SOLUTION MANUAL FOR CHEMISTRY IN CONTEXT 10TH EDITION AMERICAN CHEMICAL SOCIETY by QuentinAxel

SOLUTION MANUAL FOR CHEMISTRY IN CONTEXT 10TH EDITION AMERICAN CHEMICAL SOCIETY ANSWERS AT THE END OF EACH CHAPTER CHAPTER 1: Portable Electronics: The Periodic Table in the Palm of Your Hand

Emphasizing Essentials 1. Answer: a. Compound (2 molecules of one compound made up of two different elements). b. Mixture (2 atoms of one element plus 2 atoms of another). c. Mixture (3 different substances, two elements and one compound). d. Element (4 atoms of the same element).

2. Answer: a. element (4 molecules of one diatomic element) b. Compound (2 molecules of one compound made up of two different elements). c. Mixture (2 atoms of one element plus 2 atoms of another). d. Compound (4 molecules of one compound made up of two different elements).

3. Answer: Exact answer will vary depending on viewing size of text. An approximate measurement for the period could be 0.25 mm. Converting this to nanometers: -3 m 0.25 mm × 10 × 1 nm = 2.5×105 nm or 250,000 nm. 1 mm

10-9 m

4. Answer: Converting 10.0 nanometers to millimeters: 10.0 nm × 10−5 mm or 0.00001 mm. 5. Answer: a. 1.5  103 m b. 9.58  10–11 m c. 7.5  10–6 m

6. Answer: 1×102cm, 1×106µm, 1×109nm.

1m 1×109 nm

1000 mm =1× 1m

7. Answer: a. Group 1 and Group 17 b. 1A: lithium, sodium, potassium, rubidium, cesium, francium 7A: fluorine, chlorine, bromine, iodine, astatine c. 1A: All but hydrogen (a nonmetal) are reactive metals. 7A: All but astatine (a metalloid) are reactive nonmetals.

8. Answer: a.

b. iron, Fe; magnesium, Mg; aluminum, Al; sodium, Na; potassium, K; silver, Ag. c.

d. sulfur, S; oxygen, O, carbon, C, chlorine, Cl, fluorine, F (and others).

9. Answer: a. compound d. element

b. compound e. mixture

c. mixture f. element

10. Answer: a. heterogenous mixture d. homogenous mixture 11. Answer:

b. heterogenous mixture e. heterogenous mixture

c. heterogenous mixture

Grey spheres: electrons Black spheres: protons White spheres: neutrons

12. Answer: There are several allotropes of sulfur. The most stable and common allotrope consists of 8 atoms in a ring. Other common allotropes include rings of 5, 6, 7, 10 and larger number of atoms. Most allotropes are yellow solids, although they can be found in liquid or gaseous forms at appropriate temperatures. Most of these allotropes are created by heating sulfur of the 8-membered ring form.

13. Answer: An aluminum atom with mass number 27 has 13 protons, 14 neutrons, and 13 electrons.

14. Answer: A copper atom with a mass number 64 has 29 protons, 35 neutrons, and 29 electrons. 15. Answer: Electrical conductivity is the transport of electrons from one location to another. Thermal conductivity is the transfer of heat from one location to another. Their difference is in what is being transferred. 16. Answer: mass of Hf

178.5 g/mol

a. total mass of Hf+O's = (178.5 g/mol)+(16.00 g/mol)(2) × 100% = 84.80% Hf mass of O's (16.00 g/mol)(2) total mass of Hf+O's = (178.5 g/mol)+(16.00 g/mol)(2) mass of Be

b. total mass of Be+Cl's = mass of Cl's total mass of Be+Cl's =

× 100% = 15.20% O

9.012 g/mol (9.012 g/mol)+(35.45 g/mol)(2)

× 100% = 11.28% Be

(35.45 g/mol)(2) (9.012 g/mol)+(35.45 g/mol)(2)

× 100% = 88.72% Cl

47.88 g/mol

mass of Ti

c. total mass of Ti+O's+H's = (47.88 g/mol)+(16.00 g/mol)(4)+(1.008 g/mol)(4) × 100% = 41.31% Ti mass of O's (16.00 g/mol)(4) total mass of Ti+O's+H's = (47.88 g/mol)+(16.00 g/mol)(4)+(1.008 g/mol)(4)

× 100% = 55.22% O

mass of H's (1.008 g/mol)(4) total mass of Ti+O's+H's = (47.88 g/mol)+(16.00 g/mol)(4)+(1.008 g/mol)(4)

× 100% = 3.478% H

55.85 g/mol

mass of Fe

d. total mass of Fe+O = (55.85 g/mol)+(16.00 g/mol) × 100% = 77.73% Fe mass of O 16.00 g/mol total mass of Fe+O = (55.85 g/mol)+(16.00 g/mol) × 100% = 22.27% O

mass of Si total mass of Si+O's

28.09 g/mol (28.09 g/mol)+(16.00 g/mol)(2)

(16.00 g/mol)(2) mass of O's = (28.09 g/mol)+(16.00 g/mol)(2) total mass of Si+O's mass of B

× 100% = 46.75% Si × 100% = 53.25% O

10.81 g/mol

f. total mass of B+O's+H's = (10.81 g/mol)+(16.00 g/mol)(3)+(1.008 g/mol)(3) × 100% = 17.48% B mass of O's (16.00 g/mol)(3) total mass of B+O's+H's = (10.81 g/mol)+(16.00 g/mol)(3)+(1.008 g/mol)(3)

× 100% = 77.63% O

(1.008 g/mol)(3) mass of H's = (10.81 g/mol)+(16.00 g/mol)(3)+(1.008 g/mol)(3) total mass of B+O's+H's

× 100% = 4.891% H

17. Answer: a. 1 carbon atom (nonmetal), 2 oxygen atoms (nonmetals) b. 2 hydrogen atoms (nonmetals), 1 sulfur atom (nonmetal) c. 1 nitrogen atom (nonmetal), 2 oxygen atoms (nonmetals) d. 1 silicon atom (metalloid), 2 oxygen atoms (nonmetals)

Concentrating on Concepts 18. Answer: A variety of answers are possible. An example of an illustration of 9N purity is the time span of 1 second compared to 31.7 years. A similar example with 12 N purity is 1 second compared to 31,700 years. A volume-related example of 9N purity would be like taking 1 liter of water out of 400 Olympic-sized swimming pools full of water!

19. Answer: Answers will vary widely but could include food, drink, furniture, books, and appliances, among others. Examples of homogeneous mixtures may be air (nitrogen, N2, oxygen, O2, argon, Ar, etc.), Gatorade (water, H2O, sucrose, C12H22O11, sodium chloride, NaCl, citric acid, C6H8O7, etc.), and glass (silicon dioxide, SiO2, sodium oxide, Na2O, calcium oxide, CaO, aluminum oxide, Al2O3,

etc.). Examples of heterogeneous mixtures include books (cellulose, (C6H10O5)n, carbon black, C, titanium oxide, TiO2, polyvinyl acetate, (C4H6O2)n, etc.), granola bar (sucrose, C12H22O11, sodium chloride, NaCl, baking soda, NaHCO3, etc.), and a banana (water, H2O, glucose, C6H12O6, fructose, C6H12O6, isoamyl acetate, C7H14O2, etc.)

20. Answer: Answers will vary, depending on year selected. As of 2019, the latest technology node is 5 nm, which features a gate length of around 10 nm (https://en.wikichip.org/wiki/5_nm_lithography_process). This is equivalent to 1 nm× 10-9 m × 1 km = 1. ×10-11 km. 0 0 3 1 nm 10 m

21. Answer: The periodic table allowed gaps for unknown elements. The elements were placed into gaps based on their atomic weight and number of protons. 22. Answer: There are many steps involved during this process. Many resources are available on the Internet that describe this process (e.g., http://www.australianminesatlas.gov.au/education/fact_sheets/aluminium.html) 23. Answer: Sapphire is about three times as hard as Gorilla glass but is about 67% more dense. This means that although sapphire could greater resist scratches, a similar sized piece would weigh more than a piece of Gorilla glass. Gorilla glass has an amorphous structure composed primarily of silicon and oxygen atoms with other minority component atoms. Sapphire is a single crystal of aluminum and oxygen atoms. Both materials require high temperature melting of raw materials followed by slow cooling. Gorilla glass requires another heating step in a molten bath of salts. Sapphire requires a much higher temperature melt. Regular glass is also amorphous & is composed primarily of silicon and oxygen atoms with additives of sodium and calcium oxides. A comprehensive website that quantitatively compares the physical and optical properties of typical soda-lime glass, Gorilla glass, and quartz is found at: http://abrisatechnologies.com/specs/AT%20Specialty%20Glass%20Technical%20Capabilities%2 0Brochure.pdf

24. Answer: A thin layer of a transparent conducting material is deposited on the surface of glass. The most common material used for this purpose is indium tin oxide (ITO), which is used in applications ranging from LED displays to solar cells. Do-it-yourself enthusiasts have posted to the internet a way to coat glass using stannous chloride (SnCl2) to create a layer of conductive tin oxide.

25. Answer: When the surface of glass cools quickly in a Prince Rupert‘s drop, silicon and oxygen atoms form tight bonds that hold the material into shape. The silicon and oxygen atoms within the drop are still semi-mobile while the outer surface is hardening. When the interior of the drop cools, new bonds between silicon and oxygen form, pulling them tighter together. However, since the other layer of glass is held tightly in place, the atoms on the interior are not able to approach each other as close as optimal, resulting in internal stress. When some of the bonds between silicon and oxygen atoms in the surface of the glass are broken, the internal bonds are pulled tightly together with enough strength to further break additional bonds in the outer layer. This results in the shattering of the drop as bonds throughout the glass break or shrink. 26. Answer: Answers will vary depending on device and component choice, but typical components and sizes include length (e.g. 14.5 cm, 145 mm, 145,000 µm, 145,000,000 nm); width (e.g. 7.5 cm, 75 mm, 75,000 µm, 75,000,000 nm); thickness (e.g. 1 cm, 10 mm, 10,000 µm, 10,000,000 nm); camera lens (e.g. 0.3 cm, 3 mm, 3,000 µm, 3,000,000 nm); and speaker hole diameter (e.g. 0.03 cm, 0.3 mm, 300 µm, 300,000 nm). 27. Answer: The list of metals used in cell phones that are common in Earth‘s crust includes: aluminum, iron, potassium, magnesium, titanium, manganese, barium, and nickel. They are found in ores, minerals, and compounds.

28. Answer: A transparent material allows light to travel through it without refracting. Having a transparent screen keeps the light produced from distorting when you look at it. Additives can give solids like glass a different color or other properties like strength. Heat treatment can also add durability. 29. Answer: Gold prospectors can use panning to separate gold flakes from other solids. This involves taking the mixture and agitating it in water. This separates out the gold because it stays in the bottom of the pan and other substances float in the water and can be poured out. 30. Answer: The steps involved to convert silica sand, mostly composed of SiO2, to high-purity Si are outlined in Section 1.8. In contrast, sea sand contains many impurities such as metals (e.g., Fe, Al, Mg, K, Na, Ca, Zn, Ni, etc.) and nonmetals (e.g., B, P) that would require extensive pre-processing of the sand via chemical reactions, involving acids and high temperatures. Furthermore, the use of sea sand for industrial processes would not be sustainable and would cause a variety of environmental consequences. By disturbing sea sand, an area could be changed physically, biologically, and chemically.

31. Answer: Waste products of high-purity silicon include carbon monoxide (from reduction of the silicon), carbon dioxide (from combustion heating), compounds containing the impurities (including phosphorous, boron, and a variety of metals), and waste heat.

32. Answer: While individual cell phones may become smaller and take up less space in, say, a landfill, there may be a much higher impact on the environment, depending on the materials required for making the cell phone and the energy needed for manufacturing the components. To make the devices smaller and less expensive, different materials may be used, which may require more invasive mining or greater waste production in the manufacturing process. 33. Answer: Answers will vary according to relative weighing of factors. The grade for the “Environmental” pillar should consider the production and recycling of waste and the relative use of limited natural resources, including rare earth metals. The grade for the “Social” pillar should include both the impact of portable electronics on the quality of life of consumers as well as the impact on the lives of workers in the mining of raw materials, manufacturing of the products, and those that live in the regions impacted by mining and manufacturing. The grade for “Economic” pillar should consider the wealth generated by the mining, manufacturing, and sale of these electronics and how this wealth is distributed.

Exploring Extensions 34. Answer: Gordon Moore, one of the founders of the computer chip maker Intel, predicted in 1965 that the number of transistors per square inch on integrated circuits would double every 12 months. In 1975, he revised his prediction to double every 24 months. This prediction has held true through at least 2016. However, both Moore and current Intel CEO Brian Krzanich have recently suggested that chip makers may reach physical and economic limitations to this growth within the next 5-10 years. 35. Answer: The colors of many gemstones come from impurities in the crystal structure. For example, the purple color of amethyst comes from Fe3+ ions in a SiO2 crystal, and the red color of rubies comes from Cr3+ in an Al2O3 crystal.

36. Answer: Impurities break up the crystal structure of crystalline solids and, since properties of materials are in part dependent on structure, this will change the material properties. Throughout this chapter, we have seen impurities that change properties such as color, transparency, melting point, and electrical conductivity.

37. Answer: A thin layer of material is sandwiched between two pieces of glass. When an electrical current is passed through the glass, the material will line up according to the direction of the current, similar the liquid crystal display (LCD) of common calculators.

38. Answer:

Devices can be physically pulled apart to reveal the components containing the metals. Plastic parts such as circuit boards are either dissolved in solvent or burned to isolate the metallic components. These metals themselves may be either melted or dissolved in acids and then filtered and reconstituted to generate purer forms of the metal for other uses. A recent report describes the use of fungi to extract precious metals from electronic waste, a potentially more environmentally friendly way of recycling.

39. Answer: Apple has removed mercury and arsenic from screens and lead from solder in their electronics.

40. Answer: The two largest destinations for electronic waste in the world are in New Dehli, India, and Guiyu, China. Studies have shown air, water, and soil pollution from electronics recycling around Guiyu leading to poisoning from heavy metals such as lead and organic pollutants such as dioxins. To prevent these situations, new methods of recycling need to be developed with greater safety awareness for workers, tighter controls on emissions from recycling centers, and redesign of the electronic devices to reduce toxic components.

41. Answer: Old electronic devices could be disassembled and either parts could be reused as is or could be mechanically or chemically separated into raw materials to be used for manufacturing new devices.

42. Answer:

The H2 and SiCl4 gases are recycled through reaction to generate chlorosilanes that are used to purify the Si in earlier steps. However, CO is released, which is further oxidized to CO2, a greenhouse gas. 43. Answer: Answers will vary as there are many ways to strengthen glass. This may include heating the glass or adding different elements into the structure.

44. Answer: There were 46.89 million iPhones sold in 2018. 25% of this is 11.72 million. An iPhone 8 has a mass of 202 grams. 24% of the mass of an iPhone is Al, so one phone has 48.48 grams. This multiplied by 11.72 million iPhones is 5.68 × 105 kg. Copper is 6% of the mass of an iPhone, which is 12.12 grams per iPhone. This multiplied by 11.72 million iPhones is 1.42 × 105 kg. Cobalt is 5% of the mass of an iPhone, which is 10.1 grams per iPhone. This multiplied by 11.72 million iPhones is 1.18 × 105 kg. Each iPhone contains 300 mg of silver, multiplied by 11.72 million is 3516 kg of silver. Each iPhone contains 30 mg of gold, multiplied by 11.72 million is 351.6 kg. At current pricing, this yields: Al: $1,949,376, Cu: $862,224, Co: $4,062,740, Ag: $1,913,196, Au: $16,598,779=$25,386,315. 45. Answer: refer back to Figure 1.24. A cradle-to-cradle scenario would include recycling of metals, plastics, etc. in the phone back into a useful end product.

46. Answer: Some considerations include toxicity of materials used in the device, availability of raw materials, amount of energy required by the device, and number of uses for the device and disposable components (such as batteries).

47. Answer: To extract aluminum from ore, bauxite is crushed and dissolved in a solution of concentrated sodium hydroxide to remove aluminum oxide from the rest of the ore. The aluminum oxidesodium hydroxide mixture is then neutralized and is mixed with sodium aluminum fluoride (cryolite). At high temperatures, a carbon electrode is used to reduce the aluminum oxide to molten aluminum. This process is very energy intensive and expensive. Aluminum recycling involves collecting used aluminum, cleaning the metal, then melting the metal to remove any coating, and then cooling the metal to form solid aluminum. The recycling process uses high temperatures to melt the metal, but uses much less energy and is more cost efficient than extraction. Recycling uses more than 90 percent less energy than extraction from bauxite.

48. Answer: The increase in demand for rare earth metals amounts to about 40%. Rare earth metals are used in a wide variety of products such as cell phones, computers, rechargeable batteries, wind turbines, speakers, and fluorescent lights. It is doubtful that the U.S. could meet its demand for rare earth elements even with 100% recovery of the metals. The growth of the market for this wide variety of products outpaces the retirement of old products, many of which may not use much if any rare earth metals that could be recycled.

ANSWERS TO END-OF-CHAPTER QUESTIONS

CHAPTER 2: THE AIR WE BREATHE

Emphasizing Essentials 1. Answer: a.

0.5 L 1 breath

10 breaths 60 min × × 7.5 h = 2250 L 1 min 1h

0.5 L 10 breaths 60 min 7.5 hr 2.,250 L 1 breath 1 min 1 hr

b. Possibilities include burning less (wood, vegetation, cooking fuels, gasoline, incense), using products that pollute less (low-emission paints), and using motor-less appliances and tools (hand lawnmower, egg- beater, broom, rake)

2. Answer: a. Rn < CO < CO2 < Ar < O2 < N2 b. CO and CO2 c. CO. With concerns growing over climate change, By the time this book is in print, CO2 may be regulatedis also becoming regulated in terms of carbon taxes and other policies in some countries. as well. d. Rn (radon) and Ar (argon)

3. Answer: Examples of particulate matter found in air include dust, soot, dirt, microscopic droplets of liquid, bacteria, and viruses. PM2.5 and PM10 differ in size. The former has particles 2.5 μm or less in diameter; the latter 10 μm or less. The smaller particles are more damaging to human health.

4. Answer: 1,000,000 parts per million

a. 0.934 parts per hundred ×

0.934 parts per hundred 

100 parts per hundred

= 9340 parts per million

1,000,000 parts per million  9340 parts per million 100 parts per hundred

(Move the decimal 4 places to the right.)

b. 2 ppm ×

100 parts per hundred 1,000,000 ppm

= 0.0002 parts per hundred, or 0.0002%

100partsperhundred 2 ppm 0.0002partsperhundredor 0.0002% 1,000,000ppm (Move the decimal 4 places to the left.) 20 ppm is equivalent to 0.0020%. 50 ppm is equivalent to 0.0050%.

c. 8500 ppm ×

8,500 ppm

100 parts per hundred 1,000,000 ppm

= 0.85 parts per hundred, or 0.85%

100 parts per hundred 0.85 parts per hundred or 0.85% 1,000,000 ppm

Be careful not to confuse the absolute humidity calculated in this problem with relative humidity, which is the amount of water vapor in the air compared to the maximum possible amount of water vapor that the air can hold at a particular temperature. For example, in a rainforest, the relative humidity is usually between 75- and 95%.

d. 8 ppm is 0.0008% (move the decimal 4 places to the left).

5. Answer: a. The chemical formula tells the elements present in a compound and the atomic ratio of the elements. b. Xe (xenon), N2O (dinitrogen oxide or nitrous oxide), CH4 (methane)

6. Answer: a. Hydrocarbons are compounds that contain only the elements hydrogen and carbon. b. ethane (C2H6), propane (C3H8), pentane (C5H12), hexane (C6H14), octane (C8H18) c. Answers will vary.Hydrocarbons release energy when they undergo combustion.

7. Answer: The majority of our air is composed of nitrogen, oxygen, and water, argon, but the air is made up of other molecules such as in very small concentrations (on the order of a few1 molecules perin 100 or less). Examples of a trace substances found in air will vary, but the molecule responsible for the fragrance of a flower or fresh baking cookies are examples. Other gases such as the inert gases or carbon dioxide could also be considered trace substances. It should be noted that even though a gas may be present in trace amounts (e.g., CO2, CO, O3), it may have significant implications for pollution or climate change.

8. Answer: Nitrogen is 78.0% of the air, meaning that out of 100 air particles, 78 of them are nitrogen molecules.

500 air particles ×

500 air particles

78 nitrogen molecules 100 air particles

= 390 nitrogen molecules

78 nitrogen molecules

390 nitrogen molecules

100 air particles

Oxygen is 21.0% of the air, meaning that out of 100 air particles, 21 of them are oxygen molecules.

500 air particles ×

500 air particles

21 oxygen molecules 100 air particles

= 105 oxygen molecules

21 oxygen molecules

105 oxygen molecules

100 air particles

Argon is 0.9% of the air, meaning that out of 100 air particles, 0.9 of them are argon atoms.

500 air particles ×

0.9 argon atoms 100 air particles

= 4.5 argon atoms (or between 4 − 5 argon atoms)

0.9 argon atoms 500 air particles 4.5 argon atoms (or between 4 - 5 argon atoms) 100 air particles

9. Answer: a. Each side of the equation has 6 C, 16 H, and 14 O. b. Each side of the equation has 16 C, 36 H, and 50 O.

10. Answer: a. Yes, the mass of the reactants equals the mass of the products. The lLaw of cConservation of matter and mMass applies. b. No, the numbers of molecules are not the same (four reactant molecules vs. two product molecules). c. Yes, the numbers of each type of atom present as reactants and products are the same.

11. Answer: a. N2(g) + O2(g)  2 NO(g) (occurs at high temperature) b. O3(g)  O2(g) + O(g) (occurs in the presence of UV light) c. 2 S(s) + 3 O2(g)  2 SO3(g)

12. Answer: a. C3H8(g)  5 O2(g)  3 CO2(g)  4 H2O(g) b. 2 C4H10(g)  13 O2(g)  8 CO2(g)  10 H2O(g) c. 2 C3H8(g)  7 O2(g)  6 CO(g)  8 H2O(g) 2 C4H10(g)  9 O2(g)  8 CO(g)  10 H2O(g)

13. Answer: a. 2 C2H6(g) + 3 O2(g)  4 C(s) + 6 H2O(g) b. 2 C2H6(g) + 5 O2(g)  4 CO(g) + 6 H2O(g) c. 2 C2H6(g) + 7 O2(g)  4 CO2(g) + 6 H2O(g)

d. The balanced equations show that complete combustion requires the highest ratio of oxygen to ethane (7:2). If a 5:2 ratio is present, carbon monoxide is formed instead of carbon dioxide. If only a 3:2 ratio is available, then carbon (soot and particulate matter) is formed. Note: With less oxygen, the products are likely to be mixed, rather than pure CO or pure soot.

14. Answer: A homogenous mixture is a substance composed of many different components that are mixed well, like the air we breathe. Examples will vary, but one homogenous mixture is lemonadea solution of salt water. It is made by stirring together lemon juice, sugar, and watersalt and water together. Another example is sand from the beach. If you look closely, it is made up of a variety of different chemical components in addition to seaweed, shells, etc. vinegar which is acetic acid mixed with water.

15. Answer: In respiration, inhaled oxygen reacts with sugar in your body to produce carbon dioxide and water vapor to produce energy. Therefore, exhaled air has a decreased percentage of oxygen, and increased percentage of carbon dioxide. Oxygen is used to metabolize the food that we eat.

16. Answer: The troposphere is the layer of air closest to earth, the place where we live. It contains 75% of the air we breathe, by mass, and is where air currents and storms occur that mix the air in our atmosphere.

17. Answer: Symbolic = CO2

Particulate =

Macroscopic =

18. Answer: NO2 = nitrogen dioxide N2O = dinitrogen monoxide NO = nitrogen monoxide NCl = nitrogen trichloride N2O4 = dinitrogen tetraoxide

19. Answer:

CCl4 = carbon tetrachloride SO3 = sulfur trioxide Cl2O6 = dichlorine hexaoxide P4S3 = tetra phosphorus trisulfide

20. Answer: a. 400 parts per million ×

400 parts per million 

100 parts per hundred 1,000,000 parts per million

= 0.04 parts per hundred = 4%

100 parts per hundred  0.04 parts per humdred  4% 1,000,000 parts per million

b. Carbon monoxide is an air pollutant because when breathed into the lungs, CO can be hazardous to human health.

c. Carbon monoxide interferes with the ability of hemoglobin to carry oxygen throughout your body. If you are exposed to CO in high enough concentrations, it can cause a person to die due to lack of oxygen. Shorter term exposure leads to dizziness or a headache.

