapter 22 Cosmetics and Personal Care Antiperspirants inhibit sweating and keep the body relatively dry. Deodorants di-rectly attack odors themselves. To control the wetness of perspiration and any of its associated odors we have available two personal care products, antiperspirants and deodorants. The an-tiperspirants inhibit sweating and keep the body relatively dry. Deodorants, on the other hand, directly attack odors themselves. The most widely used of the an-tiperspirants are the aluminum chlorohydrates, A12(OH)4C12 and A12(OH)SCI. These release aluminum cations, which seem to reduce wetness by physically clos-ing the ducts of the eccrine glands for as long as several weeks. They also reduce the odor associated with the apocrine glands, probably by killing the bacteria that decompose the organic portion of the fluid. Deodorants mask odors with fragrant ingredients that cover the offending aroma and also with antibiotics that eliminate the bacteria. In addition to the alu- ` minum salts, these antibacterial agents include various salts of zinc as well as the broad-spectrum antibiotic neomycin. Since the odor itself comes from the action of bacteria on the accumulated residue of perspiration, daily washing alone often solves many of the problems. • Q U E S T 1 O N What's the difference between the action of an antiperspirant and a deodorant? 22.11 Putting a Little Color on Your Skin  The oils, waxes, polymers, and dyes of lipstick protect, soften and brighten the lips. With our hair, teeth, and skin clean and in good shape, we'll focus now on cosmetics that add color: lipsticks, eye colorings, nail polish, and face powder. Lipstick provides a soft-ening and protecting film for the lips, as well as colors ranging from soft and unobtru-sive to dazzling. About half the weight of a tube of modern lipstick is highly purified castor oil (a mixture of triglycerides obtained from plant seeds). This oil serves to dis-solve the dyes and, more importantly, to give the stick the ability to remain a waxy solid in its container yet flow smoothly as it touches the warmer lips. Most of the re-mainder of the stick is a mixture of oils, waxes, hydrocarbons, esters, lanolin (the waxy sebum of sheep), and polymers, all formulated to produce a desirable texture, melting point, ingredient mix, and film flow. In addition, the castor oil and other oils and waxes of lipstick help keep the skin of the lips moist and soft. The remaining ingredients-dyes, perfumes, and preservatives-make up a very small percentage of the weight. Major dyes of modern lipsticks include D&C Orange No. 5, known chemical-ly as a dibromofluorescein, and D&C Red No. 22, a tetrabromofluorescein (Fig. 22.14). The D&C here indicates that the Food and Drug Administration has approved these dyes for use in drugs and cosmetics. Figure 22.14 Lipstick dyes.  HO O OH Na0 O O \ I / \ / Br Br / COZNa \ I  D & C Orange No. 5 , D & C Red No. 22 4',5'-dibromofluorescein 2',4',5',7'-tetrabromofluorescein 22.11 Putting a Little Color on Your Skin • 671 Eye shadows use intensely colored, largely inorganic dyes incorporated into mixtures of beeswax, lanolin, and hydrocarbons. The colorings include ultrama-rine blue (an inorganic polymer containing aluminum, oxygen, silicon, sodium, and sulfur), iron oxides of various shades, carbon black (a very finely divided form of carbon resembling powdered charcoal), and titanium dioxide, Ti02. This last in-gredient, a white powder, is quite opaque and is useful in hiding or muting the nat-ural color of the skin as the other dyes show through. Because eyelashes turn pale near their ends, they tend to get lost against the lighter background of the skin and eyes. Mascaras give the lashes a longer look by darkening the ends for more contrast. Despite the term lengthening mascara, these cosmetics don't actually lengthen the eyelashes. They just make them seem longer by making their ends more visible against a lighter facial background. To protect the eyes against any potential for allergic reactions to synthetic dyes, the FDA re-quires that only natural dyes, inorganic pigments, and carbon black be used as mascara colorants. Otherwise, mascaras are prepared in much the same way as other cosmetics. Nail polish is simply a highly specialized, flexible lacquer that can bend with the nail rather than crack and flake. Its pigments include ultramarine blue, carbon black, organic dyes, and various oxides of iron, chromium, and other metals. These, ~ together with nitrocellulose, plasticizers, and a resin, are all dissolved in a mixture of hydrocarbons and esters, including butyl acetate and ethyl acetate. As the volatile solvents evaporate, they leave the dyes embedded in a polymeric film that grips the nail. Most commercial nail polish removers contain ordinary organic solvents, pri-marily ethyl acetate (a common solvent for the polish itself) and acetone. Since these remove the natural oils of the nail along with the hardened polish, the re-movers also contain castor oil, lanolin, or other emollients to keep fingernails and the surrounding skin soft. Face powders are a bit different from the other cosmetics of this section. Un-like lipsticks, eye shadows, and nail polishes, these powders aren't designed to re-place a natural shade with a deep or striking color. Instead, they dull the glossy shine of sebum and perspiration while at the same time adding a pleasant tint, tex-ture, and odor of their own, all without calling attention to their own presence. The composition of a typical cake of face powder appears in Table 22.4. Table 22.4 Composition of a Caked Face Powder Weight Ingredient (%) Formula Function Talc 65 Kaolin 10 A12Si05, hydrated Zinc oxide 10 Zn0 Magnesium 5 Mg(OZC-C16H32-CH3)2 stearate Zinc stearate 5 Zn(OZC-C16H32-CH3)2 Mineral oil 2 Hydrocarbons Cetyl alcohol , 1 CH3-(CHZ)l4-CHZOH Lanolin and other 2 additives Mg3(SiZ05)z(OH)Z Forms cosmetic bulk, provides desired texture Absorbs water Provides hiding power Provides texture Provides texture Emollient Binding agent Softening and coloring agents, perfumes 572 • Chapter 22 Cosmetics and Personal Care • Q U E S T 1 O N A lengthening mascara doesn't actually lengthen eyelashes, but it does make them appear to be longer. How does mascara produce this effect? 22.12 A Few Notes on Perfume  Despite the variety of personal care products we've encountered in this chapter, all share a single characteristic: a pleasant odor or flavor. (Our sense of taste is lim-ited to sweet, sour, bitter, and salt. Flavors are combinations of these four tastes with the sense of smell. Odors affect our perception of flavor.) Our perfumes, colognes, and lotions, like the products we use to color our hair Perfumes are blends of vari- and bodies, have their origins in antiquity. The word perfume itself comes from ous synthetic chemicals, ani- the Latin per (through) and fumus (smoke) and may have applied originally to mal oils, and extracts of scents carried by the smoke of incense and odorous plants used in sacred cere- fragrant plants, all dissolved monies. Today's perfumes are the products of a long history of changes in the pop- as 10 to 25% solutions in alco- ularity of different sorts of odors and of the methods of blending them. Modern hol. perfumes are blends of various synthetic chemicals, animal oils, and extracts of fragrant plants, all dissolved as 10% to 25% solutions in alcohol. Colognes are much more di- Cologne, a shortened form of eau de Cologne (from the French for "water of lute and much less expensive Cologne"), is a much more dilute and much less expensive version of a perfume, versions of perfumes. with concentrations of the fragrant oils running about a tenth those used in the per-fume. The term itself refers to the city of Cologne, Germany, where an Italian, Gio-vanni Maria Farina, settled in 1709 and began manufacturing a lotion based on citrus fruit. The product became a very popular toiletry, providing fame to the city and wealth to Farina and his heirs. For devising the odors of today's cosmetics and toiletries the modern per-fumer has available a set of some 4000 aromatic plant and animal substances and another 2000 synthetic organic chemicals. The blended fragrance itself reaches the nose in three phases. 1. The first impact, the top note, comes from components that vaporize easily and move to our nose quickly. A typical example is phenylacetaldehyde, which brings the odor of hyacinths and lilacs. The top note is the fragrance of the perfume that makes the first impression. 2. The most noticeable odor, the middle note, is produced by compounds such as 2-phenylethanol (also known as /3-phenylethyl alcohol) with its aroma of roses. 3. The end note is a residual, longer lasting scent carried by substances like cive-tone, a cyclic organic compound with a musklike odor. The end note of a per-fume is the fragrance that lingers. Civetone is the odorous component of the secretions of the Ethiopian civet cat and was originally obtained by prodding and scraping the glands of the caged an-imals. Today a more humane preparation comes from syntheses carried out in chemical laboratories. Examples of the organic compounds used in blending fragrances appear in Figure 22.15. The choice of specific ingredients depends on the nature of the ap-plication, the chemical behavior of the available materials, and safety considera tions. A nicely scented substance that oxidizes easily to a foul-smelling product could hardly be used in a face powder, which is exposed to the air for long peri-ods. In addition to these technical factors, though, consumers' perceptions and ex-pectations come into play as well. A deodorant soap, for example, might carry a strong smell suggesting the clean air of a forest, yet the scent of a lipstick must be more subtle and too weak to interfere with the taste of food and drink. These mat- CHZ CHz CH2 CHZ \ HC/ ~CH2~ ~CH2~ ~CHz~ / \ I~ ~ - 0 HC CHZ CH2 CH2 \ O \ CH2 / ~ CHZ/ \ CH2 \ CH2 O CH3 /CH~ CH~ CH3   O C-O~ /CH2~ /CHZ~ II \ CHZ CH2 CH3 / C ~ CH3 CH3 ~H Amyl salicylate Citronellol 2-Phenylethanol (jasmine) (roses, citrus) (/3-phenylethyl alcohol) (roses) Civetone (musk) 22.13 Tanning: Waves of Water, Waves of Light • 573 CH3 OH   II CHZ CHz - CH II ~ CH ' II / ,O-C-CH3 C H CH3 \CHs \ Coumarin (sweet hay) Isobornyl acetate Linalool Phenylacetaldehyde (roses, geraniums) (pine needles) (lavender) (hyacinths, lilacs) Figure 22.15 Organic fragrances. Geraniol ters of perception, both our perceptions of chemicals and the effects of chemicals on our perceptions, are topics we'll examine more closely in our final chapter. •QUESTION What are the functions or actions of the top note, middle~note, and end note of a perfume? For each of these categories name a chemical that produces the desired effect. 22.13 Tanning: Waves of Water, Waves of Light 574 • Chapter 22 Cosmetics and Personal Care The wavelength of radiation is the distance from one crest to another.The frequency of radiation is the number of waves that pass a fixed point in a specific period. of changing the appearance of the human body could pose a hazard far greater than any that might come from the synthetic or natural chemicals of our modern cos-metics. We'll understand why as we examine the science of a suntan. To understand how our bodies respond to the sun's radiation, why we get a tan by sitting in the sun, and how tanning creams and lotions work, we'll first take a closer look at the sun's rays. The sun's energy reaches the earth as electromagnet ic radiation, the same sort of phenomenon that carries radio and television sig-nals, radar, microwaves, X-rays, the ultraviolet rays of Section 19.5 and Chapter 14, and the very light and colors that stimulate the retinas of our eyes. The simplest way to discuss this form of energy follows from its resemblance to the waves of water. Both water and electromagnetic radiation move along at a measurable speed, with alternating crests and troughs. As with the waves of water, we can characterize electromagnetic radiation through its wavelength, which is simply the distance from one crest to another. What's more, since all forms of electromagnetic radia-tion travel at a fixed velocity (almost exactly 3.0 X 101~ cm/sec as long as they're moving through a vacuum) we can describe them in terms of their frequency. which__ is the number of waves that pass a fixed point in a specific period (Fig. 22.16).  Figure 22.16 Wavelength and frequency. Wavelength  Wavelength: The distance between crests 0 Time Time 1 second Frequency: The number of waves per second Wave speed = frequency Wavelength 22.13 Tanning: Waves of Water, Waves of Light • 575 These two characteristics of any wave motion, wavelength and frequency, are mutually reciprocal. That is, the larger (or smaller) the wavelength, the smaller (or larger) the frequency. The shorter the distance between two wave crests, for ex ample, the more waves will pass a fixed point over any particular period, as long as they're moving along at a uniform rate. At this point radiation takes on its own set of characteristics and our analogy to water loses its value. The energy of electromagnetic radiation, for example, de-pends directly and only on its frequency. The greater its frequency (or the shorter its wavelength), the higher its energy. For that matter, frequency is the only char-acteristic that differentiates one form of electromagnetic radiation from another. X-rays, for example, travel with a shorter wavelength and a higher frequency (and therefore a higher energy as well) than radio or television waves. It's this difference alone that makes them behave as they do. With one nanometer (nm) equal to 10-9 meter (m), visible light comes to us in a range of wavelengths from about 400 to 700 rim. Red light lies at the longer end of the spectrum, while invisible, heat-bearing infrared radiation lies beyond, at wavelengths ,~ a bit longer than 700 rim. At the shorter end of the spectrum visible light carries a blue-violet color. Still shorter wavelengths, running from about 290 to 400 nm, form the ;~ portion of the sun's ultraviolet (UV) radiation that penetrates the ozone layer and reaches the earth's surface and our exposed skin (Fig. 22.17; also see Sec. 14.8). ~ ป A suntan is simply the visible evidence of the body's attempt to protect itself from the harm this ultraviolet radiation might do. Any exposed skin is bathed in relatively --high energy, potentially damaging ultraviolet radiation. In fact, the very absorption of this radiation stimulates the body to take protective measures. As one means of shield-, ing itself, the skin begins producing the dark pigment melanin (Sec. 22.6), which screens -`out part of the radiation and helps minimize the damage. A tan, then, is the visible ev-idence of the generation of protective melanin in response to potential harm. The potential for damage comes from two adjoining segments of the sun's UV radiation, its UV-A and UV-13 regions, which affect the skin in slightly different ways. UV-13 radiation, the more powerful of the two, occupies the shorter wave length region, from 290 to 320 nm. It does part of its damage quickly, with the re- mainder coming more slowly, over a longer term. The acute injury lies in the tissue Beginning to burn from too destruction of sunburns. The results-redness, blistered and peeling skin, and much exposure to the sun's pain-are the same as for burns produced by ionizing radiation (Sec. 5.7) and by ultraviolet radiation. 700 Visible light ,ed Orant"e Yellow Green Blue Violet o-. _. ...~,.w.~....