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P IP in P A D llS lL J tZ H B io lo g ic ! molecules— proteins, carbohydrates, lipids, and nucleic a c j£j s— interact to carry out activities necessary to living cells. a bS taflny. How do you test for simple sugars? Many different food sources supply the energy that your body uses constantly. This energy is stored in the bonds of molecules called simple sugars. In this lab, you w ill test several mixtures to determine if a simple sugar is present. 824 connectED.mcaraw-hill.com ;l Skin cells— nucleic acids Fats provide more than twice the energy per gram as carbohydrates and proteins. Special lipids, callea phospholipids, make up the cellular membranes of living cells. SECTION 1 E s s e n tia l Q u e s tio n s • How can the structures of amino acids and proteins be described? • What are the roles of proteins in ceHS7 p o ly m e r: large molecules composed of many repeating units called monomers N e w V o c a b u la r y protein amino acid peptide bond peptide denaturation enzyme substrate active site Proteins M A I N I D E A Proteins perform essential functions, including struc tu ral support, tran sp o rt o f m aterials, muscle contractions, and regulation o f chem ical reactions. _ „ „ _ —_ CHEM 4 w f|| | YUU Some cleaning products, such as contact lens cleaning solution, contain enzymes. Did you ever wonder w hat an enzyme was? Protein Structure Enzymes form a class o f proteins. Proteins are organic polymers made o f amino acids linked together in a specific order. Proteins are not just large, randomly arranged chains of amino acids. To function properly, each protein must be folded into a specific three-dimensional structure. All living organisms, including the mountain goat and the plants shown in Figure 1, are composed o f proteins. In this section, you will read about how proteins are made from their amino-acid building blocks and how different types o f proteins function. A m in o a c id s As you read previously, many different functional groups are found in organic compounds. Amino acids, as their name implies, are organic molecules that have both an amino group and an acidic carboxyl group. The general structure o f an amino acid is shown below. R Amino group Variable side chain I H?N— C — C — OH Carboxyl group Hydrogen atom I H II O Each amino acid has a central carbon atom around which four groups are arranged: an amino group (—NH2), a carboxyl group (—COOH), a hydrogen atom, and a variable side chain, R. The side chains range from a single hydrogen atom to a complex double-ring structure. ■Figure 1 All living organisms contain proteins. A goat's hair, hooves, and muscles are made up of structural proteins, as are the roots and leaves of plants. 826 C hapter 23 • The Chemistry of Life Explore amino acids w ith an interactive table, f Am ino Acid Examples T a b le 1 c h 2- OH SH ch2 cn2 cn2 ch I H I H2N - C - C - O H I I H2N - C - C - O H II H I 0 H Glycine I II H 0 Serine 2 2 ch2 H2N - C - C - O H II nh I 0 H2N - C - C - O H I Cysteine II H 0 Lysine 0 % / OH 0 C \ I C / nh2 2 I \ ch2 ch2 ch2 ch2 H2N - C - C - O H H2N - C - C - O H I II H i j g I 0 / CH i I CH2 H2N - C - C - O H I II H II H Glutamic acid i ch3 ch3 H2N - C - C - O H 0 I Valine 0 H II 0 Phenylalanine Glutamine Examine the different side chains o f the amino acids shown in Table 1. Identify the nonpolar alkanes, polar hydroxyl groups, acidic and basic groups such as carboxyl and amino groups, aromatic rings, and sulfur-containing groups. This wide range o f side chains gives the different amino acids a large variety o f chemical and physical properties and is an important reason why proteins can perform so many different functions. T h e p e p t id e b o n d The amino and carboxyl groups provide conve nient bonding sites for linking amino acids together. Because an amino acid is both an amine and a carboxylic acid, two amino acids can combine to form an amide, releasing water in the process. This reaction is a condensation reaction. As Figure 2 shows, the carboxyl group of one amino acid reacts with the amino group of another amino acid to form an amide functional group. □ READING CHECK Explain how an amide functional group forms. ■Figure 2 The amino group of one amino acid bonds to the carboxyl group of another amino acid to form a dipeptide and water. The organic functional group formed is an amide linkage called a peptide bond. Peptide bond H R , H \ m- C - C - O H / H I H O II A m in o acid + R2 Rt \l-C -C -O H / H H I O II A m in o acid ^ H R2 N - C - C - N - C - C - O H / H I H O II I H O + H20 II D ip e p tid e W a te r Section 1 • Proteins 827 The amide bond that join s two am ino acids, shown in F ig u re 3, is referred to as a peptide bon d. A chain o f two or m ore am ino acids linked together by peptide bonds is called a peptide. A m olecule that consists o f two am ino acids bound together by a peptide bond is called a dipeptide. F ig u re 4 a shows the structure o f a dipeptide that is formed from the am ino acids glycine (Gly) and phenylalanine (Phe). F ig u re 4 b shows a different dipeptide, also form ed by linking together glycine and phenylalanine. Is G ly-Phe the same com pound as Phe-Gly? No, they’re different. Exam ine these two dipeptides to see that the order in which am ino acids are linked in a dipeptide is im portant. Each end o f the tw o-am ino-acid unit in a dipeptide still has a free group— one end has a free am ino group and the other end has a free carboxyl group. Each o f those groups can be linked to the opposite end o f yet another am ino acid, form ing m ore peptide bonds. Living cells always build peptides by adding am ino acids to the carboxyl end o f a growing chain. H I — C — N— P e p tid e b o n d II O ■ F ig u re 3 A peptide bond joins two amino acids to form a dipeptide. □ READING CHECK E xplain why Gly-Phe and Phe-Gly are different dipeptides. Polypeptides As peptide chains increase in length, other ways o f referring to them becom e necessary. A chain o f ten or m ore am ino acids joined by peptide bonds is referred to as a polypeptide. W hen a chain reaches a length o f about 50 am ino acids, it is called a protein. Because there are only 20 different am ino acids that form proteins, it m ight seem reasonable to think that only a lim ited num ber o f different protein structures are possible. However, a protein can have as few as 50 or m ore than a 1000 am ino acids, arranged in any possible sequence. To calculate the num ber o f possible sequences these am ino acids can have, consider that each position on the chain can have any o f 2 0 possible am ino acids. For a peptide that contains n am ino acids, there are 2 0 ” possible sequences o f the am ino acids. So a dipeptide, with only two am ino acids, can have 2 0 2, or 400, different possible am ino acid sequences. Even the smallest protein, containing only 50 amino acids, has 2 0 50, or m ore than 1 x 1 0 65, possible arrangements o f am ino acids! It is estim ated that hum an cells m ake between 80,000 and 100,000 different proteins. You can see that this is only a small fraction o f the total num ber o f proteins possible. □ READING CHECK C a lc u late the possible number of sequences for a j peptide chain comprised of four amino acids. ■ F ig u re 4 Glycine (Gly) and phenylalanine (Phe) can combine in two configurations. Describe the difference betw een the configuration o f the peptide bonds in these two dipeptides. © A i Gly H O Phe G ly c y lp h e n y la la n in e (G ly-P he) 828 C hapter 23 • The Chemistry of Life N - C - C - NN - C — - Cr -— On wH ,I / H O H I N - C - C - N - C - C - O H / H H H H H I H Phe II O I H O II Gly P h e n yla la n y lg ly cin e (P he-G ly) ■Figure 5 The folding of polypeptide chains into both helices and sheets involves amino acids in the chain held in position by hydrogen bonds. Other interactions among the various side chains are not shown here but play an important role in determining the three-dimensional shape of a polypeptide. T h re e -d im e n s io n a l p ro te in s tru ctu re Long chains o f amino acids start to fold into unique three-dimensional shapes before they are fully synthesized. The three-dimensional shape is determined by the interactions among the amino acids. Some areas o f a polypeptide might twirl into helices, which are similar to the coils on a telephone cord. Other areas might bend back and forth repeatedly into a pleated sheet structure, like the folds o f an accordion. A polypeptide chain might also fold back on itself and change direction. A given protein might have several helices, sheets, and turns, or none at all. Figure 5 shows the folding patterns o f a typical helix and a sheet. The overall three-dimen sional shape o f many proteins is globular— shaped like an irregular sphere. Other proteins have a long, fibrous shape. The shape is impor tant to the function o f the protein. If the shape o f the protein changes, it might not be able to carry out its function in the cell. D enatu ration Changes in temperature, ionic strength, pH, and other factors result in the unfolding and uncoiling o f a protein. D en atu ration is the process in which a proteins natural three-dimensional structure is disrupted. Cooking often denatures the proteins in foods. When an egg is hard-boiled, the protein-rich egg white solidifies due to the denatur ation o f its protein. Because proteins function properly only when fold ed, denatured proteins are generally inactive. The M any Functions o f Proteins Proteins play many roles in living cells. They are involved in speeding up chemical reactions, transport o f substances, regulation of cellular processes, structural support o f cells, communication within cells and among cells, cellular motion, and even serving as an energy source when other sources are scarce. S p e e d in g u p re a ctio n s In most organisms, the largest number of proteins function as enzymes, catalyzing the many reactions that occur in living cells. An enzym e is a biological catalyst. You read previously that a catalyst speeds up a chemical reaction without being consumed in the reaction. A catalyst usually lowers the activation energy o f a reaction by stabilizing the transition state. RealWorld IHEMISTRY Enzymes PAPAIN A n e x a m p le o f an e n zym e you m ig h t have used is p ap ain , fo u n d in papayas, pineapples, and o th e r p la n t sources. This e n zy m e catalyzes a re ac tio n th a t breaks d o w n p ro tein m olecules in to fre e a m in o acids. P apain is th e active in g re d ie n t in m an y m e a t ten d e rize rs . W h e n you sprinkle th e d rie d fo rm o f papain o n to m oist m ea t, th e p ap ain fo rm s a s olu tion th a t breaks d o w n th e to u g h p ro te in fibers in th e m ea t, m aking th e m e a t m o re ten d er. Watch a video about surfactants and enzymes. Section 1 • Proteins 829 Complex sugar Enzymes act on specific substrates, such as a complex sugar. Active sites Each substrate fits into the active site. The enzyme changes shape slightly to fit more tightly with the substrate. + H 20 After the reaction, the enzyme released is in its original shape and can carry out the same reaction repeatedly. The products are released; in this case the complex sugar is divided into less complex sugars. Enzyme ■ F ig u re 6 Enzymes lower the activation energy needed for a reaction to occur. Enzymes change the speed at which chemical reactions occur without being altered themselves in the reaction. ■ F ig u re 7 Hemoglobin is a globular protein with four polypeptide chains, each containing an iron group (called a heme) to I which oxygen binds. Heme How do enzymes function? The term su b strate refers to a reactant in an enzyme-catalyzed reaction, as shown in F ig u re 6 . Substrates bind to specific sites on enzyme molecules, usually pockets or crevices. The spot to which the substrates bind is called the active site of the enzyme. After the substrates bind to the active site, the active site changes shape slightly to fit more tightly around the substrates. This recognition process is called induced fit. The shapes o f the substrates must fit the shape o f the active site, in the same way that puzzle pieces or a lock and key fit together. A molecule that is only slightly different in shape from an enzyme’s normal substrate will not bind as well to the active site and might not undergo the catalyzed reaction. The structure that forms when substrates are bound to an enzyme is called an enzyme-substrate complex. The large size o f enzyme mol ecules allows them to form multiple bonds with their substrates, and the large variety of amino acid side chains in the enzyme allows a number of different intermolecular forces to form. These intermolecular forces lower the activation energy needed for the reaction in which bonds are broken and the substrates are converted to product. □ READING CHECK Describe in your own words how an enzyme works. T r a n s p o r t p r o t e in s Some proteins are involved in transporting smaller particles throughout the body. F ig u re 7 shows the protein hemoglobin, which carries oxygen in the blood from the lungs to the rest of the body. Other proteins combine with biological molecules called lipids to transport them from one part of the body to another through the bloodstream. You will learn about lipids later in this chapter. 830 C hapter 23 • The Chemistry of Life ■ F ig u r e 8 Human hair is made up of a fibrous structural j protein called keratin. SEM magnification: 500x S t r u c t u r a l s u p p o r t The sole function o f certain proteins is to form structures vital to organisms. These molecules are known as structural proteins. The most abundant structural protein in most animals is collagen, which is part o f skin, ligaments, tendons, and bones. Other structural proteins make up feathers, fur, wool, hooves, fingernails, cocoons, and hair, as shown in F ig u r e 8 . C o m m u n ic a t io n H orm ones are m essenger m olecules that carry signals from one part o f the body to another. Som e horm ones are proteins. Insulin, a fam iliar example, is a sm all (51 am ino acids) protein h orm one m ade by pancreas cells. W h en insulin is released into the bloodstream , it signals body cells that blood sugar is abundant and should be stored. A lack o f insulin often results in diabetes, a disease that results w hen there is too m uch sugar in the bloodstream . Because m odern technology has m ade possible the laboratory synthesis o f proteins, som e protein horm ones are being synthetically produced for use as m edicines. Insulin, thyroid horm ones, and growth horm ones are som e examples. B oth natural and synthetic proteins are used in a variety o f products—-from m eat tenderizer to cleaning < S B ; Incorporate information from this section into your Foldable. solutions to health and beauty aids. s e c tio n 1 REVIEW. S e c tio n S u m m a r y 1. M A IN ID E A Describe three proteins and identify their functions. • Proteins are biological polymers m ade o f amino acids th at are linked by peptide bonds. 2. Com pare the structures of amino acids, dipeptides, polypeptides, and proteins. Which has the largest molecular mass? The smallest? 3. D ra w the structure of the dipeptide Gly-Ser, circling the peptide bond. • Protein chains fold into intricate three-dim ensional structures. 4. Evaluate How do the properties of proteins make them such useful catalysts? • Proteins have many functions in the human body, including functions w ithin cells, functions betw een cells, and functions of structural support. 5. Explain how a change in tem perature m ight affect a protein's function. How do they differ from other catalysts you have studied? 6 . C ategorize Identify an amino acid from T a b le 1 th at can be classified into each of the categories in the following pairs. a. nonpolar side chain v. polar side chain b. aromatic v. aliphatic c. acidic v. basic Section 1 • Proteins 831 M A IN IDEA Essential Questions • How can the structures of monosaccharides, disaccharides, and polysaccharides be described? • What are the functions of carbohydrates in living things? N e w V o c a b u la r y carbohydrate monosaccharide disaccharide polysaccharide Carbohydrates provide energy and structural m aterial fo r living things. CH EM 4 v n , - R e v ie w V o c a b u la r y stereoisomers: a class of isomers whose atoms are bonded in the same order but are arranged differently in space es A lot of media attention has been focused on carbohydrates. Some recommend low-carb diets as a w ay of controlling weight. However, carbohydrates are an important energy source for the body. Kinds o f Carbohydrates Analyzing the term c a r b o h y d r a te offers a hint about the structure o f this group o f m olecules. Early observations that these compounds have the general chem ical form ula C „(H 2 0 ) „ and appear to be hydrates of carbon led to their being called carbohydrates. Although scientists now know that there are no full water m olecules attached to carbohydrates, the nam e has stayed. T he m ain function o f carbohydrates in living organisms is as a source o f energy, both im m ediate and stored. Foods rich in carbo hydrates include pasta, m ilk, fruit, bread, and potatoes. Carbohydrates are com pounds that contain multiple hydroxyl groups (— O H) as well as a carbonyl functional group ( C = 0 ) . These m olecules range in size from single m onom ers to polym ers made o f hundreds or even thousands of m onom er units. M o n o s a c c h a r id e s The simplest carbohydrates, often called simple sugars, are monosaccharides. The m ost com m on monosaccharides have either five or six carbon atoms. Examples o f m onosaccharides are shown in Figure 9. Notice that they have a carbonyl group on one carbon and hydroxyl groups on m ost o f the other carbons. The presence o f a carbonyl group makes these compounds either aldehydes or ketones, depending on the location o f the carbonyl group. Multiple polar groups make m onosaccharides water-soluble and give them high melting points. ■Figure 9 Glucose, galactose, and fructose are monosaccharides. In aqueous solutions, they exist in an equilibrium between their open-chain and cyclic forms. H c=o I H—C— OH H /Ic- I HO- C - H I 0 H- C OH l/H l\?H HO c — I H H -C -O H H ,/ l I ■C OH H - C - OH I OH Cyclic form H Open-chain form G lucose 832 C hapter 23 • The Chemistry of Life I I c=o c h 2o h H H I H -C -O H I I CH2OH HO £ I r /H & HO Ov h VI V/ ■c OH I H c=o H -C -O H I I HO- C - H I H -C -O H I H -C — OH I OH Cyclic form I C- H H Open-chain form G a la cto se I HO- C - H CH2OH Ov 4 )\ y a t i i h? HO c _ _ c I OH I H / i « CH2OH I H -C -O H I H -C -O H I I H H Cyclic form H - C - OH Open-chain form Fructose Glucose Fructose Sucrose Water ■Figure 10 When glucose and fructose bond, the disaccharide sucrose forms. Note that water is also a product of this condensation reaction. Remember that each ring structure is made of carbon atoms, which are not shown for simplicity. Glucose is a six-carbon sugar that has an aldehyde structure. Glucose is present in high concentration in blood because it serves as the major source o f immediate energy for the body. For this reason, glucose is often called blood sugar. Closely related to glucose is galactose, which differs only in how a hydrogen and a hydroxyl group are oriented in space around one o f the six carbon atoms. Recall that this relationship makes glucose and galactose stereoisomers. Fructose, also known as fruit sugar because it is the major carbohydrate in most fruits, is a six-carbon monosaccharide that has a ketone structure. Fructose is a structural isomer o f glucose. W hen monosaccharides are in aqueous solution, they exist in both open-chain and cyclic structures, but they rapidly interconvert forms. The cyclic structures are more stable and are the predominant form of monosaccharides at equilibrium. Note in Figure 9 that the carbonyl groups are present only in the open-chain structures. In the cyclic structures, they are converted to hydroxyl groups. D is a c c h a r id e s Like amino acids, monosaccharides can be linked together by a condensation reaction in which water is released. When two monosaccharides bond together, a d isacch arid e is formed, as shown in Figure 10. The new bond formed is an ether functional group (C -O -C ). One common disaccharide is sucrose, also known as table sugar because sucrose is used mainly as a sweetener. Sucrose is formed by the linking o f glucose and fructose. Another common disaccharide is lactose, the most important carbohydrate in milk. It is often called milk sugar. Lactose is formed when glucose and galactose bond. V o c a b u l a r y .................................. W o rd origin Polysaccharide comes from the Greek word polys, which means m a n y and the ancient Sanskrit word s a rka ra , which means s u g a r ..................................................... ■Figure 11 The glycogen found in the muscle and liver of animals is a polysaccharide made of glucose. P o ly s a c c h a r id e s Complex carbohydrate is a term used in some nutrition books and journal articles. Another name for a complex carbohydrate is p olysacch arid e, which is a polymer o f simple sugars that contains 1 2 or more monomers, or subunits. The same type of bond that joins two monosaccharides in a disaccharide also links the monomers in a polysaccharide. Glycogen, shown in Figure 11, is a polysaccharide. It is composed o f glucose subunits. It stores energy and is found mostly in the liver and muscles of humans and other animals. It is also found in some species of microorganisms including bacteria Glucose subunit and fungi. □ READING CHECK Explain the differences among a monosaccharide, a T disaccharide, and a polysaccharide. Section 2 • Carbohydrates 833 Cellulose Cross-link bond Glucose subunit ■ F ig u re 12 Two important polysaccharides are starch and cellulose, a . Starch molecules can be branched or unbranched, b . Cellulose has a linear, unbranched structure that resembles a chain-link fence. Glucose subunit €m an m Incorporate information from this section into your Foldable. Two other important polysaccharides are starch and cellulose, shown in F ig u re 1 2 . Starch and cellulose are also composed solely of glucose subunits. However, that is the only similarity among the three poly saccharides, as all three have different properties and functions. Plants make both starch and cellulose. Starch is a soft, water-insoluble molecule used to store energy, whereas cellulose is a water-insoluble polymer that forms rigid plant-cell walls, such as those found in wood. Glycogen, starch, and cellulose are composed o f glucose subunits, but they have different properties. The bonds that link the subunits together are oriented differently in space. Because o f this difference in , , , , , , , , „ , bond shape, hum ans can digest glycogen and starch but not cellulose. Digestive enzymes cannot fit cellulose into their active sites. The cellulose in the fruits, vegetables, and grains that we eat is called d ie ta ry f ib e r because it passes through the digestive system largely unchanged. s e c tio n z REVIEW S e c tio n S u m m a r y 7. MAINIDEA Explain the functions of carbohydrates in living things. • Carbohydrates are compounds that contain multiple hydroxyl groups (-0H) and a carbonyl functional group (C=0). 8 . Describe the structures of monosaccharides, disaccharides, and polysaccharides. • Carbohydrates range in size from single monomers to polymers composed of hundreds or thousands of monomers. • Monosaccharides in aqueous solution exist in both open-chain and cyclic structures. Which has the largest molecular mass? The smallest? 9. Com pare and contrast the structures of starch and cellulose. How do the structural differences affect our ability to digest these two polysaccharides? 10. Calculate If a carbohydrate has 2 n possible isomers, where n is equal to the number of chiral carbon atoms in the structure, calculate the number of possible isomers for the following monosaccharides: galactose, glucose, and fructose. 11. In te rp re t Scientific Illustrations Copy the illustration of sucrose on a separate sheet of paper, and circle the ether functional group that bonds the monomer sugars together. CH2OH .0 . HO CH,OH OH 834 C hapter 23 • The Chemistry of Life Lipids SECTION 3 M A IN IDEA Lipids m ake cell m em branes, store energy, and regulate cellular processes. E s s e n tia l Q u e s tio n s • How can the structures of fatty acids, triglycerides, phospholipids, and steroids be described? CH EM • What are the functions of lipids in living organisms? 