21. Answer: a. You will most likely find sulfur dioxide and nitrogen dioxide close to their sources (i.e., coal fired power plants and automobiles), around cities in the troposphere, although they can travel on air currents to other parts of the world.

b. Sulfur dioxide is more toxic. The U.S. Ambient Air Quality Standards sets a limit of 0.075 ppm for a one-hour exposure, as opposed to nitrogen dioxide at 0.100 ppm for a one-hour exposure. c.

0.045 parts per million 

1,000,000, 000 parts per billion  45 parts per billion 1,000,000 parts per million

22. Answer:

Concentrating on Concepts

2322. Answer:

The Hydra photograph shows sea walls, presumably built by humans (requiring fuel to be burned in the process of moving the stones). If the stones are cemented, the cement also will emit gases as it dries. The ships are giving off emissions from the burning of fuel. The restaurant might be emitting the good smells of fresh Greek food.

The Tianjin photograph is easier. The cars and buses on the road leave air prints as they burn fuel. Any spilled fuel may evaporate into the air. The haze is most likely the result of emissions from vehicles and industry nearby.

2423. Answer: Carbon monoxide: Mild CO poisoning makes you feel crummy, including headache, dizziness, and nausea. You will not be able to exert yourself in your normal manner. More severe poisoning may send you unconscious to the emergency room. Particulate matter: Mild PM poisoning will cause lung and cardiovascular distress. Again, you will not feel up to things with your normal energy level. More severe poisoning can send you to the emergency room with a heart attack. Ozone: Mild ozone poisoning will cause your eyes and throat to burn. It will aggravate your breathing and asthma. As with CO and PM, more severe ozone poisoning can send you to the emergency room.

2524. Answer:

Answers will vary depending on the answer calculated in Your Turn 2.2 and the size of the classroom. For most students, the volume of air inhaled in a day will be on the order of 10,000 L. The classroom length, width, and height measurements can be estimated in meters. One cubic meter equals 1,000 liters, so classrooms should hold a much greater volume of air than a student exhales in a day.

2625. Answer: In respiration, inhaled oxygen reacts with substances in your body to produce carbon dioxide and water vapor. Therefore, exhaled air has a decreased percentage of oxygen, and increased percentage of carbon dioxide.

2726. Answer: a. Normally, the exhaust gases are released to the atmosphere through the tailpipe and do not find their way back into the interior of the car. The tailpipe does not have a connection to the interior. However, if the gases are released into an enclosed space like a snow bank, they may seep back into the car as there is no easy escape path into the wider environment. b. CO is an odorless, colorless, and tasteless gas. 2827. Answer: Here are some possibilities: - Iron and steel would rust more slowly, prolonging the useful life of many objects made from these materials. - Fires would burn less vigorously and produce more CO and soot. Logs in your fireplace might last longer, putting out heat more slowly. - Your body can adapt (just as it does at higher elevations) to lower levels of oxygen. But in this case, the level may be too low for metabolic processes involving oxygen to occur at fast enough rates for life as we currently know it.

2928.

Answer:

CO is termed the “silent killer” because your senses cannot detect this colorless, tasteless, and odorless gas. The same term cannot be applied to pollutants such as O3 or SO2 because each has a distinctive odor that can be detected at concentrations below the level of toxicity.

3029. Answer: a. To convert from percent to ppm, move the decimal point 4 places to the right. Alternatively:

3% = 3 pph 3 pph 

1,000,000 ppm  30,000 ppm 100 pph

3% = 3 pph

3 pph ×

1,000,000 ppm 100 pph

= 30,000 ppm

1,000,000,000 ppb = 30,000,000 ppb 100 pph

1,000,000,000ppb 3pph 30,000,000ppb 100pph

b. The NAAQS for CO in an 8-hour period is 9 ppm. The concentration of CO in cigarette smoke is over three thousand times the 8-hour standard. The NAAS for CO in a 1-hour period is 35 ppm. The concentration in cigarette smoke is almost nine hundred times the 1-hour standard. c. Smokers do not die from CO poisoning because they breathe mainly air, not pure cigarette smoke.

3130. Answer: The ozone levels are not reported in the winter because of the differences in the sunlight between the summer and the winter. Even at its greatest winter intensity, the sunlight is much less intense. Sunlight is needed to produce ozone.

3231. Answer: Reporting the absolute difference, 0.01 ppm, seems to minimize the amount by which the standard is exceeded, at least in the eyes of the general public. Unless the standard is reported as well, there is no way to compare the magnitude of the difference to the magnitude of the standard. Calculating the

percentage by comparing the difference (0.01 ppm) to the standard (0.12 ppm) gives 8%, which may give people a better understanding of the amount by which the standard was exceeded.

3332.Answer: a. The elderly, the young, and people with respiratory diseases such as asthma and emphysema are most affected by ozone. b. 3 days c. Ozone is highly reactive, thus does not persist long in the atmosphere. Since no ozone is produced at night when the sun isn‘t shining, its concentration falls. d. Answers will vary. Possibilities include: overcast skies, rain, or high winds. It could be a day when fewer people are driving or that industries are shut down. e. Ozone levels in Atlanta, Georgia, are lower in December because there is less daylight in the winter months.

3433. Answer: a. The elderly, the young, and people with respiratory diseases such as asthma and emphysema are most affected by PM. b. December 21-22, December 27, December 31 c. Although PM varies in composition, most of it is less chemically reactive than ozone. It typically is removed from the air by rain or wind. d. Possibilities include smoke blowing in from a wildfire outside the city, an air inversion, large industrial releases of soot, and a volcanic eruption somewhere in the region that released ash and soot.

3534. Answer: a. 15 ppm is 0.0015% and 2% is 20,000 ppm. 15 ppm is roughly 1300 times smaller than 20,000. b. c. 2 C12H26 (l)  37 O2(g)  24 CO2(g)  26 H2O(g) d. Ultimately, burning diesel which is derived from the fossil fuel petroleum is not sustainable. In the short term, diesel engines also are old and have high emissions. So these have a high cost in terms of public health. However, the ultra-low sulfur diesel fuel is definitely a step in the right direction.

3635. Answer:

a. These regions have high population densities, high levels of vehicle emissions, possibly stagnant air, and lots of sunlight. Factors such as these lead to ozone formation. b. Possibilities include that it is overcast and/or raining in the Midwest. c. In the Sacramento Valley, air may become trapped such that air pollutants accumulate. Furthermore, the temperatures are higher and the days are sunnier, promoting ozone formation. In contrast, the air near the coastline has better circulation, which promotes better air quality. The air also is cooler and sometimes foggy.

3736. Answer: If you live in the U.S., check http://www.stateoftheair.org/, the State of the Air. You can easily count the ozone days in different states. You will find that the sunnier states in the south and southwest have higher levels of ozone beginning earlier in the year than those in the north.

3837. Answer: a. Reducing the number of cars in use will directly and indirectly reduce the concentrations of NOx, SOx, CO, CO2 and ozone in the air. b. Geographical features that lead to stagnant air, such as being situated in a valley or surrounded by mountains, may contribute to the higher ozone levels.

3938. Answer: CO is a hazard when present at the part per million level, and instruments can easily detect CO at this concentration. In contrast, radon levels are much lower, on the order of parts per 1020. Most radon detection kits sample the air over a period of time in order to get a high enough reading.

4039. Answer: a. The label could read “Low VOC paints reduce your exposure to paint fumes, minimizing the exposure and risks associated with these fumes.” b. VOCs are a player in the formation of NO2 from NO. In turn, NO2 breaks down in sunlight to produce O atoms that react with O2 molecules to produce ozone in the troposphere.

4140. Answer: a. Jogging outdoors, as opposed to sitting outdoors, increases your exposure to air pollutants because you will be breathing harder and exchanging more air during your exercise. b. Jogging indoors reduces your exposure to ozone (the O3 molecule is highly reactive and decomposes during the time it takes to transport the air inside). In contrast, particulate matter has

comparable levels inside and out (PM does not get filtered out by most air-handling equipment and it is not highly reactive). Some pollutants may be found at higher levels inside, such as the CO produced by faulty appliances.

4241. Answer: One possibility is to examine how you (and your clients, if you have them) use energy over the course of a day (heating, lighting, computing time, traveling). Reductions in energy use translate into improved air quality. This is true even for renewable energy sources such as solar and wind, because it still requires energy to manufacture and maintain the solar cells and wind turbines. Another possibility is to seek the connections between your work and air quality. For example, if you are in a medical profession, you could start better educating the public as to the health issues associated with breathing dirty air.

Exploring Extensions

42. Answer:

6 m  5 m  3 m = 90 m3 3600 mgacetone 

1000 g 1 mg



g 1  40,000 3 m3 90 m

43. Answer: This phrase refers to what can happen when individuals use a natural resource (e.g., air we breathe, water we drink) that is shared by all for their own interests and then lower the quality of this resource, which is not in the best interest of a larger group of people. Air pollution is a classic example in that people add waste to the air which in turn affects the health and well-being of others. A case in point would be an industry (group of people) that burns coal to produce electricity. In the process of doing this, oxides of nitrogen and sulfide are released into the air. Other waste products include mercury and the greenhouse gas carbon dioxide. Clearly some people benefit, perhaps even those using the electricity. But all breathe the dirty air. Depending on the concentrations of pollutants, some people may sicken or die.

44. Answer: Fossil fuels contain trace amounts of mercury. When these fuels are burned, the mercury is released into the air. Forest fires and volcanoes are natural sources of mercury air pollution. However, mercury concentrations in the air are usually low and of little direct health concern. When air-borne

mercury enters water systems, biological processes transform it to a chemical form (methylmercury, or (CH3Hg)+) that can accumulate in fish and animals that eat fish. Organisms high in the food chain, such as fish, have the highest levels of mercury. People are exposed to mercury primarily by eating fish. A person’s level of mercury exposure can be measured by testing the amount of mercury in their blood. High mercury levels can cause neurological damage and are particularly harmful to fetuses, infants, and young children.

45. Answer: Visit the EPA website through http://www.epa.gov. The Green Chemistry website can be found at https://www.epa.gov/greenchemistry. http://www.epa.gov/greenchemistry. The Presidential Green Chemistry Challenge was established by President Bill Clinton in 1995 to promote pollution prevention and industrial ecology in partnership with the chemical industry.

46. Answer: a. The rubber may have come from tires abrading as they roll along the highways. Other sources of PM include soot from incomplete combustion and dirt picked up and blown by the wind. b. Iron, aluminum, and calcium also are commonly present. Other possibilities include sodium, potassium, magnesium, and sulfur. c. The edges of the particles appear to be irregular and jagged, thus likely to cause inflammation.

47. Answer: The American Lung Association website is a good place to start. Particulate matter comes from a variety of sources and can be solids or fine suspensions (aerosols) of liquids. Ultrafine particles can penetrate the lungs more deeply than coarser particles and thus are more likely to enter the bloodstream. Once in blood vessels, these fine particles inflame cells and tissues, leading to cardiovascular disease.

48. Answer: a. This graph clearly indicates that exposure to higher carbon monoxide concentrations over longer time periods becomes increasingly life-threatening. b. CO poses a serious health threat. This gas is colorless and odorless, making it impossible to detect without a monitor or kit. Furthermore, the initial symptoms of carbon monoxide poisoning are not unique, and those suffering from the associated headaches and nausea could easily presume the symptoms are due to a flu-like illness. Untreated, individuals will ultimately lapse into a coma, after

which point they will be unable to call for assistance. For these reasons such as these, carbon monoxide detectors are life-saving devices.

49. Answer: A water-based polyurethane was produced by removing the VOCs from the varnish and replacing them with water. As the source below reports: “This may seem an obvious substitution, but, due to the particular chemistry of the reactive components of polyurethane, it is not that straightforward. The details are given here: https://www.epa.gov/greenchemistry/presidential-green-chemistry-challenge-2000-greenerreaction-conditions-award Several paint manufacturers currently market water-based polyurethanes. An internet search will quickly bring up examples.

50. Answer: The health hazards associated with isocyanate include irritation of the mucous membrane and skin, tightness in the chest, and difficulty breathing. Isocyanate is also a potential carcinogen for humans and is known to cause cancer in animals. a. Instead of using non-renewable, petroleum- based feedstocks to create adhesives, composites, and foams, Professor Wool‘s processes use feedstocks from bio-based sources. These renewable sources include flax, chicken feathers, and vegetable oils. In addition to being renewable, their production uses less water and energy and is not as toxic as the petroleum- based counterparts. b. Answers will vary. Richard Wool passed away in 2015 and his work can be summarized here: http://www1.udel.edu/udaily/2015/apr/in-memoriam-wool-040615.html and here: https://www.researchgate.net/scientific-contributions/2077713776_Richard_P_Wool. 51. Answer:

a) Benzene studies have been conducted, but they were conducted on cars that are stuck in traffic. These levels are due mainly to exhaust. The values are also much lower than the viral post suggests. Parked cars that are not running but are found in direct sunlight can have trace amounts of VOCs but they are low amounts. More information can be found at: (1) https://www.liveabout.com/is-there-toxic-benzene-in-parked-cars-3298894 (2) https://pubs.acs.org/doi/full/10.1021/es0617901 (3) https://www.livescience.com/7273-car-smell-toxic-study-finds.html (4) https://emergency.cdc.gov/agent/benzene/basics/facts.asp (5) https://www.ncbi.nlm.nih.gov/pubmed/10412670 (6) https://www.sciencedirect.com/science/article/abs/pii/S0378427405001876

b) The new car smell is due to a combination of VOCs, including ethylbenzene, formaldehyde, toluene, etc. In excess, these chemical are harmful; however,, but in the amounts found in new cars, the studies do not show that harm is caused. One example of an article is here: https://cars.usnews.com/cars-trucks/best-cars-blog/2016/09/is-that-new-car-smell-toxic.

ANSWERS TO END-OF-CHAPTER QUESTIONS

CHAPTER 3: Radiation from the Sun

Emphasizing Essentials

1. Answer: The chemical formulas of ozone and oxygen are O3 and O2, respectively. Both are gases, but they differ in their properties. Oxygen has no odor; ozone has a very sharp odor. Although both are reactive, ozone is much more highly so. Oxygen is necessary for many forms of life; in contrast, ozone is a harmful air pollutant in the troposphere. However, ozone in the stratosphere helps to protect us from the harmful ultraviolet rays of the sun.

2. Answer: a. Yes, this is over the detection minimum of 10 ppb.

0.118 parts O3 118 parts O3  or 118 ppb 1, 000, 000 parts air 1, 000, 000, 000 parts air

b. Yes, this is well over the detection minimum of 10 ppb.

25 parts O3 25,000 parts O3 or 25,000 ppb  1, 000, 000 parts air 1, 000, 000, 000 parts air

3. Answer: a. The size of the ozone “hole” varies each year, but has been estimated to be as large as 28 million km2 in area.

10 miles 

km 0.621 miles

= 16.1 km

Yes, the figure is correct, as the stratosphere extends between 15 and 30 km above the Earth‘s surface. c. Ozone absorbs UV-B and UV-C radiation.

4. Answer: The term ozone layer, while in widespread use, brings to mind an incorrect image of a blanket-like layer. In fact, even in the stratospheric region of highest concentration, ozone‘s concentration is typically less than 1 ppm and is not even the most abundant species in that region. The ozone does not completely block all UV radiation, such as a blanket might block all visible light. The ozone that is present, however, serves the essential function of absorbing some wavelengths of UV-B and reducing its intensity before it reaches the surface of the Earth, making the screen analogy more useful.

5. Answer: The air in the troposphere is simply denser than the stratosphere; the number of atoms and compounds in a given volume will be far higher. Also, the troposphere has a lower concentration of the gases like oxygen and ozone than the stratosphere. These gases are formed in the stratosphere and too reactive to mix downward. The opposite is also true, many gases formed in the troposphere, such as the NOxNOX or SOxSOX described in Chapter 2, are not common in the stratosphere.

6. Answer: a. The Dobson unit (or DU) measures the ozone in a column above a specific location on Earth. If this ozone were compressed at specified conditions of temperature and pressure, it would form a layer. A layer 3 mm thick corresponds to 300 DU. Similarly, a 1 mm layer corresponds to 100 DU. b. 320 DU > 275 DU.

Thus, 320 DU indicates more total ozone overhead.

7. Answer: a. A neutral atom of oxygen has 8 protons and 8 electrons6 valence electrons. b. A neutral atom of nitrogen has 5 valence electrons7 protons and 7 electrons. c. A neutral atom of magnesium has 12 protons and 12 electrons2 valence electrons. However, it should be noted that magnesium forms ionic compounds rather than covalent, in which electrons are not shared.

d. A neutral atom of sulfur has 6 valence electrons. 16 protons and 16 electrons

8. Answer: a. Group 22A b. beryllium, Be; magnesium, Mg; calcium, Ca; strontium, Sr; barium, Ba; radium, Ra c. The total number of electrons: Be 4, Mg 12, Ca 20, Sr 38, Ba 56, Ra 88. d. Each element in Group 2A has 2 outer electrons.

9. Answer: a. Several atoms could have this valence number: helium, He, ; Beryllium, Be; Magnesium, Mg, Calcium, Ca; Strontium, Sr; Barium, Ba; and Radium, Ra. b. potassium, KSeveral atoms could have this valence number: neon, Ne; argon, Ar; krypton, Kr; xenon, Xe; Radon, Rn. c. copper, CuSeveral atoms could have this valence number: oxygen, O; sulfur, S; selenium, Se; tellurium, Te; Polonium, Po.

10. Answer: a. b. c. d.

11. Answer:

a. There are 4 + 4(7) = 32 outer electrons

b. There are 2(1) + 2(6) = 14 outer electrons. The Lewis structure is: or

c. There are 2(1) + 6 = 8 outer electrons. The Lewis structure is: or

d. There are 2(5) = 10 outer electrons. The Lewis structure is:

e. There are 1 + 4 + 5 = 10 outer electrons. The Lewis structure is: or

f. There are 2(5) + 6 = 16 outer electrons. One possible Lewis structure is: or

Other resonance structures are possible for N2O as well.

g. There are 4 + 2(6) = 16 outer electrons. The Lewis structure is: or

12. Answer:

The Lewis structures for the oxygen molecule and the ozone molecule both follow the octet rule. In contrast, the oxygen atom has only 6 outer electrons and does not follow the octet rule. The hydroxyl radical also does not follow the octet rule and has an unpaired electron. Another resonance structure for the ozone molecule may be drawn; the other molecules do not have resonance structures.

13. Answer: a. Wave 1 has a longer wavelength than wave 2. b. Wave 1 has a lower frequency than wave 2. c. Both waves travel at the same speed.

14. Answer: a. This wavelength is in the microwave region of the spectrum. b. This wavelength is in the range of violet light in the visible region. c. This wavelength is in the infrared region of the spectrum. d. This wavelength is in the UHF/microwave region of the spectrum.

15. Answer: Colors of visible light differ in their energy, frequency, and wavelength. Orange light is lower in energy, lower in frequency, and longer in wavelength than violet light.

16. Answer: Note: c = 3.0  108 m.s–1 and E = h.v, in which h = 6.63  10-34 J.s. a. E = (6.63  10-34 J.s)(1.5  1010 s-1) = 1.0  10-24 J b. E = (6.63  10-34 J.s)(8  1014 s-1) = 5  10-19 J c. E = (6.63  10-34 J.s)(6  1012 s-1) = 4  10-21 J d. E = (6.63  10-34 J.s)(2.0  109 s-1) = 1.3  10-24 J The most energetic photon corresponds to the shortest wavelength, 400 nm.

17. Answer: Yes, the speed of light in a vacuum is a constant.

18. Answer: In order of increasing energy per photon: radio waves < infrared < visible < gamma rays

19. Answer:

c  v  and  

; c = 3.0  108 m/s

v 

3.0  108 m/ s   1.2  101 m 9 2.45  10 / s

At 1.2 × 10-1 m, this microwave radiation has a longer wavelength (and lower energy) than X-rays (at ~10-10 m), but a shorter wavelength (and higher energy) than radio waves (at ~103 m).

20. Answer: a. In order of increasing wavelength: UV-C < UV-B < UV-A b. In order of increasing energy: UV-A < UV-B < UV-C c. In order of increasing potential for biological damage: UV-A < UV-B < UV-C

21. Answer:

a. 𝜆 =

𝑐

= 3.00 × 108

𝑢

b. 𝜆 =

𝑐 𝑢

= 3.00 × 108

m s

6.79 × 1014

s 4.44 × 1012

109 nm

= 442 nm

109 nm m

= 67,600 nm

22. Answer:

1.5 × 108 km ×

1000 m km

= 500 seconds

3.00 × 108 m

23. Answer: Answers will vary. To qualify as CFCs, the compounds should contain only carbon, chlorine, and fluorine. Possibilities include:

CCl3F trichlorofluoromethane Freon 11

CCl2F2 dichlorodifluoromethane Freon 12

24. Answer: All of these make use of the fact that CFCs are inert non-toxic gases that do not burn. Hair sprays, refrigerators, and air conditioners also make use of property that their boiling points are in a range useful for a refrigerant gas or propellant.

25. Answer: a. No, a CFC molecule can contain only chlorine, fluorine, and carbon atoms. b. HCFC molecules must contain hydrogen, carbon, fluorine, and chlorine atoms, and no other atoms In order for a molecule to be classified at an HFC, it must contain hydrogen, fluorine, and carbon (but no other atoms).

26. Answer: a. Methane, CH4

Ethane, C2H6

b. Three different CFCs are based on methane. They are: CF3Cl, CCl3F, and CCl2F2. c. The most successful CFCs were CFCl3 and CF2Cl2. These Freon® compounds were widely used in the U.S. as refrigerant gases. d. Although many compounds are synthesized and tested for appropriate properties, only a few have the boiling points to serve as refrigerant gases.

27. Answer:

a. Cl. has 7 outer electrons. Its Lewis structure is

.NO2

ClO.

has 5 + 2(6) = 17 outer electrons. Its Lewis structure is

has 7 + 6 = 13 outer electrons. Its Lewis structure is

.OH has 6 + 1 = 7 outer electrons. Its Lewis structure is:

b. They all contain an unpaired electron.

28. Answer: a. The original measurements were obtained during flights of NASA‘s ER-2 research airplanes carrying measuring instruments over the Antarctic region. b. Today these measurements are usually gathered via instruments in satellites, or at ground-level. For instance, stratospheric ozone measurements may be made by a ground-based microwave radiometer at the Bordeaux Observatory in France.

29. Answer: The first graph is a more realistic representation of the relationship between the percent reduction in the concentration of ozone and the percent increase in UV-B radiation. As the ozone layer is depleted, the concentration of UV-B that can penetrate into the atmosphere rises. The second graph shows a type of inverse relationship, which is not substantiated by experimental facts.

Concentrating on Concepts

30. Answer: The message is that ground-level ozone is a harmful air pollutant. Ozone in the stratosphere, on the other hand, is beneficial because it can absorb harmful UV-B before it reaches the surface of the Earth.

31. Answer: According to legend, Achilles was a man of mighty strength with one weak point - the heel of his foot. As the story goes, his downfall was caused by an arrow, possibly poisoned, shot to his heel. Similarly, our planet is robust and has great strengths. But it has a weak point – its atmosphere. If you damage the atmosphere, you may cause the downfall of the planet.

32. Answer: a. The most energetic fraction of solar UV radiation is the UV-C light.

b. Up in the stratosphere where the air is very thin, UV-C splits oxygen molecules, O2, into two oxygen atoms, O. These in turn react with other oxygen molecules to produce ozone, O3. See the reactions of the Chapman Cycle. Without the UV-C light (which does not reach the surface of our planet), the ozone layer would not form.

33. Answer: The solution proposed in the cartoon will not work for several reasons. One is that the amount of ozone required is too large to ship up to the stratosphere (and of course we don‘t have a series of freight planes heading up there anyhow). More importantly, if the mechanism for ozone destruction remains in place, any new ozone will be destroyed as well.

3433. Answer: a. HFCs are being used to replace HCFCs. b. HFCs are greenhouse gases!

3534. Answer: Each Lewis structure has 3 × 6 = 18 electrons, and each oxygen atom has an octet of electrons. The triangular structure is not reasonable because the bond angles (60°) are much smaller than the usual bond angles.