~ri 600 500 400 Nanometers (1 nanometer = 10-9 meter) Figure 22.17 Wavelength, frequency, and energy. Lower energy Higher energy 22.11 Putting a Little Color on Your Skin • 671 Eye shadows use intensely colored, largely inorganic dyes incorporated into mixtures of beeswax, lanolin, and hydrocarbons. The colorings include ultrama-rine blue (an inorganic polymer containing aluminum, oxygen, silicon, sodium, and sulfur), iron oxides of various shades, carbon black (a very finely divided form of carbon resembling powdered charcoal), and titanium dioxide, Ti02. This last in-gredient, a white powder, is quite opaque and is useful in hiding or muting the nat-ural color of the skin as the other dyes show through. Because eyelashes turn pale near their ends, they tend to get lost against the lighter background of the skin and eyes. Mascaras give the lashes a longer look by darkening the ends for more contrast. Despite the term lengthening mascara, these cosmetics don't actually lengthen the eyelashes. They just make them seem longer by making their ends more visible against a lighter facial background. To protect the eyes against any potential for allergic reactions to synthetic dyes, the FDA re-quires that only natural dyes, inorganic pigments, and carbon black be used as mascara colorants. Otherwise, mascaras are prepared in much the same way as other cosmetics. Nail polish is simply a highly specialized, flexible lacquer that can bend with the nail rather than crack and flake. Its pigments include ultramarine blue, carbon black, organic dyes, and various oxides of iron, chromium, and other metals. These, ~ together with nitrocellulose, plasticizers, and a resin, are all dissolved in a mixture of hydrocarbons and esters, including butyl acetate and ethyl acetate. As the volatile solvents evaporate, they leave the dyes embedded in a polymeric film that grips the nail. Most commercial nail polish removers contain ordinary organic solvents, pri-marily ethyl acetate (a common solvent for the polish itself) and acetone. Since these remove the natural oils of the nail along with the hardened polish, the re-movers also contain castor oil, lanolin, or other emollients to keep fingernails and the surrounding skin soft. Face powders are a bit different from the other cosmetics of this section. Un-like lipsticks, eye shadows, and nail polishes, these powders aren't designed to re-place a natural shade with a deep or striking color. Instead, they dull the glossy shine of sebum and perspiration while at the same time adding a pleasant tint, tex-ture, and odor of their own, all without calling attention to their own presence. The composition of a typical cake of face powder appears in Table 22.4. Table 22.4 Composition of a Caked Face Powder Weight Ingredient (%) Formula Function Talc 65 Kaolin 10 A12Si05, hydrated Zinc oxide 10 Zn0 Magnesium 5 Mg(OZC-C16H32-CH3)2 stearate Zinc stearate 5 Zn(OZC-C16H32-CH3)2 Mineral oil 2 Hydrocarbons Cetyl alcohol , 1 CH3-(CHZ)l4-CHZOH Lanolin and other 2 additives Mg3(SiZ05)z(OH)Z Forms cosmetic bulk, provides desired texture Absorbs water Provides hiding power Provides texture Provides texture Emollient Binding agent Softening and coloring agents, perfumes 572 • Chapter 22 Cosmetics and Personal Care • Q U E S T 1 O N A lengthening mascara doesn't actually lengthen eyelashes, but it does make them appear to be longer. How does mascara produce this effect? 22.12 A Few Notes on Perfume  Despite the variety of personal care products we've encountered in this chapter, all share a single characteristic: a pleasant odor or flavor. (Our sense of taste is lim-ited to sweet, sour, bitter, and salt. Flavors are combinations of these four tastes with the sense of smell. Odors affect our perception of flavor.) Our perfumes, colognes, and lotions, like the products we use to color our hair Perfumes are blends of vari- and bodies, have their origins in antiquity. The word perfume itself comes from ous synthetic chemicals, ani- the Latin per (through) and fumus (smoke) and may have applied originally to mal oils, and extracts of scents carried by the smoke of incense and odorous plants used in sacred cere- fragrant plants, al I dissolved monies. Today's perfumes are the products of a long history of changes in the pop- as 10 to 25% solutions in alco- ularity of different sorts of odors and of the methods of blending them. Modern hol. perfumes are blends of various synthetic chemicals, animal oils, and extracts of fragrant plants, all dissolved as 10% to 25% solutions in alcohol. Colognes are much more di- Cologne, a shortened form of eau de Cologne (from the French for "water of lute and much less expensive Cologne"), is a much more dilute and much less expensive version of a perfume, versions of perfumes. with concentrations of the fragrant oils running about a tenth those used in the per-fume. The term itself refers to the city of Cologne, Germany, where an Italian, Gio-vanni Maria Farina, settled in 1709 and began manufacturing a lotion based on citrus fruit. The product became a very popular toiletry, providing fame to the city and wealth to Farina and his heirs. For devising the odors of today's cosmetics and toiletries the modern per-fumer has available a set of some 4000 aromatic plant and animal substances and another 2000 synthetic organic chemicals. The blended fragrance itself reaches the nose in three phases. 1. The first impact, the top note, comes from components that vaporize easily and move to our nose quickly. A typical example is phenylacetaldehyde, which brings the odor of hyacinths and lilacs. The top note is the fragrance of the perfume that makes the first impression. 2. The most noticeable odor, the middle note, is produced by compounds such as 2-phenylethanol (also known as /3-phenylethyl alcohol) with its aroma of roses. 3. The end note is a residual, longer lasting scent carried by substances like cive-tone, a cyclic organic compound with a musklike odor. The end note of a perfume is the fragrance that lingers. Civetone is the odorous component of the secretions of the Ethiopian civet cat and was originally obtained by prodding and scraping the glands of the caged an-imals. Today a more humane preparation comes from syntheses carried out in chemical laboratories. Examples of the organic compounds used in blending fragrances appear in Figure 22.15. The choice of specific ingredients depends on the nature of the ap-plication, the chemical behavior of the available materials, and safety considera tions. A nicely scented substance that oxidizes easily to a foul-smelling product could hardly be used in a face powder, which is exposed to the air for long peri-ods. In addition to these technical factors, though, consumers' perceptions and ex-pectations come into play as well. A deodorant soap, for example, might carry a strong smell suggesting the clean air of a forest, yet the scent of a lipstick must be more subtle and too weak to interfere with the taste of food and drink. These mat- CHZ CHz CH2 CHZ \ HC/ ~CH2~ ~CH2~ ~CHz~ / \ I~ ~ - 0 HC CHZ CH2 CH2 \ O \ CH2 / ~ CHZ/ \ CH2 \ CH2 O CH3 /CH~ CH~ CH3   O C-O~ /CH2~ /CHZ~ II \ CHZ CH2 CH3 / C ~ CH3 CH3 ~H Amyl salicylate Citronellol 2-Phenylethanol (jasmine) (roses, citrus) (/3-phenylethyl alcohol) (roses) Civetone (musk) 22.13 Tanning: Waves of Water, Waves of Light • 573 CH3 OH   II CHZ CHz - CH II ~ CH ' II / ,O-C-CH3 C H CH3 \CHs \ Coumarin (sweet hay) Isobornyl acetate Linalool Phenylacetaldehyde (roses, geraniums) (pine needles) (lavender) (hyacinths, lilacs) Figure 22.15 Organic fragrances. Geraniol   ters of perception, both our perceptions of chemicals and the effects of chemicals on our perceptions, are topics we'll examine more closely in our final chapter.  What are the functions or actions of the top note, middle~note, and end note of a per- • Q U E S T 1 O N fume? For each of these categories name a chemical that produces the desired effect. 22.13 Tanning: Waves of Water, Waves of Light 574 • Chapter 22 Cosmetics and Personal Care The wavelength of radiation is the distance from one crest to another.The frequency of radiation is the number of waves that pass a fixed point in a specific period. of changing the appearance of the human body could pose a hazard far greater than any that might come from the synthetic or natural chemicals of our modern cos-metics. We'll understand why as we examine the science of a suntan. To understand how our bodies respond to the sun's radiation, why we get a tan by sitting in the sun, and how tanning creams and lotions work, we'll first take a closer look at the sun's rays. The sun's energy reaches the earth as electromagnet ic radiation, the same sort of phenomenon that carries radio and television sig-nals, radar, microwaves, X-rays, the ultraviolet rays of Section 19.5 and Chapter 14, and the very light and colors that stimulate the retinas of our eyes. The simplest way to discuss this form of energy follows from its resemblance to the waves of water. Both water and electromagnetic radiation move along at a measurable speed, with alternating crests and troughs. As with the waves of water, we can characterize electromagnetic radiation through its wavelength, which is simply the distance from one crest to another. What's more, since all forms of electromagnetic radia-tion travel at a fixed velocity (almost exactly 3.0 X 101~ cm/sec as long as they're moving through a vacuum) we can describe them in terms of their frequency. which__ is the number of waves that pass a fixed point in a specific period (Fig. 22.16).  Figure 22.16 Wavelength and frequency. Wavelength  Wavelength: The distance between crests 0 Time Time 1 second Frequency: The number of waves per second Wave speed = frequency Wavelength 576 • Chapter 22 Cosmetics and Personal Care intense heat. Repeated exposure to the UV-B region over a longer period pro-duces skin cancers, especially among fairhaired, light-skinned people. Even very brief exposure can begin the formation of wrinkles and sag through the destruc-tion of collagen, one of the proteins responsible for the firmness of skin and sim-ilar tissue (Sec. 18.1). One beneficial effect of the absorption of small amounts of UV-B radiation is the generation of vitamin D (Sec. 19.5). The less energetic zone, the UV-A of longer wavelengths (320 to 400 rim), isn't as effective at tissue destruction. Instead of burning, it tends to produce a slow tan. It's not quite innocuous, though, since it adds to UV-B's ability to do its damage.  • Q U E S T I O N What single characteristic of electromagnetic radiation directly determines or de-fines its energy? 22.14 Sunscreen Chemicals The sunscreen protection factor (SPF) of a suntan or sun screen lotion reveals the fraction of ultraviolet radia-tion it allows to pass through to the skin. Commercial suntan and sunscreen products act either by blocking the UV-B se-lectively, letting the UV-A produce its slow tan, or by blocking out both regions, shielding us from the entire solar UV spectrum. The most effective shields are creams containing opaque inorganic oxides, especially zinc oxide and titanium dioxide. These scatter all the radiation, letting none through to the skin. They are usually applied to the nose and the tops of the ears, areas that receive the most di-rect exposure. Among the more widely used selective agents are p-aminobenzoic acid (PABA or ABA) and its many structural modifications. PABA does a good job of ab-sorbing UV-B radiation while letting UV-A radiation pass through to produce a tan. For this reason lotions containing PABA and similar compounds are consid-ered tanning lotions rather than sunscreens. Other UV-absorbing compounds, such as benzophenone, oxybenzone, and dioxybenzorae, absorb throughout the UV spec-trum and, sometimes in combination with PABA, provide a wider range of pro-tection. The structures of these absorbers appear in Figure 22.18. Whatever specific ingredients it may contain, the lotion's sunscreen protec-tion factor (SPF), which appears on its container, serves as a measure of its pro-tecting power. A product with an SPF of 6, for example, reduces the amount of Figure 22.18 Tanning compounds. O 11 C-OH  NHZ p-Aminobenzoic acid (PABA or ABA)  11 11 / I C-0 \ jai C I \ \ / \ / CH30 $enzophenone Oxybenzone OH O OH II O C / I I \ HOCHZ - C - CH20H ~ / CH30 Dihydroxyacetone Dioxybenzone 22.11 Putting a Little Color on Your Skin • 671 Eye shadows use intensely colored, largely inorganic dyes incorporated into mixtures of beeswax, lanolin, and hydrocarbons. The colorings include ultrama-rine blue (an inorganic polymer containing aluminum, oxygen, silicon, sodium, and sulfur), iron oxides of various shades, carbon black (a very finely divided form of carbon resembling powdered charcoal), and titanium dioxide, Ti02. This last in-gredient, a white powder, is quite opaque and is useful in hiding or muting the nat-ural color of the skin as the other dyes show through. Because eyelashes turn pale near their ends, they tend to get lost against the lighter background of the skin and eyes. Mascaras give the lashes a longer look by darkening the ends for more contrast. Despite the term lengthening mascara, these cosmetics don't actually lengthen the eyelashes. They just make them seem longer by making their ends more visible against a lighter facial background. To protect the eyes against any potential for allergic reactions to synthetic dyes, the FDA re-quires that only natural dyes, inorganic pigments, and carbon black be used as mascara colorants. Otherwise, mascaras are prepared in much the same way as other cosmetics. Nail polish is simply a highly specialized, flexible lacquer that can bend with the nail rather than crack and flake. Its pigments include ultramarine blue, carbon black, organic dyes, and various oxides of iron, chromium, and other metals. These, ~ together with nitrocellulose, plasticizers, and a resin, are all dissolved in a mixture of hydrocarbons and esters, including butyl acetate and ethyl acetate. As the volatile solvents evaporate, they leave the dyes embedded in a polymeric film that grips the nail. Most commercial nail polish removers contain ordinary organic solvents, pri-marily ethyl acetate (a common solvent for the polish itself) and acetone. Since these remove the natural oils of the nail along with the hardened polish, the re-movers also contain castor oil, lanolin, or other emollients to keep fingernails and the surrounding skin soft. Face powders are a bit different from the other cosmetics of this section. Un-like lipsticks, eye shadows, and nail polishes, these powders aren't designed to re-place a natural shade with a deep or striking color. Instead, they dull the glossy shine of sebum and perspiration while at the same time adding a pleasant tint, tex-ture, and odor of their own, all without calling attention to their own presence. The composition of a typical cake of face powder appears in Table 22.4. Table 22.4 Composition of a Caked Face Powder Weight Ingredient (%) Formula Function Talc 65 Kaolin 10 A12Si05, hydrated Zinc oxide 10 Zn0 Magnesium 5 Mg(OZC-C16H32-CH3)2 stearate Zinc stearate 5 Zn(OZC-C16H32-CH3)2 Mineral oil 2 Hydrocarbons Cetyl alcohol , 1 CH3-(CHZ)l4-CHZOH Lanolin and other 2 additives Mg3(SiZ05)z(OH)Z Forms cosmetic bulk, provides desired texture Absorbs water Provides hiding power Provides texture Provides texture Emollient Binding agent Softening and coloring agents, perfumes 572 • Chapter 22 Cosmetics and Personal Care • Q U E S T 1 O N A lengthening mascara doesn't actually lengthen eyelashes, but it does make them appear to be longer. How does mascara produce this effect? 22.12 A Few Notes on Perfume Despite the variety of personal care products we've encountered in this chapter, all share a single characteristic: a pleasant odor or flavor. (Our sense of taste is lim-ited to sweet, sour, bitter, and salt. Flavors are combinations of these four tastes with the sense of smell. Odors affect our perception of flavor.) Our perfumes, colognes, and lotions, like the products we use to color our hair Perfumes are blends of vari- and bodies, have their origins in antiquity. The word perfume itself comes from ous synthetic chemicals, ani- the Latin per (through) and fumus (smoke) and may have applied originally to mal oils, and extracts of scents carried by the smoke of incense and odorous plants used in sacred cere- fragrant plants, al I dissolved monies. Today's perfumes are the products of a long history of changes in the pop- as 10 to 25% solutions in alco- ularity of different sorts of odors and of the methods of blending them. Modern hol. perfumes are blends of various synthetic chemicals, animal oils, and extracts of fragrant plants, all dissolved as 10% to 25% solutions in alcohol. Colognes are much more di- Cologne, a shortened form of eau de Cologne (from the French for "water of lute and much less expensive Cologne"), is a much more dilute and much less expensive version of a perfume, versions of perfumes. with concentrations of the fragrant oils running about a tenth those used in the per-fume. The term itself refers to the city of Cologne, Germany, where an Italian, Gio-vanni Maria Farina, settled in 1709 and began manufacturing a lotion based on citrus fruit. The product became a very popular toiletry, providing fame to the city and wealth to Farina and his heirs. For devising the odors of today's cosmetics and toiletries the modern per-fumer has available a set of some 4000 aromatic plant and animal substances and another 2000 synthetic organic chemicals. The blended fragrance itself reaches the nose in three phases. 1. The first impact, the top note, comes from components that vaporize easily and move to our nose quickly. A typical example is phenylacetaldehyde, which brings the odor of hyacinths and lilacs. The top note is the fragrance of the perfume that makes the first impression. 2. The most noticeable odor, the middle note, is produced by compounds such as 2-phenylethanol (also known as /3-phenylethyl alcohol) with its aroma of roses. 