4 • What are some reactions that fatty acids undergo? U The w ax used to polish cars, the fat that drips out of hamburgers, and the vitamin D that fortifies the milk people drink— what do Ihese things have in common? They are all lipids. What is a lipid? • How are the structure and function of cell membranes related? A lip id is a large, nonpolar biological m olecule. Because lipids are nonpolar, they are insoluble in water. Lipids have two m ajor functions in living organism s. They store energy efficiently, and they make up m ost o f the structure o f cell m em branes. Unlike proteins and carbohy drates, lipids are n ot polymers with repeated m onom er subunits. R e v ie w V o c a b u la r y n o n p o la r: without separate positive and negative areas or dipoles N e w V o c a b u la r y F a t t y a c id s Although lipids are not polymers, many lipids have a m ajor building block in com m on. This building block is the fa tty acid, a long-chain carboxylic acid. M ost naturally occurring fatty acids contain between 12 and 24 carbon atoms. T h eir structure can be represented by the following formula. lipid fatty acid triglyceride saponification phospholipid wax steroid C H 3 (C H 2 )hCO OH M ost fatty acids have an even num ber o f carbon atoms, which is a result o f being constructed two carbons at a tim e in enzymatic reactions. Fatty acids can be grouped into two m ain categories, depending on the presence or absence o f double bonds between carbon atoms. Fatty acids that contain no double bonds are referred to as saturated. Those that have one or m ore double bonds are called unsaturated. The struc tures o f two com m on fatty acids are shown in Figure 13. E? READING CHECK Explain why oleic acid is described as unsaturated. ■Fig u re 13 Two fatty acids, which are found in many foods, including butter, are the 18-carbon unsaturated oleic acid and the 18-carbon saturated stearic acid. Explain how the structure o f the molecule is affected by the presence o f a double bond. Oleic acid O, t C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H = . C H C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 3 HO' Stearic acid O, t C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 3 HO' Section 3 • Lipids 835 ■ F ig u re 1 4 Ester bonds in a triglyceride are formed when the hydroxyl groups of glycerol combine with the carboxyl groups of the fatty acids. O O II H O C (C H 2)14C H 3 c h 2o h I CHOH C H ,O H o o II + H O C (C H 2)16C H 3 II C H - 0 - C - ( C H 2)16- C H 3 + 3 H 20 o o H O C (C H 2)18C H 3 Glycerol II C H 2 - 0 - C - ( C H 2)14- C H 3 ch 3 Fatty acids 2— o — II c — (CH2)18— c h 3 Triglyceride Water An unsaturated fatty acid can become saturated if it reacts with hydrogen. As you read previously, hydrogenation is an addition reaction in which hydrogen gas reacts with carbon atoms that are linked by multiple bonds. Each unsaturated carbon atom can pick up one hydrogen atom to become saturated. For example, oleic acid, shown in F ig u re 1 3 , can be hydrogenated to form stearic acid. The double bonds in naturally occurring fatty acids are almost all in the cis geometric isomer form. Recall that the cis isomer has identical groups oriented on the same side o f the molecule around a double bond. Because o f the cis orientation, unsaturated fatty acids have a kink, or bend, in their structure that prevents them from packing together. They do not form as many intermolecular attractions as saturated fatty acid molecules. As a result, unsaturated fatty acids have lower melting points. V ocabulary ..................................... S c ie n c e u s a g e v . C o m m o n u s a g e Saturate S cience usage: to add something to the point that no more can be absorbed, dissolved, or retained The s a lt w a te r s o lu tio n w as s a tu ra te d w ith salt. C o m m o n usage: to furnish a market with a product or products to its full purchasing capacity T r ig ly c e r id e s Although fatty acids are abundant in living organisms, they are rarely found alone. They are most often found bonded to glycerol, a molecule with three carbons, each containing a hydroxyl group. When three fatty acids are bonded to a glycerol backbone through ester bonds, a trig ly c e r id e is formed. The formation of a triglyceride is shown in F ig u re 1 4 . Triglycerides can be either solids or liquids at room temperature, as shown in F ig u re 1 5. If liquid, they are usually called oils. If solid at room temperature, they are called fats. □ READING CHECK D e s c rib e the difference between fatty acids and triglycerides. The shops in the coa sta l to w n are sa tu ra te d w ith sea shell c ra ft ite m s .. . ■ F ig u re 1 5 Most mixtures of triglycerides from plant sources are liquids because the triglycerides contain unsaturated fatty acids. Animal fats contain a larger proportion of saturated fatty acids. They are usually solids at room temperature. 836 C hapter 23 • The Chemistry of Life o II CH2- 0 - C - ( C H 2)14CH3 ■Figure 16 Soap forms by the reaction of a triglyceride and a strong base. CH2OH o O II CH - O - C - (CH2)14CH3 + 3NaOH CHOH + 3CH3(CH2)14 - C - O-Na O II c h 2- 0 - c -( c h 2)14c h 3 Triglyceride CH2OH Base Glycerol Soap Fatty acids are stored in the fat cells o f your body as triglycerides. W hen energy is abundant, fat cells store the excess energy in the fatty acids o f triglycerides. W hen energy is scarce, the cells break down the triglycerides, releasing the energy used to form them. Although enzymes break down triglycerides in living cells, the reaction can be duplicated outside o f cells by using a strong base, such as sodium hydroxide. This reaction—the hydrolysis o f a triglyceride using an aqueous solution o f a strong base to form carboxylate salts and glycerol— is sa p o n ificatio n , as shown in Figure 16. Saponification is used to make soaps, which are usually the sodium salts o f fatty acids. A soap molecule has both a polar end and a nonpolar end. Soaps are used with water to clean nonpolar dirt and oil because the nonpolar dirt and oil bond to the nonpolar end o f the soap molecules, and the polar end o f the soap molecules is soluble in water. Thus, the dirt-laden soap molecules can be rinsed away with the water. MiniLAB O b s e rv e a S a p o n ific a tio n R e a ctio n How is soap made? The reaction between a triglyceride and a strong base is called saponifica tion. A sample chemical reaction is shown in Fig u re 16. P ro c e d u re 1. Read and com plete the lab safety form. 2 . Place a 2 5 0 -m L b e a k e r on a h o t p la te . Add 2 5 g s o lid v e g e t a b le s h o r te n in g to the beaker. Turn on the hot plate to a medium setting. 3 . As the vegetable shortening melts, use a 2 5 -m L g r a d u a te d c y lin d e r to slowly add 12 mL e th a n o l and then 5 mL 6 .0 M N a O H to the beaker. W A R N IN G : E th a n o l is fla m m a b le . N a O H cau ses s k in b u rn s . W e a r g lo v e s . 4. Heat the m ixture fo r about 15 min. Use a s tir rin g ro d to occasionally stir the mixture. Do not allow it to boil. 5 . W hen the mixture begins to thicken, use to n g s to remove the beaker from the heat. A llo w the beaker to cool fo r 5 min, then place it in a cold w a t e r b a th in a 6 0 0 -m L b e a k e r. 6 . Add 2 5 mL s a tu ra te d N aC I s o lu tio n to the mix ture in the beaker. The soap is not very soluble and will appear as small clumps. 7. Collect the solid soap clumps by filtering them through a c h e e s e c lo th -lin e d fu n n e l. 8 . Using gloved hands, press the soap into an e v a p o r a tin g d is h . Remove your gloves and wash your hands. A n a ly s is 1. Explain W hat type o f bonds present in the triglycerides are broken during the saponification reaction? 2. Identify the type o f salt form ed in this chemical reaction. 3. Determ ine which is the polar end and which is the nonpolar end o f the soap molecule. Section 3 • Lipids 837 ■ Figure 1 7 A phospholipid has a polar head and two nonpolar tails. The membranes of living cells are formed by a double layer of lipids, called a bilayer. The polar heads are on the outer and inner perimeter of the membrane and the tails are on the inside of the bilayer. Outside the cell " Inside the cell Polar heads 1 hT°S^° a^er Nonpolar tails P h o s p h o lip id s Another important type o f triglyceride, a phos pholipid, is found in greatest abundance in cellular membranes. A phospholipid is a triglyceride in which one o f the fatty acids is replaced by a polar phosphate group. As shown in Figure 17, the polar part of the molecule forms a head and the nonpolar fatty acids look like tails. A typical cell membrane has two layers o f phospholipids, which are arranged with their nonpolar tails pointing inward and their polar heads pointing outward. This arrangement is called a lipid bilayer. Because the lipid bilayer structure acts as a barrier, the cell is able to regulate the materials that enter and leave through the membrane. ■ Figure 1 8 Plants produce a wax that coats their leaves. The wax protects the leaves from drying out. ItiVU11iWtWHJ>M1fc Vt The venom o f poisonous snakes contains a class of enzymes known as phospholipases. These enzymes catalyze the breakdown o f phospholipids. The venom of the eastern diamond-back rattlesnake contains a phospholipase that hydrolyzes the ester bond at the middle carbon o f phospholipids. If the larger o f the two breakdown products o f this reaction gets into the bloodstream, it dissolves the membranes o f red blood cells, causing them to rupture. Because the venom destroys the blood cells, it is referred to as a hemotoxic venom. (The prefix hemo- indicates blood.) A bite from the eastern diamondback can lead to death if it is not treated immediately. W a x e s Another type of lipid, wax, also contains fatty acids. A w ax is a lipid that is formed by combining a fatty acid with a long-chain alcohol. The general structure of these soft, solid fats with low melting points is shown below, with x and y representing variable numbers of CH 2 groups. O II CH3(CH2)x - C - O - (CH2)yCH3 Both plants and animals make waxes. Plant leaves are often coated with wax, which prevents water loss. Notice in Figure 18 how raindrops bead up on the leaves o f a plant, indicating the presence o f the waxy layer. The honeycombs that bees make are also made o f a wax, com m only called beeswax. Com bining the 16-carbon fatty acid palmitic acid and a 30-carbon alcohol chain makes a com m on form o f beeswax. Candles are sometim es made o f beeswax because it tends to burn slowly and evenly. 838 C hapter 23 • The Chemistry of Life S te r o id s Not all lipids contain fatty acid chains. Steroids are lipids that have multiple cyclic rings in their structures. All steroids are built from the basic four-ring steroid structure shown below. <i JiU m anH Incorporate information yr°™ foldable'00 Some hormones, such as many sex hormones, are steroids that function to regulate metabolic processes. Cholesterol, another steroid, is an important structural component o f cell membranes. Vitamin D also contains the four-ring steroid structure and plays a role in the formation o f bones. The Giant Marine toad, Bufo marinus, shown in F ig u re 19 uses a steroid called bufotoxin as a defense mechanism. The toad secretes the toxin from warts on its back and from glands just behind the eye. The toxin is only an irritant for humans, but in small animals the toxin causes drooling, loss o f coordination, convulsions, and death. sFcnoN i REVIEW -I jy S e c t io n S u m m a r y 12. MAIIMIDEA Describe the function of lipids. • Fatty acids are long-chain carboxylic acids that usually have between 12 and 24 carbon atoms. 13. Describe the structures of fatty acids, triglycerides, phospholipids, and steroids. • Saturated fatty acids have no double bonds; unsaturated fatty acids have one or more double bonds. • Fatty acids can be linked to glycerol backbones to form triglycerides. • Steroids are lipids that have multiplering structures. 14. List an important function of each of these types of lipids. a. triglycerides b. phospholipids c. waxes d. steroids 15. Id e n tify two reactions that fatty acids undergo. 16. Describe the structure and function of cell membranes. 17. Com pare and contrast the structures of a steroid, a phospholipid, and a wax. 18. W rite the equation for the complete hydrogenation of the polyunsaturated fatty acid linoleic acid, CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH. 19. In te rp re t Scientific Illustrations Draw the general structure of a phospholipid. Label the polar and nonpolar portions of the structure. Section 3 • Lipids 839 Nucleic Acids SECTION 4 E s s e n tia l Q u e s tio n s M A IN ID E A • What are the structural components of nucleic acids? • How is the function of DNA related to its structure? • What are the structure and function of RNA? Nucleic acids store and transm it genetic inform ation. DNA testing is becoming more routine in medicine, forensic science, genealogy, and identification of victims in disasters. Modern techniques have m ade it possible to get a useful DNA sample from surprising sources, such as a strand of hair or dried saliva on a postage stamp. R e v ie w V o c a b u la r y genetic inform ation: an inherited Structure o f Nucleic Acids sequence of RNA or DNA that causes traits or characteristics to pass from one generation to the next Nucleic acids comprise a fourth class o f biological molecules. They are the information-storage molecules of the cell. This group o f molecules got its name from the cellular location in which the molecules are primarily found—the nucleus. It is from this control center o f cells that nucleic acids carry out their major functions. A n u c le ic a c id is a nitrogen-containing biological polymer that is involved in the storage and transmission of genetic information. The monomer that makes up a nucleic acid is called a n u c le o tid e . Each nucleotide has three parts: an inorganic phosphate group, a five-carbon monosaccharide sugar, and a nitrogen-containing structure called a nitrogenous base. Examine each part of F ig u re 2 0 a . Although the phosphate group is the same in all nucleotides, the sugar and the nitrogen base vary. In a nucleic acid, the sugar o f one nucleotide is bonded to the phosphate o f another nucleotide, as shown in F ig u re 2 0 b . Thus, the nucleotides are strung together in a chain, or strand, containing alternating sugar and phosphate groups. Each sugar is also bonded to a nitrogen base that sticks out from the chain. The nitrogen bases on adjoining nucleotide units are stacked one above the other in a slightly askew position, much like the steps in a staircase. This orientation is shown in F ig u re 2 0 b . Intermolecular forces hold each nitrogen base close to the nitrogen bases above and below it. N e w V o c a b u la r y nucleic acid nucleotide ■ F ig u re 2 0 Nucleotides are the monomers from which nucleic acid polymers are formed. o HI I o ii H O - P - O ---- CH? Hi H H VC /iH m C— ■ I OH I N itro g e n -c o n ta in in g base OH Sugar N u c le o tid e Each nucleotide contains a nitrogen-containing base, a five-carbon sugar, and a phosphate group. 840 b- L I H C hapter 23 • The Chemistry of Life o Phosphate 1 -i HO P hosphate g ro u p NH, - Sugar — Base Sugar f l - 1 Base Phosphate i I Phosphate aSugar sp Base N u c le ic a cid Nucleic acids are linear chains of alternating sugars and phos phates. Attached to every sugar is a nitrogen base. Because the nucleotides are offset, the chains resemble steps in a staircase. DNA: The Double Helix You might have heard o f DNA (deoxyribonucleic acid), one o f the two types o f nucleic acids found in living cells. DNA contains the master plans for building all the proteins in an organisms body. View an animation about the structure of DNA. T h e S t r u c t u r e o f D N A DNA consists of two long chains of nucleotides wound together to form a spiral structure, as shown in F ig u r e 2 1 . Each nucleotide in DNA contains a phosphate group, the five-carbon sugar deoxyribose, and a nitrogenous base. The alternating sugar and phosphate groups in each chain make up the outside, or backbone, o f the spiral structure. The nitrogen bases are on the inside o f the structure. Because the spiral structure is composed o f two chains, it is known as a double helix. DNA contains four different nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G). As F ig u r e 2 2 shows, both adenine and guanine contain a double ring. Thymine and cytosine are single-ring structures. Looking again at F ig u r e 2 2 , notice that each nitrogen base on one strand o f the helix is oriented next to a nitrogen base on the opposite strand, in the same way that the teeth o f a zipper are oriented. The side-by-side base pairs are close enough so that hydrogen bonds form between them. Because each nitrogen base has a unique arrangement o f organic functional groups that can form hydrogen bonds, the nitrogen bases always pair in a specific way so that the optimum number o f hydrogen bonds form. As F ig u r e 2 2 shows, guanine always binds to cytosine, and adenine always binds to thymine. The G -C and A -T pairs are called complementary base pairs. ■ F ig u r e 2 1 The structure of DNA is a double helix that resembles a twisted zipper. The two sugar-phosphate backbones form the outsides of the zipper. H READING CHECK D e s c rib e what forms the teeth of the DNA zipper. Because o f complementary base pairing, the amount of adenine in a molecule o f DNA always equals the amount of thymine, and the amount o f cytosine always equals the amount o f guanine. In 1953, James Watson and Francis Crick used this observation to make one o f the greatest scientific discoveries o f the twentieth century when they determined the double-helix structure o f DNA. They accomplished this feat without performing many laboratory experiments themselves. Instead, they analyzed and synthesized the work o f numerous scientists who had carefully carried out studies on DNA. ■ F ig u r e 2 2 In DNA, base pairing exists between a double-ringed base and a single ringed base. Adenine and thymine always pair, forming two hydrogen bonds between them. Guanine and cytosine always form three hydrogen bonds when they pair. Thymine Adenine Cytosine Guanine Section 4 • Nucleic Acids 841 T h e f u n c t io n o f D N A Watson and Crick used their model to predict how DNA’s chemical structure enables it to function. DNA stores the genetic information o f a cell in the cell’s nucleus. Before the cell divides, the DNA is copied so that the new generation o f cells gets the same genetic information. Having determined that the two chains of the DNA helix are complementary, Watson and Crick realized that complementary base pairing provides a mechanism by which the genetic material o f a cell is copied. The four nitrogenous bases o f DNA serve as the letters o f the alphabet in the information-storage language of living cells. The specific sequence o f these letters represents an organisms master instructions, just as the sequence o f letters in the words of this sentence convey special meaning. The sequence o f bases is different in every species o f organism, allowing for an enormous diversity o f life-forms—all from a language that uses only four letters. It is estimated that the DNA in a human cell has about three billion complementary base pairs, arranged in a sequence unique to humans. Problem-Solving LAB Formulate a M odel H o w d o e s D N A re p lic a te ? DNA replicates before a cell divides so that each of the tw o newly form ed cells has a complete set of genetic instructions. W hen DNA begins to replicate, the tw o nucleotide strands start to unzip. An enzyme breaks the hydrogen bonds between the nitrogenous bases, and the strands separate. Other enzymes deliver free nucleo tides from the surrounding medium to the exposed nitrogenous bases, adenine hydrogenbonding w ith thymine, and cytosine bonding w ith guanine. Thus, each strand builds a com plementary strand by base-pairing with free nucleotides. This process is shown in the top diagram at the right. W hen the free nucleotides have been hydrogen-bonded into place, their sugars and phosphates bond covalently to those on adjacent nucleotides to form the new backbone. Each strand of the original DNA molecule is now bonded to a new strand. A n a ly s is The bottom diagram shows a small segment of a DNA molecule. Copy the base sequence onto a clean sheet o f paper, being careful not to make copying errors. Show the steps of replica tion to produce tw o segments of the DNA. T h in k C ritic a lly 1. D e s c rib e how the base sequence of a newly synthesized strand compares with the original strand to which it is bonded. 842 C hapter 23 • The Chemistry of Life A T C G G T T A A A C G T A G C C A A T T T G C 1 1 2. E x p la in If the original DNA segment is colored red and the free nucleotides are colored blue, w hat pattern of colors w ill the newly replicated DNA segments have? W ill all new segments have the same color pattern? 3. E x p la in how an organism m ight be affected if an error occurs during replication of its DNA. Are the effects permanent? Explain. a. DNA b. RNA O HsC^ V H ^N H .H H 0 N' H I hr H D e o x y rib o s e T h y m in e O I H Ribose Uracil ■Fig u re 23 DNA and RNA differ in their components. The two structures on the left are found in DNA. The two structures on the right are found in RNA. Identify tw o differences in the structures o f RNA and DNA. RNA RNA (ribonucleic acid) is also a nucleic acid. Its general structure differs from that o f DNA in three important ways, as shown in Figure 23. First, as you have read, DNA contains the nitrogen bases adenine, . . , cytosine, guanine, and thymine. RNA contains adenine, cytosine, guanine, and uracil. Thymine is never found in RNA. Second, RNA contains the sugar ribose. DNA contains the sugar deoxyribose, which has a hydrogen atom in place o f a hydroxyl group at one position. The third difference between DNA and RNA is a result o f these structural differences. DNA is normally arranged in a double helix in which hydrogen bonding links the two chains together through their bases. RNA is usually single-stranded, with no such hydrogen bonds forming among the bases. Whereas DNA functions to store genetic information, RNA allows cells to use the information found in DNA. You have read that the genetic information o f a cell is contained in the sequence o f nitrogen bases in the DNA molecule. Cells use this base sequence to make RNA with a corre sponding sequence. The RNA is then used to make proteins, each with an amino-acid sequence that is determined by the order of nitrogen bases in RNA. The sequences o f bases are referred to as the genetic code. Because proteins are the molecular tools that carry out most activities in a cell, the DNA double helix is ultimately responsible for controlling the thousands o f chemical reactions that take place in cells. s f c t io n 4 dAlliM:lljLM Incorporate information s®[:t'on 'nt0 your Foldable, REVIEW .......M S e c tio n S u m m a r y 20. MAINIDEA Explain the primary function of RNA and DNA. • Nucleic acids are polymers of nucleotides, which consist of a nitrogen base, a phosphate group, and a sugar. 21. Id e n tify the specific structural components of both RNA and DNA. • DNA and RNA are the informationstorage molecules of a cell. • DNA is double stranded, and RNA is single stranded. 22. R elate the function of DNA to its structure. 23. R elate the function of RNA to its structure. 24. A nalyze the structure of nucleic acids to determine what structural feature makes them acidic. 25. Predict what might happen if the DNA that coded for a protein contained the wrong base sequence. Section 4 • Nucleic Acids 843 SECTION 5 Metabolism M A IN ID E A E s s e n tia l Q u e s tio n s • How do anabolism and catabolism compare? • What is the role of ATP in metabolism? • How can the processes of photosynthesis, cellular respiration, and fermentation be compared and contrasted? R e v ie w V o c a b u la r y redox process: a chemical reaction in which electrons are transferred from one atom to another N e w V o c a b u la r y metabolism catabolism anabolism ATP photosynthesis cellular respiration fermentation M etabolism involves m any thousands o f reactions in living cells. 