3635. Answer: Here are the resonance structures for ozone: Both contain 1 double bond (expected length of 121 pm) and 1 single bond (expected length of 132 pm). But in reality, the bonds are neither single nor double. Rather, the length of each bond is intermediate between the single and double bond lengths. A reasonable prediction would be 126 or 127 pm for both Oto-O bonds, midway between the two lengths.

3736. Answer: Ozone is very reactive and quickly dissipates in the troposphere. Ozone in the stratosphere is regenerated by UV-C sunlight reacting with oxygen molecules.

3837. Answer: The O – O bond in ozone is longer and weaker than the O=O double bond in oxygen gas, so the ozone bond is easier to break.

3938. Answer: With respect to valence electron distribution, the Lewis structures of SO2 and ozone are identical. This should not be surprising, as sulfur and oxygen are in the same group on the periodic table, and thus have the same number of outer electrons. However, the atoms present in the two Lewis structures differ:

4039. Answer: The energy of a photon of a radio wave is only about one ten-millionth of the energy of a photon of UV radiation. While UV radiation has sufficient energy to interact with melanin in skin pigments, radio waves do not.

4140. Answer: The UV Index, typically a number between 1 and 15, helps people to gauge how intense the sunlight is predicted to be on a particular day. A value of 6.5 (color-coded orange) indicates that there is high risk of harm and that you should protect your eyes and skin. A value of 8-10 indicates a very high risk and above 11 is an extreme risk.

4241. Answer: Although UV-C radiation causes damage to both animals and plants, it is completely absorbed by the O2 in our atmosphere before it can reach the surface of the Earth.

42. Answer: Gel manicures use UV rays in the UVA range. This range is associated with aging of the skin and can contribute to skin cancer. An article to consult is: https://www.self.com/story/gel-manicure-uv-naillamps-and-skin-cancer.

43. Answer: Stratospheric ozone is both formed and broken down in a dynamic system called the Chapman Cycle. Unless there are disturbances to this system, the system remains in balance and there is no net change in the concentration of stratospheric ozone.

44. Answer: See the answer to question #24. These compounds are useful because they are colorless, odorless, tasteless and generally inert. However, compounds such as these have long atmospheric lifetimes. They persist in the environment and make their way up to the stratosphere where they cause harm to the ozone layer.

45. Answer: NO in the stratosphere can act as a catalyst for the destruction of ozone. ClO. acts as a catalyst in the series of reactions in which stratospheric O3c O3 molecules are changed to O2 molecules.

46. Answer: Cl. acts as a catalyst in the series of reactions in which stratospheric O3 molecules react to produce O2 molecules. As it is not consumed in the reaction, Cl. can continue to catalyze the breakdown of O3.

Exploring Extensions

47. Answer: The smaller wavelength of the Blu-ray laser allows the laser beam to etch pits in the storage material that are smaller and closer together, therefore allowing more data to be stored.

48. Answer: There are wide seasonal fluctuations in the temperatures and wind patterns in Antarctica. Development of polar stratospheric clouds of ice crystals during the long, dark, and still winter months provides reaction sites for the conversion of non-ozone depleting particles to reactive species. When the sun appears in Antarctica in late September and early October, the UV radiation releases Cl. from CFCs, initiating the destruction of ozone. The depletion in the Northern Hemisphere is not as severe as in the Southern Hemisphere. Scientists have not classified the ozone depletion over the North Pole as a “hole.” The main reason for the observed difference between the total ozone changes in the two hemispheres is that the atmosphere above the North Pole usually is not as cold. Although polar stratospheric clouds have been observed in the Arctic, the air trapped over the Arctic generally begins to diffuse out of the region before the Sun gets bright enough to trigger as much ozone destruction as has been observed in Antarctica.

49. Answer: a.

b. This free radical is very reactive in the troposphere, so it does not last long enough to reach the stratosphere.

50. Answer: a. These compounds once were manufactured as fire suppressants. They are not water-based, so are excellent for specialized uses such as libraries, aircraft, and electronics. However, their production has been halted because they have high ozone depleting potentials (ODPs). b. The two hHalons have different atmospheric lifetimes. According to data from the U.S. EPA, http://www.epa.gov/Ozone/science/ods/classone.html (accessed August 2013), the values are 65 years and 16 years, respectively, for Halon-1301 and Halon-1211. A more interesting question is why the different lifetimes, which is beyond the scope of this text.

c. At the time this graph was drawn, it was thought that no substitutes would be found for some uses of methyl bromide. However, it now is looking more likely that substitutes will be found.

51. Answer: 5 + 3(6) + 1 = 24 electrons

52. Answer: Large amounts of smog can scatter UV radiation and cause poor breathing conditions.

53. Answer: This is not likely to be a reasonable solution, as ozone released into the troposphere will be destroyed by reactions with other atomosphericatmospheric constituents before it can rise to the stratosphere.

54. Answer: O2, O3, and N2 all have an even number of valence electrons. In contrast, N3 would have 15 valence electrons. Molecules with odd numbers of electrons cannot follow the octet rule and are more reactive.

55. Answer: a. 90 + 12 = 102. The compound contains one carbon atom, no hydrogen atoms, and two fluorine atoms. The chemical formula for CFC-12 is CCl2F2. b. CCl4 contains 1 carbon atom, 0 hydrogen atoms, and 0 fluorine atoms. Therefore, the code number for CCl4 is 100 or 90 + 10. The name is CFC-10.

c. Yes, the “90” method will work for HCFCs. 90 + 22 = 112, so HCFC-22 would be composed of 1 carbon atom, 1 hydrogen atom, and 2 fluorine atoms and its chemical formula would be CHF2Cl. d. No, this method will not work for halons as there is no guideline for handling bromine.

56. Answer: Ozonators typically produce ozone either via an electrical discharge or with UV light. The former is similar to the process that produces ozone in a thunderstorm. A bolt of lightning can split O2 molecules to form O atoms. The latter uses UV-C light to split O2 molecules. In either case, the O atoms then react with another oxygen molecule to produce ozone. The ozone produced works as an effective disinfectant. It can react with many biological molecules, thereby being effective against undesired microbes and viruses. It also can react with many molecules that produce odors. a. Search the web for examples. Claims include that ozonators can: • destroy odors; tobacco, smoke, pet, cooking, and chemical • kill bacteria and airborne viruses • remove allergy causing pollen and microbes • prevent mold and mildew, the leading cause of Legionnaires Disease • eliminate toxic fumes from printing, plating processes, hair and nail salons • purify water in holding tanks and emergency storage water tanks • purify drinking water from well sources or city water supplies • remove undesirable tastes, odors, and colors. b. Ozone can be a harmful pollutant causing both damage to plants and animals. Any device that creates the gas must carefully contain it.

57. Answer: a. Factors include (1) the reactivity of the compound, because this in turn affects the length of time it will remains in the atmosphere, and (2) the presence of Cl or Br in the compound, because and , formed in the stratosphere from chlorine- and bromine- containing compounds, deplete ozone. b. Most HCFCs, developed as replacements for CFCs, would be expected to have ODP values lower than those of the CFCs. HCFCs tend to be somewhat more reactive in the troposphere and thus do not accumulate in the stratosphere. Their ODP values range from 0.01 to 0.11. c. HFCs were also developed as CFC substitutes. Without chlorine or bromine present, they generally do not have the potential to deplete stratospheric ozone. Their ODP values are 0.0.

58. Answer: Depending on location, the generation of electricity may rely on the combustion of fossil fuels such as coal.

59. Answer: a.

BrO• + ClO•  BrCl + O2 BrCl + sunlight  Br• + Cl• Br• + O3  BrO• + O2 Cl• + O3  ClO• + O2

b. The net equation is 2 O3  3 O2

60. Answer: a. See Figure 3.282.17. Most months of the year, it is not cold enough in the Arctic for PSCs to form. b. HCl + ClONO2 → Cl2 + HNO3 The nitric acid remains bound to the ice, but the chlorine gas is released to the atmosphere. c. In the atmosphere in the presence of sunlight, Cl2 → 2Cl•

61. Answer: a. This is a possible Lewis structure. b. If Cl2O2 is the actual molecule, then it will have to be broken down by UV photons to ClO. free radicals before it can react with oxygen atoms as shown in Eequations 32.8 and 32.9. This would add one additional decomposition reaction in the catalytic destruction of ozone.

62. Answer: Oxybenzone (benzophenone-3), benzophenone-1, benzophenone-8, OD-PABA, 4-Mthylbenzylidene camphor, 3-benzylidene camphor, nano-titanium dioxide nanoparticles, nano-zinc oxide nanoparticles, and benzophenone-2 are the problematic chemicals in sun care products (https://oceanservice.noaa.gov/news/sunscreen-corals.html). Safer alternatives include wearing ultraviolet protection factor sun wear and avoiding the sun during peak hours.

ANSWERS TO END-OF-CHAPTER QUESTIONS CHAPTER 4: CLIMATE CHANGE

Emphasizing Essentials 1. Answer: a. Although the average temperature has risen about 0.6 ºC in the last 30 years, changes in temperature have not been uniform across the globe. For example, more warming has occurred at the poles, especially in the Arctic, compared to the tropics. Some places on the Earth‘s surface have even cooled, yet the average global temperature has increased. b. Changes in both atmospheric greenhouse gas concentrations and global temperatures have occurred many times in the past. But those changes typically took place over many thousands of years, not over decades like they are occurring today. c. Several possible detrimental consequences include sea level rise, more extreme droughts and floods, changes in ocean chemistry, and stresses on freshwater resources.

2. Answer: These two planets are warmer than would be expected because they have atmospheric gases that produce a "greenhouse effect." Sunlight enters the atmosphere of both Earth and Venus, warming the surfaces of the planet. The atmospheric gases are able to trap some of the heat radiated by the planet surfaces. Without these gases, the planets would be the temperatures expected as a result of their distance from the Sun. Note: the high concentration of CO2 in the Venusian atmosphere (98% CO2) has led to a “runaway greenhouse effect” and resulted in a surface temperature of about 450 °C!

3. Answer: The “windows” of the greenhouse are molecules such as carbon dioxide and methane that are transparent to visible light, but absorb in the infrared region of the spectrum. The main difference

between the atmosphere and a greenhouse is that the windows of a greenhouse are a physical barrier keeping the heat inside.

4. Answer: a. b. The number of atoms of each element on either side is the same. C = 6, O = 18, H = 12. c. No, the number of molecules is not the same. There are 12 on the left, but only 7 on the right. The glucose molecule on the product side contains 24 atoms!

5. Answer: Weather is a short-term description of whatever is happening outdoors in a given place at a given time. In essence, the weather is what you see each day out your window. Climate refers to the longerterm conditions that prevail in a particular place over a period of years or decades. It takes into account the average weather data and seasonal changes.

6. Answer: a. The rest of the Sun‘s energy is either absorbed or reflected by the atmosphere. For example, Chapter 3 pointed out that oxygen and stratospheric ozone absorb certain wavelengths of UV light. This chapter points out that clouds may reflect incoming radiation back into space. b. Under steady-state conditions, 29 MJ/m2 would leave the atmosphere each day.

7. Answer: a. As of 20196, the atmospheric concentration of CO2 was a little above 41300 ppm; however, 20,000 years ago, the concentration was only about 190 ppm. Looking back to 15020,000 years ago, the concentration was about 270 ppm, still ~40% below current levels. b. The mean atmospheric temperature at present is somewhat above the 1950-1980 mean atmospheric temperature. 20,000 years ago, the mean atmospheric temperature was lower by about 9 °C. However, 120,000 years ago the mean atmospheric temperature was lower than the present temperature by only about 1 °C. c. Although there appears to be a correlation between mean atmospheric temperature and CO2 concentration, this graph does not prove causation of either by the other.

8. Answer: Even though the amount of energy emitted from the surface is more than double the amount received from the Sun, the Earth does not cool rapidly because the surface also absorbs a large amount of energy from the atmosphere. The greenhouse effect allows the atmosphere to absorb that energy.

9. Answer: a. Visible light can enter through the glass, but infrared radiation cannot leave through the glass. There also is little exchange of air with the outside, so the heat cannot be dissipated and the temperature inside the car increases. b. On clear nights, the heat from Earth can radiate up through the atmosphere and out into space. When it is cloudy, the water vapor in the clouds absorbs some of the heat, thus retaining it. c. In the desert, the temperature swings between night and day tend be more pronounced cClouds and humid air make the temperatures more uniform, as they tend to block or scatter incoming solar radiation and trap outgoing heat. Note: if the desert contains large urban areas, the pavement and buildings absorb heat during the day. This heat is released at night and thus can keep the temperature high even when the Sun has dropped. d. Dark clothing absorbs much of the light that strikes it; in contrast, lighter clothing reflects most of it. The light energy absorbed converts to heat energy, which can increase the risk of heatstroke.

10. Answer:

The actual distances measured will depend on the model kit used. In every case, however, the distance between the hydrogen atoms in a square planar arrangement will be less than the distance between the hydrogen atoms in the tetrahedral arrangement. This is because the angle separating the hydrogen atoms is greater in the tetrahedral arrangement. See photo.

11. Answer:

bent

linear

12. Answer:

trigonal pyramidal

linear

tetrahedral

13. Answer: a. 3(1) + 4 + 6 + 1 = 14 outer electrons. This is the Lewis structure.

b. The geometry around the C atom is tetrahedral, and there are no lone pairs. A H–C–H bond angle of about 109.5° is predicted. c. There are four pairs of electrons around the O atom, two of which are bonding pairs and two are nonbonded pairs. Repulsion between the two nonbonded electron pairs and their repulsion of the bonding pairs is predicted to cause the H–O–C bond angle to be slightly less than 109.5°.

14. Answer: a. 2(1) + 4 + 4 + 2(1) = 12 outer electrons. This is the Lewis structure. H C C H H H

b. There are three sets of bonding electrons around each carbon atom. To achieve maximum separation of these bonding electrons, an H–C–H bond angle of 120° is predicted. H

H C

c. This sketch shows the predicted bond angle. H

120 °

15. Answer: All can contribute to the greenhouse effect. In each case, the atoms move as the bond stretches or bends, and therefore the charge distribution changes. Unlike the linear CO2 molecule, the water molecule is bent and so its polarity changes with each of these modes of vibration.

16. Answer:

a. Use E =



to calculate the energies.

E 

(6.63  1034 J  s)  (3.00  108 m  s1) 1m 4.26 m  106 m



4.67  10 20 J

(6.63 1034 J  s)  (3.00  108 m  s1) E  1.33  1020 J 1m 15.00m  106 m b. If the vibrating molecule CO2 collides with another molecule, such as N2 or O2, the energy can be transferred to the second molecule. The energy can also be spontaneously emitted back to the atmosphere or into space.

17. Answer: When water molecules and carbon dioxide molecules vibrate, there is a change in the distribution of electrons within the molecule that allows these to absorb infrared radiation. The diatomic (and nonpolar) gases, N2 and O2, are not capable of vibrating or stretching in a way that changes the electron distribution.

18. Answer: a. Volcanic eruptions send large amounts of ash and aerosols up into the atmosphere. Often this ash remains suspended in the atmosphere for a weeks or even months. The ash reflects incoming sunlight into space and can have a cooling effect. b. CFCs reduce the concentration of ozone in the stratosphere. Because ozone is a greenhouse gas, CFCs in the stratosphere have a slight cooling effect.

19. Answer: a. C6H12O6  3 CH4 + 3 CO2 b. in one day:

1.0mgglucose 4

44gCO2 = 7.3  101molglucose  3 molCO2   1000mg 180g glucose 1molglucose 1molCO2 

in one year:

7.3 x 10-4 g CO2 365days  = 0.27 g CO2/year year day

20. Answer: a. According to the 2014 report by the IPCCEPA, the power/heating sector is was responsible for the greatest amount of global CO2 emissions. b. For the transport sector (13%), alternatives include vehicles that are powered in ways other than by burning fuels such as walking or biking. For power and heating stations (26%), alternatives include wind, solar, and nuclear. For deforestation (17%), the alternatives include changing land use policies and reforestation. For industry (1924%) and agriculture (14%), many of these same practices apply. In all cases, conservation is one way of minimizing CO2 emissions.

21. Answer: a. A neutral atom of Ag-107 has 47 protons, 60 neutrons, and 47 electrons. b. A neutral atom of Ag-109 has 47 protons, 62 neutrons, and 47 electrons. Only the number of neutrons is different.

22. Answer: The atomic mass of silver would be 108 if the two isotopes were equally abundant in nature. However, Ag-107, with an atomic mass of 106.91 g/mol, accounts for 51.8% of natural silver, and Ag-109, with an atomic mass of 108.91 g/mol, accounts for 48.2%. The average atomic mass is calculated as follows: (106.91 g/mol  0.518) + (108.91 g/mol  0.482) = 107.87 g/mol

The average atomic mass for silver is 107.87 g/mol.

23. Answer:

107.87g a.

1 mole

  6.02  1023atoms  1mole 1.79  1022g 12

atom



1.79  1022 g 

atom



9

 10  10 atoms  1.79  10 g

1.7910-22g c. 5.0010 atoms  8.951023g atom 45

24. Answer: a. 2(1.0 g/mol) + 16.0 g/mol) = 18.0 g/mol b. 12.0 g/mol + 2(35.5 g/mol) + 2(19.0 g/mol) = 121.0 g/mol c. 2(14.0 g/mol) + 16.0 g/mol = 44.0 g/mol

25. Answer: a. The mass percent of Cl in CCl3F (Freon-11) is:

3  (35.5 g/mol) 100 77.5% 12.0 g/mol 3  (35.5 g/mol) 19.0 g/mol b. The mass percent of Cl in CCl2F2 is 58.7%. c. Freon-11: 77.5 g; Freon-12: 58.7 g 23 1 mol Cl 6.02 x 10 atomsCl  d. Freon-11: 77.5 g Cl  = 1.31 1024 Cl atoms; 35.5 g Cl 1molCl

Freon-12: 9.95  1023 Cl atoms.

26. Answer:

7.5 1017 g   100  0.001% Concentration of carbon atoms = 7.5 10 22 g 0.001 partsCin livingsystems  x partsCin livingsystems  100 partsC on Earth 1,000,000partsC on Earth x = 10 ppm

27. Answer: The estimated atmospheric lifetime and its ability to absorb infrared radiation.

Concentrating on Concepts

28. Answer: a. b. c. d. e. f.

8 protons, 8 electrons, and 10 neutrons 16 protons, 16 electrons, and 19 neutrons 82 protons, 82 electrons, 157 neutrons 35 protons, 35 electrons, 47 neutrons 10 protons, 10 electrons, 9 neutrons 88 protons, 88 electrons, 138 neutrons

29. Answer: a. 199F19/9F

b. 56 26Fe56/26Fe

c. 222 86Rn222/86Rn

30. Answer: a.780.2 = 4 sig figs b. 9.003 = 4 sig figs c. 400.0 = 4 sig figs

d. 0.0025 = 2 sig figs

31. Answer:

32. Answer:

3033. Answer: Students can agree or disagree with the statement. Those that agree may cite the rapid rise in Arctic temperatures, retreating glaciers, or loss of biodiversity. Those who disagree might state that although there has been some warming, even a large amount of warming, it has not reached the stage where global climate disruption is the proper term.

3134.

Answer:

a. Before sophisticated analytical instruments were developed, miners would take caged canaries into the mines to warn them if they encountered any toxic gases (quite prevalent in mine shafts). The canaries were more sensitive to gases like CO. If the canary died, the miners knew they had to get out and into better air quickly. b. The changes that are occurring in the Arctic may be an early warning sign for the rest of the planet in terms of potential consequences of warmer global temperatures.

c. Significant amounts of methane are trapped in the frozen tundra. If the tundra thawed and released this methane into the atmosphere, this would further accelerate global warming elsewhere because methane is a greenhouse gas.

32.

Answer:

The statement is not justified because it confuses the concepts of climate and weather. Global warming refers to long-term changes in climate, not to regional seasonal anomalies. In the same way, an excessively hot summer does not mean that global warming was the cause.

3335.

Answer:

Scientists have several ways of estimating the past temperatures of the Earth. Scientists can analyze the deuterium-to-hydrogen ratio in ice cores and recreate the temperatures in the distant past. Drilled ocean cores can be analyzed for the number or type of microorganisms present. Another correlating piece of evidence is the changing alignment of the magnetic field in particles in the sediment over time.

3436.

Answer:

One initial reaction would be that the newspaper reporter has confused “the greenhouse effect” with “global warming.” The greenhouse effect is necessary for life on Earth to exist; without it the average temperature would be -15 ºC. Global warming, or the “enhanced greenhouse effect”, is what is being blamed for the rise in average global temperatures and the consequences for humans that may result.

37. Answer: Periodic changes in the shape of Earth‘s orbit and the tilt of Earth‘s axis can change Earth‘s climate. These can affect greenhouse gas concentrations, Earth‘s energy balance, and its climate.

3538.

Answer:

Oceans have absorbed about a third of the CO2 emissions. The result has been more acidic oceans, as will be discussed further in Chapter 6.

3639. Answer: Substances that absorb visible light have observable colors. For example, if the wavelengths associated with red light are absorbed, the object appears green. Because we cannot see any color

associated with either carbon dioxide gas or water vapor, we conclude they do not absorb a significant amount of visible light.

3740.

Answer:

The energy required would be smaller for each of the IR-absorbing vibrations if single bonds were present. In general, single bonds between atoms are weaker than double bonds, and therefore less energy will be required to cause stretching and bending.

3841.

Answer:

Water molecules are able to absorb microwave radiation and when they do so, they rotate faster. These rotating molecules then collide with other water molecules and can distribute the energy, heating up the entire cup. In contrast, glass (primarily silicon dioxide) is not a material that absorbs energy in the microwave region. However, the glass cup will be heated indirectly by the hot water in it.

3942.

Answer:

a. b. 2 moles of CO2 areis produced for each mole of ethanol burned.

c. 30 mol O2, because for every 1 mole of C2H5OH burned, 3 moles of O2 burn. 4043. Answer: The atmospheric lifetime is important because it helps to determine the long-term impact of the greenhouse gas. If efficient environmental removal mechanisms exist for a particular greenhouse gas (that is, if it has a short atmospheric lifetime) the gas will accumulate more slowly in the atmosphere than predicted by the rate at which it is emitted. If a greenhouse has a longer atmospheric lifetime, the atmospheric concentration of the gas will continually increase, allowing the gas to contribute to global warming for a longer period of time.

4144. Answer: The main chemical species involved in ozone depletion are O3 and CFCs, while for climate change, CO2, CH4 and N2O are the main greenhouse gases. Ultraviolet radiation breaks covalent bonds in CFCs leading to ozone depletion, while infrared radiation is absorbed and trapped by atmospheric gases causing the greenhouse and enhanced greenhouse effects. Predicted consequences of ozone depletion include increased UV exposure at the Earth‘s surface, increased occurrences of skin cancer

in humans and damage to other biological organisms. Climate change consequences include rising sea level, stresses on freshwater resources, loss of biodiversity, and ocean acidification, among others.

4245. Answer: Radiativeing forcings are perturbations that affect the amount of heat absorbed by the Earth‘s surface. Both natural and anthropogenic forcings are important. Some forcings have a warming effect (positive forcings), like greenhouse gases, and increases in solar brightness. Other forcings have a cooling effect (negative forcings) including the direct and indirect effects of aerosols, and increases in the reflectivity of the Earth‘s surface (albedo).

4346. Answer:

12metrictonsC 73106 metrictonsCH  5.5107 metrictonsC 4 16metrictonsCH 4

4447.

Answer:

This observation does not prove that global warming is taking place. It is a short-range observation that is consistent with predicted global warming trends. If the trend continues, then it may indeed be evidence for climate change. Recall climate describes regional weather changes over decades.

45.8.

Answer:

a. From this information, HFC-152a is the best choice. It has a lower GWP and a much shorter atmospheric lifetime. b. Other considerations include cost, toxicity, flammability, boiling point, and chemical stability.

4649. Answer: a. On a per capita basis, the United States would rank first. The population of the United States is smaller than that of China. b. The value for metric tons of CO2 would be higher than that for tons carbon. The former includes the mass of the oxygen; the latter does not.

4750. Answer: Under a cap-and-trade system, the total emissions from a country are set at a particular level. A certain number of pollution “permits” are issued that corresponds to the set amount of emissions. Individual companies that decrease their emissions below the target values can trade or sell their

unused permits to other companies that are less successful at lowering emissions. The purpose is to give companies an economic incentive for lowering emissions and to reach the overall emission reduction goal in the most cost-effective way. A carbon tax simply places a tax on all fossil fuels. The higher cost to consumers presumably will decrease demand and again lead to an overall decrease in emissions. In the case of a carbon tax, the total emission limits are not set.