3. The end note is a residual, longer lasting scent carried by substances like cive-tone, a cyclic organic compound with a musklike odor. The end note of a per-fume is the fragrance that lingers. Civetone is the odorous component of the secretions of the Ethiopian civet cat and was originally obtained by prodding and scraping the glands of the caged an-imals. Today a more humane preparation comes from syntheses carried out in chemical laboratories. Examples of the organic compounds used in blending fragrances appear in Figure 22.15. The choice of specific ingredients depends on the nature of the ap-plication, the chemical behavior of the available materials, and safety considera tions. A nicely scented substance that oxidizes easily to a foul-smelling product could hardly be used in a face powder, which is exposed to the air for long peri-ods. In addition to these technical factors, though, consumers' perceptions and ex-pectations come into play as well. A deodorant soap, for example, might carry a strong smell suggesting the clean air of a forest, yet the scent of a lipstick must be more subtle and too weak to interfere with the taste of food and drink. These mat- CHZ CHz CH2 CHZ \ HC/ ~CH2~ ~CH2~ ~CHz~ / \ I~ ~ - 0 HC CHZ CH2 CH2 \ O \ CH2 / ~ CHZ/ \ CH2 \ CH2 O CH3 /CH~ CH~ CH3   O C-O~ /CH2~ /CHZ~ II \ CHZ CH2 CH3 / C ~ CH3 CH3 ~H Amyl salicylate Citronellol 2-Phenylethanol (jasmine) (roses, citrus) (/3-phenylethyl alcohol) (roses) Civetone (musk) 22.13 Tanning: Waves of Water, Waves of Light • 573 CH3 OH   II CHZ CHz - CH II ~ CH ' II / ,O-C-CH3 C H CH3 \CHs \ Coumarin (sweet hay) Isobornyl acetate Linalool Phenylacetaldehyde (roses, geraniums) (pine needles) (lavender) (hyacinths, lilacs) Figure 22.15 Organic fragrances. Geraniol   ters of perception, both our perceptions of chemicals and the effects of chemicals on our perceptions, are topics we'll examine more closely in our final chapter.  What are the functions or actions of the top note, middle~note, and end note of a per- • Q U E S T 1 O N fume? For each of these categories name a chemical that produces the desired effect. 22.13 Tanning: Waves of Water, Waves of Light  In this section we'll examine still another way you can decorate your body, this time without commercial dyes, detergents, lotions, creams, perfumes, metals, or any other material substance. Despite the absence of chemicals of any kind, this mode 574 • Chapter 22 Cosmetics and Personal Care The wavelength of radiation is the distance from one crest to another.The frequency of radiation is the number of waves that pass a fixed point in a specific period. of changing the appearance of the human body could pose a hazard far greater than any that might come from the synthetic or natural chemicals of our modern cos-metics. We'll understand why as we examine the science of a suntan. To understand how our bodies respond to the sun's radiation, why we get a tan by sitting in the sun, and how tanning creams and lotions work, we'll first take a closer look at the sun's rays. The sun's energy reaches the earth as electromagnet ic radiation, the same sort of phenomenon that carries radio and television sig-nals, radar, microwaves, X-rays, the ultraviolet rays of Section 19.5 and Chapter 14, and the very light and colors that stimulate the retinas of our eyes. The simplest way to discuss this form of energy follows from its resemblance to the waves of water. Both water and electromagnetic radiation move along at a measurable speed, with alternating crests and troughs. As with the waves of water, we can characterize electromagnetic radiation through its wavelength, which is simply the distance from one crest to another. What's more, since all forms of electromagnetic radia-tion travel at a fixed velocity (almost exactly 3.0 X 101~ cm/sec as long as they're moving through a vacuum) we can describe them in terms of their frequency. which__ is the number of waves that pass a fixed point in a specific period (Fig. 22.16).  Figure 22.16 Wavelength and frequency. Wavelength  Wavelength: The distance between crests 0 Time    Time 1 second Frequency: The number of waves per second Wave speed = frequency Wavelength • Q U E S T I O N What single characteristic of electromagnetic radiation directly determines or de-fines its energy? 22.14 Sunscreen Chemicals The sunscreen protection factor (SPF) of a suntan or sun screen lotion reveals the fraction of ultraviolet radia-tion it allows to pass through to the skin. Commercial suntan and sunscreen products act either by blocking the UV-B se-lectively, letting the UV-A produce its slow tan, or by blocking out both regions, shielding us from the entire solar UV spectrum. The most effective shields are creams containing opaque inorganic oxides, especially zinc oxide and titanium dioxide. These scatter all the radiation, letting none through to the skin. They are usually applied to the nose and the tops of the ears, areas that receive the most di-rect exposure. Among the more widely used selective agents are p-aminobenzoic acid (PABA or ABA) and its many structural modifications. PABA does a good job of ab-sorbing UV-B radiation while letting UV-A radiation pass through to produce a tan. For this reason lotions containing PABA and similar compounds are consid-ered tanning lotions rather than sunscreens. Other UV-absorbing compounds, such as benzophenone, oxybenzone, and dioxybenzorae, absorb throughout the UV spec-trum and, sometimes in combination with PABA, provide a wider range of pro-tection. The structures of these absorbers appear in Figure 22.18. Whatever specific ingredients it may contain, the lotion's sunscreen protec-tion factor (SPF), which appears on its container, serves as a measure of its pro-tecting power. A product with an SPF of 6, for example, reduces the amount of Figure 22.18 Tanning compounds. O 11 C-OH  NHZ p-Aminobenzoic acid (PABA or ABA)  11 11 / I C-0 \ jai C I \ \ / \ / CH30 $enzophenone Oxybenzone OH O OH II O C / I I \ HOCHZ - C - CH20H ~ / CH30 Dihydroxyacetone Dioxybenzone • QUESTION What single characteristic of electromagnetic radiation directly determines or de-fines its energy? 22.14 Sunscreen Chemicals The sunscreen protection factor (SPF) of a suntan or sun screen lotion reveals the fraction of ultraviolet radiation it allows to pass through to the skin. Commercial suntan and sunscreen products act either by blocking the UV-B se-lectively, letting the UV-A produce its slow tan, or by blocking out both regions, shielding us from the entire solar UV spectrum. The most effective shields are creams containing opaque inorganic oxides, especially zinc oxide and titanium dioxide. These scatter all the radiation, letting none through to the skin. They are usually applied to the nose and the tops of the ears, areas that receive the most di-rect exposure. Among the more widely used selective agents are p-aminobenzoic acid (PABA or ABA) and its many structural modifications. PABA does a good job of ab-sorbing UV-B radiation while letting UV-A radiation pass through to produce a tan. For this reason lotions containing PABA and similar compounds are consid-ered tanning lotions rather than sunscreens. Other UV-absorbing compounds, such as benzophenone, oxybenzone, and dioxyber~zorae, absorb throughout the UV spec-trum and, sometimes in combination with PABA, provide a wider range of pro-tection. The structures of these absorbers appear in Figure 22.18. Whatever specific ingredients it may contain, the lotion's sunscreen protec-tion factor (SPF), which appears on its container, serves as a measure of its pro-tecting power. A product with an SPF of 6, for example, reduces the amount of Figure 22.18 Tanning compounds. O C-OH  NHZ p-Aminobenzoic acid (PABA or ABA)  / I C I \ / I C I \ \ / \ / CH30 $enzophenone Oxybenzone O OH II OH O C / I I \ HOCHZ - C - CH20H ~ / CH30 Dihydroxyacetone Dioxybenzone  The world as we see it isn't necessarily the world as it exists. In Figure 23.1 you see two horizontal lines, each ending in diagonal lines slanting one way or an-other. Most people see the horizontal line on the right as longer than the one on the left. Measure them, though, and you'll find that the two horizontal lines are of equal length. Then there's the stovepipe hat of Figure 23.2. Most peo-ple see the height of the hat as greater than the width of the brim. Again, meas-ure the height and the width and you'll find that they are the same. Misperceptions like these can be corrected easily by tests of the physical world, such as we use in applications of the sci-entific method. Figure 23.2 Is the hat taller than the brim is wide, or is it the Figure 23.1 Which line is longer? other way around? Perception, Reality, and Chemicals 583 584 • Chapter 23 Medicines and Drugs We'll also examine a technique called the double-blind experiment that allows us to learn whether the action of any particular medication results from a direct chem-ical influence of that medication, regardless of our expectations, or from the action of those very same expectations through the placebo effect, through nothing more than our faith in the substance's effectiveness. We'll start our examination of the connection between chemicals and perceptions with agents of mercy, the analgesics or painkillers. • An analgesic reduces or elimi-nates pain. An antipyretic lowers or eliminates fever. An anti-inflammatory agent reduces or eliminates inflammation. Today's leading commercial pain reliever is common aspirin. Since its initial syn- thesis in 1853 and its acceptance into medical practice at the beginning of the 20th l~ century, aspirin has become the most widely used of all drugs for the treatment of illness or injury. More aspirin has been taken over the years by more people throughout the world than any other single medication of any kind. In this examination of the extraordinary chemistry of our ordinary chemicals, aspirin must be recognized as one of the most extraordinary of all, with the power to act as an analgesic (to relieve pain), as an antipyretic (to lower fever), and as an anti-intlammatory agent (to reduce inflammation). It's effective in the treatment of rheumatoid arthritis and in preventing some types of strokes and heart attacks, those resulting from the accumulation of platelets (Sec. 23.4) in the blood vessels. It also shows promise in decreasing the risk of some forms of colon cancer. Yet it's also one of the most common of all medications, inexpensive, and available to virtually everyone, almost everywhere. Aspirin itself, the common or trade name of the chemical acetylsalicylic acid, is prepared easily through the reaction of acetic anhydride with salicylic acid CH3-C OH H O - C - CH3 -~ CH3-C - O - C - CH3 + H20 Dehydration of acetic acid . . . . . produces acetic anhydride The acetyl group II o ~ o C-oH II II -~ O C-CH3 + CH3-C-OH / \ Salicylic acid Acetic anhydride Acetylsalcylic acid Acetic acid (aspirin) The acetyl group 23.2 How Aspirin Got Its Name • 585 the removal of one water molecule from two molecules of the acid. The product is a good acerylating agent, which means that it's useful for adding the acetyl group to another molecule, as it does in the synthesis of aspirin.) What function does acetic anhydride serve in the chemical synthesis of aspirin? •QUESTION 23.2 How Aspirin Got Its Name Aspirin is the common name or trade name of acetylsalicylic acid, an analgesic, antipyretic, and anti-inflammatory medication. (Fig. 23.3). (Acetic anhydride 23.1 Aspirin Figure 23.3 Aspirin from the acetylation of salicylic acid. Although neither salicylic acid (the molecule being acetylated) nor acetylsal-icylic acid (the product itself) occurs in nature, several closely related com-pounds do. Physicians as far back as Hippocrates, the ancient Greek healer known as the Father of Medicine, knew of the curative powers of the bark of the willow tree and closely related plants, especially their antipyretic or fever-reducing properties. In 1827 willow bark yielded its active agent, salicin, to chemists of that era. A few years later this salicin was hydrolyzed to glucose and salicyl alcohol, which was in turn oxidized to salicylic acid (Fig. 23.4). The Latin term for willows, salix, gives us the name of an entire family of compounds, the salicylates, whose mole-cules resemble those of both the alcohol and the acid. It's also the term for the botanical genus of the tree itself, Salix. At about the same time, salicylic acid was also obtained from the reaction of salicylaldehyde with strong base (Fig. 23.5). This fragrant aldehyde (Sec. 16.4) was itself isolated from meadowsweet flowers, which belong to the genus Spi raea. The bark of the willow tree contains salicin, an analgesic that can be converted to salicylic acid and then to aspirin. The Latin name for the tree, salix, gives us both the botanical genus of the tree and the generic term for compounds related to salicin, the salicylates. 616 • Chapter 20 Poisons,Toxins, Hazards, and Risks  whatever it's being metabolized to) is a mutagen and caus-es the bacteria to switch back to the form for which histi-dine is a nonessential amino acid. E X E R C I S E S For Rev; ew 2, 3, 7, 8-tetrachlorodibenzo- lethal 1. Following are a statement containing a number of blanks P-dioxin mutagens and a list of words and phrases. The number of words equals acceptability oil of sassafras the number of blanks within the statement, and all but two of aspirin risk the words fit correctly into these blanks. Fill in the blanks of the body weight saccharin statement with those words that do fit, then complete the state- botulinum toxin A safrole ment by filling in the two remaining blanks with correct words carcinogens sodium cyanide (not in the list) in place of the two words that don't fit. diphtheria toxin TCDD Since anything can be harmful if we consume it in excessive half teratogens amounts or use it carelessly or improperly, everything we come in contact with presents some risk of . Be- injury tetanus toxin cause of this, we find it useful to define safety as the LDso of . One measure of lethal risk in 2, Describe, define, or identify the following: the chemicals we consume is the , which is the weight of the substance (per unit of ) that is aflatoxin OSHA to of a large population of labora- comfrey parathion tory animals. According to this measure, the deadliest chem- isoflurophate solanine ical known is , produced by a common 3• What contribution did each of the following make to the microorganism. Second and third on the list of deadly chem- subject matter of this chapter: (a) William Lowrance, (b) James icals, respectively, are and . The J. Delaney, (c) Bruce N. Ames, (d) Ira Remsen and Constantine fourth most lethal chemical is one produced by laboratory Fahlberg, (e) Harvey W Wiley? reactions carried out by humans, , which is also known by the simpler term . Other risks, not '`}~ Name a chemical affected by each of the following acts of immediately lethal, include the risk of severe birth defects, Congress and describe how the law affects our use of the chem- produced by ; the lesser genetic changes in- ical: (a) the Poison Prevention Packaging Act of 1970, (b) the duced by ; and the risk of cancer, generated by Saccharin Study and Labeling Act of 1977. . Among the carcinogens are natural products 6• In what food does each of the following chemicals occur: such as , which is a component of , (a) lactose, (b) glycyrrhizic acid, (c) myristicin, (d) oxalic acid, and the synthetic sweetener . Both of these (e) benzo(a)pyrene, (f) tetrodotoxin? chemicals are banned from use as food additives by provi- 6. What governmental agency is responsible for (a) investi- sions of the , but the sweetener is in continued ~ gating outbreaks of illness caused by food spoilage; (b) the use because of the enormous public demand for it. The reg- chemicals of beer, wine, liquor, and tobacco; (c) chemical pes- ulation of food additives is the responsibility of the ticides; (d) exposure to chemicals in the workplace; (e) chem- , an agency of the federal government. icals used as food additives? What the experiment showed was that the number of through the vacuum of space to the Earth. To test this idea, muon neutrinos coming up through the Earth to the de- scientists are now trying to determine whether the number tector was smaller than the number that reached it when of solar neutrinos arriving at the detector varies with the the Sun was overhead. These data suggest that the muon seasons. Remember that the Earth is about 3 percent neutrinos change to another type of neutrino on their way closer to the Sun in winter than in summer, and this differ- through the Earth. Those that travel only through the ence may be enough to affect our neutrino counts. neutrinos in all directions. All this really tells us is that the neutrinos also have mass and if so how much. And that, in electron neutrinos do not change from one type to another turn, may help us solve the mystery of the missing solar as they pass through the Earth. They still might change neutrinos and understand even better just how the Sun type on their long journey from the interior of the Sun produces its vast output of energy. 