4 YOU You have studied the four major kinds of biological molecules and learned that they are all present in the food you eat. What happens to these molecules after they enter your body? A n a b o lis m a n d C a ta b o lis m Many thousands o f chemical reactions take place in the cells o f a living organism. The set o f chemical reactions that occur within an organism is its m etabolism . Why are so many reactions involved in metabolism? Living organisms must accomplish two major functions in order to survive. They have to extract energy from nutrients in forms that they can use immediately as well as store for future use. In addition, they have to use nutrients to make building blocks for synthesizing all of the molecules needed to perform their life functions. These processes are summarized in Figure 24. The term catab olism refers to the metabolic reactions that break down complex biological molecules such as proteins, polysaccharides, triglycerides, and nucleic acids for the purposes o f forming smaller building blocks and extracting energy. After you eat a meal o f spaghetti and meatballs, your body immediately begins to break down the starch polymer in the pasta into glucose. The glucose is then broken down into smaller molecules in a series o f energy-releasing catabolic reactions. Meanwhile, the protein polymers in the meatballs are catabolized into amino acids. The term anabolism refers to the metabolic reactions that use energy and small building blocks to synthesize the complex molecules needed by an organism. After your body has extracted the energy from the starch in the pasta, it uses that energy and the amino-acid building blocks produced from the meat proteins to synthesize the specific proteins that allow your muscles to contract, catalyze metabolic reactions, and perform many other functions in your body. ■Figure 24 A large number of different metabolic reactions take place in living cells. Some involve breaking down nutrients to extract energy; these are catabolic processes. Others involve using energy to build large biological molecules; these reactions are anabolic processes. Describe Choose one food that you ate recently, and describe how it was metabolized. Carbohydrates Fats Proteins 844 Complex cellular molecules Interm ediate products Nutrients ingested Catabolism (nutrients broken down) C h a p te r 23 • The Chemistry of Life Amino acids Simple sugars Fatty acids Nucleotides ATP V.________________________ Anabolism (new molecules / synthesized) Proteins Polysaccharides Triglycerides Nucleic acids ADP + P Adenine Triphosphate group h 2o Ribose Adenine Diphosphate group + Ribose A + -Energy' Phosphate ADP ■ F ig u re 2 5 The breakdown of ATP provides energy for cellular processes in living organisms. E x p la in w here the energy is stored in ATP. F ig u re 2 4 shows the relationship between catabolism and anabolism . T h e nutrients listed on the left side o f the diagram are broken down into interm ediate products. These interm ediate products are used as building blocks for the products listed on the right side o f the diagram . A nother way o f conceptualizing this process is to view the nutrients ingested as the raw m aterials for the com plex cellular m olecules form ed in a living organism. V o cabulary ..................................... A c a d e m ic v o c a b u l a r y Conceptualize visualizing or conceiving an abstract idea in the mind The a to m ic c lo u d m o d e l is h a rd to con cep tu alize ........................................ □ READING CHECK E x p la in how the terms m eta b o lism , cata b o lism , and ! a n a b o lism are related. A T P C atabolism and anabolism are linked by com m on building blocks that catabolic reactions produce and anabolic reactions use. A com m on form o f potential chem ical energy also links the two processes, as shown in F ig u re 2 5 . A T P (adenosine triphosphate) is a nucleotide that func tions as the universal energy-storage m olecule in living cells. During catabolic reactions, cells harness the chem ical energy o f foods and store it in the bonds o f ATP. W h en these bonds are broken, the chem ical energy is released and used by cells to drive anabolic reactions that m ight not otherw ise occur. M ost cellular reactions have an efficiency o f only about 40% at best; the rem aining 60% o f the energy in food is lost as heat, which your body uses to keep warm. D uring catabolic reactions, cells produce ATP by adding an inor ganic phosphate group to the nucleotide adenosine diphosphate (ADP) in an endotherm ic reaction. O ne m ole o f ATP stores approximately 30.5 k j o f energy under norm al cellular conditions. D uring anabolism, the reverse reaction occurs. ATP is broken down to form ADP and inorganic phosphate in an exotherm ic reaction. Approximately 30.5 k j o f energy is released from each m ole o f ATP. Q READING CHECK D escribe what occurs when ATP becomes ADP. Section 5 • Metabolism 845 P h o to s y n th e s is What is the source of energy that fuels metabolism? For most living things, including the grass shown in F ig u r e 2 6 , certain wavelengths of sunlight provide this energy. Some bacteria and the cells o f all plants and algae are able to capture light energy and convert some o f it into chemical energy. Animals cannot capture light energy, so they get energy by eating plants or by eating other animals that eat plants. The process that converts energy from sunlight to chemical energy in the bonds o f carbohydrates is called photosynthesis. During the complex process o f photosynthesis, carbon dioxide and water yield a carbohy drate (glucose) and oxygen gas. The following net reaction takes place during photosynthesis. 6C 02 + Carbon dioxide 6H 20 Water + light energy —> C 6 H 120 6 Glucose + 602 Oxygen Photosynthesis results in the reduction o f the carbon atoms in carbon dioxide as glucose is formed. During this redox process, oxygen atoms in water are oxidized to oxygen gas. ■ F ig u r e 2 6 Grass and other green plants use certain wavelengths of sunlight as an energy source. Other living organ isms, such as cows, obtain energy by eating plants or eating other organisms that eat plants. Get help with photosynthesis and respiration. C e llu la r R e s p ira tio n Most organisms need oxygen to live. Oxygen that is produced during photosynthesis is used by living things during cellular resp iration , the process in which glucose is broken down to form carbon dioxide, water, and large amounts o f energy. Cellular respiration is the major energyproducing process in living organisms. F ig u r e 2 7 shows one use of energy in the body. This energy is stored in the bonds o f ATP. Cellular respiration is a redox process; the carbon atoms in glucose are oxidized while oxygen atoms in oxygen gas are reduced to the oxygen in water. The net reaction that takes place during cellular respiration is as follows. C 6H i 20 6 Glucose + 602 -> Oxygen 6C 02 Carbon dioxide + 6H 20 Water + energy ■ F ig u r e 2 7 Swimmers need large amounts of energy when they compete in a (t)DLILLC/CORBlS, (b)AP Photo/Joe Cavaretta race. This energy is stored in the bonds of ATP in their cells. 846 C hapter 23 • The Chemistry of Life ■Figure 28 Carbon dioxide formed during fermentation, leaves holes in the bread. These holes give bread a light, lessdense texture. Ferm entation D uring cellular respiration, glucose is com pletely oxidized, and oxygen gas is required to act as the oxidizing agent. Cells can extract energy from glucose in the absence o f oxygen, but not nearly as efficiently. W ith ou t oxygen, only a fraction o f the chem ical energy o f glucose can be released. W hereas cellular respiration produces 38 m ol o f ATP for every 1 m ol o f glucose catabolized in the presence o f oxygen, only 2 m ol o f A TP are produced per m ole o f glucose that is catabolized in the absence o f oxygen. T h is provides enough energy for oxygen-deprived cells so that they do n ot die. T h e process by which glucose is broken down in the absence o f oxygen is known as fe rm e n ta tio n . There are two com m on kinds o f ferm entation. In one, ethanol and carbon dioxide are produced. In the other, lactic acid is produced. A lc o h o lic f e r m e n t a t i o n Yeast and som e bacteria can ferm ent glucose to produce the alcohol ethanol. c 6H12o6 2 C H 3 C H 2OH G lucose Ethanol + 2C 02 + C arbon dioxide CAREERS IN rCHEMISTRY-------Baker Using a variety of chemical processes to create tasty and often beautiful creations is the job of a baker. Not only do breads and doughnuts undergo fermentation processes, but cakes and other pastries are often acid-base reactions. energy T h is reaction, called alcoholic ferm entation, is im portant in producing som e foods, as shown in Figure 28. A lcoholic ferm entation is needed to m ake bread dough rise, form tofu from soybeans, and produce the ethanol in alcoholic beverages. A nother use o f the ethanol is as an additive to gasoline, as shown in Figure 29. ■Figure 29 Ethanol is often added to gasoline and used as a fuel in some cars and trucks. Ethanol is made from grain. Explain how the use o f ethanol can reduce the dependence on fossil fuels. N O T G ASO LINE E -85 for use in Flexil Fuel Vehicles (F FV s) < Please consult your ve owner’s manual or store if you need assistan TO SEE IF YOUR VEHI Section 5 • Metabolism 847 ■ F ig u re 3 0 During strenuous activity, oxygen can be depleted in cells. Then, energy is produced without oxygen and lactic acid is produced. Soreness in muscles a day or two after the activity is a sign of lactic acid formation. L a c tic a c id f e r m e n t a t i o n Have you ever experienced muscle fatigue while running a race, like the person shown in F ig u re 3 0? D uring strenuous activity, m uscle cells often use oxygen faster than it can be supplied by the blood. W hen the supply o f oxygen is depleted, cellular respiration stops. Although anim al cells cannot undergo alco holic ferm entation, they can produce lactic acid and a small amount o f energy from glucose through lactic acid ferm entation. C 6 H 120 6 Glucose -> 2C H 3 C H (O H )C O O H Lactic acid + energy T he lactic acid that is produced is moved from the muscles through the blood to the liver. There, it is converted back into glucose that can be used in catabolic processes to yield m ore energy once oxygen becom es available. However, if lactic acid builds up in muscle cells at a faster rate than the blood can remove it, muscle fatigue results. An im m ediate burning sensation and soreness a few days later is an indica tion that lactic acid was produced in the muscles during exercise. s e c t io n s REVIEW S e c tio n S u m m a r y 26. MAINIDEA Explain why metabolism is important to living cells. • Living organisms undergo catabolism and anabolism. 27. Com pare and contrast the processes of anabolism and catabolism. • Photosynthesis directly or indirectly provides almost all living things with energy. 29. Com pare and contrast the processes of photosynthesis, cellular respiration, and fermentation. • The net equation for cellular respiration is the reverse of the net equation for photosynthesis. 28. Explain the role of ATP in the metabolism of living organisms. 30. D e te rm in e whether each process is anabolic or catabolic. a. photosynthesis b. cellular respiration c. fermentation 31. E valuate Why is it necessary to use sealed casks when making wine? 32. Calculate How many moles of ATP would a yeast cell produce if 6 mol of glucose were oxidized completely in the presence of oxygen? How many moles of ATP would the yeast cell produce from 6 mol of glucose if the cell were deprived of oxygen? 848 C hapter 23 • The Chemistry of Life careers Career: Molecular Paleontologist Acid Test Reveals Surprise "N o righ t-th in kin g paleontologist w ould do w h a t M ary did. W e d o n 't go to all this effort to dig this stu ff ou t o f the ground and then destroy it in acid." So says a colleague about Mary Schweitzer, the scientist w ho used the tech niques o f m olecular biology to discover soft tissue w here none should be— in the thighbone o f a 68-m illion-year-old T y ra n n o s a u ru s re x. Figure 2 Scientists also found blood vessels and individual cells in the soft tissue of the T. rex. M o th e r B ob W hen the fossilized T. re x, The a cid te s t To study the m edullary bone nicknam ed Bob, was recovered by paleontolo gists in 2003 from a rem ote section o f M ontana, the bones w ere encased in plaster fo r protection during transport. However, the bones and plaster w eighed more than the helicopter could lift. So the paleontologists w ere forced to break the intact thig h b on e to move the dinosaur out o f the rem ote area. Schweitzer to o k small fragm ents from the broken thighbone fo r fu rth er study. more closely, Schweitzer dissolved fragments o f the bone in dilute acid to remove calcium phosphate— a technique norm ally used to examine fresh tissue. Because a fossilized bone has usually m ineralized, it was assumed that the bone w ould com pletely dissolve in dilute acid. Yet this step yielded astonishing results— w ithin the bone was soft tissue. Under the microscope, the tissue showed w hat looked like preserved blood vessels and even individual cells, as shown in F ig u re 2. But how could soft tissue have survived 68 m illion years in the ground? The first surprise came quickly. "B ob " was a fem ale, and she had been producing eggs at the tim e o f her death. The bone Schweitzer studied is called m edullary bone. Previously, this bone tissue was know n only in birds, as shown in F ig u re 1. O vulating hens produce m edullary bone, then later use the calcium stored in the bone to make eggshells. A fte r egg production, the bone disappears. F ig u re 1 shows the m edul lary bone fo u n d in the T. rex thighbone. Figure 1 The hen bone and T. rex bone both have a hard outer bone called cortical bone (CB) and softer medullary bone (MB). M o re w o r k Schweitzer has since subjected other bones to the same acid test, and found sim ilar soft tissue and fine structures. No one knows yet just w hat these fine structures are showing, but, says a colleague, "there may be a lot o f things out there that we've missed because of our assumption of how preservation works." Clearly, more research is needed. W R ITIN G iN ^C hem istry Persuasive W ritin g It is u n lik e ly th a t d in o s au r D N A w ill be fo u n d in th es e s o ft tissues. Even so, th e discovery brings u p th e q u estio n : S hould e x tin c t anim als be cloned fro m recovered D N A ? W rite a persuasive essay expressing y o u r o p in io n . 39 Chemistry & Careers 849 ChemLAB Observe Temperature and Enzyme Action B a c k g ro u n d : Enzymes are natural catalysts used by living things to speed reactions. These proteins have specialized structures that enable them to interact with specific substances. Q u e s tio n : How does temperature affect the action of enzymes? D ata Table Water Bath Temperature (°C) Height of Foam (cm) Potato Ice water Room-temperature water M aterials red-skin potato pulp hydrogen peroxide (3% H 2 O 2 ) water 250-m L beaker (4) test tubes (4) test-tube rack test-tube clamp 25-m L graduated cylinder therm om eter ice ruler clock hot plate raw fresh liver pulp Safety Precautions Procedure i t Read and complete the lab safety form. 2. Write a hypothesis that identifies the temperature at which the enzymes are the m ost active. 3. Copy the data table on a separate sheet o f paper. 4. Place the four test tubes in the test-tube rack. 5. Measure and place 2.0 mL o f red-skin potato pulp into each test tube. 6 . Using the hot plate and ice, prepare water baths in the beakers at four different temperatures: ice water, room-temperature water, body-temperature water, and gently boiling water at or near 100°C. 7. Place one test tube in each water bath using a test-tube clamp. 8 . Measure and record the temperature o f each water bath. 9. After 5 min in the water baths, measure and place 5.0 mL of 3% H 2O 2 in each test tube. 10. Allow the reaction to proceed for 5 min. 11. Measure the height o f the foam produced in each test tube. 12. Dispose o f the contents of the test tubes as directed by your teacher and wash the test tubes. 13. Repeat Steps 4 -1 2 using 2.0 mL of beef liver pulp instead o f potato pulp. 850 C h a p te r 23 • The Chemistry of Life Body-temperature water Boiling water (near 100°C) Liver Ice water Room-temperature water Body-temperature water Boiling water (near 100°C) 14. Cleanup and Disposal Dispose o f the remaining solutions as directed by your teacher. Wash and return all lab equipment to its designated location. Analyze and Conclude 1. Make and Use Graphs Make a line graph with temperature on the x-axis and height o f foam on the y-axis. Use a different color for the potato and liver data points and lines. 2. Summarize How does temperature affect the action o f enzymes? Infer why the maximum reaction occurred at the temperature in which it did for the potato and liver. 3. Recognize Cause and Effect W hich water bath produced the least amount o f foam for each mate rial? Propose explanations for why this happened. 4. Com pare and Contrast Did the experimental data support your hypothesis in Step 2? Explain. 5. Model Write a balanced reaction for the decompo sition o f hydrogen peroxide for each reaction. How are the reactions similar? Infer why they are similar. 6. E rro r Analysis Identify potential sources o f errors for this investigation and suggest methods to correct them. INQUIRY EXTENSION Design an Experiment Would a change in pH affect the results? Design an experiment to find out. BIGIDEA Biological molecules— proteins, carbohydrates, lipids, and nucleic acids— interact to carry out activities necessary to living cells. MAIIMIDEA Proteins perform essential functions, including regulation of chemical reactions, structural support, transport of materials, and muscle contractions. • Proteins are biological polymers made of amino acids that are linked by peptide bonds. • Protein chains fold into intricate three-dimensional structures. • Proteins have many functions in the human body, including functions within cells, functions between cells, and functions of structural support. sectio n 2 VOCABULARY • • • • • • • • protein amino acid peptide bond peptide denaturation enzyme substrate active site C arb o h y d rate s MAIIMIDEA Carbohydrates provide energy and structural material for living things. VOCABULARY • Carbohydrates are compounds that contain multiple hydroxyl groups (-OH) and a carbonyl functional group (C = 0 ). • • • • • Carbohydrates range in size from single monomers to polymers composed of hundreds or thousands of monomers. carbohydrate monosaccharide disaccharide polysaccharide • Monosaccharides in aqueous solution exist in both open-chain and cyclic structures. lipids______ SECTION 3 MAIIMIDEA Lipids make cell membranes, store energy, and regulate cellular processes. • Fatty acids are long-chain carboxylic acids that usually have between 12 and 24 carbon atoms, • Saturated fatty acids have no double bonds; unsaturated fatty acids have one or more double bonds. • Fatty acids can be linked to glycerol backbones to form triglycerides. • Steroids are lipids that have multiple-ring structures. MAIIMIDEA Nucleic acids store and transmit genetic information. • Nucleic acids are polymers of nucleotides, which consist of a nitrogen base, a phosphate group, and a sugar. . DNA and RNA are the information-storage molecules of a cell. VOCABULARY • • • • • • • lipid fa tty acid triglyceride saponification phospholipid wax steroid VOCABULARY • nucleic acid • nucleotide . DNA is double stranded, and RNA is single stranded. s f c t i o n 5 M e ta b o lism--------MAIIMIDEA Metabolism involves many thousands of reactions in living cells. VOCABULARY • Living organisms undergo catabolism and anabolism. . Photosynthesis directly or indirectly provides almost all living things with energy. • metabolism • catabolism • anabolism . The net equation for cellular respiration is the reverse of the net equation for photosynthesis. • ATP • photosynthesis • cellular respiration • ferm entation C h a p te r 23 • Study Guide SECTION 1_____ M astering Concepts 33. What should you call a chain of eight amino acids? A chain of 200 amino acids? 34. Name the two types of functional groups that react together to form a peptide bond, and name the functional group in the peptide bond itself. 35. Using the symbols below to represent four amino acids, draw peptide structures for four-member chains that link them together in different orders. Amino acid 1 :B Amino acid 3: ♦ Amino acid 2: A Amino acid 4: • 36. Human Anatomy Name five parts of the body that contain structural proteins. 37. List four major functions of proteins, and give one example of a protein that carries out each function. 46. Cellular Chemistry Most proteins with a globular shape are oriented so that they have mostly amino acids with nonpolar side chains located on the inside and amino acids with polar side chains located on the outer surface. Does this make sense in terms of the nature of the cellular environment? Explain. M astering Problems 47. How many different ways can you arrange three different amino acids in a peptide? Four amino acids? Five amino acids? 48. How many peptide bonds are present in a peptide that has five amino acids? 4 9 . Proteins The average molecular weight of an amino acid residue in a polypeptide is 110 amu. What is the approximate molecular weight of the following proteins? a. Insulin (51 amino acids) b. Myosin (1750 amino acids) OH 38. Describe two common shapes found in the threedimensional folding of proteins. 39. Name the organic functional groups in the side chains of the following amino acids. a. glutamine c. glutamic acid b. serine d. lysine 40. Explain how the active site of an enzyme functions. 4 1 . Name an example of an amino acid that has an aromatic ring in its side chain. 42. Name two amino acids with nonpolar side chains and two amino acids with polar side chains. Q I NH I OH h 3c I CH, \ / CH 3 H H I I -N- -C - -C- -N - C — C I II I II H o SH ch3 H I CH2 CH, H H O H II -N -C -C -O H N -C -C I O I O I H ■ Figure 32 50. Determine how many amino acids and peptide bonds are in the peptide shown in Figure 32. 51. The average molar mass of an amino acid is llOg/mol. Calculate the approximate number of amino acids in a protein that has a molar mass of 36,500 g/mol. c = ^ I SECTION 2 ch, h 2n - c- c- oh I H II O ■ Figure 31 43. The structure shown in Figure 31 is tryptophan. Describe some of the properties you would expect tryptophan to have, based on its structure. In what class of large molecules is tryptophan a member? Explain. 44. Is the dipeptide lysine-valine the same compound as the dipeptide valine-lysine? Explain. 45. Enzymes How do enzymes lower the activation energy for a reaction? 852 C h a p te r 23 • The Chemistry of Life M astering Concepts 52. Carbohydrates Classify the following carbohydrates as monosaccharides, disaccharides, or polysaccharides. a. starch d. ribose g. fructose b. glucose e. cellulose h. lactose c. sucrose f. glycogen 53. Name two isomers of glucose. 54. What kind of bond is formed when two monosaccha rides combine to form a disaccharide? 55. Sugars Give a scientific term for each of the following. a. blood sugar c. table sugar b. fruit sugar d. milk sugar SECTION 3_________ M astering Concepts 66 . Compare and contrast the structures of a triglyceride Cellulose and a phospholipid. Starch 67. Predict whether a triglyceride from beef fat or a triglyceride from olive oil will have a higher melting point. Explain your reasoning. 68. Soaps and Detergents Explain how the structure of soaps makes them effective cleaning agents. 69. Draw a portion of a lipid bilayer membrane, labeling the polar and nonpolar parts of the membrane. ■ F ig u re 33 56. Cellulose and Starch The molecular structures of cellulose and starch are shown in Figure 33. Compare and contrast their molecular structures. 57. Chemistry in Plants Compare and contrast the func tions of starch and cellulose in plants. Explain why their molecular structures are important to their functions. 