4851. Answer: Arrhenius overestimated the temperature increased caused by a doubling of the atmospheric CO2 concentration by about a factor of two, compared to the IPCC models. The models project a range of 2-4.5 ºC increase for doubling of the CO2 concentration.

Exploring Extensions

4952. Answer: a. Students agreeing that global warming is a moral issue may cite the fact that the suffering due to global warming will not be born equally by the countries responsible for the majority of emissions. Other arguments may center on human being‘s role in the stewardship of the planet toward future generations. b. The politics of global warming mainly center on the potential mitigation legislation. Decreasing fossil fuel combustion has ramifications in nearly all sectors of the economy, and political decisions will have to be made about the most efficient way to accomplish this. Any changes from the status quo will likely encounter political opposition from special interest groups.

5053.

Answer:

a. Burning coal with high sulfur content introduces more SOx to the atmosphere. This reduces air quality, increases acid precipitation, and speeds the degradation of the environment due to acidification. b. Sulfur aerosols reflect incoming solar radiation back toward space. They also serve as nuclei around which water vapor can condense to form sunlight-reflecting cloud particles. c. India

5154. Answer: a. It has shifted to higher altitudes and chosen different plants on which to lay its eggs. The area in Mexico previously inhabited is becoming too hot and dry for the butterfly.

b. Land development is the main cause of the parts of California being uninhabitable. c. Answers can include prohibiting further development in the region, or developing breeding programs to increase the species population. (Another source: https://www.theguardian.com/environment/2014/apr/07/endangered-butterfly-species-defies-climatechange-quino-checkerspot) b. The projections show that the range in the USA, including the new elevations, will not be habitable.

5255. Answer: Here is the general equation for the complete combustion of a hydrocarbon. The coefficients must be supplied for each different hydrocarbon. CxHy +

O2 

CO2 +

H2O

Humans increase the levels of CO2 in the atmosphere by burning fossil fuels. The lifetime of CO2 in the atmosphere varies, but it tends to be removed slowly. Water vapor also is released in the process of combustion, but does not accumulate in the atmosphere because it is removed through rain, snow, and other forms of precipitation. For these reasons, the difference in the two trends does not disprove the connection between human activities and global warming.

5356.

Answer:

a. The balanced equation for the complete combustion of methane is: CH4 + 2 O2  CO2 + 2 H2O Therefore, burning 1196 mol of methane could produce 1196 mol of CO2.

44 g b. 1196mol

mol

52624g, or 52.62 kg

c. 52.62 kg × (1 metric ton/1000 kg) = 0.05262 metric tons

5457. Answer: The results of COP21 in Paris were to keep the rise in average global temperature to lower than 1.5 o C in order to protect low-lying island nations who are most threatened by sea-level rise. Countries submitted action plans for how they would limit greenhouse gas emissions, but the total increase in average temperature would be between 2.7 and 3 oC, so nations were asked to reevaluate these plans every 5 years to see if they could make additional cuts with a goal to reach carbon neutrality by the middle of the century. The need for funds to working on projects to limit greenhouse gas emissions was agreed upon, and that while developed countries will provide most of the funds, developing countries could also contribute to help the poorest countries.

5558. Answer: Solar ovens do not burn a fuel for heat, but rather use reflective surfaces to focus the sun‘s rays. Therefore, they emit no carbon dioxide when used. Solar ovens are most useful in places where forests are being cut for firewood, like Africa and South America. Increased use of solar ovens not only would decrease CO2 emissions, but also slow the rate of deforestation in these areas.

5659. Answer: Student answers will vary depending on the country they choose.

60. Answer: Student answers will vary but should center on combustion of coal.

ANSWERS TO END-OF-CHAPTER QUESTIONS

CHAPTER 85: Water Everywhere: A Most Precious Resource Emphasizing Essentials 1. Answer: a. A compound is a pure substance made up of two or more different elements in a fixed, characteristic chemical combination. Water is a compound rather than an element because it contains both the elements H and O in a 2:1 ratio, as evidenced by the chemical formula H2O. b. The Lewis structure for water is:

The molecule is “bent” because the two lone pairs (nonbonding pairs) of electrons on the oxygen atom occupy space (as do the two bonding pairs of electrons on the O atom). The shape of the water molecule maximizes the space between all these electron pairs, in accord with the VSEPR theory. 2. Answer:

a. Possibilities include washing dishes, doing laundry, flushing a toilet, showering, brushing teeth, and washing a car or truck. b. Water is naturally filtered through rocks and soil. Water evaporates to form clouds, a form of distillation. Bacteria may decompose some organic pollutants. c. Answers may include: use a process that does not require water, cut back on water consumption, use less household chemicals, use biodegradable household products, and reuse dirty water for another purpose, as in watering a compost pile. 3. Answer: a. Because water has such a high specific heat, it can moderate climate by capturing and absorbing heat from surrounding land and air. b. If ice were denser than liquid water, it would sink as it forms. As a result, lakes would freeze from the bottom up, killing the forms of life that could not tolerate freezing temperatures.

4. Answer: Water expands when it freezes due to its lower density and porous structure compared to its liquid form. The force created upon of the expansion of water‘s expansion is sufficient to break a pipe. 5. Answer: a. N and C, 3.0 – 2.5 = 0.5 O and S, 3.5 – 2.5 = 1.0 N and H, 3.0 – 2.1 = 0.9 F and S, 4.0 – 2.5 = 1.5 b. N more strongly attracts electrons than C. O more strongly attracts electrons than S. N more strongly attracts electrons than H. F more strongly attracts electrons than S. c. N–C < N–H < S–O < S–F 6. Answer: a. The Lewis structure for ammonia is

b. Each N–H bond is polar. The difference in electronegativity between N and H is 3.0 – 2.1 = 0.9.

c. The ammonia molecule is triangular pyramidal. This geometry, together with the polarity of the N–H bonds, causes the molecule to be polar. d. Ammonia is highly soluble in water. Ammonia and water both are polar molecules, and “like dissolves like.” 7. Answer: a. Yes this is also true for hydrocarbons. Distillation towers at a petroleum refinery separate hydrocarbons of different sizes by their boiling point. b. Based only on molar mass, you would expect H2O to have the lowest boiling point because its molar mass is the lowest at 18.0 g/mol. c. Water is a polar molecule while the rest are nonpolar. Both its geometry and its polar covalent bonds contribute to the formation of strong intermolecular forces. Thus, molar mass is not the only factor that contributes to the boiling point of a substance. 8. Answer: a. Examples of nonmetals include C, H, O, S, Cl, and N. Nonmetals generally have higher electronegativity values than metals. b. The electronegativity values of C, H, and O are 2.5, 2.1 and 3.5, respectively. c. The C–H bond in CH4 is nonpolar (the difference in electronegativity between C and H is small). In contrast, the O–H bonds in H2O are polar (the difference in electronegativity between O and H is large). d. The attractive forces between methane molecules (nonpolar) are relatively weak, and therefore methane boils at a temperature well below that of room temperature. In contrast, water molecules are polar and strongly attracted to each other (by hydrogen bonding). Accordingly, water has a higher boiling point and is a liquid at room temperature. 9. Answer: The arrow points to a hydrogen bond, an example of an attraction force between water molecules and not within each water molecule (as is the case for the polar covalent O–H bond). 10. Answer: a. A chlorine atom gains one electron to form a chloride ion with a charge of 1–. The octet rule is satisfied.

b. A sulfur atom gains two electrons to form a sulfide ion with a charge of 2–. The octet rule is satisfied. c. A neon atom does not form an ion. It already has 8 valence electrons.

d. A barium atom loses two electrons to form a barium ion with a charge of 2+. The octet rule is satisfied.

e. A lithium atom loses one electron to form a lithium ion with a charge of 1+. The octet rule is satisfied.

110. Answer: a. Here is the Lewis structure

b. Lewis structures: H+ and

1211. Answer: a. volume of water: 100.0 g 

1 cm3 0.9987 g

1 cm3

100.1 cm3 3

100.0 g   109 cm 0.917 g volume of ice: 

109 cm3 100.1 cm3 100 9% volume increase 3 100.1 cm b.

Concentrating on Concepts 1312. Answer: a. Add the liquids in this order: maple syrup, dishwashing liquid, and then vegetable oil (most to least dense). Three factors need to be considered: solubility, density, and the care with which each liquid is poured. Maple syrup will probably slowly dissolve in dishwashing liquid; likewise vegetable oil may be slightly soluble in the detergent. But with careful pouring, these three liquids should not easily mix and probably could be added in any order.

b. After vigorous mixing, a cloudy emulsion most likely will form. You may want to try this experiment and observe the results!

1413. Answer: Figure 5.108 shows that 97% of the water on Earth is salty water and 3% (15 L of the 500-L drum) is fresh and possibly suitable for drinking. Much of this water is not readily available for consumption, as it is locked in ice (glaciers), is below ground (must be pumped to the surface) or must be filtered or treated (lake water).

1514. Answer: a. Partially soluble. Orange juice concentrate contains some solids (pulp) that do not dissolve in water. b. Very soluble. Note that ammonia is a gas. If you ever have seen a lecture demonstration involving ammonia and water (e.g., “the ammonia fountain”), you know that ammonia dissolves almost instantly in water. Ammonia will dissolve in water in any proportion. c. Not soluble. Sometimes you can see chicken fat floating on top of aqueous chicken soup. d. Very soluble. When you add laundry detergent to your load of wash, it dissolves in the water (or at least it should dissolve – sometimes solid laundry detergent cakes together). e. Partially soluble if the chicken broth contains fat or suspended solids, neither of which will dissolve in water. Very soluble if the broth is clear and fat free. 1615. Answer: a. 9.0  109 gallons b. 3.4  1010 liters 1716. Answer: a. For Cl and Na, the electronegativity difference is 3.0 – 0.9 = 2.1. For Cl and Si, the electronegativity difference is 3.0 – 1.8 = 1.2. b. Larger differences in electronegativity are associated with ionic bonds; smaller differences with covalent bonds. c. When electronegativity differences are relatively large, one or more electrons are transferred, forming ions. When electronegativity differences are smaller, neither atom is able to release its outer electrons to the other, so the outer electrons are shared, resulting in formation of covalent bonds. In the case of SiCl4, Si and Cl form a polar covalent bond.

1817. Answer: a. 2 ppb b. It is in the form of the mercury ion. 1918. Answer: No, it exceeds the acceptable limit by 35 times. A concentration of 10 ppm is equivalent to 10 mg/L, so 350 mg/L is 350 ppm. 2019. Answer: To answer this question, calculate how many liters of solution (x) would be produced by dissolving 5.85 grams of NaCl. 1 mol NaCl 1.0 L 𝑥 L of solution = 5.85 g NaCl × × = 1.0 L of solution 58.4 g NaCl 0.10 mol The student would need a 1.0 L flask to make up the solution.

2120. Answer: a. The solution will conduct electricity and the bulb will light. Based on Table 5.58.6, CaCl2 is a soluble salt and therefore releases ions (Ca2+ and Cl–) when it dissolves. These ions carry the current. b. The solution will not conduct electricity. Although ethanol (C2H5OH) is soluble in water, it is a covalent compound and does not form ions. c. The solution will conduct electricity and the bulb will light. Sulfuric acid (H2SO4) releases ions when it dissolves: H+ and SO42–.

2221. Answer: The solution of the ionic compound KCl contains K+(aq) and Cl–(aq). In contrast, sucrose is a covalent compound that forms no ions in solution. Ions need to be present to conduct electricity.

2322. Answer: Using the trends listed in Table 5.5, aAll of these compounds are water-soluble.

2423. Answer: The concentration of Mg2+ is 2.5 M and the concentration of NO3– is 5.0 M since there are two moles of nitrate ions for every mole of magnesium nitrate.

2524. Answer: The chemical formula for calcium carbonate is CaCO3. This salt is insoluble in water according to the solubility rules for compounds containing the carbonate ion.

2625. Answer: a. HBr(aq)  H+(aq) + Br–(aq) b. H2SO3(aq)  H+(aq) + HSO3–(aq) c. HC2H3O2(aq)  H+(aq) + C2H3O2– (aq)

2726. Answer: a. HI(aq) is acidic. [H+] = [I–] > [OH–] b. NaCl(aq) is neutral. [Na+] = [Cl–] and [H+] = [OH–] c. NH4OH(aq) is basic. [NH4+] = [OH–] > [H+] 27. Answer: d. Basic; the concentration of the OH– is greater than the concentration of the H+. e. Basic; the concentration of the OH– is greater than the concentration of the H+. f. Acidic; the concentration of the H+ is greater than the concentration of the OH–. g. Acidic; the concentration of the H+ is greater than the concentration of the OH–.

28. Answer: da. [OH–] = 1  10-6 M f.c [OH–] = 2  10-8 M

2928. Answer:

eb. [H+] = 1  10-12 M gd. [H+] = 1  10-2 M

a. A solution of pH = 6 has 100 times more [H+] than a solution of pH = 8. b. A solution of pH = 5.5 has 10 times more [H+] than a solution of pH = 6.5. c. The solution with [H+] = 1  10–6 M has 100 times more [H+] than a solution with [H+] = 1  10–8 M. d. Using Eequation 5.136.9, the solution with [OH–] = 1  10–2 M has [H+] = 1  10–12 M. The solution with [OH–] = 1  10 –3 M has [H+] = 1  10–11 M. Thus, in the second solution ([OH–] = 1  10 –3 M) the [H+] is higher by a factor of 10. 3029. Answer: The 0.1 M NaOH solution has the lowest concentration of hydrogen ion (1  10–13 M) and the highest concentration of hydroxide ion, 1  10-1 M. In pure water, the hydrogen ion concentration is 1  10–7 M.

3130. Answer: a. NO3–, SO42–, CO32–, NH4+ b. For the nitrate ion, one possibility is nitric acid neutralizing sodium hydroxide. H+(aq) + NO3–(aq ) + Na+(aq) + OH–(aq) → Na+(aq) + NO3–(aq ) + H2O(l) For the sulfate ion, one possibility is sulfuric acid neutralizing sodium hydroxide. 2 H+(aq) + SO42–(aq ) + 2 Na+(aq) + 2 OH–(aq) → 2 Na+(aq) + SO42–(aq ) + 2 H2O(l) For the carbonate and ammonium ions, one possibility is carbonic acid neutralizing ammonium hydroxide. H2CO3(aq ) + 2 NH4OH(aq) → 2NH4+(aq ) + CO32–(aq ) + 2 H2O(l) Note: Ammonium hydroxide is written in its undissociated form, as explained in the text; see equation 8.7b. Similarly, carbonic acid is written in its undissociated form.

3231. Answer: a. KOH(s) → K+(aq) + OH–(aq) b. Ba(OH)2(s) → Ba2+(aq) + 2 OH–(aq) 3332. Answer: a. To prepare two liters of 1.50 M KOH, weigh 168 g of KOH and place it into a 2-liter volumetric flask. Add distilled (or deionized) water to fill the flask to the mark. Note: if you don‘t have a 2-L volumetric flask, you will need to repeat the procedure twice with a 1-L flask. b. To prepare one liter of 0.050 M NaBr, weigh 5.2 g of NaBr and place it into a 1-liter volumetric flask. Add water as in part a. c. This should be done with a 100-mL volumetric flask. Weigh 7.0 g of Mg(OH)2 and place it into a 100 mL volumetric flask. Add water as in part a.

3433. Answer: a. Each minute requires 18 L (90 L divided by 5 minutes) b. Assuming you brush your teeth twice a day, 7 days a week, the water savings would be about 14 liters. 3534. Answer: a. carbon dioxide, CO2 b. sulfur dioxide, SO2

3635. Answer: a. KOH(aq) + HNO3(aq) → KNO3(aq) + H2O(l) b. Ba(OH)2(aq) + 2 HCl(aq) → BaCl2(aq) + 2 H2O(l) c. H2SO4(aq) + 2 NH4OH(aq) → (NH4)2SO4(aq) + 2 H2O(l) 3736. Answer: a. Possibilities include sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonium hydroxide (NH4OH), magnesium hydroxide (Mg(OH)2), and calcium hydroxide (Ca(OH)2). b. In general, bases taste bitter, turn litmus paper blue (and have characteristic color changes with other indicators), have a slippery feel in water, and are caustic to your skin and eyes.

3837. Answer: Possibilities include nitric acid (HNO3), hydrochloric acid (HCl), sulfuric acid (H2SO4), sulfurous acid (H2SO3), phosphoric acid (H3PO4), carbonic acid (H2CO3), and hydrobromic acid (HBr). In general, acids taste sour, turn litmus paper red (and have characteristic color changes with other indicators), are corrosive to metals such as iron and aluminum, and release carbon dioxide (“fizz”) when mixed with a carbonate. These properties may not be observed if the acid is not sufficiently concentrated. 3938. Answer: Chocolate requires 1700 liters of water to produce a 100-gram bar. This includes the water necessary to grow and process both the cacao and the sugar used to sweeten it. A pint of beer requires about 140 L of water, mainly for growing and producing the malted barley. Processing the cacao and sugar is highly water intensive compared to processing barley. These are average global values given on tThe Water Footprint Network (http://www.waterfootprint.org).

4039. Answer: Water dissolves many substances, including a variety of acids, bases, salts, and polar molecules. It is also a common solvent, and in this sense is “universal” as well. However, water is not really a universal solvent as it does not dissolve everything. Gasoline and granite, for example, are insoluble in water. 4140. Answer: “Pure” water is usually interpreted as meaning water that has no dissolved impurities, something that is very difficult to achieve. But in reality, water is never pure. For example, if rain has fallen through the atmosphere, it will have picked up carbon dioxide, which explains why all rainwater is slightly acidic. Groundwater can easily pick up water-soluble ions, and even ice may contain suspended particulate matter or gases. Even bottled water usually contains dissolved minerals. 4241. Answer: Only water-soluble vitamins would be expected to be polar molecules. Though a fatsoluble vitamin will often have individual polar bonds or small polar regions in the molecule, overall this is out-weighed by nonpolar sections. Polar covalent bonds attract to water through hydrogen bonding and may allow the molecules to dissolve in water, while nonpolar covalent bonds favor interactions with the nonpolar chains in lipids (fats). 4342. Answer: A mercury concentration of 1.5 ppb means there are 1.5 parts of mercury for every 109 parts fish. The caution sign is necessary because mercury is toxic and capable of causing severe neurological effects in humans. The EPA has set the Maximum Contaminant Level for mercury in drinking water at 2 ppb. This is below that limit, but the caution sign is necessary because mercury is a cumulative poison. 4443. Answer: a. The electronegativities of the elements generally increase from left to right across a period (until Group 18 8A is reached) and from bottom to top within any group. Thus, the element in position 2 is predicted to have the highest electronegativity. b. Ranking the other elements is not straightforward. Element 1 is expected to be more electronegative than element 3, based on their relative positions in the same group. Element 4 will likely be more electronegative than elements 1 and 3 and less electronegative than 2. However, because element 4 is not in the same period with any other element, this prediction cannot be made with certainty. Here are the values found in references (they do not appear in Table 5.1): 0.8 for Element 1, 2.4 for Element 2, 0.7 for

Element 3, and 1.9 for Element 4. These values confirm the relative ranking in order of decreasing electronegativity: 2, 4, 1, and 3. 4544. Answer: The diatomic molecule (XY) with a polar covalent bond must be polar because the molecule is linear. An example is HCl. The H–Cl bond is polar, and so is the molecule. If the triatomic molecule contains polar bonds, the geometry of the molecule will determine if the molecule is polar or nonpolar. For example, although CO2 has polar C=O double bonds, the molecule is linear and, as a result, nonpolar. The H2O molecule has polar H–O bonds, but is bent. This geometry gives rise to a polar molecule.

4645. Answer: liquid

gas

a. The molecules in a gas should appear further apart than those in a liquid. The molecules themselves will not change, only the distances between them. As water vapor condenses, the molecules are now close enough to each other to form hydrogen bonds to each other, an intermolecular force. b. As the temperature drops to 4 °C, the water molecules approach each other most closely. Then, from 4 °C to 0 °C, they are forced somewhat apart as hydrogen bonding between molecules creates regular lattice patterns. At 0 °C, snowflakes and ice crystals form, both of which are less dense than the water at 4 °C. 4746. Answer: Like water, NH3 is a polar molecule. It has polar N–H bonds and a trigonal pyramidal geometry. Therefore, despite its low molar mass, considerable energy must be added to liquid NH3 to overcome the intermolecular forces (hydrogen bonding) among NH3 molecules.

4847. Answer: a. A single covalent bond holds the two2 H atoms together in H2. b. Hydrogen bonding is an attraction force between a H atom on one molecule and an electronegative atom on another molecule (or in some cases, between a H atom and an electronegative atom on a different part of the same molecule). c. A hydrogen atom in a molecule of H2O shares electrons with the adjacent oxygen atom in a polar covalent bond, an intramolecular force. Hydrogen bonding in a sample of water is not a sharing of electrons within a single molecule, but rather an attraction force between the polar ends of two different water molecules. 4948. Answer: a. The Lewis structure for ethanol is:

b. The cube sinks because, as is the case for most substances, the density of the solid phase is greater than the density of the liquid phase. Unlike water molecules, the ethanol molecules are closer together in solid ethanol than liquid ethanol. Therefore, solid ethanol has a greater density than liquid ethanol and it sinks.

Exploring Extensions 5049. Answer: The specific heat of a substance is the quantity of heat energy that must be absorbed to increase the temperature of 1 g of a substance by 1 °C. Heat is produced within our bodies primarily by respiration; that is, by the “burning” of food to produce carbon dioxide and water. Our bodies also absorb heat (to a limited extent) when we sit by a fire or are outside in hot weather. If water had a lower specific heat, our bodies would be more susceptible to a temperature rise both from respiration and from exposure to warm or hot conditions. One way that our bodies lose heat is through exposure to cooler conditions. If water had a lower specific heat, our bodies would be more susceptible to a temperature drop in cooler conditions. Our bodies also lose heat through excretion of urine and through sweating. Water has a relatively high specific heat and thus is a very good coolant to carry away excess heat. The loss of heat by evaporation, however, would not be affected by a change in the specific heat of water.

5150. Answer: For a given contaminant, the MCLG (a goal) and the MCL (a legal limit) are usually the same. However, the levels may differ when it is not practical or possible to achieve the health goal as set by the MCLG. This sometimes is the case for carcinogens, for which the MCLG is set at zero (under the assumption that any exposure presents a cancer risk.) 5251. Answer: Answers will vary. Questions may include: (1) what levels of THMs have been observed, (2) what health effects, if any, are associated with these levels, (3) whether the trihalomethanes were created in the treatment process and, if so, if the process should be changed, (4) what options, if any, the consumer has to remove the THMs at the faucet.