21.6 A Brief History of Polymers and Plastics. Part 1: The Roman God of Fire • 529 - CH2 H CH 3 CH2- CH2 H - CH3 CH2 - \C=C/ \C=C/ \C=C/ \C=C/ CH3 CHZ- CH2 H CH3 CHZ- CH2 H  CHZ\ /H /C=C \ CH3 CH2  Figure 21.10 Gutta-percha as trans-polyisoprene. carbons of the chain on one side of the average line of the double bonds and the methyl substituents on the other, as in Figure 21.9. In gutta-percha, another natu-rally occurring polymer of isoprene, all the double bonds are in the trans configu-ration (Fig. 21.10). With an all-trans molecular geometry, gutta-percha isn't nearly as elastic as rubber. It does find uses, though, as a covering for golf balls, in surgi-cal equipment, and as an electrical insulator, especially for underwater cables. Having completed a review of the structures of polymeric molecules, the ways they form from monomers, and some of their properties, we'll now examine some '-- of their histories. We've seen that polyisoprene can exist as geometric isomers. Can polyethylene also • Q U E S T 1 O N exist as geometric,isomers? Explain. 21.6 A Brief History of Polymers and Plastics. Part I:The Roman God of Fire  In its elasticity, rubber illustrates the importance of molecular structure as a source of physical properties. Its elasticity originates in the way its molecules coil up, which allows them to stretch out when we pull on a piece of rubber and then to spring back when we release it. Heat a piece of pure, natural rubber, though, and you'll find that as it becomes warm it loses much of its resilience. Its usual bounce becomes sloppy and it turns sticky. That happens because at high temperatures the intertwined, threadlike polyisoprene molecules slide past each other a bit too readily when we stretch the rubber and they don't pull back to their original po-sitions when we release it. Charles Goodyear, born in 1800 in New Haven, Connecticut, solved the prob-lem of sticky rubber partly by accident. Goodyear was an inventor and the son of an inventor, but he lacked the talents of a good businessman. He had already spent time in jail for his debts when he became obsessed with the idea of creating a rub-ber that retained its elasticity even when hot. He tried to perfect it for 10 years with little success until, one day in 1839, he accidentally dropped a mixture of crude rubber and sulfur onto a hot stove. When the charred mixture cooled a bit he found that it was nicely elastic, even though still warm. In 1839 neither Goodyear nor anyone else knew anything about the molecular structure of rubber. Goodyear knew only that heating rubber with sulfur worked; he had no idea why. Once again we see the importance of serendipity in science (Sec. 4.1). 530 • Chapter 21 Polymers and Plastics Charles Goodyear discovers vulcanized rubber. We know now that with heating, the sulfur and the polyisoprene molecules react to cross-link the polyisoprene molecules to one another. Figure 21.11 Vulcanized rubber. Polymeric strands of unvulcanized rubber slip past each other Vulcanization connects the strands through links of sulfur so when the rubber is heated and stretched. that the interconnected polyisoprene molecules retain their orientation when heated and stretched.   Sulfur links CHARLES GOODYEAR wxo omeo.xaeo ฐx839 f1939 ~~ ~oo . •eo    21.6 A Brief History of Polymers and Plastics. Part I:The Roman God of Fire • 531 tire treads and engine hoses and belts. Today's leading synthetic elastomer, styrene-butadiene rubber, was developed by German chemists in the early 1930s and further refined by Americans during and after World War II. It results from the copolymerization of a mixture of 75 % butadiene and 25 % styrene (Fig. 21.12), and it serves as a good substitute for natural rubber `'ฐ" -in the manufacture of various consumer goods, especially the treads of tires. Neoprene is a homopolymer produced by the polymerization of chloroprene, a monomer with a molecular structure resembling isoprene (Sec. 21.5), but with iso-prene's methyl group replaced by chlorine (Fig. 21.13). Neoprene resembles vul-canized rubber except that this synthetic substitute is much more resistant to heat and to the action of hydrocarbon solvents like gasoline and automotive greases and oils. Its properties are especially valuable in belts and other parts used in and Figure 21.12 A segment of the styrene-butadiene polymer. CH2=CH Styrene CHZ = CH - CH = CH2 Butadiene   The elastomers neoprene and styrene-butadiene rubber make up the bulk of auto and truck tires. S32 • Chapter 21 Polymers and Plastics CH2=C-CH=CH2 C1 Chloroprene  CH2=C=CH=CH2 - CH2=C~ CH /CH2~ CHZ ~C~ CH=CH2 ~ CH2=C=CH=CH2 C1 C1 C1 C1 CH2-C=CH-CH2-CHZ-C=CH-CH2-CH2-C=CH-CHZ-CHZ-C=CH-CH2-   Figure 21.13 Neoprene, polychloroprene. CI around auto engines, in the hoses of gasoline pumps, in gaskets and filling materi-al used in the construction of highways and bridges, and in the rubber stoppers found in chemistry laboratories. Neoprene was developed for commercial pro-duction by Wallace Carothers, the inventor of nylon (Sec. 21.9).  • Q U E S T I O N What element, absent from natural rubber, is present in: (a) neoprene? (b) vulcan-ized rubber?   Celluloid and other polymers that can be made to resemble ivory have helped reduce the demand for elephant tusks. 21.7 Part I1: Save the Elephants! Charles Goodyear didn't invent a new polymeric molecule or a new elastomer when he spilled a mixture of rubber and sulfur onto a hot stove; he accidentally modified a natural, polymeric elastomer and came up with an enormous improvement in its prop-erties. John Wesley Hyatt and his brother Isaiah, on the other hand, consciously and de-liberately converted a modified natural polymer into the world's first new, commercially successful synthetic plastic. They produced a plastic that hadn't existed earlier. By 1863, three years after Goodyear's death, the slaughter of the world's ele-phants for their tusks had become a serious matter, as it is even today. In that era the disappearance of elephants was threatening to disrupt the world's ivory sup ply. Ivory, a valuable luxury item of the 19th century used for jewelry ornaments, piano keys, and various other items, was becoming scarce and very expensive. Per-haps to protect the elephants but certainly to ensure a source of raw materials, the firm of Phelan and Collander, a New England manufacturer of ivory billiard balls, offered $10,000 to anyone who could devise a satisfactory substitute for the rap-idly disappearing natural ivory. John Hyatt, a 26-year-old printer born in Starkev. New York, took up the challenge. He was helped by a startling discovery made years earlier by a chemist in Basel, Switzerland. In 1846 a Swiss chemistry professor, Christian Schoenbein, had accidentally in-vented guncotton by spilling a mixture of nitric acid and sulfuric acid in the kitchen of his home and then wiping up the mess with his wife's cotton apron. He rinsed out the apron thoroughly with water and hung it up to dry near a hot stove. As it hung drying it disappeared in a sheet of flame.  21.8 Part I11: The First Synthetic Polymer • 833 The smokeless guncotton of Schoenbein's accident proved far superior to the very smoky gunpowder used at the time in warfare and it became a popular mili-v tary item. More to the point, by inadvertently inducing a reaction between the    mixture of nitric and sulfuric acids and the cellulose of the cotton apron, Schoen-bein had successfully transformed the polymeric cellulose into nitrocellulose, a compound in which varying numbers of the hydroxyl groups (-OH) of the poly-mer are converted into nitrate groups (-O-N02). (The sulfuric acid serves to catalyze the reaction.) John Hyatt won the $10,000 prize by combining camphor, a pungent substance obtained from the camphor tree, with a lightly nitrated form of Schoenbein's ni-trocellulose. The mixture forms a thermoplastic so similar to ivory that it was known for some time as artificial ivory. We now call it celluloid. With the help of his brother Isaiah, Hyatt began manufacturing celluloid in 1870 and became more successful financially than Goodyear. His synthetic billiard balls proved a bit too brittle to be useful, but the plastic did make fine dental plates, photographic film, brush handles, detachable collars, ping pong balls, and a host of other small prod-ucts. Its major defect in consumer products is its tendency to burst into flames. Movie film was once made of this highly flammable celluloid and often ignited A burning pong-pong ball made from the heat of the projector. of celluloid illustrates the Although the Hyatts had produced celluloid, the world's first successful com- flammability of the plastic. mercial plastic, they hadn't actually constructed a new polymeric chain. The plas- tic was, rather, a combination of camphor and chemically modified, naturally occurring cellulose. The credit for the world's first fully synthetic organic polymer goes to Leo Hendrik Baekeland. What are the chemical names of the three reagents or starting materials needed for • Q U E S T 1 O N the production of guncotton? 21.8 Part 111: The First Synthetic Polymer  Born in Belgium in 1863, the same year that Phelan and Collander offered its $10,000 reward for an ivory substitute, Leo H. Baekeland became an active, pro-ductive, and successful academic and industrial chemist. As a young man he emi-grated to the United States and became a citizen; eventually he was elected president of the American Chemical Society, the world's largest professional as-sociation of chemists. In 1909 Baekeland announced his preparation of the first fully synthetic polymer, a resin he called Bakelite. In the following year he founded the Bakelite Corporation to manufacture the material. Unlike any of the other polymers we've examined so far, Bakelite is a ther-mosetting plastic rather than a thermoplastic. Bakelite forms as a mixture of phenol and formaldehyde (Sec. 16.4) polymerizes. As we see in Figure 21.14, each   Left: Leo H. Baekeland, inventor of Bakelite, a condensation polymer of phenol and formaldehyde. Right: Old phonograph records made of Bakelite. These records rotated at 78 revolutions per minute and were called "78-rpm" records. 834 • Chapter 21 Polymers and Plastics  H Formaldehyde Phenol H C=0  H H H OH OH  H ~ H OH H CH2 CHZ CHZ \ ~ \ ~ ;~ - CH2 CHZ CHZ   OH  A portion of the three-dimensional condensation polymer CHZ  CH2 CH2 ~ CH2 CH2 \ I OH \ CH2 CH2 / / OH \ I OH \ OH CHZ ~ CH2 CHZ i CHZ w ~ OH \ Y OH ~\ ~ Figure 21.14 Bakelite. formaldehyde molecule bonds to two different phenol molecules, and each phenol ring bonds to three different formaldehyde molecules (with a molecule of water lost for each combination of two phenols and one formaldehyde). The geometric pos-sibilities available here produce an intricate, three-dunensional web of resinous polymeric material. 21.9 Part IV: From the Kitchen Stove to Nylon • 535 As we've seen (Sec. 21.5), Bakelite is a hard, sturdy material, resistant to heat and electricity and not easily burned or scorched. The use of other aldehydes and of other phenols, bearing groups other than hydrogens here and there on the ring, pro duces variations on Bakelite and has created an entire class of phenolic resins. Today the primary uses of the phenolic resins are as adhesives and fillers in the manufacture of plywood and fiberboard and in the production of insulating materials. A little more than 40% of all thermosetting polymers produced today belong to this class of resin. What is the chemical name of the group that unites the aromatic rings in Bakelite? • Q U E S T 1 O N (See Sec. 6.5 for help.) 4 ง 21.9 Part IV: From the Kitchen Stove to Nylon We've seen that the early advances in the development of commercially useful polymers and plastics were made by a few ingenious (and lucky) individuals, some-times quite by accident, often with little equipment. The days of major advances in polymer and plastic chemistry arriving through small accidents on hot kitchen ; stoves came to an end in the early years of the 20th century largely because of • the growing sophistication of scientific equipment and techniques; • the increasing rigor of research programs carried out in academic, industrial, and institutional laboratories; and • the development, in the 1920s, of a comprehensive understanding of the molec-ular structure of polymers.  ` Among the fruits of highly organized, well-directed, and strongly supported re-search programs is the discovery of the condensation polymer nylon by Wallace H. Carothers and his co-workers at DuPont Corporation. In 1928 Carothers (189(r1937), an Iowa-born chemist, left his post as instructor in organic chemistry at Harvard Uni-versity to lead a research group in DuPont's Wilmington, Delaware, laboratories There he began a program of fundamental research into polymers, studying how they form Wallace H. Carothers, the and what factors affect their properties. Within a few years he and his co-workers DuPont chemist who led the found that by polymerizing a mixture of adipic acid and 1,6-diaminohexane, they could research team that invented ; produce a plastic (nylon) that can be drawn out into strong, silky fibers (Fig. 21.15). nylon. Figure 21.15 Nylon, a condensation polymer.  1,6-Diaminohexane or T 11 Adipic acid II H\ hexamethylenediamine ~H ,^.b,, -C-CHZ-CH2-CHZ-CHZ-C-OH / N-CH2-CH2-CHZ-CH2-CH2-CH2-N ~ H H 1,6-Diaminohexane and adipic acid condense to form nylon, a polyamide  -CH2-C-H-CH2-CHZ-CHZ-CH2-CHZ-CH2-H-C-CHZ-CHZ-CH2-CH2-C-H-CH2-CHz-CHZ- 536 • Chapter 21 Polymers and Plastics Adipic acid is an example of a dicarboxylic acid, one containing two carboxyl groups (Sec.1Q.8). O -C-OH the carboxyl group The name adipic comes from the Latin adipem, a fat, and reflects the observation that adipic acid is one of the substances formed when fats are oxidized with nitric acid, HN03. Notice, in Figure 21.15, that the adipic acid molecule contains a chain of six car-bons, which includes the two carboxyl groups at its ends. We'll refer to this shortly. The other monomer is another six-carbon compound, 1,6-diaminohexane, with amino groups (-NH2, Sec. 17.2) at the ends of a chain of six methylene groups (-CHZ-).Another useful name for this diamine is hexamethylenediamine. With alternating units of the two monomers bonded to each other throughout the length of the chain, the structure of the polymeric molecule itself can be written as  ~NH-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-NH-C-CHZ-CHZ-CH2-CHZ-C-~-I I I I This six-carbon portion comes This six-carbon portion comes from the 1,6-diaminohexane from the adipic acid monomer monomer. Nylon Carothers and his group produced several other nylons, each a polyamide (Sec.17.7). To differentiate among all the newly formed nylons, the researchers coded each for the number of carbon atoms in each of its monomers. The one produced from the six-carbon adipic acid and the six-carbon 1,6-diaminohexane became nylon 6,6. (In fact, "66 polyamide" was its original name, before the term nylon was coined.) Another nylon, nylon 6, forms as the ring of caprolactam opens with the addition of water and the resulting amino acid undergoes polymerization (Fig. 21.16). Figure 21.16 Nylon 6. O The caprolactam ring opens on hydrolysis . . . ~C~~ O H~C NH HZO II /H HZC CHZ HO - C-CHZ-CHZ-CH2-CHZ-CHZ-N \ / \ HZC- CHZ , , , and the amino acid condenses with itself to produce . . . H Caprolactam II ,H HO-C-CH2-CHZ-CHZ-CHZ-CHZ-N\ il /H HQ - C-CH2-CHZ-CHZ-CHZ-CH2-N \ . . . nylon 6.  -CHZ-CH2-CHZ-H-C-CHz-CHZ-CH2-CHZ-CHZ H C-CHZ-CH~-CHZ-CHZ-CH2-H-C-CHZ- 21.1 O PET, a Condensation Polymer • 537 e   Left: The formation of a strand of nylon 6,6 as two chemicals, dissolved in solvents that do not mix, react with each other. Hexamethylene diamine, HZN-(CHZ)6-NH2, dissolved in water and adipoyl chloride, CIOC-(CH2)4-COCI, dissolved in another solvent, react to form nylon at the surface where the two solvents come into contact. The strand is pulled from the surface of contact. Right: A giant leg near Los Angeles, promoting the sale of nylon stockings after World War II. Nylon's first practical application to a consumer product came in 1938, when the new polymer was introduced to the public in the form of toothbrush bristles. But it was the polymer's use in stockings, first sold to consumers on a trial basis in October 1939, that made it an overwhelming commercial success. Similar to silk in its properties but far less expensive, nylon became the ideal replacement for the silk of stockings and other fashionable clothing. With the coming of World War II, fashion had to make way for the war effort. The government used most of the na-tion's limited supplies of nylon for making parachutes, ropes, and other military sup-plies. Since there wasn't enough nylon for both military and civilian uses, nylon stockings, which had become very popular and were in high demand, were rationed until the end of the war. During the war and shortly afterward, nylon stockings became a valuable item of barter in Europe and achieved the status of an infor-mal currency. Not until the early 1950s was there sufficient production capacity to fill the popular demand for "nylons," as the stockings came to be known, and to pro-vide enough of the plastic for other consumer and commercial uses. Nylon's name reflects, in a strange and devious way, one of the most appeal-ing characteristics of the stockings made from the polymer: their resistance to snag-ging and running. An early name, suggested as a more popular replacement for the technical "66 polyamide," was reorun, referring to the appeal of the stockings. That term was judged unacceptable by those at DuPont who were responsible for giving the polymer a trade name. After spelling it backward as nuron, which was still unsatisfactory, they finally agreed on nylon. Is each of the following a homopolymer or a copolymer? (a) nylon 6; (b) nylon 6,6. • Q U E S T I O N Name the monomer(s) of each. 21.10 PET, a Condensation Polymer The modern, systematic search for commercially useful polymers has led to the de-velopment of several valuable condensation and addition polymers, which we'll ex-amine in the next few sections. The commercial leader among condensation polymers is poly(ethylene terephthalate), a polyester also known as PET. We've already examined  538 • Chapter 21 Polymers and Plastics  HO-CH2-CH2-OH HO-C -OH Ethylene glycol Terephthalic acid H20 O O H20 H2O O O 0O-CH2-CHZ-O~-C \ / C-~, "O -CHZ-CH2-O~,..~„~}-C \ / C-O  O O O O O 11 11 11 11 11 -CHZ-CH2-O-C \ / C-O-CH2-CH2-O-C \ / C-O-CHZ-CHZ-O-C \ Poly(ethylene terephthalate), a polyester Figure 21.17 Poly(ethylene terephthalate). a triester in the triglycerides that form our fats and oils and that give us our soaps (Sec. 15.1). In those compounds the three hydroxyl groups (-OH) of a single glycerol molecule are all combined with the carboxyl groups (HOZC-) of the three carboxylic acids that form the triglyceride's side chains. Since each acid can contribute only one reactive group to the process, the reaction stops with the formation of the triglyceride. In 1941 the British industrial chemist John Rex Whinfield succeeded in produc-ing a polyester, poly(ethylene terephthalate), by polymerizing a mixture of ethylene - - glycol and terephthalic acid. As shown in Figure 21.17, ethylene glycol has two -OH groups with which it can form esters. Unlike the carboxylic acids of the triglycerides, though, terephthalic acid also has two -COZH groups, allowing each one of its mol-ecules to combine with two different glycol molecules. With this sort of combining power the two compounds form a copolymer whose monomeric units are linked to each other by ester groups. Chemically the process resembles the condensation of hexamethylenediamine and adipic acid to form the polyamide chain of nylon. Drawing out the poly(ethylene terephthalate) into a filament produces the world's leading synthetic polymeric fiber, known as Dacron in the United States, Tery-lene in Great Britain, and usually simply referred to as "polyester" when it's woven - into a fabric. (Other, related polyester fibers include Fortrel and Kodel.) PET also ~) ~II forms an extremely thin and extremely tough film, Mylar, used as the plastic backing Food storage bags made of for audio and video tapes and computer diskettes, as well as wrapping material for poly(ethylene terephthalate), frozen foods and bags for boil-in foods. In Western Europe PET has grown since the PET. early 1980s into the dominant commercial plastic for packaging consumer goods. [Rayon is a generic term for a group of fibers derived from cellulose, largely by replacing one or more of the hydrogens of the -OH groups on the glucose ' rings with other chemical groups. Schoenbein's guncotton (Sec. 21.7) is one form of rayon.] • Q U E S T 1 O N Fats and oils are triglycerides, with three ester functional groups per molecule. Should they be considered polyesters? Explain. 21.11 Polystyrene, an Addition Polymer • 539 21.11 Polystyrene, an Addition Polymer For other examples of polymers and plastics-one that both contributed to win-ning World War II and generated a flash of national mania (Sec. 21.13), and another that produced two Nobel Prizes in chemistry (Sec. 21.14)-we turn now to addi-tion polymers such as the polyolefins and closely related polymers.'The addition polymers we'll examine in the following several sections dominate commercial plastic production in the United States. Polyolefins are polymers of olefins, which is another and much older name for the unsaturated hydrocarbons we now know as the alkenes (Sec. 6.10). "Olefin" is a corruption of a name given to ethylene by several Dutch chemists in 1795 to re flect its character as an "oil-forming" gas in its reaction with chlorine. Since then, the term has been extended to include the entire category of hydrocarbons that, like ethylene, bear a single carbon-carbon double bond. Olefin is often used as a synonym for alkene. Polymerizing an olefin produces a polyolefin. We've already seen that polymerizing ethylene, the simplest of all the alkenes, produces polyethylene, a polyolefin we'll examine in more detail in Section 21.13. Replacing one or more of ethylene's hydrogens by other substituents gives monomers useful for preparing polymers closely related to the polyolefins and sharing many of their important properties. Replacing one of the ethylenic hydrogens by a phenyl group, for example, produces styrene, which polymerizes to the thermoplastic polystyrene (Fig. 21.18). The various techniques available for converting the raw polystyrene polymer into a ftnished prod uct provide a wide range of useful properties for the resulting plastic. Inexpensive, clear, rigid drinking glasses are made of polystyrene. In a variation known as high-im-pact polystyrene, the plastic is used to make sturdy furniture, inexpensive tableware, and stereo, television, and computer cabinets. Another form of polystyrene, a solid but lightweight polystyrene foam, is a good thermal insulator and shock absorber, useful for making picnic coolers, egg cartons, clamshell containers for fast foods, disposable Polyolefins are polymers pro-duced by the polymerization of alkenes and compounds close-ly related to them.  Figure 21.18 Polystyrene. Cups, plates, and containers made from polystyrene foam. Styrene CH2=CH Polymerization  -CH-CH2-CH-CHZ-CH CH2-CH-CHZ-CH-CHZ-CH--CH2-CH-  Polystyrene t CHZ-CH t \ /I n 540 • Chapter 21 Polymers and Plastics cups for keeping drinks hot or cold, and small polystyrene nuggets used as packing ma-terial. These foams, some of which are sold under the name Styrofoam, are made by using a gas to generate a foam of liquid polystyrene and allowing the frothy mass to cool and solidify. Chlorofluorocarbons (Sec. 14.9) were once used to generate the froth, but these have been replaced by other gases, including low-boiling alkanes. Today, well over half of all the polystyrene produced goes into inexpensive consumer products. • Q U E 8 T 1 O N What physical characteristics of polystyrene foam make it useful in consumer prod-ucts such as picnic coolers, packing materials, and cups for both hot and cold drinks? 21.12 Vinyl and Its Chemical Cousins In the realm of consumer products the word vinyl has come to mean a tough, flex-ible, and often smooth, shiny plastic that serves as an inexpensive substitute for leather. We often find vinyl purses, wallets, and jackets and other vinyl goods for sale at the lower priced counters of stores. To the chemist, though, vinyl represents a hydrocarbon group (CHZ=CH-) that can be formed by the removal of a hydrogen atom from ethylene, just as a methyl group (CH3-) and an ethyl group (CH3-CHZ-) can be produced by the removal of a hydrogen atom from methane (CH4) and ethane (CH3-CH3), respectively (Chapter 6). Moreover, just as CH3-Cl and CH3-CH2-Cl rep-resent methyl and ethyl chloride, CH2=CH-Cl is vinyl chloride. The terms poly (vinyl chloride), polyvinylchloride, and PVC all serve very nicely as names for the thermoplastic formed by the addition polymerization of vinyl chlo-ride (Fig. 21.19). The polymer forms a tough plastic, well suited to pipes, plumbing, elec- trical conduit, flooring, and both indoor and outdoor wall coverings. Among personal products, it's widely used in toys, garden hoses, and inexpensive wallets, purses, and " keyholders. Well over half of all PVC production currently goes into the construction industry, with most of it used in piping, tubing, and similar extruded materials. Because thin sheets of polyvinylchloride are relatively stiff and crack easily, it's A plasticizer is a liquid that is necessary to add a plasticizer to give them the same sort of flexibility we expect added to a plastic to soften it. from leather. Plasticizers are liquids that mix readily with a plastic and soften it. With time a plasticizer can migrate out of the plastic or otherwise deteriorate, al-lowing aged polyvinylchloride to stiffen and crack. Figure 21.19 Poly(vinyl chloride). Vinyl chloride CI-12= CH - Cl I Polymerization -CH-CH2-CH-CHZ-CH-CH2-CH-CHZ-CH-CH2-CH-CHZ-CH- C1 C1 C1 C1 C1 C1 C1 Poly(vinyl chloride) t CH2-CH t ln C1  21.12 Vinyl and Its Chemical Cousins • 541 Other useful thermoplastics come from still other monomers closely related to ethylene, including vinyl acetate, acrylonitrile, vinylidene chloride, tetrafluoroethylene, methyl methacrylate (Table 21.2), and, of course, styrene. Table 21.2 Addition Polymers Monomer Polymer i L t t Ethylene CH2=CHz Vinyl chloride CH2=CH-Cl Vinyl acetate polyethylene f CHz-CH2-~.-poly(vinyl chloride) polyvinylchloride PVC  Acrylonitrile CH2=CH-C=N polyacrylonitrile Orlon Acrilan Creslan 4CHZ-CH~  t , Vinylidine chloride CH2=CC12  Tetrafluoroethylene FZC=CF2 polytetrafluoroethylene Teflon F F C-C F F Methyl methacrylate CH2=C-C-OCH3 CH3 poly(methyl methacrylate) Lucite Plexiglas O 11 C-OCH3 CH2- C -1- I ln CH3 Styrene CH=CH2 polystyrene Styrofoam { CH i CHZ +n 11 CHz=CH-O-C-CH3 O poly(vinyl acetate) polyvinyl acetate PVA CHZ- CH I O 0=C-CH3 21.8 Part I11: The First Synthetic Polymer • 833 The smokeless guncotton of Schoenbein's accident proved far superior to the very smoky gunpowder used at the time in warfare and it became a popular mili-v tary item. More to the point, by inadvertently inducing a reaction between the mixture of nitric and sulfuric acids and the cellulose of the cotton apron, Schoen-bein had successfully transformed the polymeric cellulose into nitrocellulose, a compound in which varying numbers of the hydroxyl groups (-OH) of the poly-mer are converted into nitrate groups (-O-N02). (The sulfuric acid serves to catalyze the reaction.) John Hyatt won the $10,000 prize by combining camphor, a pungent substance obtained from the camphor tree, with a lightly nitrated form of Schoenbein's ni-trocellulose. The mixture forms a thermoplastic so similar to ivory that it was known for some time as artificial ivory. We now call it celluloid. With the help of his brother Isaiah, Hyatt began manufacturing celluloid in 1870 and became more successful financially than Goodyear. His synthetic billiard balls proved a bit too brittle to be useful, but the plastic did make fine dental plates, photographic film, brush handles, detachable collars, ping pong balls, and a host of other small prod-ucts. Its major defect in consumer products is its tendency to burst into flames. Movie film was once made of this highly flammable celluloid and often ignited A burning pong-pong ball made from the heat of the projector. of celluloid illustrates the Although the Hyatts had produced celluloid, the world's first successful com- flammability of the plastic. mercial plastic, they hadn't actually constructed a new polymeric chain. The plas- tic was, rather, a combination of camphor and chemically modified, naturally occurring cellulose. The credit for the world's first fully synthetic organic polymer goes to Leo Hendrik Baekeland. What are the chemical names of the three reagents or starting materials needed for • Q U E S T 1 O N the production of guncotton? 21.8 Part 111: The First Synthetic Polymer  Born in Belgium in 1863, the same year that Phelan and Collander offered its $10,000 reward for an ivory substitute, Leo H. Baekeland became an active, pro-ductive, and successful academic and industrial chemist. As a young man he emi-grated to the United States and became a citizen; eventually he was elected president of the American Chemical Society, the world's largest professional as-sociation of chemists. In 1909 Baekeland announced his preparation of the first fully synthetic polymer, a resin he called Bakelite. In the following year he founded the Bakelite Corporation to manufacture the material. Unlike any of the other polymers we've examined so far, Bakelite is a ther-mosetting plastic rather than a thermoplastic. Bakelite forms as a mixture of phenol and formaldehyde (Sec. 16.4) polymerizes. As we see in Figure 21.14, each   Left: Leo H. Baekeland, inventor of Bakelite, a condensation polymer of phenol and formaldehyde. Right: Old phonograph records made of Bakelite. These records rotated at 78 revolutions per minute and were called "78-rpm" records. 834 • Chapter 21 Polymers and Plastics Formaldehyde Phenol A portion of the three-dimensional condensation polymer CHZ  CH2 CH2 ~ CH2 CH2 \ I OH \ CH2 CH2 / / OH \ I OH \ OH CHZ ~ CH2 CHZ i CHZ w ~ OH \ Y OH ~\ ~ an intricate, three-dunensional web of resinous polymeric material. 21.9 Part IV: From the Kitchen Stove to Nylon • 535 As we've seen (Sec. 21.5), Bakelite is a hard, sturdy material, resistant to heat and electricity and not easily burned or scorched. The use of other aldehydes and of other phenols, bearing groups other than hydrogens here and there on the ring, pro duces variations on Bakelite and has created an entire class of phenolic resins.Today the primary uses of the phenolic resins are as adhesives and fillers in the manufacture of plywood and hberboard and in the production of insulating materials. A little more than 40% of all thermosetting polymers produced today belong to this class of resin. •QUESTION What is the chemical name of the group that unites the aromatic rings in Bakelite? (See Sec. 6.5 for help.) Figure 21.14 Bakelite. formaldehyde molecule bonds to two different phenol molecules, and each phenol ring bonds to three different formaldehyde molecules (with a molecule of water lost for each combination of two phenols and one formaldehyde). The geometric pos-sibilities available here produce 4 ง 21.9 Part IV: From the Kitchen Stove to Nylon We've seen that the early advances in the development of commercially useful polymers and plastics were made by a few ingenious (and lucky) individuals, some-times quite by accident, often with little equipment. The days of major advances in polymer and plastic chemistry arriving through small accidents on hot kitchen ; stoves came to an end in the early years of the 20th century largely because of • the growing sophistication of scientific equipment and techniques; • the increasing rigor of research programs carried out in academic, industrial, and institutional laboratories; and • the development, in the 1920s, of a comprehensive understanding of the molec-ular structure of polymers. is the discovery of the condensation polymer nylon by Wallace H. Carothers and his co-workers at DuPont Corporation. In 1928 Carothers (189(r1937), an Iowa-born chemist, left his post as instructor in organic chemistry at Harvard Uni-1 versity to lead a research group in DuPont's Wihnington, Delaware, laboratories There he began a program of fundamental research into polymers, studying how they form Wallace H. Carothers, the and what factors affect their properties. Within a few years he and his co-workers DuPont chemist who led the found that by polymerizing a mixture of adipic acid and 1,6-diaminohexane, they could research team that invented ; produce a plastic (nylon) that can be drawn out into strong, silky fibers (Fig. 21.15). nylon. Figure 21.15 Nylon, a condensation polymer.  