58. Infer how the different bonding arrangements in cellulose and starch give them such different properties. 59. The disaccharide maltose is formed from two glucose monomers. Draw its structure. 70. Where and in what form are fatty acids stored in the human body? 71. What type of lipid does not contain fatty acid chains? Why are these molecules classified as lipids? 72. Soap Draw the structure of the soap sodium palmitate (palmitate is the conjugate base of the 16-carbon saturated fatty acid, palmitic acid). Label its polar and nonpolar ends. 73. Determine whether each structure is a fatty acid, triglyceride, phospholipid, steroid, or wax. Explain your reasoning. 60. The hydrolysis of cellulose, glycogen, and starch produces only one monosaccharide. Why is this so? What monosaccharide is produced? 61. Digestion Disaccharides and polysaccharides cannot be broken down in the absence of water. Why do you think this is so? Include an equation in your answer. 62. Draw the structure of the open-chain form of fructose. Circle all chiral carbons, and then calculate the number of stereoisomers with the same formula as fructose. 63. Sugars Compare and contrast the molecular formula, molecular weight, and functional groups found in glucose and fructose. 64. Historical Perspective Carbohydrates are not hydrates of carbon as the name suggests. Explain how this misconception occurred. M astering Problems 65. Complex Carbohydrates Stachyose is a tetrasaccharide that contains two D-galactose units, one D-glucose unit, and one D-fructose unit. Each sugar unit has a molecular weight of 180 g/mol before it is linked together in this tetrasaccharide, and one water molecule is released for each two sugar units that come together. What is the molecular weight of stachyose? 0 b - O - P11 - O — c h 2 1 O o I II CH — O — C - CH2 o h 2c II - o - c- ch2 M astering Problems 74. The fatty acid palmitic acid has a density of 0.853 g/mL at 62°C. What will be the mass of a 0.886-L sample of palmitic acid at that temperature? 75. Polyunsaturated Fats How many moles of hydrogen gas are required for complete hydrogenation of 1 mol of linolenic acid, whose structure is shown below? Write a balanced equation for the hydrogenation reaction. CH3CH2CH = (CHCH2CH) 2 = CH(CH2)7COOH C h a p te r 23 • Assessment 853 SECTION 4____ 87. How many grams of glucose can be oxidized completely by 2.0 L of O 2 gas at STP during cellular respiration? M astering Concepts 76. What three structures make up a nucleotide? 77. Name two nucleic acids found in organisms. 78. Explain the roles of DNA and RNA in the production of proteins. 79. Where in living cells is DNA found? 80. Describe the types of bonds and attractions that link the monomers together in a DNA molecule. 88. Life Processes Compare the net reactions for photo synthesis and cellular respiration with respect to reactants, products, and energy. MIXED REVIEW_________ 89. Draw the carbonyl functional groups present in glucose and fructose. How are the groups similar? How are the groups different? 9 0. List the names of the monomers that make up proteins, complex carbohydrates, and nucleic acids. 9 1. Describe the functions of proteins, carbohydrates, lipids, and nucleic acids in living cells. A Adenine Q Cytosine U Uracil Q Guanine 9 2. Write balanced equations for photosynthesis, cellular respiration, and the hydrolysis of lactose. 9 3. Write a balanced equation for the synthesis of sucrose ■ Figure 34 from glucose and fructose. 81. Classify the nucleic acid structure shown in Figure 34 as DNA or RNA and explain your reasoning. 82. In the double-helical structure of DNA, the base guanine is always bonded to cytosine, and adenine is always bonded to thymine. What do you expect to be the relative proportional amounts of A, T, C, and G in a given length of DNA? 83. DNA Replication One strand in a DNA molecule has the following base sequence. What is the base sequence of the other strand in the DNA molecule? C-C-G-T-G-G-A-C-A-T-T-A Mastering Problems 84. A triplet code is a sequence of three bases in RNA that codes for one amino acid in a peptide chain or protein. How many RNA bases are required to code for a protein that contains 577 amino acids? 85. DNA Comparisons A cell of the bacterium E sch erichia c o li has about 4.2 x 106 base pairs of DNA, whereas each human cell has about 3 X 109 base pairs of DNA. What percentage of the size of the human genome does the E. c o li DNA represent? SECTION 5______________ Mastering Problems 86. Energy Calculate and compare the total energy in kj that is converted to ATP during the processes of cellular respiration and fermentation. 854 C h a p te r 23 • The Chemistry of Life THINK CRITICALLY 9 4. Make and Use Graphs A number of saturated fatty acids and values for some of their physical properties are listed in Table 2. a. Make a graph plotting melting point versus number of carbon atoms. b. Graph density versus the number of carbon atoms. c. Draw conclusions about the relationships between the number of carbon atoms in a saturated fatty acid and its density and melting point values. d. Predict the approximate melting point of a saturated fatty acid that has 24 carbon atoms. T a b le 2 Physical Properties of Saturated Fatty Acids Number of Carbon Atoms Melting Point (°C) Density (g/mL) (values at 60-80°C ) Palmitic acid 16 63 0.853 Myristic acid 14 58 0.862 Arachidic acid 20 77 0.824 Caprylic acid 8 16 0.910 Docosanoic acid j 22 80 0.822 Stearic acid 18 70 0.847 Laurie acid 12 44 0.868 Name 9 5. Calculate Approximately 38 mol of ATP are formed when glucose is completely oxidized during cellular respiration. If the heat of combustion for 1 mol of glucose is 2.82 x 103 kJ/mol and each mole of ATP stores 30.5 kJ of energy, what is the efficiency of cellular respiration in terms of the percentage of available energy that is stored in the chemical bonds of ATP? 9 6. Recognize Cause and Effect Some diets suggest severely restricting the intake of lipids. Why is it not a good idea to eliminate all lipids from the diet? I/VRITINGin ^ Chem istry 103. Cholesterol Use the library or the Internet to research cholesterol. Write a newspaper article about cholesterol that is written for a teenage audience. Make sure the following questions are answered in the article. Where is this molecule used in your body? What is its function? Why is too much dietary cholesterol considered to be bad for you? Is genetics a factor in high cholesterol? E Q a Document-Based Questions Fatty Acids O m ega-3 a n d o m ega-6 f a t t y acids are f a t t y acids th a t g e t th e ir nam es f r o m th e ir structures. T hey c o n ta in a d o u b le b o n d e ith e r three o r s ix carbo n ato m s f r o m the end o f the f a t t y a c id cha in. These f a t t y acids have a b e n e fic ia l effect on h e a lth because the y lo w e r b a d cholesterol levels a n d raise g o o d cholesterol levels in the blood. Levels o f om ega-3 a n d o m ega-6 f a t t y acids w ere s tu d ie d in sa lm o n fr o m three d iffe r e n t sources as w e ll as in the fe e d used in sa lm o n fa rm in g . ■ F ig u re 35 9 7. Analyze Insulin is a protein that functions as an important hormone in the human body. People who are diabetic often do not produce enough insulin, and must inject themselves with an insulin solution to maintain their health. Use Figure 35 to infer how a person should care for a bottle of insulin. Figure 36 shows the p e rc e n t o f om ega-3 a n d o m eg a-6 f a t t y a cids c o m p a re d to the to ta l a m o u n t o f lip id s in the samples. Data obtained from: Hamilton, M.C. et al. 2005. Environmental Science Technology 39:8622-8629. Concentration of Fatty Acids A 0m ega-3 acid 9 8. Calculate If a double-stranded section of DNA has adenine as 2 0 % of its bases, what percent of the other three bases are present in the DNA strand? CHALLENGE PROBLEM 9 9. Calculate how many moles of ATP a human body can produce from the sugar in a bushel of medium-sized Red Delicious apples. Use the Internet to find the information you need to solve this problem. 10 CIIMIII ATIVE R E V I E W ______ 100 . a. Write the balanced equation for the synthesis of ethanol from ethene and water, b. If 448 L of ethene gas reacts with excess water at STP, how many grams of ethanol will be produced? 101. Identify whether each of the reactants in these reactions is acting as an acid or a base. a. HBr + H20 —» H 30 + + Br~ b. NH 3 + HCOOH —» NH4+ + HCOCT c. h c o 3_ + H20 —> c o 32 - + H 30 + 20 30 Percent lipids ■ Figure 36 104. Which type of fish had the most omega fatty acids? 105. Based on this study, which type of salmon would you recommend to people who want to maximize the amounts of omega-3 and omega-6 fatty acids in their diets? 106. Infer from the graph why the farm-raised and supermarket salmon contains more omega-3 and omega-6 fatty acids than wild salmon. 1 02 . What is a voltaic cell? C h a p te r 23 • Assessment 855 1. W hich is N O T true o f carbohydrates? 4. A. Monosaccharides in aqueous solutions convert continuously between an open-chain structure How much NaOH, in grams, is required to completely neutralize 50.0 mL o f 0.100M HCl? A. 0.200 g B. 5.00 g and a cyclic structure. B. The monosaccharides in starch are linked together by the same kind o f bond that links the C. 0.125 g D. 2 0 0 g m onosaccharides in lactose. C. All carbohydrates have the general chemical formula C „(H 20 )„ . D. Cellulose, made only by plants, is easily digestible Use th e ta b le b e lo w to a n s w e r Q u e s tio n s 5 to 7. Nucleotide Data for Samples of Double-Stranded DNA by humans. 7 165 231 D 7 2. W hich is N O T a difference between RNA and DNA? number A. DNA contains the sugar deoxyribose, while RNA percent 20.8 7 29.2 7 contains the sugar ribose. B. RNA contains the nitrogen base uracil, while number ? 402 7 7 percent ? 32.5 ? 7 number 7 7 194 234 percent ? 7 22.7 27.3 203 7 7 7 7 DNA does not. C. RNA is usually single-stranded, while DNA is usually double-stranded. D. DNA contains the nitrogen base adenine, while RNA does not. number percent 266 28.4 21.6 U se th e g r a p h b e lo w to a n s w e r Q u e s tio n 3. 50.0 mL 0.100M HCl Titrated with 0.100M NaOH 5. W hat is the % T o f Sample IV? A. 28.4% C. 71.6% B. 78.4% D. 21.6% 6 . Every nitrogen base found in a DNA molecule is part o f a nucleotide o f that molecule. The A nucleotide, C nucleotide, G nucleotide, and T nucleotide have molar masses o f 347.22 g/mol, 323.20 g/mol, 363.23 g/mol, and 338.21 g/mol respectively. What is the mass o f 1 mol o f Sample I? A. 2.79 X 10 5 g C. 2.6390 X 10 5 g B. 2.7001 X 105 g D. 2.72 X 105 g 7. How many molecules o f adenine are in one molecule Volum e NaOH added (mL) 3. W hich chemical indicator would be most effective in identifying the equivalence point of this titration? A. methyl orange, pH range o f 3.2—4.4 B. phenolphthalein, pH range o f 8 .2 -1 0 C. thymol blue, pH range o f 8 .0 - 9 .6 D. bromothymol blue, pH range of 6.0—7.6 856 C h a p te r 23 • The Chemistry of Life o f Sample II? A. 402 B. 434 C. 216 D. 175 8 . W hich is not a structural isomer of C H 2 = C H C H 2C H = C H C H 3? A. C H 2 = C H C H 2C H 2C H = C H 2 B. C H 3C H = C H C H 2C H = C H 2 C. c h 3c h = c h c h = c h c h 3 d. c h 2 = c = c h c h 2c h 2c h 3 SAT SUBJECT TEST: CHEMISTRY 9. The sequence o f bases in RNA determ ines the U se th e ta b le b e lo w to a n s w e r Q u e s tio n s 1 5 -1 7 . sequence o f am ino acids in a protein. Three bases D ata fo r Elem ents in th e Redox Reaction code for a single am ino acid; for example, CAG is Zn + H N 0 3 - > Z n (N 0 3)2 + N 0 2 + H20 the code for glutamine. How many am ino acids are coded for in a strand o f RNA 2.73 x 10 4 bases long? U se th e d ia g r a m b e lo w to a n s w e r Q u e s tio n 10. Zn O II ChUChUCH, -C- -H 0 none Zn in Zn(N03)2 + 2 none H in HN03 +1 none H in H20 10. W hich type o f functional group is in this none N in HN03 compound? N in N02 U se th e d ia g r a m b e lo w to a n s w e r Q u e s tio n 11. ? no 3- +4 none N in Zn(N03)2 H H Br H H I I I I 0 in HN03 I F—C —C —C —C—C —H I I I H I n ° 3- I Cl H Br H —2 no 3- 0 in N02 ? none 0 in Zn(N03)2 7 no 3- 0 in H20 11. Give the IUPAC nam e for this organic compound. 12. W hat is the condensed structural formula of none - 2 15. W hich element forms a monatomic ion that is a spectator in the redox reaction? heptane? A. EXTENDED RESPONSE Zn D. H B. O C. N U se th e d ia g r a m b e lo w to a n s w e r Q u e s tio n 13. E. 0 2 16. W hat is the oxidation number o f N in Zn(N 0 3) 2 ? c — A. B. c — c — c — c c +1 +2 D. + 5 E. + 6 C. + 3 c—c 13. A student records the name o f the alkane represented 17. W hat is the element that is oxidized in this reaction? by this carbon skeleton as 2 -ethyl 3 ,3 -dimethyl pentane. Evaluate whether this is the correct name A. B. C. D. E. for the compound. 14. Compare and contrast aliphatic and aromatic compounds. Zn O N H o 3 NEED EXTRA HELP? If You Missed Q uestion. . . Review Section . . . 1 2 3 4 5 6 23.2 23.4 19.4 19.4 23.4 23.4 23.4 8 9 10 11 12 13 14 15 16 17 21.4 23.4 22.1 23.1 21.2 21.2 21.5 9.3 19.1 19.1 C h a p te r 23 • Assessment 857 R IP in F A Nuclear chemistry has a vast range of applications, from the production of electricity to the diagnosis and treatment of diseases. 1 Nuclear Radiation 2 Radioactive Decay 3 Nuclear Reactions 4 A pplications and Effects o f Nuclear Reactions How do chain reactions occur? When the products of one nuclear reaction cause additional nuclear reactions to occur, the resulting chain reaction can release large amounts of energy in a short period of tim e. In this lab, you w ill explore chain reactions by modeling them w ith dominoes. There's a good chance that you or someone you know has been helped by nuclear chemistry. From the magnetic properties of protons that enable MRIs, to the radiation used in X-rays, PET scans, and hundreds of other tests and treatments, research in nuclear chemistry has resulted in some of the most powerful tools available to modern medicine. ypes of Radiation lake a layered-look book. Label it as shown, se it to help you organize inform ation about le different types of radiation. i l S R ! ■if'"'■ ' , ‘t ■*’> ' ’^1 connectED.nicaraw-hill.com SECTION 1 E s s e n tia l Q u e s tio n s • How was radioactivity discovered and studied? • What are the key properties of alpha, beta, and gamma radiations? R e v ie w V o c a b u la r y nucleus: the extremely small, posi tively charged, dense center of an atom that contains positively charged protons, neutral neutrons, and is surrounded by empty space through which one or more negatively charged electrons move N e w V o c a b u la r y radioisotope X-ray penetrating power T a b le Nuclear Radiation M A I N I D E A Under certain conditions, some nuclei can e m it alpha, beta, or gam m a radiation. CH EM 4 YOU T h e D is c o v e ry o f R a d io a c tiv ity You have studied various form s o f chem ical reactions. Atoms can gain, lose, or share valence electrons, but the identity o f the atoms does not change. Nuclear reactions, which you will study in this chapter, are different. Nuclear chem istry is concerned with the structure o f atomic nuclei and the changes they undergo. W hereas chem ical reactions involve only small energy changes, nuclear reactions involve much larger energy changes. T a b le 1 offers a com parison o f chem ical reactions and nuclear reactions. In 1895, Germ an physicist W ilhelm Roentgen (1 8 4 5 -1 9 2 3 ) found that invisible rays were emitted when electrons bom barded the surface o f certain materials. These invisible rays caused photographic plates to darken, and Roentgen named these high-energy emissions X - r a y s . At that time, French physicist H enri Becquerel (1 8 5 2 -1 9 0 8 ) was studying m inerals that emit light after being exposed to sunlight, a phenomenon called phosphorescence. Building on Roentgens work, Becquerel wanted to determ ine whether phosphorescent m inerals also emitted X-rays. i Comparison of Chemical and Nuclear Reactions Chemical Reactions Occur when bonds are broken and formed Involve only valence electrons Associated with small energy changes Atoms keep the same identity although they might gain, lose, or share electrons, and form new substances Temperature, pressure, concentration, and catalysts affect reaction rates 860 If you w ake up while it is still dark, the glowing numbers on your dock let you know w hat time it is. M any docks use a type of radiation to m ake the numbers glow. The word ra d iatio n might cause you to think about nudear power plants or dangerous, highly radioactive substances. However, less dangerous forms of radiation are often used in everyday objects, such as clocks. C h a p te r 24 • Nuclear Chemistry Nuclear Reactions Occur when nuclei combine, split, and emit radiation Can involve protons, neutrons, and electrons Associated with large energy changes Atoms of one element are often converted into atoms of another element Temperature, pressure, and catalysts do not normally affect reaction rates Becquerel discovered by chance that phosphorescent uranium salts produced spontaneous emissions that darkened photographic plates. He observed this phenomenon even when the uranium salts were not exposed to light. Chemist Marie Curie (1867-1934) and her husband Pierre Curie (1859—1906) took Becquerel’s mineral sample, called pitchblende, and isolated the components emitting the rays. They concluded that the darkening o f the photographic plates was due to rays emitted from the uranium atoms present in the mineral sample. Marie Curie named the process by which materials give off such rays radioac tivity; the rays and particles emitted by a radioactive source are called radiation. F ig u re 1 shows the darkening o f photographic film that is exposed to radiation emitted by radium salts. The work o f Marie and Pierre Curie was extremely important in establishing the origin o f radioactivity and developing the field of nuclear chemistry. In 1898, the Curies identified two new elements, polonium and radium, on the basis o f their radioactivity. Henri Becquerel and the Curies shared the 1903 Nobel Prize in Physics for their work. Marie Curie also received the 1911 Nobel Prize in Chemistry for her work with polonium and radium. □ READING CHECK E x p la in what Marie and Pierre Curie concluded about I the darkening of the photographic plates. ■ F ig u re 1 Radium salts are placed on a special emulsion on a photographic plate. After the plate is developed, the emulsion shows the dark tracks left by radiation emitted by the radium salts. Types o f Radiation After reading about the discovery o f radioactivity, you might wonder what types o f radiation are emitted by radioactive nuclei or which nuclei are radioactive. Recall that isotopes are atoms o f the same element that have different numbers of neutrons. Isotopes o f atoms with unstable nuclei are called rad ioisotop es. These unstable nuclei emit radiation to attain more stable atomic configurations in a process called radioactive decay. During radioactive decay, unstable atoms lose energy by emitting radiation. The three most common types o f radiation are alpha (a ), beta ((3), and gamma (7 ). Table 2 summarizes some o f their important properties. Later in this chapter, you will learn about other types of radiation that can be emitted in a nuclear reaction. T a b le 2 Properties of Alpha, Beta, and Gamma Radiation Property Symbol Composition Description of radiation Charge Mass Approximate Energy Relative penetrating power Alpha Radiation Beta Radiation Gamma Radiation a (3 K alpha particles beta particles high-energy electromagnetic radiation helium nuclei, ^He electrons photons 2+ 1- 0 6.64 x 10-27 kg 9.11 x 10-31 kg 0 5 MeV 0.05 to 1 MeV 1 MeV blocked by paper blocked by metal foil not completely blocked by lead or concrete Section 1 • Nuclear Radiation 861 Zinc-sulfidecoated screen ■ F ig u re 2 The effect of an electric field depends on the charge and mass of the radiation. Positively charged alpha particles deflect toward the negative plate. Negatively charged beta particles deflect toward the positive plate. The lighter beta particles undergo the larger deflection. Gamma rays have no charge and are not affected by an electric field. E rnest Rutherford (1 8 7 1 -1 9 3 7 ), who perform ed the famous gold foil experim ent that helped define m odern atom ic structure, identified alpha, beta, and gamma radiation when studying the effects o f an electric field on the em issions from a radioactive source. As you can see in F ig u re 2, gamm a rays carry no charge and are not affected by the electric field. Alpha particles carry a 2 + charge and are deflected toward the negatively charged plate. Beta particles carry a 1 — charge and are deflected toward the positively charged plate. Because beta particles are less massive than alpha particles, they undergo a larger deflection. □ READING CHECK Explain how Rutherford determined whether each of 1 the three types of radiation had a positive or negative charge or was i unchanged. j Incorporate information from this^sectionjnto A lp h a p a r tic le s A n alpha particle ( a ) has the same com position as a helium nucleus— two protons and two neutrons—and is therefore given the symbol jH e. T he charge o f an alpha particle is 2 + due to the presence o f the two protons. Alpha radiation consists o f a stream o f alpha particles. Because o f their mass and charge, alpha particles are relatively slow-moving compared with other types o f radiation. Thus, alpha particles are not very penetrating— a single sheet o f paper stops alpha particles. As you can see in F ig u re 3 , radium -226, an atom whose nucleus contains 8 8 protons and 138 neutrons, undergoes alpha decay by em itting an alpha particle. ■ F ig u re 3 A radium-226 nucleus undergoes alpha decay to form radon-222 and an alpha particle. Evaluate What is the number o f protons and neutrons in radium-226 and radon-222? + 226 3 88 R rxa Radium-226 862 C h a p te r 24 • Nuclear Chemistry 2I I Rn Radon-222 m 2 He Alpha particle ■ F ig u re 4 An iodine-131 nucleus undergoes beta decay to form xenon-131 and a beta particle. w E xplain How d oes b eta decay affect the mass number o f the decaying nucleus? 131, 53 > Iodine-131 In examining F ig u re 3 , note that the reaction is balanced. That is, the sum o f the mass numbers (superscripts) and the sum o f the atomic numbers (subscripts) on each side o f the arrow are equal. Also note that when a radioactive nucleus emits an alpha particle, the product nucleus has an atomic number that is lower by 2 and a mass number that is lower by 4. B e ta p a r t ic le s A beta particle is a very fast-moving electron that is emitted when a neutron in an unstable nucleus converts into a proton. Beta particles are represented by the symbol (3 or e- . They have a 1 — charge. Their mass is so small compared with the mass o f nuclei involved in nuclear reactions that it can be approximated to zero. Beta radiation consists o f a stream o f fast-moving electrons. An example o f the beta decay process is the decay o f iodine-131 into xenon-131 by beta-particle emission, as shown in F ig u re 4 . Note that the mass number o f the product nucleus is the same as that of the original nucleus (they are both 131), but its atomic number has increased by 1 (54 instead o f 53). This change in atomic number occurs because a neutron is converted into a proton, as shown by the following equation. V ocabulary .................................. W o r d o r ig in Radiation comes from the Latin word ra d ia re which means to r a d ia t e ................... n —»p + (3 As you might recall, the number o f protons in an atom determines its identity. Thus, the formation o f an additional proton results in the transformation from iodine-131 to xenon-131. Also, note that the electric charge in the equation above is conserved. The neutron is neutral. The proton has a 1+ charge and the beta particle has a 1 — charge. Because beta particles are both lightweight and fast-moving, they have greater penetrating power than alpha particles. A thin sheet of metal foil is required to stop beta particles. G a m m a r a y s Gamma rays are photons, which are high-energy (short wavelength) electromagnetic radiation. They are denoted by the symbol -y. Because photons have no mass and no charge, the emission of gamma rays does not change the atomic number or mass number o f a nucleus. Gamma rays almost always accompany alpha and beta radia tion, as they account for most of the energy loss that occurs as a nucleus decays. For example, gamma rays accompany the alpha-decay reaction of uranium-238. 