5352. Answer:

a. Nitrate ion (NO3–) and nitrite ion (NO2–). b. In the body, oxygen is needed to metabolize (“burn”) glucose to produce energy. c. The nitrate ion is not volatile. It is a solute that does not evaporate or decompose with heat. Instead, the water in the nitrate-containing solution will evaporate

5453. Answer: a. The major source of lead in the water was from corrosion of lead-containing pipes. This occurred after the city switched their source of water to the Flint River without effective water treatment that included the addition of anti-corrosion agents. b. Elevated levels of lead in the blood are especially damaging to children and pregnant women and can cause learning disabilities, behavioral problems, and mental retardation. Chronic exposure to high levels of lead can also affect the health of adults, causing abdominal pain, nausea, depression, and short-term memory loss. c. The source of water has been switched to Detroit‘s treated water supply. d. States recently reporting elevated lead in tested water samples include: Pennsylvania, New York, New Jersey, Ohio, Texas, and California. Other cities with high lead levels currently in tap water samples include: Newark, Milwaukee, Chicago, Pittsburgh, Buffalo, Cincinnati, Philadelphia, Boston, and Atlantic CityBaltimore. However, many other cities may also have high levels of Pb due to the pervasive use of lead pipes for drinking water lines across the U.S. and most other countries. 5554. Answer: The two most common desalination techniques are distillation and reverse osmosis. Both of these require energy to remove salts from seawater or brackish water, and thus inherently are expensive. If a less expensive option is available, such as hauling fresh water from a distance, then this option is used. 5655. Answer: a. The Great Lakes–St. Lawrence River Basin Sustainable Water Resources Agreement involved states and provinces bordering the Great Lakes: Minnesota, Wisconsin, Illinois, Indiana, Michigan, Ohio, Pennsylvania, New York, Quebec, and Ontario. The waterway is shared by the United States and Canada. b. The Great Lakes house the largest freshwater system on Earth, about 21% of the world‘s total freshwater supply and about 84% of the fresh water in North America. As fresh water becomes scarce in other regions in North America or the world, some have suggested piping the water from the Great Lakes to the southwestern U.S. (just as oil is transported from one region to another). The agreement was, in part, in response to other areas seeking freshwater sources. 5756. Answer:

Coffee beans that have been soaked in water are placed in a container in which liquid carbon dioxide is injected. The nonpolar solvent, liquid CO2, attracts caffeine based on the generalization “like dissolves like.” This caffeine extract can then be removed from the coffee bean mixture, allowing further processing to the final product. 5857. Answer: Several options exist for purifying water while hiking. A traditional method is to boil it. Boiling kills many (but not all) microorganisms that may make you sick but requires time and will not remove chemical contamination. Boiling also requires fuel and may release soot and CO2 to the environment. Another method of water purification is with iodine. It is easy and effective in twenty minutes, but iodine should not be used long-term. In addition, pregnant women and people with thyroid conditions should avoid purification with iodine. While iodine renders water bacteriologically safe, it doesn't remove chemical contaminants. Many people dislike the taste of iodine-treated water. A third method of water purification is to use a filtering device. Filtration has the advantage that it does not require chemicals and removes many of the microorganisms not killed by boiling or iodine treatment. While filters are the most expensive option, a good filter pumps out good water in a few minutes and is reusable. Municipal water preparation applies a combination of methods, such as charcoal and sand for filtration and chemical treatment with flocculating agents or chlorine to remove sediment or disinfect respectively. 5958. Answer: The bond energy of an O–H bond is 467 kJ/mole, or about 10 times greater than the maximum energy of a hydrogen bond. Actually, the hydrogen bonds between water molecules is 20 kJ/mole, this means that the bond energy of an O–H bond is about 20 times greater than the bond energy of a hydrogen bond in water. 6059. Answer: a. Mining waste, gas and oil operations, cement production. b. Organic mercury is a carbon compound that contains mercury. These compounds tend to be nonpolar, so they accumulate in fatty tissue that also is comprised of nonpolar molecules (like dissolves like). 6160. Answer:

a. Glycine contains several polar bonds and has several polar areas in its molecule (everything but the –CH2 region). Bond Electronegativity Difference O–H 3.5 – 2.1 = 1.4 O–C 3.5 – 2.5 = 1.0 N–H 3.0 – 2.1 = 0.9 N–C 3.0 – 2.5 = 0.5 b. Yes. Hydrogen bonding is possible with O–H and N–H bonds, both of which glycine contains. c. Because glycine has polar bonds located in several areas of the molecule and has a relatively small molar mass, glycine should be soluble in water. 6261. Answer: a. In the local area of this author, the water is considered hard, and must be softened for use in washing machines and dishwashers. Many companies offer water softener units for sale. b. Hard water can be treated by chemical methods. A water softener works on the principle of ion exchange. A special resin captures the hard water ions (Mg2+ and Ca2+) while releasing the softer sodium ions (Na+). 6362. Answer: A complex question! First, you would need to determine the environmental rules and regulations in your region. Most likely, these would apply to releases of chemicals into the soil, air, and water. Then, you would need to monitor what is being released by the industry, in what amounts, and with what occurrence. Compliance with environmental controls, economic factors, and community acceptance of the plant all will affect the success of this plant. 6463. Answer: The properties of fire resistance, chemical stability, and electrical insulation made PCBs highly valued for a variety of applications in plastics, paints, and rubber products. Their chemical structures with C–C, C–H, and C–Cl bonds make PCBs highly nonpolar molecules. Since generally “like dissolves like”, the highly nonpolar PCBs can be retained in the fat tissues of creatures. PCBs have been shown to cause cancer in animals, possibly cancer in humans, and recent evidence suggests that they may belong to a classification of chemicals known as endocrine disruptors. These substances are linked to reproductive and development effects. 6564. Answers:

a. The PUR Purifier of Water is made by Proctor and Gamble and sold as a packet of chemicals that can be added to a sample of nonpotable water. Each packet contains a powdered flocculent, iron (II) sulfate, and a disinfectant, calcium hypochlorite. The contents are added to 10 liters of non-potable water, the water is stirred for 5 minutes and the solids are allowed to settle. The water is then poured into another container by filtering it through a cotton cloth. After 20 minutes, the disinfectant inactivates any microbes present (including viruses) and the water is ready for consumption. b. Here are a few comparisons. Both systems offer comparable water disinfection, with one catch. The personal Lifestraw does not protect against viruses, but the PUR system does. Both have different uses: one is portable (Lifestraw) and can be used immediately. The other processes a larger volume of water and filters water by gravity instead of by mouth suction. Thus, a larger quantity of water can be purified in a shorter time. Finally, the water filtered with a personal Lifestraw lacks the chemical aftertaste that occurs following treatment with the PUR system. 6665. Answer: If a contaminant is tested and found to be above a SMCL standard, it may cause water to look, taste, or smell bad. For example, at certain concentrations manganese discolors water and can stain laundry. Although this water is still safe to drink, many people would not drink what is otherwise potable water. Public water systems can remove contaminants when they become higher than the recommended SMCL value, thus producing palatable drinking water.

6766. Answers: a. As of 2019Currently, 88over 90 substances have health-based standards established under the Safe Drinking Water Act. The EPA uses the Unregulated Contaminant Monitoring Rule program every 5 years to establish a list of no more than 30 unregulated contaminants to be monitored by public water systems.and collect data for those contaminants suspected to be present in drinking water. b. The EPA uses a CCLThe Unregulated Contaminant Monitoring Rule (UCMR) contaminants are largely based on the Contaminant Candidate List (CCL), which lists to determine what unregulated contaminants could be researched and possibly added as substances to be regulated. This follows the precautionary principle that “stresses the wisdom of acting, even in the absence of full scientific data, before the adverse effects to human health or the environment become significant or irrevocable.” c. The EPA lists “pesticides, disinfection byproducts, chemicals used in commerce, waterborne pathogens, pharmaceuticals, and biological toxinscyanotoxins, metals,

pesticides, pesticide manufacturing byproducts, brominated haloacetic acid (HAA) groups, alcohols, and other semivolatile chemicals” in its CCL/UCMR. An example of a specific substance from the UCMRCCL-43 list is Halon 1011 (bromochloromethane), used as a fire-extinguishing fluid and as a solvent to make pesticidesgermanium, which is found in a variety of magmatic and sedimentary ore deposits and coal ash worldwide. A full list of contaminants may be found online at: https://www.epa.gov/dwucmr/fourthunregulated-contaminant-monitoring-rule. 6867. Answer: The 2016 theme was Water and Jobs. A presentation could include highlights from the unwater.org website. 6968. Answer: a. As of Dec. 2019, May 2016, the approximate atmospheric concentration of CO2 was 41204 ppm. b. The concentration of carbon dioxide in the atmosphere is increasing because humans are burning fossil fuels and cutting down forests which absorb CO2. c. Here is the Lewis structure. . d. No, you would not. Carbon dioxide is is a non-polar compound, and sea water is a polar solution of primarily water and Group 1 and 2 sodium chlorides. “Like dissolves like.” Even so, carbon dioxide is slightly soluble in seawater and dissolves to form carbonic acid, H2CO3. 69. Fluorine is not a heavy metal, it is a halogen non-metal halogen.

ANSWERS TO END-OF-CHAPTER QUESTIONS CHAPTER 56: ENERGY FROM COMBUSTION

Emphasizing Essentials 1. Answer:

a. Answers may vary. Possibilities include wood, coal, natural gas, charcoal, gasoline, diesel fuel, jet aviation fuel, petroleum wax, and beeswax. These share properties such as being flammable, releasing carbon dioxide and water when burned, and releasing air pollutants when burned. Another possible fuel is hydrogen, but it produces water on combustion (not carbon dioxide). Biofuels are another possible answer and share characteristics to those above. b. Of the fuels listed, the fossil fuels are coal and natural gas. Gasoline, diesel fuel, jet aviation fuel, and petroleum wax are derived from fossil fuels. c. Wood, charcoal, hydrogen, biofuels, and beeswax are renewable.

2. Answer: a. CO2, carbon dioxide. b. SO2 is an air pollutant. Although sulfur is present in low concentration in coal, large amounts of coal are burned and collectively large amounts of SO2 are released. c. Nitrogen is present in the air (~80% of atmospheric gases). The nitrogen present in air reacts with O2 (also present in air) at high temperatures to form NO:

d. Revisit Chapter 2 for the details. From the EPA website: “Particle exposure [of any size] can lead to a variety of health effects. For example, numerous studies link particle levels to increased hospital admissions and emergency room visits and even to death from heart or lung diseases. Both longand short-term particle exposures have been linked to health problems. Long-term exposures, such as those experienced by people living for many years in areas with high particle levels, have been associated with problems such as reduced lung function and the development of chronic bronchitis and even premature deaths.”

3. Answer: a. The coal is in the burner, producing the heat. b. The higher pressure serves two purposes. First, it raises the boiling point of the water, as in a pressure cooker, where high pressure forces higher temperatures for creating steams, this creates higher cooking temperatures. Secondly, it compresses the resulting water vapor. c. The body of water absorbs heat from the steam (a gas) and cools it into water (a liquid) in the condenser. A large body of water will have a lower temperature increase than a smaller body of water.

4. Answer: a. The fuel in the burner is a source of potential energy. When burned, some of its potential energy is converted to heat through combustion. The heat is converted into kinetic energy of the vaporized water molecules (steam). b. The kinetic energy of the steam is converted to mechanical energy by spinning a turbine. c. The mechanical energy generated from the spinning turbine is converted to electrical energy by rotating a wire in a magnetic field. d. The electrical energy, carried to the city by the power lines, lights bulbs and heats homes.

5. Answer: a. Given: 5.00x108 J/s and 1 year. b. Find: Total electrical energy in 1 year. c. Plan: If 5.00x108 J/s convert time to years using conversions in order to determine total joules. Then factor the percent efficiency with that total amount of joules. d.

5.00 x 108 J 3600s 24 h 365days    s h day year e. Execute: = 1.58  1016 J of electricity generated per year 1.58 ×1016 J = 4.2  1016 J of heat for electricity generated per year 0.375

f. Given: 30 kJ/g coal. g. Find: Total mass of coal burned in 1 year. h. Plan: Using the calculation above that 1.58x1016 J of heat is produced (though not all is converted to electricity due to decreased efficiency of energy conversions, 37.5%), convert from total energy to metric tons. Execute:

1g 11  j. 1.58x10 J produced × = 5.3  10 g per year 1000 J 30 kJ i.

5.3 × 1011 g ×

1 kJ

1 metric ton 106 g

= 5.3  105 metric tons

6. Answer: a. Photosynthesis. b. Any fossil fuel (or one derived from fossil fuels) will do: coal, natural gas, petroleum, diesel fuel, and gasoline. Wood, ethanol, or some forms of biodiesel would also be valid answers.

7. Answer: The grades of coal differ in the percent carbon that they contain as well as the percent impurities (such as sulfur). The significance is two-fold. First, lower grades of coal with less carbon produce less energy when burned. Second, coals with higher amounts of impurities such as sulfur emit more pollutants when burned.

8. Answer: Drawbacks to coal include (1) the health issues and dangers to mine workers who mine it, (2) the environmental harm caused by coal mining, especially to waterways and habitats for a variety of species (including human beings), (3) the pollutants it releases when burned, including mercury and sulfur dioxide, and (4) the carbon dioxide it releases when burned, a greenhouse gas.

9. Answer: A typical power plant burns 1.5 million tons of coal each year. The first calculation is for coal with 50 ppb mercury; the second is for 200 ppb.

x ton Hg 1.5  106 ton coal



50 ton Hg 1  109 ton coal

x ton Hg 200 ton Hg  6 1 109 ton coal 1.5 10 ton coal

x = 0.075 ton Hg

x = 0.30 ton Hg

Assuming mercury concentrations in the range of 50-200 ppb, the plant releases between 0.075 and 0.30 ton of Hg per year.

10. Answer: Hydrocarbons are alike in many ways. These include that they all consist only of the elements carbon and hydrogen. Furthermore, they are alike in that they are flammable and can produce carbon dioxide, carbon monoxide and soot when burned in addition to water vapor. They all are insoluble in water. Hydrocarbons differ in many ways, including in the number of C and H atoms they contain. They also differ in their boiling or melting points. Some hydrocarbons contain double or triple bonds while others only contain single bonds.

11. Answer: a. ethane and butane b. C2H6 and C4H10

and c. Chemical formulas such as C4H10 are compact and easy to write. The same is true for condensed structural formulas, at least in this particular case. Although structural formulas take longer to draw and take up more space, they clearly reveal the arrangement of all the bonds and atoms.

12. Answer:

n-nonane is C9H20 and n-dodecane is C12H26.

13. Answer:

b. There only one other true isomer:

14. Answer: Pentane should be a liquid because room temperature (20 °C) is below its boiling point (36 °C) but above its melting point (–130 °C). Triacontane should be solid at room temperature because room temperature is below its melting point (66 °C). Propane should be a gas because room temperature is above its boiling point (–42 °C).

15. Answer: a. Hydrocarbons separate due to differences in their boiling points. b. Hydrocarbons separated at positions A and B have lower boiling points and are more volatile than the hydrocarbons separated at position C. The hydrocarbons separated at positions A and B have fewer carbons in their structures than those separated at position C. The hydrocarbons at position D will be less volatile or not volatile at all, compared to those at position C. The hydrocarbons separated at position D have more carbon atoms than the hydrocarbons separated at C. c. The hydrocarbons separated at A will be gases at room temperature and can be used as fuels and starting materials for manufacturing. Those separated at B will be liquids, and can be used as motor fuels and as industrial solvents. Position D contains solid residue material that is rich in many complex compounds as well as many hydrocarbons. In addition to waxes and asphalt, these tars can be further separated into other useful compounds. The hydrocarbons separated at C are used as kerosene or diesel fuel or may be cracked.

16. Answer: a. b.

30 g C 2 H 6 c. 1.0 mol C2H6 



1 mol C 2 H 6

52 kJ g C 2H 6 = 1600 kJ/mol C2H6 (to 2 significant figures)

17. Answer: a. C7H16 + 11 O2 → 7 CO2 + 8 H2O 2

1 3 g0C H 1 m k5 C g 7 1 70H 1  6  6 10C 0 .2 k 7gH1 6

H o 7

l4 8k C1J 7  1.2  1 6 H 1 16 m C 7 H1 o 7g 6l 1

18. Answer:

70 Cal 

19. Answer:

4.184 kJ 1000 J 1 beat   1 Cal 1 kJ 1J



1 min = 3700 min 80 beats



92 kcal 

4 .18 4kJ = 380 kJ 1 kcal

20. Answer: a. exothermic b. endothermic c. endothermic

21. Answer: a. Bonds broken in the reactants 1 mol N≡N triple bonds

= 1(946 kJ)

= 946 kJ

3 mol H–H single bonds

= 3(436 kJ)

= 1308 kJ

Total energy absorbed in breaking bonds

= 2254 kJ

Bonds formed in the products 6 mol N–H single bonds

= 6(391 kJ)

= 2346 kJ

Total energy released in forming bonds = 2346 kJ

= 92 kJ

Net energy change is (+2254 kJ) + (2346 kJ)

The overall energy change is negative, characteristic of an exothermic reaction.

b. Bonds broken in the reactants 1 mol H–H single bonds

= 1(436 kJ)

= 436 kJ

1 mol Cl–Cl single bonds

= 1(242 kJ)

= 242 kJ

Total energy absorbed in breaking bonds

= 678 kJ

Bonds formed in the products 2 mol H–Cl single bonds

= 2(431 kJ)

= 862 kJ

Total energy released in forming bonds = 862 kJ

= 184 kJ

Net energy change is (+678 kJ) + (862 kJ)

The overall energy change is negative, characteristic of an exothermic reaction.

22. Answer: a. Bonds broken in the reactants 2 mol H–H single bonds

= 2(436 kJ)

= 872 kJ

1 mol C≡O triple bonds

=1(1073 kJ)

=1073 kJ

Total energy absorbed in breaking bonds

Bonds formed in the products

=1945 kJ

1 mol C–O single bonds

=1(336 kJ)

= 336 kJ

1 mol O–H single bonds

=1(467 kJ)

= 467 kJ

3 mol C–H single bonds

=3(416 kJ)

=1248 kJ

Total energy released in making bonds

=2051 kJ

Net energy change is (+1945 kJ) + (2051 kJ)

= 106 kJ

The overall energy change is negative, characteristic of an exothermic reaction.

b. Bonds broken in the reactants 1 mol H–H single bonds

= 1(436 kJ)

1 mol O=O double bonds

= 1(498 kJ) = 498 kJ

Total energy absorbed in breaking bonds

= 436 kJ

= 934 kJ

Bonds formed in the products 2 mol O–H single bonds

= 2(467 kJ)

= 934 kJ

1 mol O–O single bonds

1(146 kJ)

= 146 kJ

Total energy released in making bonds

= 1080 kJ

Net energy change is (+934 kJ) + (1080 kJ)

= 146 kJ

The overall energy change is negative, characteristic of an exothermic reaction.

c. Bonds broken in the reactants 2 mol Br–Cl single bonds

= 2(217 kJ) = 434 kJ

Total energy absorbed in breaking bonds

= 434 kJ

Bonds formed in the products 1 mol Br–Br single bonds 1 mol Cl–Cl single bonds

= 1(193 kJ)

= 193 kJ

= 1(242 kJ)

= 242 kJ

Total energy released in making bonds

= 435 kJ

Net energy change is (+434 kJ) + (435 kJ) = 1 kJ The overall energy change is negative, characteristic of an exothermic reaction. The reaction is very weakly exothermic.

23. Answer:

a. b. Bonds broken in the reactants: 1 mol C=C double bonds = 1(598 kJ)

= 598 kJ

2 mol O–H single bonds = 2(467 kJ)= 934 kJ 4 mol C–H single bonds = 4(416 kJ) = 1664 kJ Total energy absorbed in breaking bonds = 3196 kJ

Bonds formed in the products: 1 mol C–C single bonds = 1(356 kJ) = 356 kJ 5 mol C–H single bonds = 5(416 kJ) = 2080 kJ 1 mol C–O single bonds = 1(336 kJ) = 336 kJ 1 mol O–H single bonds = 1(467 kJ)= 467 kJ Total energy released in forming bonds = 3239 kJ

Net energy change: (3196 kJ) + (3239 kJ) = 43 kJ Because the energy released in forming bonds is greater than the energy absorbed in breaking bonds, the net energy change is negative and the overall reaction is exothermic.

24. Answer: a. None of these are isomers. All have different chemical formulas. b. No, no other isomers are possible for ethene.

c. One other isomer is possible, although it contains a very distinct functional group, called an ether. Here is its condensed structural formula: CH3–O–CH3.

25. Answer: a.

CH3

CH3 – C – CH3

CH – CH3

CH2

CH–CH3

CH3 – C – CH3

CH3

b. The second and third are identical. c. Several other isomers are possible. Here are two.

CH3 H

26. Answer: Section 2.13 described the catalytic converters in automobiles. Section 3.109 described the catalytic destruction of ozone by chlorine free radicals.

27. Answer: Cracking is necessary because the demand for the mid-range hydrocarbons (C7-C12) found in gasoline exceeds the amount produced by the distillation of crude oil.

28. Answer: a.

The C-C single bond in the center of the molecule and one of the C-H single bonds must be broken. A second C-C single bond must be broken so that a C=C double bond can be formed in its place. A new C-H single bond must form on the shorter product.

b. Bonds broken in the reactants 2 mol C–C single bonds

= 2(356 kJ)

= 712 kJ

1 mol C–H single bonds

= 1(416 kJ)

= 416 kJ

Total energy absorbed in breaking bonds

Bonds formed in the products

= 1128 kJ

1 mol C–H single bonds

= 1(416 kJ)

= 416 kJ

1 mol C=C double bonds

= 1(598 kJ)

= 598 kJ

Total energy released in forming bonds

=1014 kJ

Net energy change is (+1128 kJ) + (–1014kJ) = 114 kJ The overall energy change has a positive sign, characteristic of an endothermic reaction.

29. Answer: A biofuel is a renewable fuel derived from a biological source, such as trees, grasses, animal waste, or agricultural crops. Examples include wood, charcoal, ethanol, and biodiesel.

30. Answer: a. The hydroxyl functional group, –OH. All of the compounds are alcohols. b. Ccarbon dioxide, CO2, and water, H2O. c. These three compounds are similar in chemical composition and differ only in number of CH 2 groups. Each have hydrogen bonding as their predominant intermolecular force, but methanol would have the lowest boiling point because it has the lowest molecular mass of the group. d. n-propanol, an alcohol with three carbon atoms, is the most similar to glycerol (which also is an alcohol and has three carbon atoms). However, glycerol contains three –OH groups (one on each carbon) in comparison to the one in n-propanol.

31. Answer: a. Starch and cellulose are both large molecules built by linking together repeating units of a small molecule, glucose. More technically, starch and cellulose are polymers of glucose (see Chapter 11). b. Starch is digestible by humans; in contrast, cellulose is not. This has to do with the different ways carbon atoms link together the glucose units between the two polymers.

32. Answer: a.

b. Cellulose is one of the primary components of wood. Cellulose is a polymer made up of glucose building blocks. As a result, burning cellulose gives products comparable to burning glucose.

33. Answer: a. The source of biodiesel is a triglyceride (a fat or an oil). In contrast, the source of ethanol can be cellulose, a starch, or a sugar. b. Biodiesel is produced by a one-step reaction (transesterification). In contrast, ethanol is produced by fermentation which requires several steps followed by distillation to separate the ethanol. c. On complete combustion, both produce CO2 and H2O.

d. Ethanol is miscible with water in any proportion (as any bartender knows). In contrast, biodiesel is insoluble in water. This difference is important because ethanol has to be blended with gasoline with care, so as not to introduce any water into the fuel mixture.

34. Answer: a. Both biodiesel and ethanol contain C, H, and O. Additionally, ethanol refers to a very specific chemical, CH3CH2OH, whereas biodiesel really is a class of molecules that can have varying proportions of C, H, and O within the group. The proportions, however, are different, with biodiesel containing a lower % oxygen (and higher % of carbon and hydrogen). Note that for biodiesel, the proportions vary slightly, depending on which biodiesel molecule is selected. b. Biodiesel is a much larger molecule, containing upwards of 50 –CH2– groups along with at least two oxygen atoms. In contrast, ethanol is simply CH3CH2OH. O || c. Biodiesel contains a functional group, with two oxygen atoms: –C–O–C–. As you will see in Chapter 11, this is the ester functional group. Ethanol contains the hydroxyl group, –OH.

35. Answer: Figure 6.55.6 gives the energy released per gram for the combustion of several fuels. Assuming the densities of octane and ethanol are similar (a good assumption) one gallon of gasoline releases more energy than one gallon of ethanol. (44.4 kJ/g of gasoline vs. 26.8 kJ/g of ethanol) This makes sense, because ethanol is an oxygenated fuel; it contains oxygen and thus is already “partially burned.”

36. Answer:

Crude oil is a conventional energy source when it is easy to access, such as from existing surface oil wells. In contrast, crude oil is unconventional when located under many feet of seawater or in oil shales. This oil is more difficult (and expensive) to extract.

Concentrating on Concepts

37. Answer: Although the availability of a fuel is important to evaluating its sustainability, other considerations apply as well. To be sustainable, the use of the fuel to produce energy needs to promote healthy economies, healthy ecosystems, and healthy communities (the Triple Bottom Line). Some of the current and past practices for burning coal are not sustainable in terms of the air pollutants emitted when burned (NOx, SO2, mercury, particulate matter) and the damage done to land and water when the coal is extracted from the earth. Burning coal is

not carbon neutral, as currently practiced, because of the emission of CO2. Burning coal also releases mercury into the environment. Finally, coal mining continues to be a risky operation both for miners and their local communities.

38. Answer: A primary component of wood is cellulose, with a chemical formula that can be approximated with that of glucose, C6H12O6. Given that the ratio of carbon-to-oxygen in glucose is 1:1, the chemical formula for this soft coal most likely would contain much more oxygen than common types of coal. The same is true for hydrogen, because the ratio of carbon-to-hydrogen in glucose is 1:2.