Adipic acid II 1,6-Diaminohexane or H\ hexamethylenediamine ~~,^.b,, -C-CHZ-CH2-CHZ-CHZ-C-OH / N-CH2-CH2-CHZ-CH2-CH2-CH2-N ~ H H 1,6-Diaminohexane and adipic acid condense to form nylon, a polyamide p ~,_~ _ . U ,€t- :~ O -CH2-C-H-CH2-CHZ-CHZ-CH2-CHZ-CH2-H-C-CHZ-CHZ-CH2-CH2-C-H-CH2-CHz-CHZ- 536 • Chapter 21 Polymers and Plastics Adipic acid is an example of a dicarboxylic acid, one containing two carboxyl groups (Sec.1Q.8). O -C-OH the carboxyl group The name adipic comes from the Latin adipem, a fat, and reflects the observation that adipic acid is one of the substances formed when fats are oxidized with nitric acid, HN03. Notice, in Figure 21.15, that the adipic acid molecule contains a chain of six car-bons, which includes the two carboxyl groups at its ends. We'll refer to this shortly. The other monomer is another six-carbon compound, 1,6-diaminohexane, with amino groups (-NH2, Sec. 17.2) at the ends of a chain of six methylene groups (-CHZ-).Another useful name for this diamine is hexamethylenediamine. With alternating units of the two monomers bonded to each other throughout the length of the chain, the structure of the polymeric molecule itself can be written as  ~NH-CHZ-CHZ-CHZ-CHZ-CHZ-CHZ-NH-C-CHZ-CHZ-CH2-CHZ-C-~-I I I I This six-carbon portion comes This six-carbon portion comes from the 1,6-diaminohexane from the adipic acid monomer monomer. Nylon Carothers and his group produced several other nylons, each a polyamide (Sec.17.7). To differentiate among all the newly formed nylons, the researchers coded each for the number of carbon atoms in each of its monomers. The one produced from the six-carbon adipic acid and the six-carbon 1,6-diaminohexane became nylon 6,6. (In fact, "66 polyamide" was its original name, before the term nylon was coined.) Another nylon, nylon 6, forms as the ring of caprolactam opens with the addition of water and the resulting amino acid undergoes polymerization (Fig. 21.16). Figure 21.16 Nylon 6. O The caprolactam ring opens on hydrolysis . . . ~C~~ O H~C NH HZO II /H HZC CHZ HO - C-CHZ-CHZ-CH2-CHZ-CHZ-N \ / \ HZC- CHZ , , , and the amino acid condenses with itself to produce . . . H Caprolactam II ,H HO-C-CH2-CHZ-CHZ-CHZ-CHZ-N\ il /H HQ - C-CH2-CHZ-CHZ-CHZ-CH2-N \ . . . nylon 6.  -CHZ-CH2-CHZ-H-C-CHz-CHZ-CH2-CHZ-CHZ H C-CHZ-CH~-CHZ-CHZ-CH2-H-C-CHZ- 21.10 PET, a Condensation Polymer • 537 e   Left: The formation of a strand of nylon 6,6 as two chemicals, dissolved in solvents that do not mix, react with each other. Hexamethylene diamine, HZN-(CHZ)6-NH2, dissolved in water and adipoyl chloride, CIOC-(CH2)4-COCI, dissolved in another solvent, react to form nylon at the surface where the two solvents come into contact. The strand is pulled from the surface of contact. Right: A giant leg near Los Angeles, promoting the sale of nylon stockings after World War II. Nylon's first practical application to a consumer product came in 1938, when the new polymer was introduced to the public in the form of toothbrush bristles. But it was the polymer's use in stockings, first sold to consumers on a trial basis in October 1939, that made it an overwhelming commercial success. Similar to silk in its properties but far less expensive, nylon became the ideal replacement for the silk of stockings and other fashionable clothing. With the coming of World War II, fashion had to make way for the war effort. The government used most of the na-tion's limited supplies of nylon for making parachutes, ropes, and other military sup-plies. Since there wasn't enough nylon for both military and civilian uses, nylon stockings, which had become very popular and were in high demand, were rationed until the end of the war. During the war and shortly afterward, nylon stockings became a valuable item of barter in Europe and achieved the status of an infor-mal currency. Not until the early 1950s was there sufficient production capacity to fill the popular demand for "nylons," as the stockings came to be known, and to pro-vide enough of the plastic for other consumer and commercial uses. Nylon's name reflects, in a strange and devious way, one of the most appeal-ing characteristics of the stockings made from the polymer: their resistance to snag-ging and running. An early name, suggested as a more popular replacement for the technical "66 polyamide," was reorun, referring to the appeal of the stockings. That term was judged unacceptable by those at DuPont who were responsible for giving the polymer a trade name. After spelling it backward as nuron, which was still unsatisfactory, they finally agreed on nylon. Is each of the following a homopolymer or a copolymer? (a) nylon 6; (b) nylon 6,6. • Q U E S T I O N Name the monomer(s) of each. 21.10 PET, a Condensation Polymer The modern, systematic search for commercially useful polymers has led to the de-velopment of several valuable condensation and addition polymers, which we'll ex-amine in the next few sections. The commercial leader among condensation polymers is poly(ethylene terephthalate), a polyester also known as PET. We've already examined  538 • Chapter 21 Polymers and Plastics  HO-CH2-CH2-OH HO-C -OH Ethylene glycol Terephthalic acid H20 O O H20 H2O O O 0O-CH2-CHZ-O~-C \ / C-~, "O -CHZ-CH2-O~,..~„~}-C \ / C-O  O O O O O 11 11 11 11 11 -CHZ-CH2-O-C \ / C-O-CH2-CH2-O-C \ / C-O-CHZ-CHZ-O-C \ Poly(ethylene terephthalate), a polyester Figure 21.17 Poly(ethylene terephthalate). a triester in the triglycerides that form our fats and oils and that give us our soaps (Sec. 15.1). In those compounds the three hydroxyl groups (-OH) of a single glycerol molecule are all combined with the carboxyl groups (HOZC-) of the three carboxylic acids that form the triglyceride's side chains. Since each acid can contribute only one reactive group to the process, the reaction stops with the formation of the triglyceride. In 1941 the British industrial chemist John Rex Whinfield succeeded in produc-ing a polyester, poly(ethylene terephthalate), by polymerizing a mixture of ethylene - - glycol and terephthalic acid. As shown in Figure 21.17, ethylene glycol has two -OH groups with which it can form esters. Unlike the carboxylic acids of the triglycerides, though, terephthalic acid also has two -COZH groups, allowing each one of its mol-ecules to combine with two different glycol molecules. With this sort of combining power the two compounds form a copolymer whose monomeric units are linked to each other by ester groups. Chemically the process resembles the condensation of hexamethylenediamine and adipic acid to form the polyamide chain of nylon. Drawing out the poly(ethylene terephthalate) into a filament produces the world's leading synthetic polymeric fiber, known as Dacron in the United States, Tery-lene in Great Britain, and usually simply referred to as "polyester" when it's woven - into a fabric. (Other, related polyester fibers include Fortrel and Kodel.) PET also ~) ~II forms an extremely thin and extremely tough film, Mylar, used as the plastic backing Food storage bags made of for audio and video tapes and computer diskettes, as well as wrapping material for poly(ethylene terephthalate), frozen foods and bags for boil-in foods. In Western Europe PET has grown since the PET. early 1980s into the dominant commercial plastic for packaging consumer goods. [Rayon is a generic term for a group of fibers derived from cellulose, largely by replacing one or more of the hydrogens of the -OH groups on the glucose ' rings with other chemical groups. Schoenbein's guncotton (Sec. 21.7) is one form of rayon.] • Q U E S T 1 O N Fats and oils are triglycerides, with three ester functional groups per molecule. Should they be considered polyesters? Explain. 21.11 Polystyrene, an Addition Polymer • 539 21.11 Polystyrene, an Addition Polymer For other examples of polymers and plastics-one that both contributed to win-ning World War II and generated a flash of national mania (Sec. 21.13), and another that produced two Nobel Prizes in chemistry (Sec. 21.14)-we turn now to addi-tion polymers such as the polyolefins and closely related polymers.'The addition polymers we'll examine in the following several sections dominate commercial plastic production in the United States. Polyolefins are polymers of olefins, which is another and much older name for the unsaturated hydrocarbons we now know as the alkenes (Sec. 6.10). "Olefin" is a corruption of a name given to ethylene by several Dutch chemists in 1795 to re flect its character as an "oil-forming" gas in its reaction with chlorine. Since then, the term has been extended to include the entire category of hydrocarbons that, like ethylene, bear a single carbon-carbon double bond. Olefin is often used as a synonym for alkene. Polymerizing an olefin produces a polyolefin. We've already seen that polymerizing ethylene, the simplest of all the alkenes, produces polyethylene, a polyolefin we'll examine in more detail in Section 21.13. Replacing one or more of ethylene's hydrogens by other substituents gives monomers useful for preparing polymers closely related to the polyolefins and sharing many of their important properties. polystyrene, the plastic is used to make sturdy furniture, inexpensive tableware, and stereo, television, and computer cabinets. Another form of polystyrene, a solid but lightweight polystyrene foam, is a good thermal insulator and shock absorber, useful for making picnic coolers, egg cartons, clamshell containers for fast foods, disposable Polyolefins are polymers pro-duced by the polymerization of alkenes and compounds close-ly related to them. Figure 21.18 Polystyrene. Cups, plates, and containers made from polystyrene foam. Styrene CH2=CH Polymerization  -CH-CH2-CH-CHZ-CH CH2-CH-CHZ-CH-CHZ-CH--CH2-CH-  Polystyrene t CHZ-CH t \ /I n 540 • Chapter 21 Polymers and Plastics cups for keeping drinks hot or cold, and small polystyrene nuggets used as packing ma-terial. These foams, some of which are sold under the name Styrofoam, are made by using a gas to generate a foam of liquid polystyrene and allowing the frothy mass to cool and solidify. Chlorofluorocarbons (Sec.14.9) were once used to generate the froth, but these have been replaced by other gases, including low-boiling alkanes. Today, well over half of all the polystyrene produced goes into inexpensive consumer products. • Q U E 8 T 1 O N What physical characteristics of polystyrene foam make it useful in consumer prod-ucts such as picnic coolers, packing materials, and cups for both hot and cold drinks? 21.12 Vinyl and Its Chemical Cousins In the realm of consumer products the word vinyl has come to mean a tough, flex-ible, and often smooth, shiny plastic that serves as an inexpensive substitute for leather. We often find vinyl purses, wallets, and jackets and other vinyl goods for sale at the lower priced counters of stores. To the chemist, though, vinyl represents a hydrocarbon group (CHZ=CH-) that can be formed by the removal of a hydrogen atom from ethylene, just as a methyl group (CH3-) and an ethyl group (CH3-CHZ-) can be produced by the removal of a hydrogen atom from methane (CH4) and ethane (CH3-CH3), respectively (Chapter 6). Moreover, just as CH3-Cl and CH3-CH2-Cl rep-resent methyl and ethyl chloride, CH2=CH-Cl is vinyl chloride. The terms poly(vinyl chloride), polyvinylchloride, and PVC all serve very nicely as names for the thermoplastic formed by the addition polymerization of vinyl chlo-ride (Fig. 21.19). The polymer forms a tough plastic, well suited to pipes, plumbing, elec- trical conduit, flooring, and both indoor and outdoor wall coverings. Among personal products, it's widely used in toys, garden hoses, and inexpensive wallets, purses, and " keyholders. Well over half of all PVC production currently goes into the construction industry with most of it used in piping, tubing, and similar extruded materials. Because thin sheets of polyvinylchloride are relatively stiff and crack easily, it's A plasticizer is a liquid that is necessary to add a plasticizer to give them the same sort of flexibility we expect added to a plastic to soften it. Vinyl chloride CHZ = CH - Cl I Polymerization -CH-CH2-CH-CHZ-CH-CH2-CH-CHZ-CH-CH2-CH-CHZ-CH- C1 C1 C1 C1 C1 C1 C1 Poly(vinyl chloride) t CH2-CH t ln C1  21.12 Vinyl and Its Chemical Cousins • 541 Other useful thermoplastics come from still other monomers closely related to ethylene, including vinyl acetate, acrylonitrile, vinylidene chloride, tetrafluoroethylene, methyl methacrylate (Table 21.2), and, of course, styrene. Table 21.2 Addition Polymers Monomer Polymer i L t t Ethylene CH2=CHz Vinyl chloride CH2=CH-Cl Vinyl acetate polyethylene f CHz-CH2~ poly(vinyl chloride) polyvinylchloride PVC  Acrylonitrile CH2=CH-C=N polyacrylonitrile Orlon Acrilan Creslan -~CHZ-CH~  t , Vinylidine chloride CH2=CC12  Tetrafluoroethylene FZC=CF2 polytetrafluoroethylene Teflon F F C-C F F O Methyl methacrylate CH2=C-C-OCH3 CH3 poly(methyl methacrylate) Lucite Plexiglas O C-OCH3 CH~,- C -1- I ln CH3 Styrene CH=CH2 polystyrene Styrofoam { CH i CHZ ~-n CHz=CH-O-C-CH3 O poly(vinyl acetate) polyvinyl acetate PVA CHZ- CH I O 0=C-CH3 542 • Chapter 21 Polymers and Plastics A broken car window made of safety glass. A sheet of Bubble gum made from polyvinylacetate. polyvinylacetate sandwiched between two sheets of glass prevents the broken glass from disintegrating into flying slivers. Articles made from or coated with Teflon, a tough, stable, heat-resistant, nearly friction-free polymer of tetrafluoro-ethylene, CF2=CFz. Polymerization of vinyl acetate produces polyvinylacetate, a plastic with a wide range of properties and an equally wide range of applications. As a thermoplastic with a low softening temperature it's useful in coatings and adhesives. A sandwich of two panes of glass bonded to a central sheet of the material forms a shatter-proof or safety glass. While the glass can break, it won't shatter into dangerous slivers. Safety glass of this kind is used in car windows. Mixed with a sweetener, some flavoring, and other ingredients, polyvinylacetate replaces the chewy chicle of chewing gum. (Chicle itself is a rubberlike polymer ob-tained from the sap of the sapodilla tree.) Partially polymerized vinyl acetate serves as a binder in water-based house paints. As the water evaporates, the low-molecular-weight polymer present in the paint polymerizes further, forming a tough sheet that binds the pigment to the coated surface. Polyacrylonitrile, a thermoplastic that's drawn out into fine threads and woven into synthetic fabrics such as Orlon, Acrilan, and Creslan, comes from the poly-merization of acrylonitrile (CIZ=CH-CN). Putting two chlorines on the single carbon of ethylene converts it into vinylidene chloride (CH2=CC12), the major monomer of Saran. Sheets of this polymer form a nearly impregnable barrier to food odors, which makes it useful for wrapping foods that are to be stored near each other in a refrigerator. Teflon results from the polymerization of tetrafluoroethylene (CFZ=CF2), a monomer obtained by replacing all of ethylene's hydrogens with fluorines. Teflon's great chemical stability, its resistance to heat, its mechanical toughness, and its nearly friction-free surface make it useful as a coating for bearings, valve seats, gaskets, and other parts of machinery that take heavy wear. Since things don't eas-ily stick to it, Teflon also makes a fine coating for cooking utensils such as pots and pans. Teflon was first prepared at DuPont in 1938; commercial production began 10 years later. In molecular structure methyl methacrylate is a bit further removed from ethylene. Its polymer forms a very hard, clear, colorless plastic that appears in consumer products as Lucite and Plexiglas. It's used in making glasses, camera lenses, and other optical equipment, in costume jewelry, and as windows in aircraft. 21.13 Polyethylene, the Plastic That Won the War and Gave Us the Hula-Hoop • 543 Of the polymers described in this section, which contain the element: (a) oxygen, • Q U E S T I O N (b) chlorine, (c) nitrogen, (d) fluorine?  