29 2 U ~ > 29 o T h + 2 H e + 2 ^ The 2 in front o f the 'y symbol indicates that two gamma rays of different frequencies are emitted. Because gamma rays have no effect on mass number or atomic number, it is customary to omit them from nuclear equations. Section 1 • Nuclear Radiation 863 ■ F ig u re 5 The Chandra Observatory, launched in July 1999, photographed X-rays emitted from a cool gas cloud surrounding the black hole at the center of a neighboring galaxy. As you have learned, the discovery o f X-rays helped set the stage for the discovery o f radioactivity. X-rays, like gamma rays, are a form of high-energy electromagnetic radiation. However, X-rays are not pro duced by radioactive sources and their energy is lower than that o f gamma rays. They are emitted when inner electrons are knocked out and electrons from higher energy levels drop down to fill the vacancy. F ig u re 5 shows an X-ray image taken in space. It allows astronomers to observe objects not visible in optical images. The presence of X-rays indicates phenomena such as exploding stars or black holes. Hospitals and dentists have machines that produce X-rays when a beam of electrons strikes a metal target. The familiar X-ray images are produced as the beam o f X-rays passes easily through soft tissue but is partly blocked by hard tissue, such as bone. Q READING CHECK C o m p are and c o n tra s t X-rays and gamma rays. P e n e t r a t in g p o w e r The ability o f radiation to pass through matter is called penetrating power. Alpha particles have a low penetrating power because they move slowly due to their large mass, and their 2 + charge causes them to lose energy quickly through interactions with other particles. The penetrating power o f beta particles is higher because they are smaller and faster than alpha particles. However, they can still interact with particles and can be stopped by thin shielding. Gamma rays are highly penetrating. Because they have no charge and no mass, the probability o f matter stopping them is low. s ectio n 1 REVIEW S e c tio n S u m m a r y 1. MAINIDEA List the different types of radiation and their charges. • Wilhelm Roentgen discovered X-rays in 1895. 2. Compare the subatomic particles involved in nuclear and chemical reactions. • Henri Becquerel, Marie Curie, and Pierre Curie pioneered the fields of radioactivity and nuclear chemistry. • Radioisotopes emit radiation to attain more stable atomic configurations. 864 C h a p te r 24 • Nuclear Chemistry 3. Explain how you know whether the reaction is chemical or nuclear when an atom undergoes a reaction and attains a more-stable form. 4. Calculate Table 2 gives approximate energy values in units of MeV. Convert each value into joules using the following conversion factor: 1MeV = 1.6 x 10~13J. 5. Summarize Make a time line that summarizes the major events that led to the understanding of alpha, beta, and gamma radiation. s e c t io n 2 E s s e n tia l Q u e s tio n s Why are certain nuclei radioactive? How are nuclear equations balanced? How can you use radioactive decay rates to analyze samples of radioisotopes? R e v ie w V o c a b u la r y r a d io a c tiv it y : the process by which some substances spontaneously emit radiation N e w V o c a b u la r y transmutation nucleon strong nuclear force band of stability positron emission positron electron capture radioactive decay series half-life radiochemical dating Radioartive Decay M A I N I D E A Unstable nuclei can break apart spontaneously, changing the identity of atoms. CHEM 4 YOU To m ake sure that containers have the correct amount of fluid, some manufacturing processes use radioactivity. Detectors measure the number of particles produced by radioactive decay after they pass through the containers. For instance, a half-full bottle of juice would allow too much radiation to pass through and would not pass inspection. N u c le a r S t a b ility Except for the emission o f gamma radiation, radioactive decay involves the conversion o f an element into another element. Such a reaction, in which an atom’s atomic number is altered, is called tran sm u tatio n . W hether an atom spontaneously decays and what type o f radiation it emits depends on its neutron-to-proton ratio. An atom’s nucleus contains positively charged protons and neutral neutrons. Protons and neutrons are referred to as nucleons. Despite the strong electrostatic repulsion forces among protons, all nucleons remain bound in the dense nucleus because o f the strong nuclear force. The stro n g n u clear force acts on subatomic particles that are extremely close together and overcomes the electrostatic repulsion among protons. The fact that the strong nuclear force acts on both protons and neutrons is important. Two protons repel each other, but because neu trons are neutral, a neutron that is adjacent to a positively charged proton creates no repulsive electrostatic force. Yet these two adjacent particles are held together by the strong nuclear force. Likewise, two adjacent neutrons create no electrostatic force, but they, too, are held together by the strong nuclear force. Thus, the presence of neutrons adds an attractive force within the nucleus, as illustrated in F ig u re 6 . The number o f neutrons in a nucleus is important because nuclear stability is related to the balance between electrostatic and strong nuclear forces. ■Figure 6 The electrostatic force, represented by the purple arrows, acts between two charged particles. It is repulsive between two protons. The strong nuclear force, represented by the green arrows, acts between any two or more nucleons and is always attractive. In f e r W hat is th e e ffe c t o f the e le c tro s ta tic fo rce b e tw e e n tw o n eu tro n s? B e tw e e n a p ro to n a n d an e le ctro n ? Proton Proton Neutron Neutron Proton Neutron Section 2 • Radioactive Decay 865 The Band of Stability 130 120 110 100 90 c o ■§ 80 h- 70 -Q 60 Z 50 0 o i_ V E N e u t r o n - t o - p r o t o n r a t i o To a certain degree, the stability o f a nucleus can be correlated to its neutron-toproton (n/p) ratio. For atoms with low atomic numbers ( < 2 0 ), the m ost stable nuclei are those with neutron-toproton ratios o f 1:1. For example, helium (^He) has two neutrons and two protons, and a neutron-to-proton ratio o f 1:1. As atomic num ber increases, m ore and more neutrons are needed to produce a strong nuclear force that is sufficient to balance the electrostatic repul sion force between protons. Therefore, the neutron-toproton ratio for stable atoms gradually increases, reaching a m axim um o f approximately 1.5:1 for the largest atoms. An example o f this is lead ( 2^ P b ). W ith 124 neutrons and 82 protons, lead has a neutron-toproton ratio o f 1.51:1. Cp READING CHECK E xplain why the neutron-to-proton ratio of stable nuclei increases as the atomic number increases. 40 30 T h e b a n d o f s t a b i l i t y Exam ine the plot o f the 20 10 0 Number of protons ■Figure 7 The band of stability is the region where all stable nuclei fall when plotting the number of neutrons versus the number of protons. As the atomic number increases, the neutron-to-proton ratio (n/p) increases from 1:1 to 1.5:1. □ GRAPH CHECK Find the number of protons above which the neutron-toproton ratio starts to differ from 1:1. num ber o f neutrons versus the num ber o f protons for all known stable nuclei shown in Figure 7. N otice that the slope o f the plot indicates that the num ber of neutrons required for a nucleus to be stable increases as the num ber o f protons increases. This correlates with the increase in the neutron-to-proton ratio o f stable nuclei with increasing atom ic number. The area on the graph w ithin which all stable nuclei are found is known as the band of stability. As shown in Figure 7, jHe and ^ P b are both positioned within the band o f stability although they have a different neutron-toproton ratio. All nuclei outside the band o f stability— either above or below— are radioactive and undergo decay in order to gain stability. After decay, the new atom is positioned m ore closely to, if not within, the band o f stability. The band o f stability ends at lead-208; all elem ents with atom ic numbers greater than 82 are radioactive. E^l READING CHECK D e fin e the band of stability and relate it to the value of the neutron-to-proton ratio. T y p e s o f R a d io a c tiv e D e c a y The type o f radioactive decay a particular radioisotope undergoes depends to a large degree on the underlying causes for its instability. Atoms lying above the band o f stability generally have too many neutrons to be stable, whereas atoms lying below the band o f stability tend to have too many protons to be stable. Depending on the relative num ber o f neutrons and protons, atoms can undergo different types o f decay—beta decay, alpha decay, positron emission, or electron capturefeto gain stability. 866 C h a p te r 24 • Nuclear Chemistry B e ta d e c a y A radioisotope that lies above the band o f stability is unstable because it has too many neutrons relative to its number o f pro tons. For example, unstable *gC has a neutron-to-proton ratio o f 1.33:1, whereas stable elements o f similar mass, such as l\(Z and ^N, have neutron-to-proton ratios o f approximately 1:1. It is not surprising, then, that 6C undergoes beta decay, as this type o f decay decreases the num ber o f neutrons in the nucleus. 14C ^ 14N + (3 V ocabulary ................................ S c ie n c e u s a g e v. C o m m o n u s a g e Unstable S cience usage: spontaneously radioactive U nstab le a to m s decay to reach a m ore sta b le state. C o m m o n usage: not firm or fixed in F ig u re 8 a shows the beta decay o f carbon-14 into nitrogen-14. Note that the atomic number o f the product nucleus, 'yN, has increased by one. The nitrogen-14 atom now has a stable neutron-to-proton ratio of 1:1. Thus, beta emission has the effect of increasing the stability o f a neutron-rich atom by increasing its atomic number, that is by lowering its neutron-to-proton ratio. The resulting atom is closer to, if not within, the band o f stability. one place Th e c h a ir is u nsta b le because one o f its legs is s h o rte r th a n the o th e r . ............... □ READING CHECK E x p la in why radioisotopes above the band of stability are unstable. A lp h a d e c a y All nuclei with more than 82 protons are radioactive and decay spontaneously. Both the number o f neutrons and the number o f protons must be reduced in order to make these radioisotopes stable. These very heavy nuclei often decay by emitting alpha particles. For example, polonium -210 spontaneously decays into lead-206 by emitting an alpha particle. “ “P o - ^ P b + ^He F ig u re 8 b shows the alpha decay of polonium-210 into lead-206. The atomic number o f ^ P o decreases by 2 and the mass number decreases by 4 as the nucleus decays into 82Pb. H READING CHECK C a lc u la te how the neutron-to-proton ratio changes j when polonium-210 decays into lead-206. ■ F ig u re 8 Depending on where nuclei lie on the band of stability, they can emit a beta particle or an alpha particle. C o m p a re a n d c o n tra s t b eta decay and alpha decay in terms o f the atomic number o f the nuclei involved in the reaction. 14 N Nitrogen-14 14/ Polonium-210 Carbon-14 Beta particle Beta decay Alpha particle Alpha decay Section 2 • Radioactive Decay 867 P o s itr o n e m is s io n a n d e le c t r o n c a p tu r e For nuclei with low neu tron-to-proton ratios, two com m on radioactive decay processes occur: positron em ission and electron capture. These two processes tend to increase the neutron-to-proton ratio o f the neutron-poor atom, bringing the atom closer to, if not within, the band o f stability. P o sitro n em ission is a radioactive decay process that involves the em ission o f a positron from a nucleus. A p o sitro n is a particle with the same mass as an electron but opposite charge; thus, it is represented by the symbol |3+ or e +. During positron emission, a proton in the nucleus is converted into a neutron and a positron, and then the positron is emitted. Boron- Carbon-11 Positron F ig u re 9 shows the positron em ission o f a carb o n -11 nucleus. C a rb o n -11 lies below the band o f stability and has a low neutron-toproton ratio o f approximately 0.8:1. C arb o n -11 undergoes positron em ission to form b o ro n -11. Positron em ission decreases the num ber of protons from six to five, and increases the num ber o f neutrons from five to six. The resulting atom, ^ B , has a neutron-to-proton ratio o f 1 .2 : 1 , which is within the band o f stability. Electron capture is the other com m on radioactive-decay process that decreases the num ber o f protons in unstable nuclei lying below the band o f stability. E lectro n cap tu re occurs when the nucleus o f an atom draws in a surrounding electron, usually one from the lowest energy level. This captured electron com bines with a proton to form a neutron. Positron emission o • + Electron §7 Rb Rubidium-81 X-ray photon Electron capture ■ F ig u re 9 When a nucleus under goes positron emission or captures an electron, the number of protons decreases by one. p + e ~ —>n T he atomic num ber o f the nucleus decreases by 1 as a consequence o f electron capture. The form ation o f the neutron also results in an X -ray photon being emitted. These two characteristics o f electron capture are shown in the electron capture o f rubidium -81 in F ig u re 9 . The bal anced nuclear equation for the reaction is shown below. C o m p are and c o n tra s t h o w th e n u m b e r o f p ro to n s a n d n e u tro n s c h a n g e d u rin g p o s itr o n e m is s io n a n d e le c tro n c a p tu re . + a’Rb K r + X -ray photon The five types o f radioactive decay you have read about in this chapter are sum marized in T a b le 3. □ READING CHECK List the decay processes that result in an increased neutron-to-proton ratio and a decreased neutron-to-proton ratio. T a b le 3 Summary of Radioactive Decay Processes Type o f Radioactive Decay Particle Em itted Change in Mass Num ber Change in Atom ic Num ber decreases by 4 decreases by 2 Alpha decay jH e Beta decay |3 or e- no change increases by 1 Positron emission 3+ or e+ no change decreases by 1 Electron capture X-ray photon no change decreases by 1 Gamma emission 1 no change no change 868 C h a p te r 24 • Nuclear Chemistry W riting and Balancing Nuclear Equations The radioactive decay processes you have just read about are all exam ples o f nuclear reactions. N uclear reactions are expressed by balanced nuclear equations ju st as chem ical reactions are expressed by balanced chem ical equations. However, in balanced chem ical equations, numbers and types o f atom s are conserved; in balanced nuclear equations, mass num bers and charges are conserved. BALANCING A NUCLEAR EQUATION NASA uses the alpha decay o f plutonium - 238 (294^u) as a heat source on spacecraft. W rite a balanced equation fo r this decay. A N A LY ZE THE PROBLEM You are given that a plutonium atom undergoes alpha decay and forms an unknown product. Plutonium-238 is the initial reactant, while the alpha particle is one of the products of the reaction. The reaction is summarized below. 238 9 4 Pu u ?Z X + 2^He You must determine the unknown product of the reaction, X. □ Known Unknow n reactant: plutonium-238 C^Pu] decay type: alpha particle emission C^He) mass number of the product A = ? atomic number of the product Z = ? reaction product X = ? SOLVE FOR THE UNKNOW N 238 = A + 4 A = 238 — 4 = 234 Apply th e conservation of m ass num ber. Solve for A. Thus, the mass number of X is 234. 94 = Z + 2 Z = 94 - 2 = 92 Apply th e conservation of charges. Solve for Z. Thus, the atomic number of Y is 92. The periodic table identifies the element as uranium [U], 238 94Pu & 239a2U + 2He □ W rite the balanced nuclear equation. EVALUATE THE ANSW ER The correct formula for an alpha particle is used. The sums of the superscripts and subscripts on each side of the equation are equal. Therefore, the charge and the mass number are conserved. The nuclear equation is balanced. PRACTICE Problem 6 . Write a balanced nuclear equation for the reaction in which oxygen-15 undergoes positron emission. 7. Thorium-229 is used to increase the lifetime of fluorescent bulbs. What type of decay occurs when thorium-229 decays to form radium-225? 8. Challenge The figure at right shows one way that bismuth-212 can decay, producing isotopes A and B. a. Write a balanced nuclear equation for this decay. b. Identify the isotopes A and B that are produced. 212 R: 83 Bl Bismuth-212 Section 2 • Radioactive Decay 869 ■ F ig u re 1 0 Uranium-238 undergoes 14 different radioactive decay steps before forming stable lead-206. ... 92 “ I Uranium-238 Decay Series ! Alpha decay Mb 91 y ft* r % W— — 1 ft 90 / 14 / a .a V ft E / 87 E o < p& 86 85 p 84 / 83 82 0 / W St able isotope 1 r U 200 202 204 206 208 210 212 214 216 218 220 222 224 226 228 230 232 234 236 238 M ass n u m b e r R a d io a c tiv e S e rie s A ra d io a c tiv e d e ca y series is a series o f nuclear reactions that begins with an unstable nucleus and results in the form ation o f a stable nucleus. As F ig u re 1 0 shows, uranium -238 first decays to thorium -234, which in turn decays to protactinium -234. Decay reactions continue until a stable nucleus, lead-206, is formed. □ GRAPH CHECK List each step in the decay of uranium-238. Include the type of decay and the resulting product. R a d io a c tiv e D e c a y R a te s Explore half-life. You m ight wonder how there could be any naturally occurring radioiso topes found on Earth. After all, if radioisotopes undergo continuous radioactive decay, won’t they eventually disappear? Furthermore, radioisotopes have been decaying for about 4.6 billion years— the span o f Earths existence. Yet, naturally occurring radioisotopes are not u ncom m on on Earth. Som e radioisotopes, such as carb on -14, are continuously form ed in the upper atm osphere o f Earth. O thers are formed in the universe, during stellar nucleosynthesis for instance. Radioisotopes can also be synthesized in laboratories. The differing decay rates o f isotopes also contribute to their presence on Earth. Radioactive decay rates are measured in half-lives. A h a lf- life is the tim e required for on e-h alf o f a radioisotopes nuclei to decay into its products. For example, the half-life o f the radioisotope strontium -90 is 29 years. I f you had 10.0 g o f strontium -90 today, 29 years from now you would have 5.0 g left. T a b le 4 shows how this decay continues through four half-lives o f strontium -90. F ig u re 11 presents the data from the table in term s o f the percent o f strontium -90 remaining after each half-life. The decay continues until a negligible amount o f stron tium -90 remains. □ READING CHECK D e fin e the term half-life. 870 C h a p te r 24 • Nuclear Chemistry The Decay of Strontium-90 Table 4 Number of Half-Lives Elapsed Time Decay of Strontium Amount of Strontium-90 Present 0 Oy 1 0 .0 g 1 29 y 1 0 .0 g x (1) = 5 .0 0 g 2 58 y 3 87 y 10.0 g x (y )(y )(y ) = 1 -25 g 4 116 y 10.0 g x (y)(-j)(4-)(y) = 0-625 g =2.50 g 10.0 g x (y )(y ) T h e data in Table 4 can be sum m arized in a simple equation represent ing the decay o f any radioactive elem ent. = N „ | ■Figure 11 The graph shows how the amount of strontium in a sample changes as a function of the number of half-lives. Get help with exponential graphing. Rem aining A m o un t of Radioactive Element N Number of half-lives (1 half-life = 29 years) N is th e rem aining am ount. N 0 is th e inital am ount. n is th e n u m ber o f h alf-lives th a t have passed. The amount remaining is equal to the initial amount times one-half raised the number of half-lives that have passed. The exponent n can also be replaced with the equivalent quantity t / T , w here t is the elapsed tim e and T is the duration o f the half-life. Note that t and T m ust have the sam e units o f tim e. N = N „ ( i) ',r T his type o f expression is know n as an exponential decay function. Figure 11 shows the graph o f a typical exponential decay function— in this case, the decay curve for strontium -90. Cp GRAPH CHECK Infer how much strontium remains after 1.5 half-lives. Each radioisotope has its own characteristic half-life. Half-lives for several radioisotopes are given in Table 5. N otice the large range o f values for half-lives, from m illionths o f a second to billions o f years! Table 5 Half-Lives of Several Radioisotopes Radioisotope Polonium-214 Symbol Half-Life 214Po 84ro 163.7 /zs Cobalt-60 S P Radon-222 J I Ra 5.272 y 3.8 d Phosphorus-32 n 14.28 d Carbon-14 146c 5730 y Uranium-238 23982u 4.46 x 109y Section 2 • Radioactive Decay 871 CALCULATING THE AM O UN T OF REMAINING ISOTOPE Krypton-85 is used in indicator lights o f appliances. The half-life of krypton-85 is 11 y. How much of a 2.000-mg sample remains after 33 y? □ AN A LYZE THE PROBLEM You are given a known mass of a radioisotope with a known half-life. You must first determine the number of half-lives that passed during the 33-year period. Then, use the exponential decay equation to calculate the amount of the sample remaining. Known Unknown Initial amount = 2.000 mg A m o u n t re m a in in g = ? m g Elapsed time CO = 33 y Half-life [T] = 11 y □ SOLVE FOR THE UNKNOW N Number of half-lives [n] S elapsed tim e(f) haif-life[7] 33 v n B f g i = 3.0 half-lives S ubstitute t = 3 3 y and T = 11 y. A m o u n t re m a in in g = [initial amount] (■ =• W rite th e exponential decay equation. ■ ■ y A m o u n t re m a in in g Ej (2000 mg] l^A m o u n t re m a in in g = [2.000 mg] E3 D eterm in e the num ber of half-lives passed during the 33 y. S ubstitute initial am ount = 2 .0 0 0 mg 3.0 and n = 3. = 0 .2 5 0 0 m g EVALUATE THE ANSW ER Three half-lives are equivalent to >or (gj- The answer [0.25 mg] is equal to (■Tj of the initial amount. The answer has two significant figures because the number of years has two significant figures, n does not affect the number of significant figures. PRACTICE Problems Do additional problems J ^ S 9 . Bandages can be sterilized by exposure to gamma radiation from cobalt-60, which has a half-life of 5.27 y. How much of a 10.0-mg sample of cobalt-60 is left after one half-life? Two half-lives? Three half-lives? 10. If the passing of five half-lives leaves 25.0 mg of a strontium-90 sample, how much was present in the beginning? 11. C h alle n g e The table shows the amounts of radioisotopes in three different samples. To the nearest gram, how much will be in Sample B and Sample C when Sample A has 16.2 g remaining? Sample 872 Radioisotope Half-life Amount (g) A cobalt-60 5.27 y 64.8 B tritium 12.32 y 58.4 C strontium-90 28.79 y 37.6 C h a p te r 24 • Nuclear Chemistry S g | MiniLAB M o del Radioactive Decay How do radioactive isotopes decay? P ro c e d u re S 7. Place all o f the tails-up pennies back in the plastic cup. 8 . Repeat Steps 3 through 7 as many times as needed until no pennies remain. ife 1. Read and com plete the lab safety form. 2. Place 100 pennies in a plastic cup. 3. Place your hand over the top o f the cup and shake the cup several times. 4. Pour the pennies into a shoebox. Remove all the pennies that land heads-up. These pennies represent atom s o f the radioisotope that have undergone radioactive decay. 5. Prepare a data table to record the num ber of rem aining pennies (tails-up pennies). 6 . Count the num ber o f pennies that remain, and record this num ber in your data table. A n a ly s is 1. Construct a graph of T ria l N u m b e r v. N u m b e r o f P e n n ie s R e m a in in g from your data table. Draw a curve through the plotted points. 2. Calculate how many trials it took for 50%, 75%, and 90% o f the sample to decay. 