39. Answer: Petroleum > Natural Gas ~ Coal > Nuclear > Hydroelectric ~ Wood. The three largest energy sources are non-renewable fossil fuels. The renewable sources, hydroelectric and wood, are the smallest contributors. Solar and wind power are not yet visible on the graph as separate items, though the combined category of other renewable energy has risen above wood and hydroelectric.

40. Answer: The processes of combustion (for carbon-based fuels) and photosynthesis (for green plants) both involve CO2 and H2O, but as the reactants for photosynthesis and the products of combustion. Combustion takes fuels with high potential energy and converts them to products with low potential energy (CO2 and H2O). In contrast, starting with CO2 and H2O, photosynthesis involves a series of chemical reactions to produce O2 and glucose, substances of high potential energy. The processes also

differ in that photosynthesis requires the input of energy (in the form of sunlight) and combustion releases energy (in several forms, including heat and light).

41. Answer: Answers may vary. Here is one example: Wouldn’t you rather spill a drop of hot coffee on you than the whole cupful at the same temperature? Although the drop and the cup full of coffee may initially have the same temperature, you will receive a bigger burn from the bigger volume of coffee because it has the higher heat content. Heat is a form of energy. In contrast, temperature is a measurement that indicates the direction heat will flow. Heat always flows from an object at high temperature to an object at lower temperature. This means that if hot coffee is added to cold coffee, heat will flow from the hot liquid to the cold liquid, and the final temperature of the mixture will be between the original temperatures of

the two individual solutions. Heat depends on the temperature and on how much material is present.

42. Answer:

The first law of thermodynamics states that energy is neither created nor destroyed; it only changes form. However, this statement does not take into effect our limited ability to capture and use energy in all of its forms. We also cannot look at the first law of thermodynamics in a way isolated from the second law, which dictates that in energy transformations heat is usually produced. Heat is not always a useful form of energy for our needs and dissipates unharnessed. The energy of fossil fuels is stored in the form of chemical bonds. An energy crisis arises when demand exceeds supply. Unless we are better able to capture energy in usable forms, we will indeed have an energy crisis – not due to a shortage of absolute energy but a shortage in our ability to use the energy available. This is especially apparent in the case of solar energy.

43. Answer: If the enthalpy is exothermic and the randomness is increased, the reaction will be spontaneous. If the enthalpy is exothermic and the randomness is decreased, the reaction is spontaneous at low temperatures only. If the enthalpy is endothermic and the randomness is increased, the reaction is spontaneous at high temperatures only. If the enthalpy is endothermic and the randomness is decreased, the reaction is never spontaneous.A royal flush is an ace, king, queen, jack, and ten of the same suit. It is a highly improbable hand in poker (1 in about 650,000 five-card hands). It exhibits a higher degree of order (low entropy) and is more highly valued than a simple high card hand (a higher degree of entropy with a lower degree of order). The hand with the least entropy wins!

44. Answer:

Let x represent the C=O bond energy in H2CO.

Bonds broken in the reactants: 2 mol C–H single bonds

= 2(416 kJ)

832 kJ

1 mol C=O double bonds

= 1(x kJ)

x kJ

1 mol O=O double bonds = 1(498 kJ)

498 kJ

Total energy absorbed by breaking bonds

= (832 + x) kJ

Bonds formed in the products 2 mol O–H single bonds

= 2(467 kJ)

934 kJ

2 mol C=O double bonds

= 2(803 kJ)

1606 kJ

Total energy released in forming bonds

= 2540 kJ

Net energy change: (+832 + x kJ + 498) – (2540 kJ) = 465 kJ Rearranging the equation:

x kJ = 465 + 2540 – 1330 kJ x = 745 kJ

This value is less than the bond energy for C=O double bonds in carbon dioxide reported in Table 5.1. The C=O double bonds in carbon dioxide are stronger than the C=O double bond in formaldehyde.

45. Answer: CFCs are stable because the bond energies for C–Cl and C–F are large compared to other bond energies. It takes less energy to release Cl atoms from CFCs because the C–Cl bond energy (327 kJ/mol) is lower than the C–F bond energy (485 kJ/mol). HFCs, with their C–F bonds and (no C–Cl bonds) release no Cl atoms.

46. Answer: a. The C–F single bond requires 485 kJ/mol, the C–Cl single bond requires 327 kJ/mol, and the C– Br single bond requires 285 kJ/mol to break the bond. The C–Br bond is the weakest. Thus, when halon-1211 absorbs UV radiation, bromine atoms are likely to form and react with ozone. b.

In this molecule, the C–Cl bond has the lowest bond energy and thus is broken most easily.

47. Answer: From Figure 6.55.6, fuels containing oxygen have lower energy content per gram than those without oxygen. For example, ethanol and glucose have proportionately more oxygen than the other fuels listed. In essence, they are already “partially burned (oxidized) and thus their energy content is lower when you look at the values per gram of fuel.

Here are the values in kilojoules per mole:.

methane (CH ): 50.1 kJ  16.05g = 802 kJ/mol 4

1mol

octane (C H ): 44.4 kJ  114 g = 5.06  103 kJ/mol 8

1mol

coal (C H O NS): 32.8 kJ  1908g = 6.26  104 kJ/mol 135 96 9 1 mol 1g

ethanol (C2H6O): 26.8 kJ  46 g = 1.23  103 kJ/mol

1 mol

glucose: (C H O ): 14.1 kJ  180 g = 2.54  103 kJ/mol 6

1mol

With kilojoules per mole, though, the trend observed is different. Here, the fuels with higher numbers of carbon atoms in their chemical formulas (and hence higher molar masses) release more energy when burned. Compare methane and n-octane to see the contrast clearly.

48. Answer: a. Considering only the molar heats of combustion, octane, with more atoms and more chemical bonds, has a greater heat of combustion than butane. However, comparisons should be based on the same amount of each substance, such as the heat released per gram of each fuel.

H1 l 8 4 C 7 k. 54 5k 0J 1m 8o , the heat released per gram octane burned.   1m 8o H1 l 811 C 4 . g8H 21 8C g 8H C1 H1 l 04 .C 2 9k 4o 2 8 k5 J9 1m , the heat released per gram butane burned.   1m 4o H1 l 058 C . 14H1 0gg4H1

Here the values are much closer. It is not possible to establish a trend with just two data points. Even so, notice that the smaller hydrocarbon releases slightly more heat per gram than the larger one. Because heat comparisons should be made based on the same mass of fuel, you will have to educate your friend on this point. b. Candle wax is composed of high molar mass hydrocarbons. Looking at the values from part a, the heat of combustion per gram is expected to be slightly smaller and the heat of combustion per mole is expected to be larger than octane.

49. Answer: a. When n = 1, the balanced equation is

To calculate the heat evolved we use the same method as in Problem 5.16.

Bonds broken in the reactants 1 mol C≡O triple bonds

= 1(1073 kJ)

= 1073 kJ

3 mol H–H single bonds

= 3(436 kJ)

= 1308 kJ

Total energy absorbed in breaking bonds

= 2381 kJ

Bonds formed in the products 4 mol C–H single bonds

= 4(416 kJ)

= 1664 kJ

2 mol O–H single bonds

= 2(467 kJ)

= 934 kJ

Total energy released in forming bonds

= 2598 kJ

Net energy change is (+2381 kJ) + (2598 kJ) = 217 kJ b. Reactions with n greater than 1 will release more energy as n becomes larger, assuming that we are viewing the energy per mole of the hydrocarbon formed (not per gram). There will always be n C≡O triple bonds to break and (2n + 1) H–H single bonds to break. The number of C–H bonds forming will be (2n + 2), the number of O–H bonds forming will be 2n, and the number of C–C single bonds forming will be n – 1. Combining these terms shows that as n becomes larger, more and more energy will be released.

50. Answer:

a. The Lewis structure for dimethyl ether is: b. The structural formula for diethyl ether is:

c. The common structural feature is an oxygen atom between two carbon atoms.

51. Answer:

a. The compounds n-octane and iso-octane have nearly identical heats of combustion. This makes sense because they have the same number and types of bonds. However, they have very different octane ratings. Therefore, the octane rating is not a measure of the energy content of a substance. b. Knocking produces an objectionable pinging sound, reduced engine power, overheating, and possible engine damage. c. The higher- octane blends are more expensive to produce because they require more “processing,” including energy-intensive cracking reactions that convert lower octane fuels into higher octane ones. d. The octane ratings tell you nothing about whether or not oxygenates are present. Although oxygenates are one way to improve the octane rating, they are not the only way.

52. Answer: Although n-octane and iso-octane have different chemical structures, they have the same number and types of bonds that are broken upon combustion. The same products (CO2 and H2O) are formed. Therefore, one would expect the heats of combustion to be quite similar.

53. Answer:

fuels | |

nonrenewable

renewable biodiesel

ethanol

coal

natural gas

petroleum

One way to indicate the terms fossil fuels (orange) and biofuels (green) is by color.

All can be used as a starting material for biodiesel

54. Answer:

triglycerides | |

fats

oils

butter

lard

olive oil

soybean oil

55. Answer:

The ethanol is produced by the fermentation of starch or grains (renewable fuels); the green plants that produced the starch or grains removed CO2 from the atmosphere when growing. Burning the ethanol merely returned this CO2 to the atmosphere. Nobody argues about this. However, they do argue about the energy costs in planting, fertilizing, and watering the

crops. They also argue that the ecosystems in place before the land was converted to agriculture were more effective in removing CO2 from the atmosphere.

56. Answer: a. Petroleum diesel contains small amounts of sulfur. In contrast, triglycerides (the starting material for biodiesel) do not. b. Petroleum diesel is a hydrocarbon, that is, it contains only carbon and hydrogen (no oxygen). In contrast, biodiesel contains oxygen and therefore burns more cleanly.

Exploring Extensions

57. Answer: Two pieces of evidence are needed to defend this statement: (1) the amount of mercury released by burning coal, and (2) the public health hazards of mercury as related to this amount. This evidence is readily available; for example, many government documents cite the evidence. In regards toRegarding the former, here is a quote from a USGS (United States Geological Survey, http://pubs.usgs.gov/fs/fs095-01/) document (found online at http://pubs.usgs.gov/fs/fs095-01/):: “In February 1998, the U.S. Environmental Protection Agency (EPA) issued a report citing mercury emissions from electric utilities as the largest remaining anthropogenic source of mercury released to the air. EPA officials estimated that about 50 tons of elemental mercury are emitted each year from U.S. coal-burning power plants, with lesser amounts coming from oil- and gas-burning units. According to EPA estimates, emissions from coal-fired utilities account for 13 to 26 percent of the total (natural plus anthropogenic) airborne emissions of mercury in the United States.” In regardsRegarding to the latter, mercury in the form of methylmercury is a potent neurotoxin. From the same source: “The mercury (Hg) directly emitted from power plants generally is not considered harmful; however, in the natural environment, mercury can go through a series of chemical transformations that convert elemental mercury to a highly toxic form that is concentrated in fish and birds (fig. 1). The most toxic form of mercury is methylmercury, an organic form created by a complex bacterial conversion of inorganic mercury…Cases of mercury poisoning have been documented in people who eat contaminated fish for prolonged periods, both in the United States and abroad. Pregnant women and subsistence fishermen are particularly vulnerable.”

58. Answer: a. Via their exhaust pipes, cars emit three criteria pollutants: CO, particulate matter, and NO. They

also emit CO2, a greenhouse gas. b. The truth of this statement depends on the assumption that the citizen drives a car, which may not be the case. Furthermore, it depends on how much the citizen drives as well as the fuel efficiency of vehicle driven. Finally, it also depends on the power source of the vehicle, an internal combustion engine or otherwise. For example, look for more about electric vehicles in Chapter 87.

59. Answer: The price of electricity varies by locality, but according to www.electricchoice.com, the average cost of electricity in the U.S. in 2015 was 12.5 cents per kW-h.

Using a 75 watt incandescent bulb for 10,000 hours would consume 75000 W-h of electricity. Using an 18 watt compact fluorescent bulb for 10,000 hours would consume 18000 W-h of electricity.

75 watt incandescent bulb:

75000 W − h x

18 watt compact fluorescent bulb:

18000 W − h x

1 kW−h x $0.125 = $9.37 1000 W−h kW−h

1 kW−h 1000 W−h

$0.125 kW−h

= $2.25

These calculations indicate an electricity savings of $9.37 – $2.25 = $7.12 over the life of a compact fluorescent bulb.

To be most accurate, the lifetime of incandescent bulbs should also be taken into account. Incandescent bulbs burn out after ~750 hours, so 10,000 hours of use would require the use of 10,000/750 = 13.33 incandescent bulbs.

At a popular online retailer, a six-pack of 75 W incandescent bulbs costs $7.97 (or $1.33 each) and a fourpack of 18 W compact fluorescent bulbs costs $5.97 (or $1.49 each). Therefore, the cost of 13.33 incandescent bulbs would be $17.71. When compared to the cost of one compact fluorescent bulb ($1.49), it can be seen that an additional savings of $16.22 can be realized by using the longer lasting compact fluorescent bulbs. Note: The price of compact fluorescents has been dropping, so it might make sense to recheck the prices.

60. Answer: Opinions may vary. At least one of the authors of this text does not like this comparison. She feels that neither of these questions necessarily means anything in and of itself. A person might be able to recite the second law of thermodynamics, and yet not understand its universal significance. Similarly, a person might have read a play by William Shakespeare and yet not be able to gain any perspective on human relations. A more meaningful comparison across the “Two Cultures” could require a higher level of engagement. For example, consider wanting to communicate something about an important societal topic – say global climate change in some part of the planet. One way to do this might be to draft an environmental statement. Another could be to create some form of art to convey the complexities of the climate.

61. Answer: The details will depend on the year in which the research is done. Consult Chemical & Engineering News for some excellent articles. To evaluate economic health, environmental health, and societal health, see “Viewing America‘s Energy Future in Three Dimensions.” (http://www.rti.org/sites/default/files/resources/bk-0006-1106-temple.pdf). Accessed July 2016.

62. Answer: Consider a natural gas (methane) explosion that releases energy: CH4 + 2 O2  CO2 + 2 H2O

The bond energies involved are: C–H single bonds, 416 kJ/mole; O=O double bonds, 498 kJ/mole; H–O single bonds, 467 kJ/mole; C=O double bonds, 803 kJ/mole. The bond energies of the products are larger than those of the reactants, and thus the release more energy when forming than was necessary to break the bonds of the reactants. This will lead to a large negative net energy change indicating an exothermic reaction.

63. Answer: From the propylene glycol industry, read: https://www.repsol.com/en/products-andservices/chemicals/product-range/propylene-glycol-pharmaceuticalgrade/index.cshtmlhttp://www.propylene-glycol.com/food.html “Propylene glycol USP/EP (pharmaceutical grade) has been approved for use as a food additive under the E-number E 1520. In direct food contact it is mainly used as  

solvent and carrier of flavor or color in the food and beverage manufacturing processes, to make drinks, biscuits, cakes, sweets thickener, clarifier and stabilizer in food and beverage such as beer, salad dressings or baking mixtures.”

 

64. Answer: Here are some events to put on a timeline:. 1854 – TEL first synthesized in Germany 1921 – TEL‘s use as a gasoline additive discovered at General Motors 1923 – Leaded gasoline was introduced to the market 1923-25 – Eleven plant workers die from TEL poisoning 1930-1960s – numerous studies of lead‘s toxicity 1976 – EPA begins phase-out of leaded gasoline 1986 – Phase-out of lead complete in the U.S. 2000s – Phase-out in most other countries complete

65. Answer: As gasoline additives go, this one ranks high. It is more than double the value of any listed in Table 65.4. The structural formula of TEL shows four ethyl groups (– C2H5) around a central lead atom. It is highly branched!; j Just as iso-octane has a high octane rating because of all of its “branches,” so does TEL.

66. Answer: a. Thise sketch shows that the catalyzed pathway requires less activation energy than the uncatalyzed pathway:.

b. In Chapter 2, catalysts were discussed in connection with removing NO from automobile exhaust. Nitrogen oxide can react with oxygen to form NO2, a criteria pollutant. NO is also involved in forming ozone in the troposphere and contributes to acid rain. To reduce pollution, it is important to reduce NO emissions.

67. Answer: Recall that in an endothermic reaction, the potential energy of the products is greater than the potential energy of the reactants. The opposite is true for an exothermic reaction.

Breaking 1 mole O=O double bonds

Forming 2 moles N=O double bonds = 2 x (–630 kJ)

Breaking 1 mole NN triple bonds 2NO (products) Net energy change N2 + O2

68. Answer: The advantages of using natural gas to fuel vehicles include: (1) the lower amounts of pollutants released into the atmosphere such as VOCs, CO, NOx, and SOx, (2) natural gas burns more cleanly and completely than gasoline, and (3) natural gas releases more energy per gram than gasoline. Disadvantages include: (1) the difficulty in transporting and dispensing a gas (compared to a liquid) as well as the lack of “natural gas stations,” (2) like petroleum, natural gas is a non-renewable fossil fuel, and (3) the combustion of natural gas produces carbon dioxide, a greenhouse gas.

ANSWERS TO END-OF-CHAPTER QUESTIONS

CHAPTER 76: Energy from Alternative Sources

Emphasizing Essentials

1. Answer: One carbon atom can differ from another in the number of neutrons (such as C-12 and C-13) and in the number of electrons (carbon ions do exist, but we do not discuss them in this text). All carbon atoms differ from all uranium atoms in the number of protons, neutrons, and electrons. Carbon atoms also differ from uranium atoms in their chemical properties.

2. Answer:

The symbol N represents the element nitrogen and stands for the naturally occurring mixture of all isotopes. The symbols 14N and 15N represent very specific isotopes with mass numbers of 14 and of 15, respectively.

3. Answer: a. 94 protons b. Np (neptunium), Pu (plutonium) c. 86 protons

4. Answer: a. C-14 has 6 protons and 8 neutrons b. C-12 has 6 protons and 6 neutrons c. H-3 has 1 proton and 2 neutrons d. Tc-99 has 43 protons and 56 neutrons

5. Answer: E represents energy, m represents mass lost in a nuclear transformation, and c represents the speed of light.

6. Answer: Nuclear equation: Chemical equation:

S(g) + O2(g)  SO2(g)



In both equations, the reactants are on one side with the products on the other. Also in both, the mass of products equals the mass of reacts.



In a chemical equation, the elements do not change their identities in the process of being converted from reactants to products and the same number of atoms of each kind must appear on both sides of the equation. Because the information is not relevant, the atomic or mass numbers are not listed.



In a nuclear equation, the identity of the elements may change, or at least the mass number may change. The values for both the atomic and mass numbers are often included. Finally, symbols for nuclear radiation are included (as is the case for a neutron shown in the equation above).

7. Answer:

  

An alpha particle is a helium nucleus consisting of 2 protons and 2 neutrons. It carries a +2 charge and is represented by α or 42He . A beta particle is an electron emitted from the nucleus of an atom. It carries a negative one charge and is represented by the symbol β or 10 e . A gamma ray is a high energy photon emitted from the nucleus of an atom. It is represented by the symbol γ or 00𝗒00γ.

8. Answer: Subscripts: 94 + 2 = 96 on the left, 96 + 0 = 96 on the right Superscripts: 239 + 4 = 243 on the left; 242 + 1 = 243 on the right

9. Answer: a. The alpha particle may have come from the radioactive decay of another radioisotope. b. 01 n 10n represents a neutron. c. Curium-243 represents an unstable intermediate in the nuclear reaction. This isotope has an extremely short lifetime, decomposing immediately upon formation into Cm-242 with an accompanying neutron.

10. Answer: The target isotope must have been Cm-242. Here is the nuclear equation:.

11. Answer: Neutrons are needed to initiate the process of nuclear fission of U-235:.

The fission products include two2 or three3 neutrons that can initiate more fission reactions. In this manner, a self-sustaining chain reaction can be established in which the products of one reaction initiate another.

12. Answer: a.

13. Answer: A represents the control rod assembly, B represents the cooling water out of the core, C represents the control rods, D represents the cooling water into the core, and E represents the fuel rods.

14. Answer:

The nuclear segment shown on the left in Figure 7.57 contains the reactor core, the heart of the reactor where energy is produced. The non-nuclear portion is everything in the center and right of the diagram, and includes the turbine and electrical generators. The non-nuclear portion also contains the secondary and tertiary water systems, neither of which comes into direct contact with the reactor core. Although not labeled in Figure 7.57, the tertiary cooling system represents the system involving the cooling tower and water pumped directly from asome body of water.

15. Answer: The primary coolant is the liquid surrounding the fuel bundles and control rods, a liquid that comes in direct contact with the nuclear reactor to carry away heat. The heat from the primary coolant is transferred to the secondary coolant, water in the steam generators that does not come in contact with the reactor. The steam generators are separated from the nuclear reactor, so the secondary coolant is not housed in the containment dome.

16. Answer: a. b. Boron can be used in control rods because it is a good neutron absorber.

17. Answer:

b. In a particulate form such as a powder or a dust, plutonium can be inhaled. If the plutonium particles become lodged in the lungs, the ionizing radiation they emit (alpha particles) can damage lung cells. The decay products from U-235 also are radioactive and can damage tissue. c. Iodine accumulates in the thyroid gland. d. After about 10 half-lives, samples have decayed to very low levels. The half-life of Pu-239 is about 24,000 years, so the timescale for a decrease to background level is on the order of hundreds of thousands

of years. The half-life of I-131 is 8.5 days, so 10 half-lives is 85 days or about 3 months. A sample of I131 will decay to low levels on a timescale of months.

18. Answer: a. A change in both the mass number and atomic number occur with alpha emission. b. A change in the atomic number occurs with beta emission. c. No change in either atomic number or mass number occurs with gamma emission.

19. Answer: 235 92 231

U 23190Th + 42He

Th 231Pa + 0e

-1

227 Pa 89 Ac+ 42He

231

227 89

0 Ac 227 90Th + 1e

4 Th 223 88Ra + 2He

227

219 Ra 86 Rn + 42He

223 88

20. Answer:

For this type of question, it is helpful to construct a chart:.

# of half-lives

% remaining

% decayed

100

12.5

87.5

6.25

93.75

3.12

96.88

1.56

98.44

21. Answer: The half-life is 6 hours. The mass of the radioisotope falls from 100 mg to 50 mg in 6 hrs, and then from 50 mg to 25 mg in the next 6 hours.

22. Answer: Perhaps someday it can. However, solar energy is diffuse, unequally distributed over Earth‘s surface, and still presents us with challenges to economically capture and store.

23. Answer: Each Si atom is surrounded by 8 electrons, but the atom in the center (the one that is doping the semiconductor) is surrounded by 9 electrons. Silicon is in Group 144A and has 4 outer electrons. Thus, central atom in the figure must have 5 outer electrons. This is consistent with an element in Group 155A such as arsenic, so this is an n-type silicon semiconductor.

24. Answer: The efficiency is reduced because some of the materials in the cell reflect radiant energy or absorb to it resulting in the production of heat instead of an electric current.

Concentrating on Concepts

25. Answer: Alchemists were perhaps the first practical chemists, but they did not have the advantage of knowing anything about atomic structure or nuclear reactions. No chemical reaction can produce gold from another element; a nuclear reaction is required. Even if they had envisioned a nuclear reaction that would produce gold from another isotope, they clearly did not have the means to accomplish this. The situation has indeed changed, and modern- day chemists could design experiments to change lead into gold. The question now is why anyone would want to, as the cost would be prohibitive.

26. Answer: The natural abundances of U-238 and U-235 are 99.3% and 0.7%, respectively. U-235 can be induced to undergo nuclear fission and thus is suitable as a fuel for nuclear power plants and nuclear weapons. Because U-235 has such a low natural abundance, it is more difficult to obtain in large quantities. Also, it is extremely difficult to separate U-235 from U-238. Had U-235 been readily available, far more countries would have had access to nuclear weapons.

27. Answer: a. All means of separation depend on the tiny mass difference between U-235 and U-238. For example, it is possibly to separate them by converting the uranium sample to gaseous UF6 and then use gas diffusion. A large high-speed centrifuge also can be used to separate these gas molecules. b. The uranium must be enriched to provide a critical mass of U-235 to sustain the chain reaction responsible for energy production in the reactor. c. First, the enrichment procedure is both expensive and energy intensive, so the minimum enrichment level capable of sustaining a chain reaction is preferred. Second, reactors using 80-90% fuels would have safety concerns due to the increased possibility of an uncontrolled chain reaction. Third, such reactors would also have significant security issues. The highly enriched fuel can be used directly in nuclear weapons, making the reactors potential terrorist targets. d. The difference in the isotopes of uranium is in their nuclear masses. This difference is not enough to significantly affect the chemical reactivity of the two isotopes. For chemical separation, the isotopes of uranium would need to behave differently in a chemical reaction of one sort or another.