21.13 Polyethylene, the Plastic That Won the War and Gave Us the Hula-Hoop  Accounting for about 16.6 million tons or over 40% of all plastic production in the United States annually, polyethylene clearly represents the most important polymer of the U.S. plastics industry. In its two principal commercial forms (high-density polyethylene and low-density polyethylene, which we'll examine shortly) it also illustrates very nicely the connection between the structure of a polymeric molecule and the properties of the plastic it forms. know as low-density polyethylene (LDPE). As the chains of LDPE form, they branch sporadically into short offshoots from the main line of the polymer. These ` ~~'~ short branches kee the ma'or strands of the ol mer from fallin into an thin P J P Y g Y g ~-resembling a coherent, well-organized pattern. Instead they form a tangled, ran- domly oriented network of strands, somewhat like a large ball of fuzz (Fig. 21.20). Figure 21.20 Disorganized The result is a low-density, soft, waxy, flexible, relatively low melting plastic that ac- polymeric strands of low- counts for a little over half of all the polyethylene produced in the United States. density polyethylene. More of this LDPE goes into producing trash bags than into any other single prod- uct. Industrial and commercial packaging, food wrappers, and plastic shopping bags are close behind. As in World War II, the coating of electrical wires and ca-bles remains an important use. Polymerized by a different method, the polyethylene chains can grow on and on without branching, thereby generating high-density polyethylene (HDPE).This Regions of form of the plastic was first produced in Germany in the early 1950s by Karl . ., i " crystallinity Ziegler, a German chemist born near the end of 1898. Ziegler prepared HDPE by carrying out the polymerizations in the presence of certain highly specialized (~~' ~-~~-•"~ 1 organometallic catalysts, which consist of combmations of orgamc molecules and metal atoms joined to each other by covalent bonds. These catalysts control the way the monomers link to each other as they polymerize. In HDPE the long molecular chains aren't fixed into a tangled web as they are in the LDPE, so they can align themselves into localized areas of tightly packed strands, mimicking here and there the orderly structure of crystals such as sodium chloride and sucrose. With many regions of close packing and a high degree of crys-tallinity, HDPE is a denser, harder, higher melting, and more rigid polymer than LDPE (Fig. 21.21). We saw another example of this same sort of relationship between molecular structure and physical properties in the fats and oils of Chapter 15. Figure 21.21 Polymeric strands of high-density polyethylene with regions of crystallinity. 544 • Chapter 21 Polymers and Plastics Teflon results from the polymerization of tetrafluoroethylene (CFZ=CF2), a monomer obtained by replacing all of ethylene's hydrogens with fluorines. Teflon's great chemical stability, its resistance to heat, its mechanical toughness, and its nearly friction-free surface make it useful as a coating for bearings, valve seats, gaskets, and other parts of machinery that take heavy wear. Since things don't eas-ily stick to it, Teflon also makes a fine coating for cooking utensils such as pots and pans. Teflon was first prepared at DuPont in 1938; commercial production began 10 years later. In molecular structure methyl methacrylate is a bit further removed from ethylene. Its polymer forms a very hard, clear, colorless plastic that appears in consumer products as Lucite and Plexiglas. It's used in making glasses, camera lenses, and other optical equipment, in costume jewelry, and as windows in aircraft. 21.13 Polyethylene, the Plastic That Won the War and Gave Us the Hula-Hoop • 543 Of the polymers described in this section, which contain the element: (a) oxygen, •QUESTION (b) chlorine, (c) nitrogen, (d) fluorine? 21.13 Polyethylene, the Plastic That Won the War and Gave Us the Hula-Hoop Accounting for about 16.6 million tons or over 40% of all plastic production in the United States annually, polyethylene clearly represents the most important polymer of the U.S. plastics industry. In its two principal commercial forms (high-density polyethylene and low-density polyethylene, which we'll examine shortly) it also illustrates very nicely the connection between the structure of a polymeric molecule and the properties of the plastic it forms. As we might imagine, the phys-ical properties of a piece of bulk plastic depend partly on the molecular structure of the monomer that forms it and partly on the average length of its polymeric chains. As we'll see shortly, a third factor also comes into play: the way polymeric chains organize themselves as they constitute the bulk of the material. Polyethylene itself was first prepared in 1934 in the laboratories of Imperial Chemical Industries, in Great Britain, and went into commercial production there five years later as World War II was about to begin. The first practical use of the plastic was as insulation on the electrical wiring of military radar sets. Considering the critical importance of aircraft radar to the survival of Britain in the early years of the war, we could easily designate polyethylene as the plastic that won the war. know as low-density polyethylene (LDPE). As the chains of LDPE form, they branch sporadically into short offshoots from the main line of the polymer. These short branches kee the ma'or strands of the ol mer from fallin into an thin P J P Y g Y g ~-resembling a coherent, well-organized pattern. Instead they form a tangled, ran- domly oriented network of strands, somewhat like a large ball of fuzz (Fig. 21.20). Figure 21.20 Disorganized The result is a low-density, soft, waxy, flexible, relatively low melting plastic that ac- polymeric strands of low- counts for a little over half of all the polyethylene produced in the United States. density polyethylene. More of this LDPE goes into producing trash bags than into any other single prod- uct. Industrial and commercial packaging, food wrappers, and plastic shopping bags are close behind. As in World War II, the coating of electrical wires and ca-bles remains an important use. Polymerized by a different method, the polyethylene chains can grow on and on without branching, thereby generating high-density polyethylene (HDPE).This Regions of form of the plastic was first produced in Germany in the early 1950s by Karl . ., i " crystallinity ,  Ziegler, a German chemist born near the end of 1898. Ziegler prepared HDPE by carrying out the polymerizations in the presence of certain highly specialized (~~' ~-~~-•"~ 1 organometallic catalysts, which consist of combmations of orgamc molecules and metal atoms joined to each other by covalent bonds.These catalysts control the way the monomers link to each other as they polymerize. In HDPE the long molecular chains aren't fixed into a tangled web as they are in the LDPE, so they can align themselves into localized areas of tightly packed strands, mimicking here and there the orderly structure of crystals such as sodium chloride and sucrose. Figure 21.21 Polymeric strands of high-density polyethylene with regions of crystallinity. 544 • Chapter 21 Polymers and Plastics Hula-hoops in action.  Of approximately 7.7 million tons of HDPE produced in the United States in 2000, most went into the manufacture of bottles and other containers designed to hold a variety of liquids, including drinks, bleach, antifreeze, and engine oil. It's also used in fabricating shipping drums and automobile gasoline tanks. Historically, HDPE's in-troduction into consumer products was as the Hula-Hoop, a large plastic hoop placed at the waist and twirled with hulalike motions. The craze swept the United States in the late 1950s; its memory survives today largely in collections of national trivia. •QUESTION What is the major use of the LDPE produced in the United States? for making Polymers and Plastics Hula-hoops in action. 21.14 A Nobel Prize for Two We have seen repeatedly that the physical and chemical properties of a substance depend on the structure of its molecules or ions. Among polymers, for example, we saw that the way individual glucose molecules are joined to each other determines whether they form starch or cellulose (Sec. 16.11), and that the geometry of the double bond in the polyisoprene chain determines whether it forms rubber or gutta-percha (Sec. 21.5). The effects of molecular structure on the properties of a plastic appear again in the polymerization of propylene. Figure 21.22 shows a small portion of the polypropylene chain, with emphasis on the orientation of the methyl substituents that appear on every other carbon of the polymer. There are three different ways these methyl groups can be arranged: l. They can all protrude from the same side of the stretched-out, zig-zag molecu-lar chain (isotactic polymer). 2. They can appear on alternating sides (syndiotactic polymer). 3. They can be oriented randomly (atactic polymer). 21.15 Silicates, Polymers of the Lithosphere • 545 ~ WW-_O_W_O_o-Wo : .~i Syndiotactic (alternating sides) Atactic (random) .„ The terms for the three orientations come from the Greek taktos, meaning ordered, which is modified by the prefixes iso- (same), syndio- (two together), and a- (not). In 1953 Ziegler (Sec. 21.13) and Giulio Natta, Italian-born (1903) professor of industrial chemistry at the Milan Polytechnic, independently prepared the highly ordered polypropylenes, thereby creating the first stereochemically ordered poly-mers. For their pioneering work Ziegler and Natta shared the 1963 Nobel Prize in chemistry. As we might expect from our knowledge of the effects of molecular order on the melting points of triglycerides and on the hardness of the polyethyl-enes, the highly ordered isotactic and syndiotactic polypropylenes are higher melt-ing, more crystalline, and harder than the atactic. Today almost 8 million tons of polypropylene are produced in the United States each year, most of it going into the manufacture of automobile trim and battery cases, carpet filaments and backing, fabrics, small items such as toys and housewares, and the hard plastic caps used on containers made of other materials. •QUESTION Which of the polymers ofTable 21.2 could exist in isotactic and syndiotactic forms? 21.15 Silicates, Polymers of the Lithosphere Not all polymers are organic compounds. Probably the most important and cer-tainly the most abundant of the inorganic polymers are compounds of silicon and oxygen. The clays, rocks, and inorganic soils of the earth's crust are made mostly of these two elements. On average, oxygen constitutes about 46% of the mass of the planet's outer layer of land and ocean bed; silicon, about 28%. Taking into ac-count the difference in their atomic weights, this corresponds to a ratio of almost three atoms of oxygen for every atom of silicon. Figure 21.22 The polypropylenes. 546 • Chapter 21 Polymers and Plastics Figure 21.23 Tetrahedral carbon and tetrahedral silicon. The tetrahedral carbon of methane The tetrahedral silicon of the silicates (the oxygens either are anionic or they are bonded to another silicon.) Most of the solid crust consists of polymers with repeating units of silicon dioxide (Si02) and of ionic aggregates such as Si03, Si04, Si205, Si401~ , and so forth. In these, four oxygens surround each tetracovalent silicon in much the same way as four hydrogens occupy the four corners of a tetrahedral methane molecule (Fig. 21.23). But while methane's hydrogens are monovalent, the oxygen atoms are divalent, so they ei-ther carry a negative ionic charge or bond to a second silicon atom. Bonding of any or all of the oxygens at the corners of the tetrahedra to still other tetrahedral silicons pro-duces threadlike, sheetlike, and three-dimensional, inorganic, silicate polymers. With the other elements of the crust interspersed among them, these inorganic polymers form much of the substance of the earth's rocks and minerals. One form of the mineral asbestos consists of a double strand of the silicate tetrahedra (Fg. 21.24). Asbestos was once used in brake linings and cigarette filters and as insulation in hous-es, schools, and office buildings. Inhaling asbestos fibers has been shown to produce mesothelioma, a cancer of the lungs and the cavity of the chest and the abdomen. Since the mid-1970s the mineral has been abandoned as an insulating material in con-struction. Its use in consumer products is now prohibited by law. Two-dimensional sheets of silicate polymers form micas, clays, and talcs, while quartz is a three-dimensional lattice of silicon dioxide (SiOZ). In the quartz lattice (Fig. 21.25) every oxygen is shared by two different silicon atoms, one at the center of each of two adjacent tetrahedra that are connected through the oxygen. Each silicon atom owns, in effect, exactly half of each of the four oxygens bonded to it (with the other half assigned to the other silicon atom bonded to the oxygen). With this arrangement, the molecular formula of quartz becomes Si02. Figure 21.24 A double-stranded asbestos polymer. 548 • Chapter 21 Polymers and Plastics • QUEST1ON Of PET and polypropylene, which plastic is preferred forth e manufacture oft he bodies of soft drink bottles? Why? Which is preferred fort he manufacture of large bot-tles for water, milk, and liquid detergent? Why? PERSPECTIVE - The Problem with Plastics Unlike metal, discarded plastic boxes and bottles don't corrode and decay. Unlike paper and cloth, ordinary plas-tic bags and wrappings aren't degraded by the weather or by the action of the microorganisms of the soil. Plas-tics, as a rule, simply aren't biodegradable. That is, the microorganisms that inhabit the soil can't degrade plas-tics to the simpler substances that form our natural environment. Plastic litter lies by the side of the road and in our parks and beaches, virtually unchanged by weather or microor-ganisms, until it's gathered up for proper disposal. (An es timated 60% of all the debris collected from our beaches consists of plastics of one sort or another,) environment by chemically induced degradation. Impregnat- ing the plastic with a substance that promotes its decompo-sition without significantly affecting its properties can cause it to decay much like paper or cloth. Incorporating a readily biodegradable form of starch, cellulose, or protein, for ex-ample, attracts soil microorganisms into the discarded plas-tic. As the microorganisms feed on these nutrients they also clip the long molecular chains of the polymers into shorter segments, causing the plastic to decompose. Alternatively, chemical activators can be added to the plastic so that con-tinued exposure to sunlight leads to degradation. Either one of these treatments leaves the plastic suit-able only for decomposition rather than for recycling and, therefore, does nothing to slow the introduction of plas tics, or their degradation products, into the environment. simpler substances that form our natural environment. 22.7 Hair: Curling the Keratin • 565 Adjacent protein strands of dry hair are held in place partly by hydrogen bonds. Hydrogen bonding with water allows protein polymers to slide past each other when hair is wet IN -C N-C N-C N-C H H H H O O O O N-C N -C N-C IN -C H H H H Drying hair removes water and fixes a new orientation of strands. Figure 22.12 The chemistry of a wet wave.   To accomplish all this, permanent waving kits (such as those described in the opening demonstration) contain two essential parts: a waving lotion and a neu-tralizer. Most waving lotions are slightly basic solutions of thioglycolic acid, a compound that effectively transfers the hydrogen of its own sulfur to the cys-tine units and cleaves them to cysteines. The result resembles what we'd get if S66 • Chaptsr 22 Cosmetics and Personal Cars C O HZN-CH-C-OH O HZN- CH- C - OH  CHZ-S-S-CHz O CHz-SH HZN-CH-C-OH cystine cysteine  • Q U E S T I O N The curl of a permanent wave is produced by breaking covaient bonds between two strands of keratin, reorganizing the strands, then re-forming the covalent bonds. Atoms of which element are connected by the covalent bonds that are broken and re-formed? 