3. Evaluate the half-life o f the radioisotope if the tim e between each trial is 1 min. 4. Determ ine how the results w ould change if you used 100 dice instead of pennies. In this case, you w ould assume that any dice that lands with the six side facing up represents a decayed atom and is removed. R a d io c h e m ic a l d a t i n g C hem ical reaction rates are greatly affected by changes in tem perature, pressure, and concentration, and by the presence o f a catalyst. In contrast, nuclear reaction rates rem ain con stant regardless o f such changes. In fact, the half-life o f any particular radioisotope is constant. Because o f this, radioisotopes can be used to determ ine the age o f an object. T h e process o f determ ining the age o f an ob ject by m easuring the am ount o f a certain radioisotope rem aining in that ob ject is called ra d io c h e m ic a l d atin g. C o n n e c t io n s Biology A type o f radiochem ical dating known as car bon dating is used to m easure the age o f artifacts that were once part o f a living organism . C arbon dating m akes use o f the radioactive decay o f ca rb o n -14, w hich is form ed by cosm ic rays in the upper atm osphere at a fairly constant rate. These ca rb o n -14 atoms becom e evenly spread throughout E arth s biosphere, where they m ix with stable carb o n -12 and ca rb o n -13 atom s. Plants use carbon dioxide from the environment, w hich contains all carbon isotopes, to build m ore com plex molecules through the process o f photosynthesis. W hen animals eat plants, the ca rb o n -14 atom s that were part o f the plant becom e part o f the animal. Because organism s are constantly taking in carbon com pounds, they contain the sam e ratio o f ca rb o n -14 to carb o n -12 and carb o n -13 found in the atm osphere. However, after they die, organisms no longer ingest new carbon com pounds, and the ca rb o n -14 they already contain con tinues to decay. T h e ca rb o n -14 undergoes beta decay to form n itro g en -14. “C - ^ + p C a rb o n -14 has a half-life o f 5730 years. Because the amount o f stable carbon in the dead organism rem ains constant while the carb o n -14 continues to decay, the ratio o f unstable carbon-14 to stable carbon-12 and ca rb o n -13 decreases. Section 2 • Radioactive Decay 873 ■ F ig u re 1 2 Using the radiocarbon dating method on organic materials, such as ash and charcoal found at the Great Pyramid of Giza, scientists estimate the pyramid to be more than 4000 years old. By measuring this ratio and com paring it to the nearly constant ratio present in the atmosphere, the age o f an object can be estimated. For example, if an o b jects C -14 to (C -12 + C -13) ratio is one-quarter of the ratio measured in the atmosphere, the object is approximately two half-lives, or 11,460 years old. C arbon-14 dating is lim ited to accurately dating objects up to approximately 45,000 years o f age. This m ethod was used to date the Great Pyramid o f Giza, shown in F ig u re 12. The decay process o f a different radio isotope, uranium -238 to lead-206, is com m only used to date objects such as rocks. Because the half-life o f uranium -238 is 4.5 x 10 9 years, it can be used to estimate the age o f objects that are too old to be dated using carb o n -14. By radiochem ical dating o f m eteorites, the age o f the solar system has been estimated at 4.6 X 10 9 years. REVIEW S e c tio n S u m m a r y 12. MAINIDEA Describe what happens to unstable nuclei. • The conversion of an atom of one element to an atom of another by radioactive decay processes is called transmutation. 13. Explain how you can predict whether or not an isotope is likely to be stable if you know its number of neutrons and protons. • Atomic number and mass number are conserved in nuclear reactions. 15. Predict the nuclear equation for the alpha decay of radium-226 used on the tips of older lightning rods. • A half-life is the time required for half of the atoms in a radioactive sample to decay. 16. Calculate how much of a 10.0-g sample of americium-241 remains after four half-lives. Americium-241 is a radioisotope commonly used in smoke detectors and has a half-life of 430 y. • Radiochemical dating is a technique for determining the age of an object by measuring the amount of certain radioisotopes remaining in the object. 17. Calculate After 2.00 y, 1.986 g of a radioisotope remains from a sample that had an original mass of 2.000 g. a. Calculate the half-life. b. How much of the radioisotope remains after 10.00 y? 14. Describe the forces acting on the particles within a nucleus and explain why neutrons are the glue holding the nucleus together. 18. Graph A sample of polonium-214 originally has a mass of 1.0 g. Express the mass remaining as a percent of the original sample after a period of one, two, and three half-lives. Graph the percent remaining versus the number of half-lives. Approximately how much time has elapsed when 20% of the original sample remains? 874 C h a p te r 24 • Nuclear Chemistry Pixtal/SuperStock SECTION 2 SECTION 3 Nuclear Reactions • How are mass and energy related? M A I N ID E A Fission, the splitting of nuclei, and fusion, the combining of nuclei, release tremendous amounts of energy. • How do nuclear fission and nuclear fusion compare and contrast? CH EM E s s e n tia l Q u e s tio n s • What is the process by which nuclear reactors generate electricity? 4 YOU R e v ie w V o c a b u la r y mass number: the number after an element's name, representing the sum of its protons and neutrons N e w V o c a b u la r y induced transmutation transuranium element mass defect nuclear fission critical mass breeder reactor nuclear fusion thermonuclear reaction On a hot summer day, you step outside and feel the intense heat of the Sun. Nuclear reactions within the Sun release enough energy to w arm Earth and other planets in the solar system for billions of years. It is no surprise, then, that scientists are trying to use this same type of nuclear reaction to produce electricity. Induced Transmutation All nuclear reactions, or transm utations, that have been described thus far are examples o f radioactive decay, where one elem ent is converted into another elem ent by the spontaneous em ission o f radiation. How ever, transm utations can also be forced, or induced, by bom barding a stable nucleus with a neutron or with high-energy alpha, beta, or gam m a radiation. In 1919, Ernest Rutherford perform ed the first laboratory conversion o f one elem ent into another element. By b om barding n itrog en -14 with high-speed alpha particles, oxygen-17 and hydrogen-1 were form ed. This transm utation reaction is illustrated in F ig u re 1 3 and the reaction is shown below. XyN + ^He—> + }H As Rutherford dem onstrated, nuclear reactions can be induced, in other words, produced artificially. The process, which involves striking nuclei with high-velocity particles, is called ind u ced tra n sm u ta tio n . In the case o f charged particles, such as the alpha particles used by Rutherford, the incident particles must be moving at extrem ely high speeds to overcom e the electrostatic repulsion between themselves and the target nucleus. Because o f this, scientists have developed methods to accelerate charged particles to extrem e speeds by using very strong electrostatic fields and m agnetic fields. Particle accelerators are m achines built to produce the high-speed particles needed to induce transm utation. Since Rutherfords first experim ents involving induced transm utation, scientists have used the technique to synthesize hundreds o f new isotopes in the laboratory. ■ F ig u re 1 3 When an alpha particle bombards a nitrogen-14 atom, an atom of oxygen-17 and an atom of hydrogen-1 are produced. + * He Bombarding alpha particle 1?N Target nitrogen atom ’ SO Oxygen atom ?H Hydrogen atom Section 3 • Nuclear Reactions 875 T r a n s u r a n iu m e le m e n t s The elem ents immediately following uranium in the periodic table— elem ents with atom ic num bers 9 3 and greater— are known as the tra n su ra n iu m elem en ts. All transuranium elem ents have been produced in the laboratory by induced transm uta tion and are radioactive. M any transuranium elem ents have been nam ed in honor o f their discoverers or the laboratories at which they were created. Scientists continue their ongoing efforts to synthesize new transuranium elem ents and study their properties. EXAMPLE Problem IN D U C E D T R A N S M U T A T IO N R E A C TIO N E Q U A T IO N S W rite a balanced nuclear equation fo r the induced transm utation o f oxygen-16 into nitrogen-13 by proton bombardment. An alpha particle is em itted from the nitrogen atom in the reaction. □ □ ANALYZE THE PROBLEM You are given all of the particles involved in an induced transmutation reaction. Because the proton bombards the oxygen atom, they are reactants and must appear on the reactant side of the reaction arrow. Known Unknow n reactants: oxygen-16 and a proton products: nitrogen-13 and an a-particle n u c le a r e q u a tio n fo r th e re a c ta n t = ? SOLVE FOR THE UNKNOW N Nuclear formula for oxygen-16: ’ gO Use the periodic tab le to obtain the atom ic num ber of oxygen. Nuclear formula for nitrogen-13: 12N Use th e periodic ta b le to obtain th e atom ic num ber of nitrogen. Nuclear formula for proton: p Nuclear formula for alpha particle: ^He ’ JjO + p - ^ ’ yN + jH e W rite th e balanced nuclear equation. EVALUATE THE ANSW ER A proton has a charge of 1+ and a mass number of 1. Therefore, both charge and mass number are conserved. The formula for each participant in the reaction is also correct. The nuclear equation is written correctly. 19. Write the balanced nuclear equation for the induced transmutation of aluminum-27 into sodium-24 by neutron bombardment. An alpha particle is released in the reaction. 5 20 . Write the balanced nuclear equation for the alpha-particle bombardment of 2g®Pu. One of the reaction products is a neutron. 2 1 . C h alle n g e Archeologists sometimes use a procedure called neutron activation analysis to identify elements in artifacts. The figure at right shows one type of reaction that can occur when an artifact is bombarded with neutrons. If the product of the process is cadmium-110, what was the target and unstable isotope? Write balanced nuclear equations for the process to support your answer. 876 C h a p te r 24 • Nuclear Chemistry Neutron ' Target p U n s ta b le ^ *, isotope Product Binding Energy Variation o x ■ Figure 1 4 The binding energy per nucleon is a function of the mass number. Light nuclei gain stability by undergoing nuclear fusion. Heavy nuclei gain stability by undergoing nuclear fission. 3li 0 01 3 C >i 31 h. 01 e 01 3» JC .e 3 Mass number □ GRAPH CHECK ; Describe how the binding energy varies as a function of the mass number. Nuclear Reactions and Energy In your study o f chem ical reactions, you read that mass is conserved. For m ost practical situations this is true—but, it is n ot accurate. E in s te in 's e q u a t i o n A lbert E insteins equation relates mass and energy. It states that any reaction produces or consum es energy due to a loss or gain in m ass. Energy and mass are equivalent. Note that because c 2 is large, a sm all change in m ass results in a large change in energy. E n e rg y E q u iv a le n t o f M ass A E = A m c2 A E is th e change in energy, in Joules. Am is the change in m ass, in kg. c is th e speed of light. The change in energy is equal to the change in mass times the square of the speed of light. M a s s d e f e c t a n d b in d in g e n e r g y Scientists have determ ined that the m ass o f the nucleus is always less than the sum o f the masses o f the individual protons and neutrons that com prise it. This difference in mass betw een a nucleus and its com ponent nucleons is called the m ass defect. W h en nucleons com bine together to form an atom, the energy corresponding to the mass defect is released. Conversely, energy is needed to break apart a nucleus into its nucleons. T he nuclear binding energy can be defined as the am ount o f energy needed to break one m ole o f nuclei into individual nucleons. The larger the binding energy per nucleon, the m ore strongly the nucleons are held together, and the m ore stable the nucleus is. Less-stable atoms have lower binding ener gies per nucleon. In other words, it is harder to break apart a nucleus with a high binding energy than a nucleus with a low binding energy. Figure 14 shows the average binding energy per nucleon versus the mass num ber. Note that the binding energy per nucleon reaches a m axim um around a mass num ber o f 60. Elem ents with a mass num ber near 60 are the m ost stable. Section 3 • Nuclear Reactions 877 C a lcu la tin g M a s s D efect You can calculate the mass defect o f an isotope if you know the mass of the isotope and the num ber and masses o f its components. Applying the equation A £ = A m e 2, you can then derive the equivalent binding energy. Mass defect = m nuc|eus - [N pm p + /Vnm n] where m nuc|eus is the mass of the nucleus, m p is the mass o f a proton, m n is the mass o f a neutron, N p is the num ber of protons, and /Vn is the num ber o f neutrons. If you start w ith the mass o f the atom, you have to take into account the mass o f the electrons. To do so, the mass of a hydrogen atom, which is composed of a proton and an electron, is used instead o f the mass of a proton. The equation is then: Mass defect = m isotope - [N pm H - A/nm n] Use the fo llo w in g values fo r the calculations: m H m 1.007825 amu and m n = 1.008665 amu. The accepted value fo r c is 3.00 x 108 m/s. To calculate the energy in Joules, you can convert the masses into kilograms using 1 amu = 1.660540 x 10~27 kg. Apply the Strategy Calculate the mass defect and binding energy o f lithium-7. The mass o f lithium-7 is 7.016003 amu. In typical chem ical reactions, the energy produced or consumed is so small that the accom panying changes in mass are negligible. In contrast, the mass changes and associated energy changes in nuclear reactions are significant. For example, the energy released from the nuclear reaction o f 1 kg o f uranium is equivalent to the energy released during the chem ical com bustion o f about four billion kilogram s o f coal. Nuclear Fission V o c a b u l a r y ......................... A c a d e m ic v o c a b u la r y Generate to bring into existence, to originate by a physical or chemical process F ire generates a lo t o f h e a t ................ Binding energies in Figure 14 indicate that heavy nuclei tend to be unstable. To gain stability, they can fragm ent into several smaller nuclei. Because atoms with mass numbers around 60 are the m ost stable, heavy atoms (those with mass num bers greater than 60) tend to fragment into smaller atoms in order to increase their stability. The splitting o f a nucleus into fragments is known as nuclear fission. The fission o f a nucleus is accompanied by a very large release o f energy. Nuclear power plants use nuclear fission to generate power. The first nuclear fission reaction discovered involved uranium -235. As you can see in Figure 15, when a neutron strikes a uranium -235 nucleus, it undergoes fission. B ariu m -141 and krypton-92 are just two o f the many possible products o f this fission reaction. In fact, scientists have identi fied more than 2 0 0 different product isotopes from the fission o f a uranium -235 nucleus. □ READING CHECK Explain why heavy atoms undergo nuclear fission. 878 C hapter 24 • Nuclear Chemistry ■Figure 15 When bombarded with a neutron, uranium-235 forms unstable uranium-236, which then splits into two lighter nuclei and additional neutrons. The fission of uranium-235 is accompanied by a large release of energy. + (Unstable nucleus) C h a in r e a c t io n s E ach fission o f uranium -235 releases additional neutrons, as shown in Figure 15. I f one fission reaction produces two neutrons, these two neutrons can cause two additional fissions. I f those two fissions release four neutrons, those four neutrons could then produce four m ore fissions, and so on, as shown in Figure 16. This self-sustaining process in w hich one reaction initiates the next is called a chain reaction. As you m ight im agine, the num ber o f fissions and the am ount o f energy released can increase rapidly. T h e explosion from an atom ic bom b is an exam ple o f an uncontrolled chain reaction. ■Figure 16 When uranium nuclei undergo fission, they release neutrons, which trigger more fission reactions. The ongoing reactions are characteristics of a nuclear chain reaction. View an animation about chain reactions. # Q n (neutron) Fission fragment m 2! i u nucleus # Section 3 • Nuclear Reactions 879 ■ F ig u re 17 Whether a nuclear reaction can be sustained depends on the amount of matter present. In a subcritical mass, the chain reaction does not start because neutrons escape before causing enough fission to sustain the chain reaction. In a supercritical mass, neutrons cause more and more fissions and the chain reaction accelerates. View an animation about critical mass. Subcritical mass Supercriticalmass A sample o f fissionable m aterial must have sufficient mass in order for a chain reaction to occur. I f it does not, neutrons escape from the sample before they can start the chain reaction by striking other nuclei. A sample that is not massive enough to sustain a chain reaction is said to have subcritical mass. A sample that is massive enough to sustain a chain reaction has c ritic a l m ass. W hen a critical mass is present, the neutrons released in one fission cause other fissions to occur. I f much m ore mass than the critical mass is present, the chain reaction rapidly escalates. This can lead to a violent nuclear explosion. A sample o f fissionable m aterial with a mass greater than the critical mass is said to have supercritical mass. F ig u re 17 shows the effect o f mass on the initiation and progression o f a fission reaction. □ READING CHECK C o m p are subcritical mass and critical mass. nuclear power plant are the reactor under the dome and the cooling tower. 880 C h a p te r 24 • Nuclear Chemistry N u c le a r R e a c to rs Nuclear fission produces the energy generated by nuclear reactors. This energy is prim arily used to generate electricity at nuclear power plants, such as the one shown in F ig u re 18. A com m on fuel is fissionable uranium (IV ) oxide (U O 2 ) encased in corrosion-resistant rods. U -238 is the m ost abundant isotope (99% ) o f uranium. U -235, which makes up 0.7% o f the natural uranium, has the rare property o f being able to undergo induced fission; U -235 atoms undergo fission when hit by a neutron. T he fuel used in nuclear power plants is enriched to contain 3% uranium -235, the am ount required to sustain a chain reaction, and is called enriched uranium. Additional rods, often made o f cadmium or boron, control the fission process inside the reactor by absorbing neutrons released during the reaction. Keeping the chain reaction going while preventing it from racing out o f control requires precise m onitoring and continual adjusting o f the control rods. Much o f the concern about nuclear power plants focuses on the risk o f losing control o f the nuclear reactor, possibly resulting in the accidental release o f harm ful levels o f radiation. The Three Mile Island accident in the United States in 1979 and the Chernobyl accident in Ukraine in 1986 provide examples o f why controlling the reactor is critical. F ig u re 1 9 shows the city o f Pripyat, located 3 km from Chernobyl. The city was completely abandoned after the accident. vario images GmbH & Co.KG/Alamy ■ F ig u re 1 8 The main parts of a ■ F ig u re 1 9 The city of Pripyat was deserted after the accident at the Chernobyl power plant. The fission within a nuclear reactor is started by a neutron-emitting source and is stopped by positioning the control rods to absorb all o f the neutrons produced in the reaction. The reactor core contains a reflector that acts to reflect neutrons back into the core, where they will react with the fuel elements, also called fuel rods. A coolant, usually water, circulates through the reactor core, to carry off the heat generated by the nuclear fission reactions. The hot coolant heats water that is used to power steam-driven turbines, which produce electric power. Nuclear power plants and fossil-fuel burning power plants are similar; heat from a reaction—nuclear fission or chemical combustion o f coal is used to generate steam. The steam then drives turbines that produce electricity, as shown in the nuclear power plant illustrated in F ig u re 2 0 . The other major components o f a nuclear power plant are also illustrated in F ig u re 2 0 . View an animationaboutnuclear power plants. ■ F ig u re 2 0 A nuclear reactor produces heat that drives the formation of steam. The energy from the steam spins a turbine which produces electricity. The steam is eventually cooled and recycled. The water used to cool the steam enters the cooling tower where steam is released to the atmosphere. — Containment structure Control rods Hot coolant Steam Steam generator Steam turbine (high-energy steam spins turbines and generates electricity) Warm water Fuel elements Cool water Reactor coolant not to scale -Carbon moderators Large body of water Section 3 • Nuclear Reactions 881 Because o f the hazardous radioactive fuels and fission products present at nuclear power plants, a dense concrete structure is usually built to enclose the reactor. T he m ain purpose o f the containm ent structure is to shield personnel and nearby residents from harmful radiation. As the reactor operates, the fuel rods are gradually depleted and products from the fission reactions accumulate. Because o f this, the reactor must be serviced periodically. Spent fuel rods are extracted from the reactor, as shown in F ig u re 2 1 , and can be reprocessed and repack aged to m ake new fuel rods. Som e fission products, however, are extrem ely radioactive and cannot be used again. These products must be stored as nuclear waste. Risks o f accidents, such as the ones m entioned in F ig u re 2 2 , have to be taken into account when operating nuclear power plants. However, the storage o f highly radioactive nuclear waste is still one o f the m ajor issues surrounding the debate over the use o f nuclear power. Approxi mately 2 0 half-lives are required for the radioactivity o f nuclear waste m aterials to reach levels acceptable for biological exposure. For some types o f nuclear fuels, the wastes rem ain substantially radioactive for thousands o f years. A considerable am ount o f scientific research is devoted to the disposal o f radioactive wastes. Highly radioactive m ateri als from the reactor core are first treated with advanced technologies that ensure the materials will not deteriorate over a very long period o f tim e. Treated wastes are then stored in sealed containers that are buried deep underground. A nother issue is the lim ited supply o f the uranium -235 used in the fuel rods. O ne option is to build reactors that produce new quantities o f fissionable fuels. Reactors able to produce m ore fuel than they use are called breed er reacto rs. Although the design o f breeder reactors poses many difficult technical problems, they are currently in operation in several countries. ■ F ig u re 21 The interior of a reactor is filled with water. A crane is used to extract and replace fuel rods. Q READING CHECK In fe r how the storage of nuclear wastes affects the I environment. ■ F ig u re 22 T h e N u cle a r A g e The discovery of X-rays in 1895 initiated a series of breakthroughs in understanding atomic nuclei. Today, nuclear chemistry applications involving medicine, weaponry, and energy affect the lives of people worldwide. 1919 J The first artificially induced nuclear reaction causes the transmutation of nitrogen into an iso tope o f oxygen by bom barding nitrogen gas w ith alpha particles. 1934 Enrico Fermi's experiments result in the world's first nuclear fission reaction. Fermi's subsequent research will pioneer nuclear power generation. 1900 ^1 1895 The first X-ray photographs fuel intense inter est among the sci entific community. 882 C hapter 24 • Nuclear Chemistry 1898 Marie and Pierre Curie discover the radioactive elements polonium and radium. Their work establishes the early fram ework for the study of nuclear chemistry. 