28. Answer:

a. The fuel rods have to be replaced periodically because the fission products build up in them over time. These fission products absorb neutrons, thus slowing the chain reaction. b. Once fuel rods are removed, they are placed in pools to cool. If the reactor is in the United States, the fuel rods are left in storage, usually in the vicinity of the reactor as there is no central nuclear repository to accept nuclear waste. In many other parts of the world, they are reprocessed into secondary nuclear fuels.

29. Answer: The Palo Verde power plant produces energy through the process of nuclear fission. Coal and oil burning plants generate energy by burning fossil fuels.

30. Answer: Water is a better choice as a neutron adsorbent than graphite because water does not burn and because it has a higher specific heat than graphite. Water can more effectively adsorb and help dissipate excess heat in the reactor.

31. Answer: a. The subscript for each element is its atomic number, which can be found in the periodic table or in a list of elements. The subscript for the neutron is zero, which requires knowing or finding the charge of a neutron in a reference table. b. The superscripts cannot be omitted because nuclear equations must specify a specific isotope and this is something that cannot be determined by looking at the periodic table or another reference.

32. Answer: Thorium is found with uranium as it is part of the natural decay series of uranium.

33. Answer: After 7 half-lives, 99% of a sample has decayed which is a reasonable approximation of being “gone.” However, actually the radioactivity is not gone, as 0.78% of the radioactive sample still remains. Thus, if

you start with a large amount of a radioactive substance (for example, 2000 pounds), after 7 half-lives you still have about 10 pounds of radioactive substance left!

34. Answer: a. Bananas are rich in potassium (K). One of the naturally -occurring isotopes of potassium (K-40) is radioactive, thereby adding to the radioactivity in bananas. b. Because the natural abundance of K-40 is only 0.01%, the vice president could have stated that bananas are weakly radioactive and that this radioactivity is natural. Potassium-40 has a long half-life (on the order of billions of years), so it is undergoing radioactive decay very slowly. c. No. Bananas are a good source of potassium, an essential nutrient. The amount of K-40 in bananas is not significant enough to consider eliminating bananas from your diet on the basis of their radioactivity. Furthermore, any potassium (radioactive or not) that you ingest is not retained. Potassium is lost through sweat and in urine.

35. Answer: Fossil fuels were formed as the result of photosynthetic processes that took place hundreds of millions of years ago. Solar energy was a necessary ingredient in the formation, so the energy that is stored in chemical bonds in fossil fuels was originally obtained from the Sun.

36. Answer: One strategy to promote the use of environmentally cleaner electricity could be to provide a tax break or a subsidy for companies that produce electricity without consuming fossil fuels. Changes in the tax system could be imposed that reflect the true dollar and environmental costs of burning fossil fuels.

37. Answer: PV devices have demonstrated their practical utility for satellites, highway signs, security and safety lighting, navigational buoys, and automobile recharging stations.

38. Answer: Answers may vary but can include any two of these: wind, tidal/wave, hydroelectric, geothermal, etc. Wind energy pros include the lack of a need for fuel, its cleanliness, and lack of disruption of farmland. One controversial wind energy con is that some point to the harm of flying birds. Other cons are the upfront expense, the noise of the turbines, and the unpredictability of the wind. (https://www.justenergy.com/blog/wind-energy-pros-and-cons/) One pro of tidal energy is that it is a predictable phenomenon and that energy can be produced at low speeds. Tidal/wave energy may have similar environmental impacts as dams, but studies are still being conducted. Other cons of tidal/wave energy are that stations have to be constructed near land and they are expensive. (https://energyinformative.org/tidal-energy-pros-and-cons/ ) . Hydroelectric dams have pros including their reliability and flexibility once constructed to change flow and output. Cons of hydroelectric dams are their environmental impacts on fish, their cost, and the effect of droughts on their output. (https://energyinformative.org/hydroelectric-energy-pros-and-cons/) . Geothermal energy has pros including the lack of a need for fuel, small land footprints, and its availability everywhere. Its cons include environmental impacts, the potential to cause earthquakes, upfront expense, and cost effectiveness by location. (https://energyinformative.org/geothermal-energy-pros-and-cons/ ). Exploring Extensions

3839. Answer: To decommission a nuclear power plant means to shut it down permanently. In the United States, the Nuclear Regulatory Commission‘s (http://www.nrc.gov) is a good source of information on the status of nuclear power plants, functional or decommissioned. Decommissioning has four stages: 1. Removing the spent nuclear fuel from the reactor core and from the spent fuel pools 2. Moving the spent nuclear fuel to short-term storage or to a reprocessing plant 3. Waiting until the radioactivity has sufficiently decreased at the nuclear power plant, and 4. Dismantling the nuclear power plant.

3940. Answer: a. In the equation E = mc2, the speed of light (c) is 3.00 × 108 meters/second. In order to have joules (J) as the unit of energy (E), the mass (m) must be in kilograms. In addition, use the conversion factor of 1 joule = 1 kilogram-meter2/second2. Here is the calculation:. 2

8 1J 103 J 1 kg   3.0010 m  3 2 2 50.1 kJ 1 kJ  mass, g  10 g  s   kg - m /s  

The mass loss is 5.57 × 10-10 g

b. To produce 50.1 kJ of energy, the ratio of masses is 1.00 g of methane burned to

5. 57 × 10

-10

g methane converted to energy, or about 1.80 × 109 to 1.

c. The amount of energy released per gram of reactant in a chemical reaction is relatively much smaller than that released per gram of reactant in a nuclear reaction. Therefore, very little mass is actually converted to energy in a chemical reaction, so it is reasonable to apply the Einstein equation only to nuclear reactions.

4041. Answer: In the equation E = mc2, the speed of light (c) is 3.00 × 108 meters/second. In order to have joules (J) as the unit of energy (E), the mass (m) must be in kilograms. In addition, use the conversion factor of 1 joule = 1 kilogram-meter2/second2. Here is the calculation:. 2

 3.00108 m  1 kg 1J 2 2 E  0.0265 g  103 g     s kg - m /s  

E  2.39  1012 J

4142. Answer: a. The sum of the masses of the reactants is 5.02838 g, and the sum for the products is 5.00878 g. The difference is 0.0196 g. b. To use Einstein‘s equation, E = mc2, you need to pay close attention to the units. The speed of light is 3.00 × 108 meters/second. In order to have joules (J) as the unit of energy, convert the mass from grams to kilograms (kg). In addition, use the conversion factor of 1 J = 1 kg-meter2/second2. Whew! Here is the calculation: .

4243. Answer: Lise Meitner (1878–1968) was an Austrian-born nuclear physicist. She and Otto Hahn discovered the element protactinium. After leaving Nazi Germany in 1938, she found a post at the Nobel Physical Institute in Stockholm. She continued her research there and, together with her nephew Otto Frisch, did theoretical calculations to support Hahn‘s experimental work on splitting the uranium nucleus. Meitner and Frisch called the process “nuclear fission.” During the war, she refused to work on the atomic bomb. In 1947 the Swedish Atomic Energy Commission established a laboratory for her where she worked on an experimental nuclear reactor. Marie Curie (1867-1934) was a Polish-born physicist and chemist. Together with her husband, Pierre, she studied X-rays. In 1903, Marie and Pierre Curie jointly received the Nobel Prize in physics. In 1911, Marie also was awarded the Nobel Prize in Chemistry. Although the two women carried out research in the same fledging area of nuclear chemistry, there is no record that they ever personally collaborated on any investigations. In fact, Marie Curie was said to have rejected Lise Meitner‘s application to work with her in Paris. More information about these two scientists can be found at https://www.forbes.com/sites/melaniefine/2019/11/07/marie-curie-and-lisemeitner/#c6e8604683d7http://www.users.bigpond.com/Sinclair/fission/LiseMeitner.html and in Women in Chemistry, a joint publication of the American Chemical Society and the Chemical Heritage Foundation.

The Curies and Lise Meitner are honored for their work with elements 96 and 109 on the periodic table.

4344. Answer: Tritium, H-3, is a radioisotope of hydrogen. Hydrogen is a gas at room temperature, so it is unlikely that the gas itself is contained in the watches. Several descriptions of this watch mention the stainless steel screw-on back, again making it unlikely that tritium gas was present inside the watch. Most likely, the tritium is in a compound in the luminous paint. The paint also contains a phosphor, that is, a compound that glows (is phosphorescent) when hit by ionizing radiation such as the beta particles emitted by tritium. Indeed, these watches can glow brightly as claimed by the advertisement.

4445. Answer: Benefits would include electric power for the community, no greenhouse gas emissions for the operation of the plant (although emissions occurred during its construction), no SO2 and NOx emissions while producing power, and possibly employment for community members at the power plant. Cost of the plant might also be cited as a benefit, depending on the available alternatives. Risks would relate to the nuclear fuel used in the reactor – its production, transport, use, storage and/or transport of waste after use, and any possible release of radioisotopes to the community due to a plant accident.

4546. Answer: Similarities between a coal-fueled power plant and nuclear-fueled power plant include:   

Both contain a steam generating loop where liquid water is turned to steam. The gaseous water turns a turbine to create electricity, and then is re-condensed to form liquid water again. The turbine that produces electricity is the same. Each power plant includes a cooling water loop with an external body of water as the cooling source.

Differences between a coal-fueled and nuclear-fueled power plant include:  

The source of the energy to heat the water which turns the turbine is from nuclear fission reactions in the nuclear power plant and from the burning of coal in the coal power plant The nuclear-fueled power plant has an additional cooling loop (the primary coolant) to cool the reactor core. This coolant is a closed loop so that the secondary coolant is not contaminated with radioactive material.

4647. Answer: Mirrors or lenses could be used to concentrate solar energy on a collection array in space and send the electricity back to Earth. This technology would counteract one of the major limitations of current solar technology – the light from the Sun spreads out over Earth and is relatively weak. Unlike Earth-based solar collectors, orbiting collecting satellites would also have the advantage of being in the light all the time.

Source: http://www.thespacereview.com/article/214/1(accessed July 2016).

4748. Answer: Photovoltaic materials have been incorporated into building facades, canopies over parking areas, windows, and skylights. These materials generate electricity from sunlight. The durability of the materials is still under study.

4849. Answer: Crystalline silicon is used for the production of photovoltaic cells. Two of the common methods for synthesizing crystalline silicon are Czochralski Crystal Growth and Float Zone Crystal Growth, two different processes that involve manipulating silicon in different physical states. For more details regarding these processes, see: Source: (1) https://www.tf.uni-kiel.de/matwis/amat/elmat_en/kap_6/advanced/t6_1_3.html (2) https://www.tf.uni-kiel.de/matwis/amat/elmat_en/kap_6/illustr/i6_1_1.html#_dum_7 http://www.siliconfareast.com/crystal.htm. (accessed December 2012).

To cope with the shortage of silicon, the photovoltaic industry is undergoing a series of changes. Companies are pursuing business models to increase productivity and secure silicon supply. Researchers are developing and testing a number of different synthetic molecules for the next generation of photovoltaic collectors.

4950. Answer: Student answers will vary, based on the sustainability and cost of the chosen energy source.y.

5051. Answer: a. As of 20192, the largest PV power plant in the United States and in the world is in Yuma County, Arizonais the Solar Star facility near Rosamond, California. When completed in 2015, it was the world‘s largest solar farm; however, the world‘s largest facilities are now located in India (Pavagada Solar Park, #1 and Bhadia Solar Park, #3), China (Tengger Desert Solar Park, #2), and Egypt (Benban Solar Park, #4). b. Again as of 20192, Golmud, China and Neuhardenberg, GermanyIndia, China, Egypt, and the United Arab Emirates, have two of the world‘s largest PV power plants. c. Factors include: (1) having land available for the array, (2) living in a climate with weather favorable to solar collection, (3) having economic conditions that promote an investment with a long-term payback, (4) having the infrastructure to transmit the electricity to population centers.

ANSWERS TO END-OF-CHAPTER QUESTIONS

CHAPTER 87: Energy Storage

Emphasizing Essentials

1. Answer: a. Oxidation is a process in which an atom, ion, or molecule loses one or more electrons. Reduction is a process in which an atom, ion, or molecule gains one or more electrons. b. Electrons are transferred from the species losing electrons to the species gaining electrons.

2. Answer: a. Oxidation. Iron loses two electrons to form the iron(II) ion. b. Reduction. The nickel(IV) ion gains two electrons to form the nickel(II) ion. c. Oxidation. Each chloride ion loses an electron to form a neutral chlorine atom. These atoms combine to form a chlorine molecule (Cl2).

3. Answer: Zn(s) is oxidized to Zn2+ in zinc oxide. O2(g) is reduced to O2- in zinc oxide.

4. Answer:

A galvanic cell is a type of electrochemical cell that converts the energy released in a chemical reaction into electrical energy. An example of a galvanic cell, an alkaline cell, is shown in Figure 8.12b5. A battery is a series of galvanic cells connected together. An example is the lead–acid storage battery made of several galvanic cells. Note: the term “battery” commonly is used interchangeably with “cell” (galvanic cell). For example, sometimes the D cell (a type of galvanic cell) is referred to as a D cell battery.

5. Answer: Electric current (an amount of charge per second) is measured in amps (A). In contrast, the electrical potential or the “pressure” behind this current is measured in volts (V).

6. Answer:

a. The anode is Zn(s). The oxidation half-reaction is:

b. The cathode is Ag(s). The reduction half-reaction is:

7. Answer: a. oxidation half-reaction: Li(s) ---> Li+ + e– reduction half-reaction: I2(s) + 2 e–  --- > 2 I– b. overall cell equation: 2 Li(s) + I2(s) ---> 2 LiI(s) c. The oxidation half-reaction Li(s) ---> Li+(aq) + e– occurs at the anode. The reduction half-reaction I2(s) + 2 e–  --- > 2 I–(aq) occurs at the cathode.

8. Answer: a. The voltage from both kinds of cells is the same (1.5 V) because voltage depends on the chemical reaction that is producing the electrical energy and not on the size of the electrodes. b. The amount of current (A) produced by a cell depends on the size of the cell. Larger cells contain more materials and can sustain the transfer of electrons over a longer period. For example, the larger D alkaline cell can generate 120 A/hr of current, whereas a tiny AAA alkaline cell generates less current at 12 A/hr.

9. Answer: a. laptop computer: lithium-ion b. cell phone: lithium-ion c. digital camera: lithium-ion d. calculator alkaline, for example AA or AAA

10. Answer: a. Oxidation half-reaction: Zn → Zn2+ + 2 e– b. Reduction half-reaction: Hg2+ + 2 e– → Hg

c. Mercury was once widely used in batteries. By 1990, an awareness of the dangers of mercury in urban trash had grown. Mercury is a toxic metal and (in some forms) can accumulate in the biosphere. Safer batteries and the need to recycle batteries led to the passage of the MercuryContaining and Rechargeable Battery Management Act (The Battery Act) in 1996.

11. Answer: a. The electrolyte completes the electrical circuit. It provides a medium for transport of ions, thus allowing charge to be transferred. b. KOH(aq) (in a paste-like form) c. concentrated sulfuric acid

12. Answer: a. Pb(s) + SO42–(aq) → PbSO 4(s) + 2 e– PbO2(s) + 4 H+(aq) + SO 42–(aq) + 2 e– → PbSO 4(s) + 2 H 2O(l)

b. The first half-reaction shows electrons being lost, so it represents oxidation. The second half-reaction shows electrons being gained, so it represents reduction. c. Lead is oxidized, so lead is the anode. While not as obvious, the lead dioxide or lead(IV) oxide is reduced (note the electrons on the left side of the half-reaction). Thus, lead dioxide is the cathode.

13. Answer: It represents the reduction half-reaction. The conversion of O2 to H2O requires a supply of electrons.

14. Answer: In the combustion of hydrogen and oxygen, chemical energy is released in the form of heat and light, often explosively. In a fuel cell using the same chemical reaction, the chemical energy is released in a controlled manner in the form of electricity.

15. Answer: The first half-reaction takes place at the anode (hydrogen is oxidized). The second half-reaction takes place at the cathode (oxygen is reduced).

16. Answer: PEM stands for proton exchange or polymer electrolyte membrane. As in the fuel cell shown in Question 15, H2(g) is oxidized to form H+(aq). In the PEM fuel cell H+(aq) moves through the membrane to react with O2(g) (which is reduced) to form water. There is no membrane in the fuel cell in Question 15. In addition, the electrodes differ between the two types of fuel cells as do the electrolytes. The PEM has a solid polymer electrolyte membrane coated with a Pt-based catalyst and the other fuel cell uses a KOH(aq) solution as its electrolyte. Finally, the PEM fuel cell operates at room temperature and the one used for the space mission does not.

17. Answer: Pressurized hydrogen gas enters the fuel cell on the anode side. When hydrogen molecules come in contact with the Pt catalyst, they split into two H+ ions and two electrons. The electrons are conducted through the external circuit, returning to the cathode side of the PEM fuel cell. Meanwhile, the protons are transported across a proton-exchange membrane (PEM), where they meet oxygen atoms that are formed from pressurized oxygen gas that enters the fuel cell on the cathode side. The combination of protons and oxygen atoms forms water that is transported out of the fuel cell.

18. Answer:

19. Answer: Advantages of the hydrogen FCV include: (1) it produces none of the harmful combustion products of an internal combustion engine (e.g., CO, PM, NO, and the greenhouse gas CO2) and (2) it does not run on fossil fuels, thus saving these fuels for applications for which replacement fuel options are more limited, such as to fuel aircraft.

20. Answer: a. K(s) + ½ H2(g)  KH(s)

b. KH(s) + H2O(l)  H2(g) + KOH(aq) c. Because lithium is less dense than potassium, a given mass will weigh less. This offers an advantage in the handling and transportation of a storage cell. In addition, lithium metal is less reactive than potassium metal, which makes it safer to use in the manufacturing of metal hydride storage systems.

21. Answer: Before we can use hydrogen fuel cells more widely, we will need to meet the challenges of the safely producing, transporting, and storing large quantities of hydrogen. Concentration on Concepts

22. Answer: The term ‘energy density‘ usually refers to the energy in Watt-hours per unit mass of a battery (Wh/kg). To calculate Watt-hours: battery voltage x Amp-hour capacity.

23. Answer: A battery contains positive and negative electrodes that are separated by a chemical electrolyte, which may be a liquid, paste, or dry powder. When a battery is connected to an electrical circuit, a series of chemical reactions occur. One of the reactions at the anode generates positive ions and electrons. The positive ions flow into the electrolyte, while the electrons travel through the external circuit to perform work (illuminating a bulb, powering a device, etc.). A separate chemical reaction occurs at the cathode, where the incoming electrons recombine with ions taken out of the electrolyte, thereby completing the circuit.

24. Answer: These batteries derive their voltage from different sets of chemical reactions. A rechargeable battery (such as a Ni-Cd battery) is one in which the oxidation-reduction reaction can be reversed with the input of energy (such as plugging the battery into an electrical outlet).) This recharges the battery. The oxidation-reduction reactions in a non-rechargeable battery, such as an alkaline battery, cannot easily be reversed. Since no simple way exists to recharge alkaline batteries, they are discarded once they stop producing electrical energy.

25. Answer:

A fuel cell is an electrochemical cell that produces electricity by converting the chemical energy of a fuel directly into electricity, without burning the fuel. In contrast, an electrolytic cell is a type of electrochemical cell in which electrical energy is converted to chemical energy. These cells are directly opposite in functionality;: one uses chemical energy to produce electricity and the other converts electricity into chemical energy. In a hydrogen fuel cell, hydrogen and oxygen are combined to form water and release 249 kJ/mole of water formed: H2(g) + ½ O2 (g)  H2O (g) + 249 kJ

In an electrolytic cell, 249 kJ/mole of water must be added to change water to hydrogen and oxygen: 249 kJ + H2O(g)  H2(g) + ½ O2(g)

Therefore, one process is an exothermic reaction and the other an endothermic reaction.

26. Answer: The primary difference is thatBoth Pb-acid batteries and fuel cells these produce electricity using different chemical reactions. In addition, aA lead–acid storage battery converts chemical energy into electrical energy by means of a reversible reaction. No reactants or products leave the “storage” battery and the reactants can be reformed during the recharging cycle. A fuel cell also converts chemical energy into electrical energy but the reaction is not reversible. A fuel cell continues to operate only if fuel and oxidant are continuously added, which is why it is classified as a “flow” battery.

27. Describe the importance of a separator in primary and secondary batteries. What would happen if the anode and cathode were allowed to touch inside a battery? Explain. Answer: The separator isolates the anode and cathode compartments. If these two electrodes are allowed to come into contact, a short circuit will result, leading to excessive heat generation. This heat could be sufficient to ignite the organic-based electrolyte, resulting in a condition referred to as “thermal runaway” and battery fire.

28. Answer: a. “ZPower is taking the leading role in launching the next generation of rechargeable, silver-zinc batteries for microbattery applications. This advanced battery offers superior performance over

traditional microbattery technologies - delivering 40% more energy than lithium-ion and 2-3 times the energy of nickel metal-hydride. ZPower batteries also offer a green solution since 95% of the battery elements can be recycled and reused. The mercury-free design is inherently safe due to its water-based electrolyte which is not susceptible to thermal runaway.” http://www.zpowerbattery.com/ b. oxidation half-reaction (zinc is oxidized):

reduction half-reaction (silver is reduced):

29. Answer:

a. a.

b. The manufacturer’s goal of retaining 90% of the initial battery voltage after 15 minutes of continuous use has not been achieved. 90% of the initial 6.56 V is 5.90 V, a level that was reached when the cell phone had been used for only 11 minutes.

30. Answer: The primary question is likely to be that of fuel economy. How do the new hybrids compare to other vehicles on the market? Follow–up questions could include queries about purchase price, safety record, maintenance costs, battery lifetime, environmental impacts, and available tax credits. All of these factors will influence the costs of purchasing and operating the car. The relative importance of each factor will depend on personal choices and on the region of the country where the car is being purchased and driven.

31. Answer: Answers will vary. Some advantages: better fuel economy; smaller, more efficient engines and greater use of electric power helps reduce harmful gas emissions. Some disadvantages: more expensive due to the need for a large, complicated battery/motor system; life-cycle analysis shows that these may not be as sustainable as originally thought due to battery fabrication and recycling issues.

32. Answer: A Toyota gasoline-battery hybrid car (for example the Prius) has a gasoline engine sitting side-byside with a nickel metal hydride battery and an electric motor. The engine drives the motor to recharge the battery. In addition, regenerative braking recharges the cells in the battery, during which the kinetic energy of the car is stored as electrical energy.

33. Answer:

All EVs (electric vehicles) share a common technology – the use of electricity to power the vehicle and rechargeable batteries as an energy storage device. If the power goes out, you could drive your vehicle only as far as the energy stored in its batteries would allow. Gasolinepowered vehicles also would be limited. Given that an electrical outage would also render inoperable the pumps at a gasoline filling station, your driving would be limited by the fuel left in your gas tank. Note that in a severe storm, which may topple trees and down power lines, nobody is likely to be driving anywhere! 34. Answer: The widespread use of hydrogen fuel could dramatically improve urban air quality by reducing the levels of particulate matter and SOx produced by internal combustion engines.

35. Answer: The space program required reliable, relatively lightweight power sources. Fuels cells, when compared to other types of batteries that were available at that time, met those specifications and did not “run down” or require recharging. A fuel cell will continue to operate as long as fuel is available.

36. Answer: The bond energies listed in Table 6.24.4 for bonds breaking and forming in gases can be used to calculate the following heats of combustion. These differ somewhat from the values given in the beginning of this chapter, where the product water is given in the liquid state.

H2(g) + ½ O2(g) → H2O(g) heat of combustion = 249 kJ/mol CH4(g) + 2 O2(g) → CO2(g)+ 2 H2O(g) heat of combustion = 814 kJ/mol In each case, the units of the calculated heat of combustion can be changed to kJ/gram by dividing by the molar mass of the fuel.