22.8 Toothpaste, the Fresh Abrasive Bright, clean teeth appear to be healthy teeth. But while we see a rich foam as the clearest indication that the toothpaste is doing its job, those same surfactants that pro-   duce the foam are among the least important cleansing agents of a good dentifrice. They aren't what keep teeth clean and healthy, and a few powdered dentifrices don't even contain them. In fact, the Food and Drug Administration doesn't consider a sur-factant to be an active ingredient of a toothpaste. What's needed for a good denti-frice is an effective abrasive. To understand why takes a bit of dental chemistry. A healthy tooth is covered by a layer of enamel that serves both to grind food and to protect the interior regions of the tooth itself. As in bone, calcium makes up most of this extremely hard surface, which is composed largely of the mineral hy- Toothpaste, a combination of droxyapatite, Calo(POq)6(OH)2. Despite its toughness, the enamel is susceptible abrasives, detergents, flavorings, to acids that come from a thin, adhesive, polysaccharide film called plaque. and, in many cases, fluorides Bacteria of the mouth continuously convert some of the sugars of our food and other ingredients that into this plaque, which attaches to the enamel and serves as a home to still other bac- protect against decay. teria. These other bacteria, in turn, convert the plaque into an acid that erodes the calcium and the phosphate from the shield of hydroxyapatite that protects the tooth. Plaque is a thin layer of a When enough erosion has occurred microorganisms can pass through the weak- polysaccharide that sticks to ened barrier to begin their work on the interior. The result is dental caries, better the surface of teeth and known as tooth decay or cavities. harbors bacteria. The key to keeping teeth free of cavities lies in removing the accumulated plaque, and that depends more on grinding it away with a good dental abrasive than on the detergent action of a surfactant. With daily removal of the plaque, the calcium and phosphate normally present in saliva replace any that might have been removed by mouth acids. As long as no bacteria have entered the body of the tooth itself, this re- , constitution process, known as remineralization, returns the enamel to its original strength. To be useful as a dental abrasive the grinding agent must be harsh enough to remove accumulated plaque, yet not grind away the enamel itself. Table 22.2 pres-ents some of the chemicals used as abrasives in commercial dentifrices. Table 22.2 Typical Dentifrice Abrasives Abrasive Formula Calcium carbonate Calcium pyrophosphate Dibasic calcium phosphate Hydrated aluminum oxide Magnesium carbonate Talc Titanium dioxide Tricalcium phosphate CaC03 CaZP20~ CaHPOq Al(OH)3 MgC03 Mg3(Si205)2(OH)2 TiOZ Ca3(POq)2 22.8 Toothpaste, the Fresh Abrasive • 567 Fluoride ions also help maintain the strength of the enamel. Fluorides are present in toothpastes largely in the form of stannous fluoride (SnF2), sodium monofluorophosphate (Na2P03F), and sodium fluoride (NaF). The fluoride ^ seems to act by • replacing some of the hydroxy groups in the enamel's hydroxyapatite, con-verting it to a harder mineral, fluoroapatite, which is more resistant to erosion by acids, and • suppressing the bacteria's ability to generate acids. Although not our principal protection against tooth decay the surfactants of toothpaste formulations do effectively remove loose debris from the mouth and 568 • Chapter 22 Cosmetics and Personal Care •QUESTION What is the principal function of a good toothpaste in keeping teeth clean and cavity-free? The dermis is the portion of the skin that contains nerves, blood vessels, sweat glands, and the active portion of the hair follicles, and also sup-ports the upper layer, the epidermis. The stratum corneum is the outermost layer of skin, a pro-tective shield consisting of 25 to 30 layers of dead cells. Table 22.3 Composition of aTypical Dentifrice Weight Ingredient Formula (%) Function Water H~O 39 Solvent and filler Glycerol CHZ-CH-CHZ 32 Humectant,retainsmoisture I I I OH OH OH Dibasic calcium CaHP04 27 Abrasive phosphate Carrageenan A carbohydrate of 1 Thickening agent and seaweed stabilizer Fluorides and other 1 Enamel hardener: additives sweeteners and preservatives also give us the sense of cleanliness. Almost all dentifrices contain a bit of saccha-rin and some flavoring or fragrance to leave us with a sense of sweetness and fresh-ness after brushing. The components of a typical toothpaste appear in Table 22,.3. 22.9 To Make Our Skin Moist, Soft, and . . . On average, about a quarter of every dollar we spend for cosmetics goes toward the care of our skin with moisturizers and emollients (softeners): hand. face. and body soaps; and deodorants and antiperspirants. We've already examined the chem- /' istry of soaps and detergents in Chapter 13; here and in the next section we'll tak~ up the means by which we keep Qur skin-the organ that envelops our bodies~ ' moist, soft, and inoffensive. ' If an organ is a group of tissues that perform one or more specific functiovs. as the heart pumps blood or the kidneys filter it, then our skin is indeed an organ. the largest one of all. Its functions range from the obvious coverina of our bc~dies "~ and protection from damage by foreign matter and microorganisms, to the more subtle tasks of regulating body temperature, sensing the stimuli provided 1-y the outside world, and even synthesizing compounds such as vitamin D (Sec. 19.5). The skin itself is made up of two major layers, the underlying dermis, which contains nerves, blood vessels, sweat glands, and the active portion of the hair fol-licles, and which also supports the upper layer, the epidermis (Fig. 22.5). The epi-dermis consists of several tiers of cells. At its bottom, resting on top of the dermis, " is a single sheet of cells that divide continuously, always pushing upward. As they move toward the outside of the skin, driven along by new cells coming up from be-neath, they lose their ability to divide and eventually die. By the time they become the lifeless, outermost layer of the skin, the stratum corneum, they have been trans-formed into keratin, the same protein that forms the hair. The stratum corneum itself is a layer of 25 to 30 tiers of these dead cells whose sole function is to protect us against the outside world, including the world,Qf our ,  22.10 ...Inoffensive • 569 cosmetics and toiletries. The condition of this layer depends mostly on its water con-tent. Too much moisture nourishes the growth of fungi and other microorganisms; too little dries it out, producing flaking and cracking. A water content of 10% is j ust about right for the stratum corneum. The body supplies protection to the skin with the sebum secreted by the se-baceous glands of hair follicles. This oily substance coats the adjacent skin, lubri-cating and softening its dead keratin (as well as the hair's), and lowering the rate at which water evaporates from its surface. These sebaceous glands occur only at the hair follicles themselves. No sebum coats the skin of the hairless regions of the body, such as the palms of the hands and the soles of the feet. Commercial cosmetic lotions and creams are emulsions, or colloidal dis-persions (Sec.13.5) of two or more liquids that are insoluble in each other (usu-ally an oil and water). These personal care products act in much the same way as sebum. A contemporary form of cold cream, one of the oldest and most com-mon of the skin moisturizers, consists of an emulsion of about 55 % mineral oil, 19% rose water,l3% spermaceti (a wax obtained from the sperm whale),12% beeswax, and about 1 % borax (a mineral that combines sodium borate and water). A typical vanishing cream, which fills in wrinkles and appears to make them vanish, incorporates about 70% water, 20% stearic acid (partly as its sodi-um salt; Table 15.1), and 10% glycerol (also known as glycerin; Sec. 13.8), with Skin lotions and creams soften traces of potassium hydroxide, preservatives, and perfumes. In the more freely the lifeless cells of the stratum -hป„flowing hand and body lotions, water and oils replace some of the waxes of the corneum. ~, creams. Since the function of these lotions and creams is to keep the outer layer of skin moist, they are most effective when applied after a bath or shower, while the skin is still damp. The dermis, epidermis, and stratum corneum are layers of the organ known as the skin. •QUESTION What is their sequence, from top to bottom? What is the composition or structure of each? 570 • Chapter 22 Cosmetics and Personal Care •QUEST1ON What's the difference between the action of an antiperspirant and a deodorant? Antiperspirants inhibit sweating and keep the body relatively dry. Deodorants di-rectly attack odors themselves. To control the wetness of perspiration and any of its associated odors we have available two personal care products, antiperspirants and deodorants. The an-tiperspirants inhibit sweating and keep the body relatively dry. Deodorants, on the other hand, directly attack odors themselves. The most widely used of the an-tiperspirants are the aluminum chlorohydrates, A12(OH)4C12 and A12(OH)SCI. These release aluminum cations, which seem to reduce wetness by physically clos-ing the ducts of the eccrine glands for as long as several weeks. They also reduce the odor associated with the apocrine glands, probably by killing the bacteria that decompose the organic portion of the fluid. Deodorants mask odors with fragrant ingredients that cover the offending aroma and also with antibiotics that eliminate the bacteria. In addition to the alu- ` minum salts, these antibacterial agents include various salts of zinc as well as the broad-spectrum antibiotic neomycin. Since the odor itself comes from the action of bacteria on the accumulated residue of perspiration, daily washing alone often solves many of the problems. 22.11 Putting a Little Color on Your Skin  The oils, waxes, polymers, and dyes of lipstick protect, soften and brighten the lips. With our hair, teeth, and skin clean and in good shape, we'll focus now on cosmetics that add color: lipsticks, eye colorings, nail polish, and face powder. Lipstick provides a soft-ening and protecting film for the lips, as well as colors ranging from soft and unobtru-sive to dazzling. About half the weight of a tube of modern lipstick is highly purified castor oil (a mixture of triglycerides obtained from plant seeds). This oil serves to dis-solve the dyes and, more importantly, to give the stick the ability to remain a waxy solid in its container yet flow smoothly as it touches the warmer lips. Most of the re-mainder of the stick is a mixture of oils, waxes, hydrocarbons, esters, lanolin (the waxy sebum of sheep), and polymers, all formulated to produce a desirable texture, melting point, ingredient mix, and film flow. In addition, the castor oil and other oils and waxes of lipstick help keep the skin of the lips moist and soft. The remaining ingredients-dyes, perfumes, and preservatives-make up a very small percentage of the weight. Major dyes of modern lipsticks include D&C Orange No. 5, known chemical-ly as a dibromofluorescein, and D&C Red No. 22, a tetrabromofluorescein (Fig. 22.14). The D&C here indicates that the Food and Drug Administration has approved these dyes for use in drugs and cosmetics. Figure 22.14 Lipstick dyes.  HO O OH Na0 O O \ I / \ / Br Br / COZNa \ I  D & C Orange No. 5 , D & C Red No. 22 4',5'-dibromofluorescein 2',4',5',7'-tetrabromofluorescein 542 • Chapter 21 Polymers and Plastics  A broken car window made of safety glass. A sheet of Bubble gum made from polyvinylacetate. polyvinylacetate sandwiched between two sheets of glass prevents the broken glass from disintegrating into flying slivers.   Articles made from or coated with Teflon, a tough, stable, heat-resistant, nearly friction-free polymer of tetrafluoro-ethylene, CF2=CFz. Polymerization of vinyl acetate produces polyvinylacetate, a plastic with a wide range of properties and an equally wide range of applications. As a thermoplastic with a low softening temperature it's useful in coatings and adhesives. A sandwich of two panes of glass bonded to a central sheet of the material forms a shatter-proof or safety glass. While the glass can break, it won't shatter into dangerous slivers. Safety glass of this kind is used in car windows. Mixed with a sweetener, some flavoring, and other ingredients, polyvinylacetate replaces the chewy chicle of chewing gum. (Chicle itself is a rubberlike polymer ob-tained from the sap of the sapodilla tree.) Partially polymerized vinyl acetate serves as a binder in water-based house paints. As the water evaporates, the low-molecular-weight polymer present in the paint polymerizes further, forming a tough sheet that binds the pigment to the coated surface. Polyacrylonitrile, a thermoplastic that's drawn out into fine threads and woven into synthetic fabrics such as Orlon, Acrilan, and Creslan, comes from the poly-merization of acrylonitrile (CIZ=CH-CN). Putting two chlorines on the single carbon of ethylene converts it into vinylidene chloride (CH2=CC12), the major monomer of Saran. Sheets of this polymer form a nearly impregnable barrier to food odors, which makes it useful for wrapping foods that are to be stored near each other in a refrigerator. Teflon results from the polymerization of tetrafluoroethylene (CFZ=CF2), a monomer obtained by replacing all of ethylene's hydrogens with fluorines. Teflon's great chemical stability, its resistance to heat, its mechanical toughness, and its nearly friction-free surface make it useful as a coating for bearings, valve seats, gaskets, and other parts of machinery that take heavy wear. Since things don't eas-ily stick to it, Teflon also makes a fine coating for cooking utensils such as pots and pans. Teflon was first prepared at DuPont in 1938; commercial production began 10 years later. In molecular structure methyl methacrylate is a bit further removed from ethylene. Its polymer forms a very hard, clear, colorless plastic that appears in consumer products as Lucite and Plexiglas. It's used in making glasses, camera lenses, and other optical equipment, in costume jewelry, and as windows in aircraft. 21.13 Polyethylene, the Plastic That Won the War and Gave Us the Hula-Hoop • 543 •QUESTION Of the polymers described in this section, which contain the element: (a) oxygen, (b) chlorine, (c) nitrogen, (d) fluorine? 21.13 Polyethylene, the Plastic That Won the War and Gave Us the Hula-Hoop Accounting for about 16.6 million tons or over 40% of all plastic production in the United States annually, polyethylene clearly represents the most important polymer of the U.S. plastics industry. In its two principal commercial forms (high-density polyethylene and low-density polyethylene, which we'll examine shortly) it also illustrates very nicely the connection between the structure of a polymeric molecule and the properties of the plastic it forms. As we might imagine, the phys-ical properties of a piece of bulk plastic depend partly on the molecular structure of the monomer that forms it and partly on the average length of its polymeric chains. As we'll see shortly, a third factor also comes into play: the way polymeric chains organize themselves as they constitute the bulk of the material. •QUESTION What is the major use of the LDPE produced in the United States? Polyethylene itself was first prepared in 1934 in the laboratories of Imperial Chemical Industries, in Great Britain, and went into commercial production there five years later as World War II was about to begin. The first practical use of the plastic was as insulation on the electrical wiring of military radar sets. Considering the critical importance of aircraft radar to the survival of Britain in the early years of the war, we could easily designate polyethylene as the plastic that won the war. The techniques used for those early polymerizations produce what we now know as low-density polyethylene (LDPE). As the chains of LDPE form, they branch sporadically into short offshoots from the main line of the polymer. These short branches kee the ma'or strands of the ol mer from fallin into an thin P J P Y g Y g ~-resembling a coherent, well-organized pattern. Instead they form a tangled, ran- domly oriented network of strands, somewhat like a large ball of fuzz (Fig. 21.20). Figure 21.20 Disorganized The result is a low-density, soft, waxy, flexible, relatively low melting plastic that ac- polymeric strands of low- counts for a little over half of all the polyethylene produced in the United States. density polyethylene. More of this LDPE goes into producing trash bags than into any other single prod- uct. Industrial and commercial packaging, food wrappers, and plastic shopping bags are close behind. As in World War II, the coating of electrical wires and ca-bles remains an important use. Polymerized by a different method, the polyethylene chains can grow on and on without branching, thereby generating high-density polyethylene (HDPE).This Regions of form of the plastic was first produced in Germany in the early 1950s by Karl . ., i " crystallinity ,  Ziegler, a German chemist born near the end of 1898. Ziegler prepared HDPE by carrying out the polymerizations in the presence of certain highly specialized (~~' ~-~~-•"~ 1 organometallic catalysts, which consist of combmations of orgamc molecules and metal atoms joined to each other by covalent bonds.These catalysts control the way the monomers link to each other as they polymerize. In HDPE the long molecular chains aren't fixed into a tangled web as they are in the LDPE, so they can align themselves into localized areas of tightly packed strands, mimicking here and there the orderly structure of crystals such as sodium chloride and sucrose. With many regions of close packing and a high degree of crys-tallinity, HDPE is a denser, harder, higher melting, and more rigid polymer than LDPE (Fig. 21.21). We saw another example of this same sort of relationship between molecular structure and physical properties in the fats and oils of Chapter 15. Figure 21.21 Polymeric strands of high-density polyethylene with regions of crystallinity. 544 • Chapter 21 Polymers and Plastics Hula-hoops in action. Of approximately 7.7 million tons of HDPE produced in the United States in 2000, most went into the manufacture of bottles and other containers designed to hold a variety of liquids, including drinks, bleach, antifreeze, and engine oil. I