1941—45 Manhattan Project scientists develop uranium and plutonium bombs, which were dropped on Hiroshima and Nagasaki, Japan, in 1945 and ended World War II. Nuclear Fusion Recall fro m th e binding en erg y d iag ram in F ig u re 1 4 th at a m ass RealWorld CHEMIS Nuclear Fusion n u m b er o f abou t 6 0 has the m o st stable atom ic configuration. Thus, it is possible to bin d to g eth er tw o o r m o re light (m ass n u m b er less than 6 0 ) ■ and less-stable nuclei to fo rm a single m ore-stable nucleus. T h e com b ining o f a to m ic nuclei is called nuclear fusion. N uclear fusion reactions, w hich are responsible for the p ro d u ctio n o f the heaviest elem ents, are ■ capable o f releasing v e ry large am o u n ts o f energy. You already have som e everyd ay know ledge o f this fact— th e Sun is pow ered by a series o f fusion reactio n s as h ydrogen atom s fuse to form helium atom s. 4 }H —> 2(3 + jH e + en ergy Scientists have spent several decades research in g nuclear fusion. It is a p rom isin g so u rce o f en erg y and has several advantages co m p ared to SOLAR FUSION Nuclear fusion nu clear fission. Lightw eight isotopes used to fuel the reaction s, such as reactions are responsible for the glow and heat from stars such as the Sun. The temperature of the Sun's core is about 15,000,000 K. It is so hot and dense that hydrogen nuclei fuse to produce helium. After billions of years, the Sun's hydrogen w ill be mostly depleted. Its temperature will rise to about 100,000,000 K, and the fusion process will then change helium into carbon. hydrogen, are ab u ndant. Fusion reaction p ro d u cts are n ot generally rad ioactive. N u clear fusion p rod u ces large am ou nts o f energy. Fusion reaction s p ro d u ce m o re en erg y p er unit o f m ass o f fuel than fission reaction s. T h is cou ld solve th e problem o f the increasing needs for electricity in the w o rld s societies. U nfortunately, th ere are m ajor problem s th at m u st be o vercom e on a co m m ercially viable scale. O ne su ch p roblem is that fusion requires extrem ely h igh energies to initiate and sustain a reaction . T h e required energy, w hich is achieved only at extrem ely high tem peratures, is need ed to o v erco m e th e electrostatic repulsion betw een the nuclei in the reaction . B ecau se o f the en ergy requirem ents, fusion reaction s are also k now n as thermonuclear reactions. A tem p erature o f 5 ,0 0 0 ,0 0 0 K is required to fuse h ydrogen atom s. T his tem p eratu re— and even higher tem p eratu res— have been achieved using an atom ic explosion to initiate the fusion p rocess, but this ap p roach is n o t p ractical for controlled electric p ow er generation. t 1 9 4 9 Radiocarbon dat ing allows scientists to determine the age of artifacts made from plant-based materials as old as 45,000 years. • 1960s Scientists research using high-energy radiation to treat cancer. Clinical trials bring dramatic improvement in the treatment and cure of malignant tumors. 2 0 0 6 The Cassini spacecraft explores the Saturn system. Cassini is powered by technology that converts heat from the radioactive decay of plutonium into electricity. 1 9 7 9 , 1 9 8 6 Nuclear power plant accidents at Three Mile Island, Pennsylvania, and Chernobyl, Ukraine, focus world attention on the dangers asso ciated with nuclear power. • 2 0 1 0 Scientists using NASA's Fermi Gamma- ray Space Telescope discover two massive bubbles, one above and one below the core of the Milky Way. They are thought to be the result of activity from either a black hole or star formation. S e c tio n 3 • Nuclear Reactions 883 Poloidal field magnet Toroidal field magnet Vacuum chamber ■Figure 23 A tokamak reactor, a ring-shaped reactor, uses strong magnetic fields to contain the intensely hot fusion reaction and keep it from direct contact with the reactor interior walls. The poloidal magnets follow the shape of the reactor and the toroidal magnets wrap around the reactor. Obviously, m an y problem s m u st be resolved before fusion becom es a practical en ergy source. A n o th er significant problem is confinem ent o f the reaction . T here are cu rren tly n o m aterials capable o f w ithstanding the trem en d ou s tem peratures th at are required by a fusion reaction. M uch o f the cu rren t research centers arou nd an apparatus called a tokam ak reactor. Th e nam e tokamak com es from Russian and m eans toroidal ch a m ber with an axial m agnetic field. A tokam ak reactor, shown in Figure 23, is a donut-shaped device that uses strong m agn etic fields to con tain the fusion reaction . W h ile significant progress has been m ade in the field o f fusion, tem peratures high enough for continuous fusion have n ot yet been sustained for long periods o f time. SECTION 3 REVIEW S e c tio n S u m m a r y • Induced transmutation is the bombardment of nuclei with particles in order to create new elements. • In a chain reaction, one reaction induces others to occur. A sufficient mass of fissionable material is necessary to initiate the chain reaction. • Fission and fusion reactions release large amounts of energy. 22. M AINIDEA Com pare and contrast nuclear fission and nuclear fusion reactions. Describe the particles that are involved in each type of reaction and the changes they undergo. 23. Describe the process that occurs during a nuclear chain reaction and explain how to monitor a chain reaction in a nuclear reactor. 24. Explain how nuclear fission can be used to generate electric power. 25. Form ulate an argument supporting or opposing nuclear power as your state's primary power source. Assume the primary source of power currently is the burning of fossil fuels. 26. Calculate What is the energy change (AE) associated with a change in mass {Am) of 1.00 mg? 27. In te rp re t Graphs Use the graph in F ig u re 1 4 to answer the following questions. a. Why is the isotope ^Fe highest on the curve? b. Are more stable isotopes located higher or lower on the curve? c. Compare the stability of Li-6 and He-4. 884 C h a p te r 24 • Nuclear Chemistry SECTION 4 Applications and Effects ofjsluclear Reactions M A I N I D E A N uclear reactions have m any useful applications, but th e y also have harm ful biological effects. E s s e n tia l Q u e s tio n s • What are several methods used to detect and measure radiation? CH EM • How is radiation used in the treatment of disease? 4 • What are some of the damaging effects of radiation on biological systems? R e v ie w V o c a b u la r y isotope: an atom of the same element with the same number of protons but different number of neutrons v n . , | U U Almost everyone gets cuts or scrapes from lime to time. Usually, the first thing you do is dean the injury and cover it with a bandage to keep out germs. One of the many uses of radiation is to sterilize medical bandages. Detecting Radioactivity You read earlier th at Becquerel discovered radioactivity because o f the effect o f radiation on photograp h ic plates. Since this discovery, several o th er m eth od s have b een devised to d etect radiation. People w ho w ork N e w V o c a b u la r y n ear radioactive sources, for exam ple, m igh t be required to w ear a ionizing radiation radiotracer th erm olu m in escen t d osim eter (T L D ) badge, w hich contains a tiny crystal. R adiation excites electrons w ithin the crystal. To determ ine the rad iation dose, the crystal is heated, and the electrons retu rn to their grou n d states, em itting light. R adioactivity readers d etect this light as a m easure o f the radiation dose to w hich a w orker has been exposed. M onitorin g the radiation dose received by people w ho w ork near rad ioactive sources is im p ortan t to ensure th eir safety. R adiation energetic enough to ionize m atter w ith w hich it collides is called ionizing radiation. Th e G eiger co u n ter is an ionizing radiation d etection device. As show n in Figure 24, a G eiger cou n ter consists o f a m etal tube filled w ith a gas. In the cen ter o f the tube is a wire that is co n n ected to a pow er supply. W h en ionizing radiation penetrates the end o f the tube, the gas inside the tube absorbs the radiation and form s ions and free electrons. T h e free electrons are attracted to the wire, causing an electric cu rren t. A m eter built into the Geiger cou n ter m easures the cu rren t flow through the ionized gas. This cu rren t m easurem ent is used to determ in e the am ou nt o f ionizing radiation present. ■Figure 24 A Geiger counter is used to detect and measure radiation levels. Ionizing radiation produces an electric current in the counter. The current is displayed on a scaled meter, whereas a speaker produces audible sounds. Gas molecules are ionized by the radiation Counter and audio device Electrode (positively charged) Metal tube (negatively charged) Nonionized gas molecules Window Ionizing radiation S e c tio n 4 • Applications and Effects of Nuclear Reactions 885 ■Figure 25 Scintillation counters are used to detect the presence of ionizing radia tion. An ionizing radiation excites the electrons in the phosphors. As the electrons return to their ground states, they emit photons, which are then detected by the photodetector. A n o th er d etection device is a scintillation counter. Scintillations are b rief flashes o f light p rodu ced w hen ionizing radiation excites the electrons in certain types o f atom s o r m olecules called phosphors. A scintillation co u n ter contains a base m aterial— often a plastic, a crystal, o r a liquid— con tain ing phosphors, as shown in Figure 25. Ionizing radiation that strikes the scintillation cou n ter can transfer energy either directly to the phosphors o r to the base m aterial, w hich then transfers the en ergy to the phosphors. This energy excites electrons in the ph os ■Figure 26 Gauges such as the one phors. As these electrons retu rn to their grou n d states, they release pictured use beta emission from krypton, promethium, or strontium. The radioactive source is placed on one side of the paper, and a detector is on the other side. Most beta particles are absorbed by the paper, but the percentage that are able to travel through to the detector indicates the thickness of the paper. energy in the form o f light. This light is transm itted through the base m aterial to a p h otod etector that con vert the light to an electrical signal. The n u m ber and brightness o f the scintillations give a m easure o f the am ou nt o f ionizing radiation. □ READING CHECK S u m m a rize how a scintillation detector works. Uses o f Radiation W ith p roper safety procedures, radiation can be useful in m any scien tific exp erim ents and industrial applications. F or instance, neutron activation analysis is used to detect trace am ounts o f elem ents present in a sample. C om p u ter-ch ip m anufacturers use this technique to analyze the com position o f highly purified silicon wafers. In the process, the sam ple is bom barded with a beam o f neutrons from a radioactive source, causing som e o f the atom s in the sam ple to becom e radioactive. T h e type and am ount o f radiation em itted by the sam ple is used to determ ine the types and quantities o f elem ents present. N eutron activa tion analysis is a highly sensitive m easurem ent technique capable o f detecting quantities o f less than 1 x 1 0 ~ 9 atom s in a sample. Beta em ission is another application o f radiation. It is used to m easure paper thickness, as shown in Figure 26. 886 C h a p te r 24 • Nuclear Chemistry U s in g r a d io is o t o p e s R adioisotopes can also be used to follow the cou rse o f an elem en t th rou g h a ch em ical reaction . F o r exam ple, C O 2 gas co n tain in g rad ioactive c a r b o n -14 isotopes has been used to study glucose fo rm atio n in photosynthesis. 6 C 0 2 + 6 H 20 - nhght> C 6 H 120 6 + 6 0 2 B ecau se the C O 2 co n tain ing c a r b o n -14 is used to trace the progress o f ca rb o n th ro u g h th e reactio n , it is referred to as a rad iotracer. A radiotracer is a rad ioiso to p e th at em its n on -ion izing radiation and is used to signal th e p resen ce o f an elem ent o r specific substance. Th e fact that all o f an elem en ts isotopes have the sam e ch em ical properties m akes th e use o f radioisotopes possible. Thus, replacing a stable atom o f an elem en t in a reactio n w ith one o f its isotopes does n ot alter the ^ v . n t l V I I 3 I l \ T ------------------- -n R adiatio n Therapist Under the supervision of a physician, a radiation therapist administers radiation treatment to patients. Radiation therapists work closely with patients and must be compas sionate and supportive. Training programs prepare radiation thera pists to use particle accelerators and other forms of technology. Knowledge of radiation hazards is an important part of this job. reaction . R ad io tracers are im p o rtan t in a n u m b er o f areas o f chem ical research , p articu larly in analyzing the reactio n m echan ism s o f com plex, m ultistep reaction s. R ad io tracers also have im p o rtan t uses in m edicine. Io d in e -1 3 1 , for exam ple, is co m m o n ly used to d etect diseases associated w ith the thyroid gland. If a p roblem is suspected, the patient will drink a solution con tain in g a sm all am o u n t o f io d in e -131. A fter the iodine is absorbed, the a m o u n t o f iod ine taken up by the thyroid is m easured and used to m o n ito r th e fu n ction in g o f th e thyroid gland. □ READING CHECK D e fin e rad iotracer. T r e a t in g c a n c e r R adiation can pose serious health problem s for h u m an s b ecau se it can dam age o r destroy healthy cells. However, rad iation can also d estroy unhealthy cells, such as can cer cells. All can cers are ch aracterized by the rapid grow th o f abnorm al cells. This grow th ca n p ro d u ce m asses o f ab n orm al tissue, called m alignant tu m ors. R adiation th erapy is used to treat can cer b y destroying the ca n ce r cells. In fact, ca n ce r cells are m o re susceptible to d estru ction by rad iation than healthy ones. Figure 27 shows a brain scan with a m align an t tum or. A fter rad iation treatm en t, the baseline returns to n orm al. U nfortunately, in the p rocess o f destroying unhealthy cells, rad iation also destroys som e healthy cells. D espite this m ajor draw back, ■Figure 27 Radiation can be used to treat rad iation th erapy has b eco m e one o f the m o st effective treatm ent cancer. MRI images taken before treatment and after 4 and 10 months of treatment show the decrease in the size of the tumor. options in the fight against cancer. S e c tio n 4 • Applications and Effects of Nuclear Reactions 887 ■Figure 28 Gamma rays emitted by the radiotracers absorbed by the patients are mea sured with this detector. The image on the right shows different areas of the brain emitting gamma rays. These images might help doctors locate a tumor or observe a brain function. U s in g p o s it r o n e m is s io n A n o th er radiation-based m edical diagnostic tool is called p ositron em ission transaxial tom ograph y (P E T ). In this proced u re, a rad io tracer that decays by positron em ission is injected into the p atien ts b loodstream . Positrons em itted by the rad io tracer cause g am m a -ra y em issions that are then detected by an array o f sensors surrou n d in g the patient, as show n in Figure 28. P E T scans can be used to diagnose diseases o r study the parts o f the brain that are activated un d er given circu m stan ces, also shown in Figure 28. Biological Effects o f Radiation A lthough radiation has a n u m b er o f m edical and scientific applications, it can be v ery harm ful. T h e dam age p rodu ced from ionizing radiation absorbed by the b od y depends on several factors, such as the type of radiation, its energy, the type o f tissue absorbing the radiation, the p enetrating power, and the distance from the source. Figure 29 shows an exam ple o f such dam age. Connection¥9 Biology H igh-energy ionizing radiation is dangerous because it can fragm ent and ionize m olecules w ithin biological tissue. A free radical is an atom o r m olecule that contains one or m ore unpaired electrons and is one exam ple o f the highly reactive products o f ionizing radiation. In a biological system, free radicals can affect a large num ber o f oth er m olecules and ultimately disrupt the operation o f norm al cells. Ionizing radiation dam age to living systems can be classified as either som atic o r genetic. Som atic dam age affects only nonreproductive body tissue. It includes burns and can cer caused by dam age to the cell’s grow th m echanism . G enetic dam age can affect offspring by dam aging reproductive tissue. Such dam age is difficult to study because it m ight n ot b ecom e apparent for several generations. ■Figure 29 Radiation can disrupt cell processes and damage skin. Infer Is the lesion pictured here somatic or genetic? | j| \ ■VVv. 1 1 1 1 1 8 8 888 C h a p te r 24 • Nuclear Chemistry D o s e o f r a d i a t i o n A dose o f radiation refers to the am ou nt o f rad iation a b od y absorbs fro m a rad ioactive source. Two units, th e rad an d th e rem , are co m m o n ly used to m easure doses. T h e rad , w hich stands for rad iation -ab sorb ed dose, is a Table 6 Effects o f S hort-term R adiation Exposure Dose (rem) Effects on Humans m easu re o f th e am o u n t o f rad iation that results in the ab so rp tion o f 0 .0 1 J o f en erg y p er k ilogram o f tissue. T he dose in rads, 0-25 how ever, d oes n o t acco u n t for the en erg y o f the radiation, the type o f living tissue absorbing the rad iation , o r the tim e o f the 25-50 exp osu re. To a cc o u n t for these factors, the dose in rads is m ultiplied by a n u m erical facto r th at is related to the radiations effect on the tissue involved. T h e result o f this m ultiplication is 100-200 a unit called the rem . T h e rem , w hich stands for roentgen equivalent for m an , is n am ed after W ilhelm R oentgen, who d iscovered X -ra y s in 1 895. T a b le 6 su m m arizes the sh o rt-te rm 500 no detectable effects temporary decrease in white-blood-cell population nausea, substantial decrease in white-blood-cell population 50% chance of death within 30 days of exposure effects o f rad iation on h u m an s, depending o n the dose. A v ariety o f so u rces con stan tly b om b ard you r b od y with rad iation . Y o u r exp o su re to these sou rces results in an average annual rad iatio n exp o su re o f 1 0 0 - 3 0 0 m illirem s o f h igh -en ergy rad iation o r 0 .1 - 0 .3 rem s. T a b le 7 shows y ou r annual exposure to co m m o n rad iation sources. I n t e n s i t y a n d d is t a n c e T h e intensity o f radiation depends Watch a video about radioisotopes. on th e d istan ce fro m the so u rce as show n by the equation below. T h e farth er aw ay the so u rce, the low er the intensity. T h e intensity o f rad iation is m easu red in am ou nt o f radiation p er u n it o f tim e a n d /o r surface, su ch as m re m /s -m 2. Radiation Intensity and Distance _ , 2 M ** 1 t j 2 and d 2 a re tw o distances from the source. ^ 2 “ 2 / , is th e intensity a t </lf and l 2 is the intensity a t d 2. The intensity of a radiation at a distance d, from the source multiplied by the square of the distance equals the intensity of the radiation at a distance dj multiplied by the square of the distance. Table 7 Average Annual Radiation Exposure Source Average Exposure (mrem/y) Cosmic radiation 20-50 Radiation from the ground 25-175 Radiation from buildings 10-160 Radiation from air 20-260 Human body (internal) Medical and dental X-rays Nuclear weapon testing Air travel Total average -20 50-75 <1 5 100-300 S e c tio n 4 • Applications and Effects of Nuclear Reactions 889 oblem-Solvinq LAB Interpret Graphs How does distance affect radiation exposure? W hen one of the reactors at the Chernobyl nuclear pow er plant exploded, the im m ediate vicinity o f the pow er plant was highly contam inated and declared a dead zone. The radiation spread over thousands o f kilome ters. However, th e intensity o f the radiation decreased w ith th e distance from the reactor. Radiation Intensity Versus Distance From Source A n a ly s is The graph to the right shows the intensity of a radioactive source versus the distance from the source. Note how the intensity of the radiation varies w ith th e distance from the source. The unit o f radiation intensity is millirems per second per square meter. This is the am ount of radiation striking a square m eter o f area each second. Distance from source (m) T h in k C ritic a lly 1. Evaluate How does the radiation exposure change as the distance doubles from 0.1 m to 0.2 m? How does it change as the distance quadruples from 0.1 m to 0.4 m? 2. Formulate in words th e mathematical relationship described in your answer to Question 1. SECTION 4 REVIEW S e c tio n S u m m a r y • Different types of counters are used to detect and measure radiation. • Radiotracers are used to diagnose disease and to analyze chemical reactions. • Short-term and long-term radiation exposure can cause damage to living cells. 3. Interpret Graphs Determ ine the distance from the source at which the radiation decreased to 0.69 mrem/s*m2. This intensity is the maximum radiation exposure intensity considered safe. {Hint: Use the equation kfjn = c/22/c/12.) Section Self-Check 28. MAINIDEA Explain one way in which nuclear chemistry is used to diagnose or treat disease. 29. Describe several methods used to detect and measure radiation. 30. Com pare and contrast somatic and genetic biological damage. 31. Explain why it is safe to use radioisotopes to diagnose medical problems. 32. Calculate A lab worker receives an average radiation dose of 21 mrem each month. Her allowed dose is 5,000 mrem/y. On average, what fraction of her yearly dose does she receive? 33. In te rp re t D ata Look at the data in T a b le 7. Suppose someone is exposed to the maximum values listed for average annual radiation from the ground, from buildings, and from the air. What fraction would the person receive of the minimum short-term dose (25 rem) that causes a temporary decrease in white blood cell population? 890 C h a p te r 24 • Nuclear Chemistry c a r e e r s Career: Archaeologist N e u tr o n A c t iv a t io n A n a ly s is In th e Andes m ountain range, m ore than 500 years ago, a young girl was sacrificed to appease th e gods. As was th e custom o f th e ancient Incas, pottery and other artifacts w ere buried w ith her. Neutron activation analysis perform ed on pottery such as th e vessel in F ig u re 1 allow ed archaeologists to determ ine the origin o f th e soil from which th e pottery was made. Concentration of Elements Sample ID = CPA1260 Irrad. tim e = 5 s Decay tim e = 25 min Counting tim e = 12 min 100,000 10,000 1000 100 10 1 0 800 1600 2400 3200 Energy (keV) Figure 2 A gamma-ray spectrum indicates the concentration of different elements in a sample. Figure 1 Neutron activation analysis allowed comparison of soil and pottery to determine where this Incan vessel was made. D e te c tin g e le m e n ts Neutron activation analysis is a m ethod o f detecting elements in a m aterial. A small sample o f th e material is first exposed to a strong neutron source. Neutron bom bardm ent produces radioisotopes in about three-fourths o f th e elements. W hen the radio isotopes decay, they em it gam m a rays w ith energies th a t are characteristic o f the elem ent. A gam m a detector is used to measure the sample's radiation output. Gamma rays of d iffe re n t energies produce peaks at different places on graphs, such as the one in F ig u re 2. Each peak corresponds to a specific elem ent. Some elem ents have more than one peak because they em it gam ma rays o f different energies. The height o f the peak, or the area under the peak, indicates the concentration of the elem ent in th e sample. This m ethod can be used to search for just one elem ent or many elements in a sample. The process can detect extrem ely low concentrations of elements, as low as parts per billion. A d v a n ta g e s Most forms o f chemical analysis require vaporization, dissolution, or alteration o f the analyzed sample in some way. Neutron activation analysis is a nondestructive process th a t can be used to study liquid, solid, or gas eous samples. Sensitive items, such as forensic evidence, meteorites, or artifacts, can be ana lyzed w ith o u t harm. Uses Analyzing the composition o f artifacts such as pottery allow ed scientists to establish the origin of the clay used to make the objects th a t w ere buried w ith the young, sacrificed girl. Astonishingly, the clay did not come from local soil but from the Incan capital and other religious centers. Representatives from the Incan Empire traveled to remote places, bringing pottery and other artifacts w ith them , to perform rituals. WRITINGiNKhemistry A n a ly z e Look at the graph in F igure 2. Write an explanation about how a technician could use the graph to determine the elements present in the irradiated sample. Is the height of the peaks important? Which element is found in the greatest concentration in the sample? What are the approximate energies of gamma rays emitted by this element? Chemistry & Careers 891 C h e m L A B ______ (L — Investigate Radiation Dosage Background: Radiation is a term that causes fearful responses in people. However, not all radiation is dangerous. We are surrounded by radiation from space and from natural radioactivity on Earth. Radiation can also be used in a safe and controlled way for medical purposes. Question: What methods are effective in minimizing exposure to radiation? 8 . Place the alpha source on the 10-cm m ark, and place a heavy piece o f cardboard between the source and the Geiger counter. 9 . M easure and record the highest reading. 10. Place the source on the 3 0 -cm m ark, and place the piece o f cardboard on the 10 -cm m ark. M easure and record the radiation. 1 1 . Place the piece o f cardboard on the 2 0 -cm mark, and repeat the m easurem ent. Materials alpha source beta source gam m a source Geiger counter piece o f cardboard piece o f plastic m eterstick 1 2 . Place the piece o f plastic between the source, and counter and record the highest reading. 13. Repeat Steps 8 - 1 2 with the beta source and the gam m a source. 14. Cleanup and Disposal Return all lab equipment and radiation sources to the designated location. R em em ber to wash your hands with soap and water after com pleting the lab. clock Safety Precautions WARNING: Radioactive sources can be harmful. Wash hands and arms thoroughly before handling objects which go to the mouth, nose, or eyes. Do not eat or drink in laboratories where radioactive sources are used. Do not handle radioactive sources if you have a break in the skin below the wrist. Do not use—and immediately report to your teacher—any sealed disc containing a radioactive source which is damaged. Procedure 1. Read and com plete the lab safety form. 2 . Using what you know about types o f radiation, write a hypothesis about how pieces of cardboard and plastic will affect the radiation dose. 3. Create a table to record your data. Analyze and Conclude 1. Summarize How does distance affect the am ount o f radiation from a source? 2. Compare and Contrast Does the experim ental data support your hypothesis? 3. Explain Based on the data, explain why you were required to w ear goggles and a lab apron in this lab. 4. Recognize Cause and Effect W hich radiation source was least affected by the cardboard and plastic shields? Explain why this source is different from the other two sources. 5 . Infer Did the position o f the piece o f cardboard influence the results? Explain why or why not. 6. Observe and Infer W h at can you say about the penetrating power o f X -rays based on the fact that you have to wear a lead shield at the dentist to p rotect your body from the radiation? 4 . Place the m eterstick on the lab station with the Geiger counter at the zero-end. 5. Place the alpha source at the 10-cm m ark, and record the highest reading on the Geiger counter. 6 . Repeat the m easurem ent with the source at 20 cm and 30 cm. 7 . Repeat Steps 5 and 6 with the beta source and gam m a source. 892 C h a p te r 24 • Nuclear Chemistry INQUIRY EXTENSION Research Find references that list and quantify the exposure to radiation that we receive in everyday life. Calculate your average annual exposure, and describe m ethods that could reduce this dosage. B IG ID E A Nuclear chemistry has a vast range of applications, from the production of electricity to the diagnosis and treatment of diseases. MAIIMIDEA Under certain conditions, some nuclei can emit alpha, beta, or gamma radiation. • Wilhelm Roentgen discovered X-rays in 1895. • Henri Becquerel, Marie Curie, and Pierre Curie pioneered the fields of radioactivity and nuclear chemistry. VOCABULARY • radioisotope • X-ray • penetrating power • Radioisotopes emit radiation to attain more-stable atomic configurations. s e c tio n 2 Radioactive Decay MAIIMIDEA Unstable nuclei can break apart spontaneously, changing the identity of atoms. • The conversion of an atom of one element to an atom of another by radioactive decay processes is called transmutation. • Atomic number and mass number are conserved in nuclear reactions. • A half-life is the time required for half of the atoms in a radioactive sample to decay. N = N ^ i ) 'o r N = N ^ ) " • Radiochemical dating is a technique for determining the age of an object by measuring the amount of certain radioisotopes remaining in the object. s e c tio n 3 VOCABULARY • transmutation • nucleon • strong nuclear force • band of stability • positron emission • positron • electron capture • radioactive decay series • half-life • radiochemical dating Nuclear Reactions__ MAIIMIDEA Fission, the splitting of nuclei, and fusion, the combining of nuclei, release tremendous amounts of energy. • Induced transmutation is the bombardment of nuclei with particles in order to create new elements. • In a chain reaction, one reaction induces others to occur. A sufficient mass of fissionable material is necessary to initiate the chain reaction. • Fission and fusion reactions release large amounts of energy. VOCABULARY • induced transmutation • transuranium element • mass defect • nuclear fission • critical mass • breeder reactor • nuclear fusion • thermonuclear reaction E = m e2 « rn n M i Applications and Effects of Nuclear Reactions MAIIMIDEA Nuclear reactions have many useful applications, but they also have harmful biological effects. • Different types of counters are used to detect and measure radiation. VOCABULARY • ionizing radiation • radiotracer • Radiotracers are used to diagnose disease and to analyze chemical reactions. • Short-term and long-term radiation exposure can cause damage to living cells. Il4 l = ^2^2 C h a p te r 24 • Study Guide SECTION 1_______ SECTION 2 M astering Concepts M astering Concepts 34. Compare and contrast chemical reactions and nuclear reactions in terms of energy changes and the particles involved. 35. Match each numbered choice on the right with the correct radiation type on the left. 1 . high-speed electrons a. alpha 2 . 2 + charge, blocked easily b. beta 3. no charge, electromagnetic c. gamma radiation 42. What is the strong nuclear force? On which particles does it act? 43. Explain the difference between positron emission and electron capture. 44. Categorize each type of radioactive decay. a. Mass number and atomic number are unchanged. b. Mass number remains the same and atomic number decreases. 45. What is the significance of the band of stability? 46. What is a radioactive decay series? When does it end? O + 1— Radioactive source — y 47. Radioisotopes What are the factors that determine the amount of a given radioisotope in nature? Band of Stability ^ A Charged plates Q) E ■ Figure 30 36. Figure 30 shows alpha particles, beta particles, and gamma rays passing through a screen and between two charged plates. What can you infer about the identity of a, b, and c? Explain your answer. 3 7. What is the difference between X-rays and gamma rays? M astering Problems 38. Dental crown Uranium-234 is used to make dental crowns appear brighter. The alpha decay of uranium-234 produces what isotope? 39. Detecting Material Flaws Flaws in welded metal parts of airplanes can be identified by placing the isotope iridium-192 on one side of the weld and photographic film on the other side to detect gamma rays that pass through. How does the gamma ray emission affect the atomic number and mass number of the iridium? 40. Colored Glass Thorium-230 can be used to provide coloring in glass objects. One method of producing thorium-230 is through the radioactive decay of actinium-230. Is this an example of alpha decay or beta decay? How do you know? 41. Plastic Bags Thin sheets of plastic are used to make items such as grocery bags. The sheets move under a source of promethium-147, emitting beta particles. The radiation intensity, measured under the plastic sheets, is used to monitor the thickness of the plastic. During this process, promethium changes into which element? 894 C h a p te r 24 • Nuclear Chemistry Number of protons ■ Figure 31 48. In which region(s) in Figure 31 are you likely to find a. stable nuclei? b. nuclei that undergo alpha decay? c. nuclei that undergo beta decay? d. nuclei that undergo positron emission? 49. Carbon-14 Dating Carbon-14 dating makes use of a specific ratio of two different radioisotopes. Define the ratio used in carbon-14 dating. Why is this ratio constant in living organisms? Mastering Problems 50. Calculate the neutron-to-proton ratio for each atom. a. tin-134 c.carbon-12 b. silver-107 d.carbon-14 51. Complete the following equations. ,B i- 2r ,He b. 2f 3Np-931',F239 83^* it + T ' ?: •** 7 94PaU + ? 52. Write a balanced nuclear equation for the alpha decay of americium-241. 53. Write a balanced nuclear equation for the beta decay of cesium-137. 54. Bone Formation The electron capture of strontium-85 can be used by physicians to study bone formation. Write a balanced nuclear equation for this reaction. 55. Nuclear Safety The half-life of tritium (JH) is 12.3 y. If 48.0 mg of tritium is released from a nuclear power plant during the course of a mishap, what mass of the nuclide will remain after 49.2 y? After 98.4 y? 56. Static Charge Static charge can interfere with the production of plastic products by attracting dust and dirt. To reduce it, manufacturers expose the area to poloni um-210, which has a half-life of 138 days. How much of a 25.0-g sample will remain after one year (365 days)? 57. The half-life of polonium-218 is 3.0 min. If you start with 2 0 .0 g, how long will it be before only 1 .0 g remains? 58. An unknown radioisotope exhibits 8540 decays per second. After 350.0 min, the number of decays has decreased to 1250 per second. What is the half-life? SECTION 3__________ M astering Concepts 59. Define transmutation. Are all nuclear reactions also transmutation reactions? Explain. 60. Relate binding energy per nucleon to mass number. 61. Referring to Figure 7, would you expect 2oCa to be radioactive? Explain. 62. W hat is a chain reaction? Give an example of a nuclear chain reaction. 63. Explain the purpose of control rods in a nuclear reactor. 64. Why is the fuel of a nuclear reactor enriched? M astering Problems 69. Smoke Detectors Americium-241, a radioisotope used in smoke detectors, is produced by bombarding plutonium-238 with neutrons to produce plutonium-240, which is bombarded with neutrons to produce plutonium-241. The plutonium-241 decays to americium-241. Write the balanced nuclear equations for each reaction. 70. Exit Signs Exit signs are coated with a paint containing phosphors. These phosphors are activated by the radioisotope tritium ( ^H), produced by bombarding lithium- 6 with neutrons to produce lithium-7. The lithium-7 then undergoes alpha decay to produce the tritium. Write balanced nuclear equations for both steps. 71. Control Rods Bombarding uranium-235 with neutrons produces samarium-149, which is used in nuclear reactor control rods. What other element is produced? 72. The Sun }H + jH —> ^He + y is one of the fusion reactions in the Sun. The mass of }H is 1.007825 amu, the mass of [H is 2.014102 amu, and the mass of ^He is 3.016029 amu. a. What is the mass defect of ^He? b. What energy is released by the process? SECTION 4____________ M astering Concepts 73. What property of isotopes allows radiotracers to be useful in studying chemical reactions? 74. Which unit of radiation dose, rem or rad, is most useful for describing the effect of radiation on living tissue? 75. PET Scans In PET scans, the radiotracer emits positrons, which travel a few millimeters before interacting with electrons. How can the original radiotracer be detected? Intensity v. Distance From the Source ■ F ig u re 32 65. Describe what is meant by the terms critical mass, subcritical mass, and supercritical mass. Which is shown in Figure 32? How can you tell? 66 . Explain how it is possible that fission (the splitting of nuclei) and fusion (the combining of nuclei) both release tremendous amounts of energy. 67. Describe the current limitations of fusion as a power source. 68 . Why does nuclear fusion require so much heat? How is heat contained within a tokamak reactor? Distance from the source ■ Figure 33 76. Figure 33 shows a simplified graph of radiation intensity versus distance from the source. Explain this graph and what it implies about a method of reducing the effects of radiation exposure. C h a p te r 24 • Assessment 895 M a s te rin g P roblem s 87. Sheet Metal A company plans to monitor the thickness of sheet metal during production. What would you recommend the company do to determine a safe distance for workers from the gamma source? Decay Series Source ......................................... ? «*g **~ »■ ■ F igure 34 7 7 . Figure 34 shows the position of two workers near a radioactive gamma source. The worker at Position A is 2.5 m from the source and receives an exposure of 0.98 mrem/s*m2. The worker at Position B receives an exposure of 0.50 mrem/s-m2. What is the distance of the worker at Position B from the source? 7 8 . A worker stands near a machine that uses a cobalt-60 gamma source to sterilize medical equipment. The workers dose 2.0 m from the source is 0.85 mrem/s-m2. What is the workers dose at a distance of 3.5 m? 7 9 . Safe Exposure The intensity of a radioactive source is 1.15 mrem/s*m 2 at a distance of 0.50 m. What is the minimum distance a person could be from the source to have a maximum exposure of 0.65 mrem/s*m2? Mass number ■ Figure 35 88 . Figure 35 shows part of the decay series of a radio isotope. For each segment on the graph, tell whether alpha decay or beta decay occurs, and identify the change in atomic number and mass number. 89. Make and Use Graphs Thorium-231 decays to lead207 by emitting the following particles in successive steps: (3, a , a , (3, a , a , a , (3, |3, a . Plot each step of the decay series on a graph of mass number versus atomic number. Label each plotted point with the symbol of the radioisotope. 90. Apply Chemical treatment is often used to destroy 80. Technetium-104 has a half-life of 18.0 min. How much of a 165.0 g sample remains after 90.0 minutes have passed? 81. A bromine-80 nucleus can decay by gamma emission, positron emission, or electron capture. What is the product nucleus in each case? 82. The half-life of plutonium-239 is 24,000 y. How much nuclear waste generated today will remain in 1 0 0 0 years? 83. Red Blood Cells A medical researcher is using a chromium-51 source to study red blood cells. The gamma-emission intensity at a distance of 1.0 m is 0.75 mrem/s*m2. At what distance would the intensity drop to 0.15 mrem/s-m2? 84. The binding energy per nucleon reaches a maximum around what mass number? Explain how this number is related to the fission and fusion processes. 85. You have an alpha source, a beta source, and a gamma source. Design a plan to use a Geiger counter, paper, and foil to determine the identity of each source. 86 896 . What is the half-life of radon-222 if a sample initially contains 150 mg and only 18.7 mg after 11.4 days? C h a p te r 24 • Nuclear Chemistry harmful chemicals. For example, bases neutralize acids. Why can’t chemical treatment be applied to destroy the fission products produced in a nuclear reactor? 91. Compare A biological concern about working around some radioactive materials is the radioactive dust a person might inhale. Compare the effect of alpha radiation outside the body and inside the body. 92. Interpret Small radioactive sources are often used for laboratory experiments. The radioactive substance is enclosed in a metal container with a small window. A gamma source might be covered with a stainless steel window. What would you expect the window of an alpha source to be like? Why? 93. Analyze Some radioisotopes used for medical imaging have half-lives as short as several hours. Why is a short half-life beneficial? Why is it a problem? 94. Infer The production of electricity at nuclear fission reactor facilities is controversial. Think about the benefits and dangers of this technology. Explain your opinion about whether nuclear reactors should be used. CHALLENGE PRORI FM 95. W R IT IN G Use the information in Table 8 to calculate the mass defect and binding energy of deuterium ( jH), a hydrogen isotope involved in fusion reactions in the Sun. T a b le 8 Mass of Particles Particle Mass (amu) Hydrogen 1.007941 Deuterium 2.014102 Neutron 1.008665 a. Find the mass of the nucleons. b. Find the mass defect by subtracting the mass of the nucleons from the mass of the deuterium. c. Find the binding energy using the conversion 1 amu = 931.49 MeV. CUMULATIVE REVIEW 9 6 . Identify each property as chemical or physical. a. The element mercury has a high density. b. Solid carbon dioxide sublimes at room temperature. c. Zinc oxidizes when exposed to air. d. Sucrose is a white crystalline solid. 9 7 . Why does the second period of the periodic table contain eight elements? 9 8 . Draw each molecule and show the locations of hydrogen bonds between the molecules. a. two water molecules b. two ammonia molecules c. one water molecule and one ammonia molecule 9 9 . W hat process takes place in each situation? a. a solid air-freshener cube getting smaller and smaller b. dewdrops forming on leaves in the morning steam rising from a hot spring d. a crust of ice forming on top of a pond c. 1 0 0 . If the volume of a sample of chlorine gas is 4.5 L at 0.65 atm and 321 K, what volume will the gas occupy at STP? 1 0 1 . The temperature of 756 g of water in a calorimeter increases from 23.2°C to 37.6°C. How much heat was given off by the reaction in the calorimeter? 1 0 2 . Explain what a buffer is and why buffers are found in body fluids. 1 0 3 . Explain how the structure of benzene can be used to explain its unusually high stability compared to other unsaturated cyclic hydrocarbons. ► C h e m is tr y 104. Marie Curie and Irene Curie Joliot Research and report on the lives of Marie Curie and her daughter, Irene Curie Joliot. What kind of scientific training did each receive? What was it like to be a female chemist in their time? What discoveries did each make? 105. Nuclear Waste Evaluate environmental issues associated with nuclear wastes. Research the Yucca Mountain nuclear waste disposal plan, the Hanford nuclear site, or a local nuclear facility. Prepare a poster or multimedia presentation on your findings. 106. Radioactive Sources Students in your school might not realize how beneficial radioactive sources can be. Create a poster showing some common, beneficial uses of radioactive sources. Be sure to point out safeguards that are taken to ensure the sources are safe. DBQ Document-Based Questions Half-Lives The National Institute o f Standards and Technology (NIST) maintains a database o f radionuclide half-lives. In 1992, researchers at NIST measured the half-lives shown in Table 9. Data obtainedfrom: Unterweger, M.P., Hoppes, D.D., andSchima, F.J. 1992. Newand revisedhalf-lifemeasurements results, Nud. Instrum. Meth. Phys. Res, A312:349-352. T a b le 9 Half-Lives Radionuclide Half-life Fluorine-18 1.82951 h Molybdenum-99 | Samarium-153 65.9239 h 46.2853 h 107. Fluorine-18 is used in medical imaging. If a lab has a sample containing 15 g of fluorine-18, how much fluorine-18 will remain in the sample after 8 .0 h? 108. Technetium-99 can be used for diagnostic tests of the heart and lungs. Because of technetium-99’s very short half-life, medical facilities produce it from molybdenum-99. If the facility has a 25-g sample of molybdenum-99, how much will it have one week (168 h) later? 109. Samarium-153 is used in the production of a drug to treat pain from bone tumors. Radiation released by the samarium hinders the tumor growth, thereby reducing pain. How much of a 1.0 g sample of samarium-153 is left after 4 days (96 h)? C h a p te r 24 • Assessment 897 MULTIPLE CHOICE 1. Geologists use the decay of p otassium -40 in volcanic 4. W h ich statem ent is N O T true of alpha particles? rocks to determ ine their ages. Potassium -40 has a A . They carry a charge o f 2 + . half-life o f 1.26 x 1 0 9 years, so it can be used to date B. They are represented by the symbol jHe. very old rocks. If a sample o f rock 3.15 x 1 0 8 years C. They are m ore penetrating than (1 particles. old contains 2.73 X IO* 7 g o f potassium -40 today, D. They have the sam e com position as helium nuclei. how m uch potassium -40 was originally present in the rock? A . 1.71 X IO" 8 g C . 3.25 X 10 7 g B . 2.30 X 1 0 _ 7 g D. 4 .3 7 X 1 0~ 6 g Use the graph below to answ er questions 5 a n d 6. 130 to generate neutrons by bom barding stable beryllium induced transm utation? sB + n C. ^Be •^ B + ? H f n D. iB e + it N. 100 </i ¥/X\ c yu WM Bandof stability o / * 4-* i r s 3 80 AH' Oi C m <4_ /O o /■ } r , x v — Q) 60 n/p atio = 1.28 y _Q ¥ E SO /iH 3 2 40 JT / :r / 30 j/ ji f 20 is the balanced nuclear equation describing this B. *Be + refjresents a table atorr 110 atoms. A neutron is released in the reaction. W hich ^B + n ■ 120 _ Each point or the nranh atom s with deuterons ( jH ), the nuclei o f deuterium A. 4 Be + The Band o f S tability 062P h 1 1\28 ruv 140 2 . In the early 1930s, van de G raaf generators were used 's + n 10 0 Use the fig u re below to answ er question 3. n/pratio = 1.0 1 0 10 1 1 2030 40 50 60 70 80 90 Num ber o f protons 5. W h y will calciu m -35 undergo positron emission? A . It lies above the line of stability. V B. It lies below the line of stability. c C . It has a high n eutron-to-proton ratio. D. It has an overabundance o f neutrons. 6 . Based on its position relative to the band o f stability, which process will jJjZn undergo? A+B J A. beta decay B. electron capture C . nuclear fusion Reaction coordinate D. positron emission nuclear fusion 7. A solution of 0 .600 M HC1 is used to titrate 15.00 m L 3. W hich is N O T a correct description o f this reaction? o f KOH solution. The end point o f the titration is A . This is a synthesis reaction. reached after the addition of 27.13 m L o f HC1. B . This reaction releases energy. W hat is the concentration o f the KOH solution? C. This reaction is endotherm ic. A . 9.00 M C. 0.332M D. This reaction will occu r spontaneously. B. 1.09M D. 0.0163M 898 C h a p te r 24 • Nuclear Chemistry SHORTANSWFR .CHEMISTRY Use the fig u r e below to an sw er questions 8 to 10. Use the fig u re below to answ er Q uestions 14 a n d 15. e~ flow Zinc Copper t 8 1 4 . D uring which segments are particles changing . Identify the an od e and cath od e o f this apparatus. states o f m atter? A. AB, CD, E F B. AB, EF C. BC , CD, DE 9 . W rite the oxidation half-reaction. 1 0 . Explain the function o f the salt bridge in this D. BC , EF E . BC , DE apparatus. 1 5 . D uring which segm ents are particles losing 1 1 . Predict the p rodu cts o f this reaction. kinetic energy? A l ( N 0 3 ) 3 (aq) + C a S 0 4 ( a q ) - > A. BC , D E B. AB, D E C. AB, CD, E F EXTENDED RESPONSE D. BC, D E, EF E. AB, CD, DE 1 6 . In the first steps o f its radioactive decay series, Use the fig u re below to an sw er Q uestions 12 a n d 13. th o riu m -232 decays to rad iu m -228, which then decays to actin iu m -228. W h at are the balanced + + + HF nuclear equations describing these first two decay H20 steps? h 3o + 1 2 . Identify the acid and the base for the forward reaction. Explain how you can tell. 1 3 . Explain how you can identify the conjugate acid and conjugate base for the forward reaction. A. 232Th 90 i n 2 2 8 n B. l o T h 2 2 8 C. 2 9oTh 2 2 8 90 i n D. 232Th 22=Ra + 2t 1 t ie , 228 88 Ra 88 . 88 88 Ra 88 Ra 90 i n E. 232Th W h a t are they? , 2 2 8 2 2 8 p + e > 88 Ka ' + ^He 2 2 8 88 Ra + e+, 2ggRa - 88 Ra, «Ra ■ 89 Ac ■ 22 8 89 2 2 8 89 Ac + e Ac + e - e' 2 g8A c 228 Ac 8 9 - + e- N E E D E X T R A H ELP? I f Y o u M is s e d Q u e s tio n . . . R e v ie w S e c t io n . . . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 2 4 .2 2 4 .3 1 5 .5 2 4 .1 2 4 .2 2 4 .2 1 8 .4 2 0 .1 2 0 .1 2 0 .1 9 .2 1 8 .1 1 8 .1 1 2 .4 1 2 .4 2 4 .2 C h a p te r 24 • Assessment 899