37. Answer: a.

b. This type of fuel cell is convenient because it runs on a liquid fuel, gasoline, rather than using gaseous hydrogen. Currently, most nations have an infrastructure for gasoline refueling. However, the liquid fuel is still petroleum-based and therefore non-renewable. It also burns to produce CO2, a greenhouse gas. Therefore, although such fuel cells may find specialty applications in the near future, their long-term prospects are not promising.

38. Answer: a. When water boils, the hydrogen bonds between water molecules (intermolecular forces) are disrupted. No bonds are broken within the water molecules. b. When water is electrolyzed, the covalent bonds within water molecules are broken.

39. Answer: Both batteries and supercapacitors are used for energy storage. Whereas supercapacitors feature fast charging/discharging, batteries require longer times. Hence, batteries are most useful for portable electronics and providing a driving range for electric vehicles. In contrast, supercapacitors are most useful for providing vehicle acceleration or other quick-discharge applications. The cost of supercapacitors is often greater than batteries, and they store much less energy per unit weight than batteries. However, supercapacitors can last millions of charge/discharge cycles, whereas batteries start losing significant capacity after 1000 cycles or less.

40. Answer:

Answers will vary. For portable electronic applications, Li-ion batteries are the best choice; however, considering cost and lifetime, alkaline primary batteries are the best choice for most low-tech uses (remote controls, etc.).

41. Answer: An energy input of 249 kJ/mol is required in the electrolysis of water. Most of this energy comes from the burning of fossil fuels in conventional power plants. The inherent inefficiency associated with transforming heat into work limits the usefulness of large-scale electrolysis and makes the process energy intensive. Although not technically feasible yet, using the power of the sun to produce hydrogen from water could be more thermodynamically efficient and would certainly be a far more sustainable method.

42. Answer: i) combustion of fossil fuels; not sustainable since this consumes a limited resource and results in the release of greenhouse gases. ii) electrolytic splitting of water; more sustainable than i) since no GHG emissions are produced and water is plentiful. However, this requires a large input of energy, which is often generated by fossil-fuel power plants! If the power comes from renewable sources (e.g., wind, solar, etc.), then this would represent a sustainable alternative. iii) fermentation – conversion of biomass into sugar-rich feedstocks that can be fermented; highly sustainable since this process does not result in GHG emissions and uses bacteria to break down organic matter found in the biomass. This is in very early stages of development, and currently has issues with slow rates and low yields of H2 production.

43. Answer: a. 1.0 molH  2mol Na  23.0 g Na 46.0 g Na 2

b. 1.110 kJ

1molH 2

1mol Na

1molH2 2mol Na 23.0 g Na    2.10105gNa 249 kJ 1molH2 1mol Na

c. Using the result from part a: 46.0g Na 

1 kg Na 3

10 g Na

$165  1kg Na $7.59

44. Answer: a.

Advantages of H2

Disadvantages of H2

Transportation

Electricity

 lightweight fuel  saves fossil fuels if the hydrogen is derived from renewable sources  can be used in fuel cells  potentially explosive  currently difficult to store, handle  low energy density

 large supply available from water through electrolysis  fuel cells using H2 are practical for some applications  expensive to extract H2 from water  difficult to transport, store, and handle

b. Personal decisions about the use of hydrogen as a fuel for transportation and/or the production of electricity should be based largely on the real advantages and disadvantages of this fuel in the two different applications. 45. Answer: The “Bagdad Battery” is about 2000 years old from the Parthian period (250 BCE to CE 150). The clay jar (5½ inches high by 3 inches across) has an asphalt plug that seals the opening and holds in place a copper sheet, rolled into a tube. A copper disc held in place by more asphalt caps the bottom and holds the tube. A narrow iron rod stuck through the asphalt hangs down into the center of the copper tube without touching it. While no written record tells as to the exact function of the jar, scientists speculate that the item was used to electroplate items, that is putting a layer of one metal (gold) onto the surface of another (silver). The jar becomes a battery capable of generating a small current (about 1.1V) when filled with an acidic liquid like vinegar or a fermented drink. Source: www.smith.edu/hsc/museum/ancient_inventions/battery2.html. (accessed December, 2012)

Exploring Extensions

46. Answer:

a. Hydrogen is oxidized as it gained an oxygen atom to become water. Oxygen gained hydrogen atoms, so it got reduced. b. In the first equation, carbon is oxidized as it gained oxygen atoms to become carbon dioxide. In the second more complex equation, oxygen is reduced when it gained hydrogen atoms to become water. The carbon in octane lost hydrogen atoms to become a product which gained an oxygen. The change to both reactants fits this non-electron definition of oxidation and reduction.

47. Answer: a. Tough call. For metals such as iron and aluminum, we have large supplies of ore that are relatively accessible. Other metals, however, are either less abundant or less easily extracted from the Earth. In some cases, then, it is just not feasible to “mine in new places.” True, we could reduce consumption and recycle. Some countries, regions, and cities have been more successful in promoting these efforts than others. b. Challenges include: (1) making battery recycling made more convenient for consumers, (2) making recycling cost-effective for those responsible for the infrastructure of the recycling efforts, and (3) thinking in terms of cradle–to–cradle in battery design.

48. Answer: Tragedy of the commons occurs when a resource is common to all and used by many, but has no one in particular responsible for it. As a result, the resource may be destroyed or significantly degraded by overuse to the detriment of all that use it. This is how tragedy of the commons was defined in Chapter 21. Metals are mined around the world, and are used to manufacture many items, including batteries. The tragedy occurs with a cradle–to–grave mentality in which we all use materials and then dispose of them as a dead-end. Decreasing the use of toxic materials such as lead and cadmium, recycling, cradle–to–cradle design for product reuse, and decreased consumption will all play in to reducing our need for new metal materials from our common Earth resources.

49. Answer: Here are ways that some of the principle of green chemistry might apply. Note: these principles are listed on the inside front cover. and described in more detail in Chapter 0. 1. “It is better to prevent waste than to treat or clean up waste after it is formed.” For example, stations are now set up to receive and recycle lead storage batteries. These batteries are no longer sent to landfills or junk yards. 2. “It is better to minimize the amount of materials used in the production of a product.”

For example, find ways to use less silicon in a PV cell, find ways to reduce the packaging for batteries (for example, “button” batteries often come in a plastic package to prevent point of purchase theft. Find another way to prevent theft) 3. “It is better to use and generate substances that are not toxic.” For example, stop using or minimize the use of batteries that contain toxic metals. This already has been done for mercury batteries. Also, develop new batteries that don’t contain cadmium, lead, and other toxic materials.

50. Answer: While water vapor is not considered a criteria air pollutant (and it is highly unlikely it ever would be at a future date), it nonetheless is a greenhouse gas. Excess water in the atmosphere could therefore contribute to global warming. However, water vapor naturally cycles in and out of our atmosphere and is unlikely to be a concern. Although some cities in dry areas are noticeably more humid because of human activities and “wet” urban landscapes, it is unlikely that excess water vapor would have an effect globally.

51. Answer: Candlelight Origin

The hot gases that burn and emit light.

Immediate energy source

The hydrocarbon wax, either produced by bees or from petroleum.

Original energy source

Sunlight that drove photosynthesis, which in turn produced the plants from which bees gathered their food (or years ago died and formed fossil fuels).

Products

CO2, H2O and small amounts of soot and CO.

Environmental costs

Primarily the health effects of the particulate matter and soot produced. Also, the greenhouse gas produced, CO2.

Advantages

Convenient, pleasing to view.

Disadvantages

Produce dirty soot and may cause a fire if unattended.

Light in a battery-powered flashlight Origin

A wire that glows when it is heated to a high temperature.

Immediate energy source

A chemical reaction in the battery

Original energy source

Several possibilities, depending on what energy source was used to produce the battery. Could have been fossil fuel consumption (originally solar energy) or nuclear power plant (nuclear fission).

Products

The end products are different chemicals in the battery while the byproducts are those that are produced during the manufacture of the battery, bulb, and flashlight.

Environmental costs

All those associated with the production and disposal of the battery materials, as well as the side products during the combustion of fossil fuels (or nuclear fission) used in its manufacture.

Advantages

Portable, convenient, clean for the user.

Disadvantages

Somewhat expensive, becomes waste when energy is spent.

Light from an electric light bulb Origin

A wire that glows when it is heated to a high temperature.

Immediate energy source

Several possibilities, depending on what energy source was used to produce the electricity (e.g. burning coal or nuclear power plant).

Original energy source

The Sun or the ancient stellar synthesis that produced the uranium and other metals on our planet.

Products

The light bulb is very clean at the site where it is used, but produces pollutants such as NOx, SO2, CO2 and particulate matter at the power plant (if coal, natural gas, or fuel oil combustion) or spent nuclear fuel (if nuclear).

Environmental costs

All those associated with the production and disposal of the light bulb, as well as the side products during the combustion of fossil fuels (or nuclear fission) used to provide the electricity.

Advantages

Convenient, safe, inexpensive.

Disadvantages

Few to the user, except that the energy costs incandescent light bulbs are relatively high in comparison to using a fluorescent bulb or a light emitting diode (LED).

52. Answer: a. Factors include: (1) Iceland has geothermal energy, (2) sShipping costs for fuels are high to Iceland, (3) Iceland has some remote areas, which can be difficult to connect to a grid, (4) the recent economic and banking crisis that hit Iceland particularly hard underscores the necessity of fuel sufficiency, and (5) the geothermal power plants are also attracting tourists. For example, search the internet for the Blue Lagoon Geothermal Spa. b. As ofIn 2009, Iceland had the world’s first commercial hydrogen fueling station. Although it seemed as though a hydrogen economy would be realized by the end of the decade, as of 2019, there are only three hydrogen-fueled vehicles in production (Toyota Mirai, Hyundai Nexo, and Honda Clarity). The main problems with widespread adoption of fuel cell technology for automotive applications are related to the costs associated with filling stations and fuel transportation, as well as the high carbon emissions from the production of hydrogen gas. In addition, on the roadways you will see some hydrogen-fueled vehicles and buses. Plans are also underway to use hydrogen to fuel fishing vessels. c. Whatever Iceland learns about the distribution of hydrogen fuel, refueling stations, and consumer use will most certainly be helpful in informing others about the benefits and challenges of moving towards a “hydrogen” economy. Answers will vary, depending on the country in which you live.

ANSWERS TO END-OF-CHAPTER QUESTIONS

CHAPTER 9: The World of Polymers and Plastics

Emphasizing Essentials

1. Answer:

Cotton, silk, rubber, wool, and DNA are examples of natural polymers. Synthetic polymers include Kevlar, polyvinyl chloride (PVC), Dacron, polyethylene, polypropylene, and polyethylene terephthalate.

2. Answer: The 4Rs are reduce, reuse, recycle, and recover, with reduce being the option of choice. Given that paper is such a large part of the MSW stream, reducing paper waste could be a priority in practically any career. There may be options to reduce the use of bottled water as well, assuming that you get drinking water from the tap as is the case in many places. Designing a purchasing policy to reduce packaging waste is another possibility. Recycling, of course, is always an option in any workplace. In some cases, so is composting; for example, with coffee grounds.

3. Answer: The n on the left side of the equation gives the number of monomers that react to form the polymer. This n is a coefficient. In contrast, the n on the right side is a subscript and represents the number of repeating units in the polymer.

4. Answer: The R·

represents a free radical. It functions to initiate the polymerization.

5. Answer:

a. At the molecular level, increasing the length of the polymer chain would increase its molar mass and the extent of its interactions with neighboring chains. This would be expected to somewhat increase the polymer‘s rigidity, strength, and melting point. b. At the molecular level, aligning polyethylene chains with one another means that the structure is more crystalline and highly ordered. This would be expected to give the polymer slightly more density, more rigidity, and more strength. The melting point would also increase. c. At the molecular level, this would be just the opposite of the previous answer. The structure would be less crystalline, less ordered, and possibly somewhat tangled. This would be expected to make the polymer slightly less dense, less rigid, and not as strong. The melting point would decrease.

6. Answer: The bottle on the left most likely is made of low-density polyethylene; the one on the right highdensity polyethylene. The molecular structures of LDPE and HDPE help explain at a molecular level

the difference in properties. LDPE is a more highly -branched polymer, lessening molecular attractions between the chains and causing the plastic to be softer and more easily deformed. HDPE molecules, with fewer branches, can more closely approach each other, increasing the molecular attractions.

7. Answer: To serve as monomers, hydrocarbons must have a C=C double bond (and contain no elements other than C and H). Here are two possibilities other than ethylene.

propylene

styrene

8. Answer: A repeating head-to-tail arrangement is not possible for ethylene because all the hydrogen atoms in the molecule are identical. The molecule contains no “head” or “tail.”

9. Answer: Each ethylene monomer has a molar mass of 28 grams. To determine the number of monomers in the polymer, divide 40,000 (the molar mass of the polymer) by 28 (the molar mass of the monomer). The result is 1428 monomers, or 1400 to two significant figures. To determine the number of carbon atoms present in the polymer, note that each monomer contains two carbon atoms (H2C=CH2). Accordingly, the polymer contains 2 × 1428 carbon atoms, or 2856 carbon atoms. In round numbers, there are roughly 3000 carbon atoms.

10.

Answer: a. H

H H C

H C

C H C

C H

b. Styrene has the chemical formula: C8H8. c. The molar mass of a styrene monomer is 104 grams. A polystyrene molecule made up of 5,000 monomers will have a molar mass of about 104 g x 5,000 = 520,000 g (or 520 kg).

11.

Answer: This is the tail-to-tail, head-to-head arrangement of PVC formed from three monomer units.

12.

Answer: These are different. The top segment represents the “head-to-tail, head-to-tail” arrangement. The Cl atoms in each case are on alternate carbon atoms. It makes no difference if the atom is on the “top” or on the “bottom” of the chain (these positions are equivalent). In contrast, the bottom segment is “head-to-head, tail-to-tail.” The Cl atoms are on adjacent carbon atoms.

13.

Answer: The polymerization of butadiene is an example of addition polymerization.

14.

Answer: Note that the question posesasks “most likely.” For plastic use, “most likely” changes over time so the answers are a moving target. For example, PVC is being phased out in many uses.

a. PET, polyethylene terephthalate b. HDPE, high density polyethylene c. PVC, polyvinyl chloride (“vinyl”) d. PP, polypropylene

e. LDPE, low density polyethylene f. PS, polystyrene g. HDPE, high density, polyethylene

15. Answer: a.

16.

Answer: Recycling Code

Plastic

Recycling Code

Plastic

PET

LDPE

HDPE

PVC

Most of the containers and bottles in a food or drug store are HDPE (if they are opaque or translucent) or are PET if they are transparent. You may, of course, find other plastics.

17.

Answer: a. phenyl group, alkene b. hydroxyl group (or alcohol) c. phenyl group, carboxylic acid d. amine, carboxylic acid

e. amine f. carboxylic acid

18.

Answer: This molecule contains a carboxylic acid, a hydroxyl group, an ester, and an amine functional group. Note: Although beyond the scope of this text, the –OH group attached to a benzene ring is classified as a phenol, rather than as an alcohol.

19.

Answer: Terephthalic acid contains two carboxylic acid groups. Phenylenediamine contains two amine groups. These two monomers react in a condensation polymerization to form amide linkages between the phenyl groups.

20.

Answer: a. Pentanoic acid.

21.

Answer: Silk has many desirable properties, including being strong, lightweight, waterproof, somewhat stretchy, and can be dyed. Nylons are a class of polymers (polyamides) that are modeled after silk.

22.

Answer: a. A blowing agent is a gas (or a substance capable of producing a gas) used to manufacture a foamed plastic. For example, a blowing agent is used to produce Styrofoam from PVC. b. Carbon dioxide can replace the CFCs or the HCFCs that once were used as blowing agents. Although CO2 is a greenhouse gas, it still is preferable because CFCs and HCFCs both deplete the ozone layer as well as being potent greenhouse gases.

23. Answer: a. Assuming that both are in plastic jugs, you would use slightly less HDPE with one container instead of two. b. You would use less PET, but perhaps more disposable cups (or water and soap to wash cups). c. You would use less HDPE for a smaller container (and also less energy to transport a lower weight, if the detergent contained less water). 24. Answer: a. Postconsumer content includes all types of waste: newspapers, cardboard, foam cups, packing peanuts, 2-liter bottles, and plasticware. Preconsumer content includes waste created in the manufacturing process, such as scraps of fabric, plastics, paper, wood, and food. b. Not necessarily. For example, most PET soda bottles are made from petroleum products and do not include recycled PET.

Concentrating on Concepts

25. Answer: BelowHere is one possible way to show the relationship between the given terms do this. Other examples could be added for natural and synthetic polymers.

Polymer natural protein

synthetic nylon

26. Answer: Polypropylene (PP) is a tough plastic and bottle caps need to be tough, standing up to repeated use and not losing their shape or their threads. However, PP melts at a higher temperature than PET and has different properties. So somewhere in the recycling process, PP needs to be separated from PET. In essence, in most cases, the caps need to be removed from the bottles. Beverage companies are currently seeking alternatives.

27. Answer: Photosynthesis is the process that occurs when green plants use the energy of sunlight to synthesize glucose from carbon dioxide and water.

28. Answer: Factors other than the chemical composition of the monomer(s) influence the properties of the polymer. These include length of the chain (the number of monomer units), the three-dimensional arrangement of the chains, the degree of branching in the chain, and orientation of monomer units within the chain (such as head-to-tail).

29. Answer: We will use ethylene as the simplest example, but students may choose other similar monomers. Here is the ethylene monomer:

With a free radical catalyst, it polymerizes to form polyethylene:.

Both the monomer and the polymer are hydrocarbons; that is, they are made from the elements carbon and hydrogen. As such, both burn to produce CO2 and H2O. Also, both are nonpolar and less dense than water. Beyond this, the compounds are very different. For example, at room temperature, ethylene is a reactive gas, and polyethylene is a relatively unreactive solid.

30. Answer: 



For addition polymerization, the monomer must have a C=C double bond. Although some monomers have benzene rings as part of their structures (styrene, for example), the double bond involved in addition polymerization must not be in the ring. An example is the formation of PP from propylene. For condensation polymerization, each monomer must have two functional groups that can react and eliminate a small molecule such as water. For example, an alcohol and a carboxylic acid can react to eliminate water. An example is the formation of PET from ethylene glycol and terephthalic acid.

31. Answer: In vinyl chloride, each carbon atom has three3 bonds (2 single bonds and 1 double bond). These three3 bonds form an equilateral triangle (trigonal) and the Cl–C–H bond angle is about 120°. In the polymer, each carbon atom is connected to other atoms by four4 single bonds. The double bond is no longer present, and the four bonds point to the corners of a tetrahedron with a bond angle of about 109°.

32. Answer: a. Here is the Lewis structure for the monomer:.

b. When Acrilan fibers burn, one of the combustion products is the poisonous gas hydrogen cyanide, HCN.

33. Answer: a.

b. A repeating head-to-tail arrangement is not possible for Teflon for the same reason it is not possible for ethylene. The monomer does not have a “head” or a “tail.” c. Both of these compounds contain no C-H bonds. As a result, neither is flammable. Furthermore, both compounds are stable and generally unreactive.

34. Answer: From the bond energies in Table 5.1, it requires 598 kJ/mol to break C=C double bonds. The formation of CC single bonds releases 356 kJ/mol. If we consider the reaction of two ethylene monomers, two double bonds are broken and replaced with four single bonds (two bonds between the C atoms of the monomers, one between the first monomer and the second, and a bond extending to what would be the third ethylene monomer). Here is the calculation: (2 × 598 kJ/mol) + (4 × 356 kJ/mol) = 228 kJ/mol. Thus, the reaction is exothermic. 35. Answer: No. Because only bonds between carbon atoms are involved in the calculation (not the CH or CF bonds), the answer would be the same and exothermic for both.

36. Answer: The heat of combustion of polyethylene would be most similar to that of octane. Both are hydrocarbons consisting of carbon-carbon single bonds. The other fuels contain different atoms (and thus different bonds would be broken and formed).

37. Answer: Recycling involves materials that are already in use and possibly headed for the landfill. For example, recycling involves PET bottles or aluminum cans. Waste prevention reduces the amount of materials that are used and need to be disposed of (or reused); for example, how much plastic is used in the manufacture of an item. Although both aim to minimize waste, waste prevention is the option of choice. For more information on waste prevention, visit the U.S. EPA website.

38. Answer:

a. PLA stands for polylactic acid, a polymer. b. The monomer of PLA is lactic acid. In the United States, lactic acid is produced from corn. c. Reasons include that (1) corn is a renewable resource, (2) PLA is compostable, and (3) PLA is not a petroleum-based polymer. d. (1) Although corn is a renewable resource, corn is a crop with its share of controversies. These include the degradation of the land on which it is grown and the runoff of fertilizers and pesticides into nearby waterways. (2) Although PLA is compostable, this is true only in industrial composters that most communities do not have. It degrades slowly if at all in a landfill. (3) Although no oil is used in its production, fuels such as petroleum are nonetheless used in the growing of corn and its transportation. 39. Answer: a. From the bond energies in Table 6.25.1, it requires 598 kJ/mol to break C=C double bonds. The formation of CC single bonds releases 356 kJ/mol. If we consider the reaction of two ethylene monomers, two double bonds are broken and replaced with four single bonds (two bonds between the C atoms of the monomers, one between the first monomer and the second, and a bond extending to what would be the third ethylene monomer). Here is the calculation:

(2 × 598 kJ/mol) + (4 × 356 kJ/mol) = 228 kJ/mol.

With 1000 monomers joining, we multiply the -228 kJ/mol by 500 and the heat released will be 114,000 kJ or 1.14  105 kJ.

b. The reaction is so exothermic that, in the early days of polymer manufacturinge, polymerization vessels exploded. Manufacturers realized that conditions needed to be carefully controlled to avoid this.

40. Answer:

The monomer with 2 –OH groups is ethylene glycol:

The monomer with 2 –COOH groups is terephthalic acid:

41. Answer: When the piece of plastic is stretched, the strip narrows and “necks.” The molecules become aligned parallel to each other in the direction of the pull. This alteration is not reversible, and if the pulling continues, the plastic breaks. When the same pulling force is applied to a piece of paper, the paper tears rather than stretches. The cellulose molecules in paper are held rigidly in place and are not free to align.

42. Answer: a. Branched LDPE would not be strong enough to protect against accidental cuts or punctures. b. Uses could include body armor of all types and marine applications such as ropes, fishing line, and sails. Source: https://www.packagingcomposites-honeywell.com/spectra/product-info/spectra-fiber/ The website of Allied Signal reports: “Our Spectra® fiber is one of the world's strongest and lightest fibers. A bright white polyethylene, Spectra fiber is, pound-for-pound, 10 times stronger than steel and up to 40 percent stronger than aramids. It floats, resists chemicals and water, and exhibits superior fiber-to-fiber abrasion.”

43. Answer:

a. Reduce: using tap water instead of water in plastic bottles (PET). Bringing your own container to a grocery to buy grains and beans in bulk, rather than buying these in packaging (HDPE and LDPE). Recycle: rerecyclecycling of detergent containers and shampoo bottles (HDPE). Reuse: refill a bottle multiple times rather than disposing of it after one use (PET, HDPE and other specialty plastics such as polycarbonates). Recover: recover the energy in paper products by using them as fuel to start a fire in a wood stove or send to a commercial source for use in a power plant. b. It takes energy to produce plastic, both in obtaining the feedstocks (such as petroleum) and in the refining and manufacturing process. The fuels burned to produce this energy generate air pollutants such as particulate matter (soot) and NOx. Reduced use translates to reduced emissions translates to better air quality. Another example relating to public health is plastic in the environment, because plastic degrades slowly or not at all. Plastics in the waterways (large pieces or tiny ones) can disrupt ecosystems, provide breeding places for pests such as mosquitoes, and be ingested by birds and fish. 44. Answer: The Big Six polymers are generally large (in fact huge) molecules with few polar groups. Furthermore, many are hydrocarbons (HDPE, LDPE, PS, PP) and therefore would not be expected to dissolve in polar solvents such as water. The generalization explained in Chapter 58 is that “like dissolves like.” So many polymers, including HDPE and LDPE, soften in hydrocarbons or chlorinated hydrocarbons because these nonpolar solvents interact with the nonpolar polymeric chains.

45. Answer: Acetone dissolves the polymer, destroying the cavities created with a blowing agent during manufacture. The polymer collapses on itself and is a denser solid piece of polystyrene because the empty cavities have been removed. An analogy would be to pop bubble wrap. The plastic collapses on itself.

46. Answer: a. Starch is a polymer of glucose. Many foods are a source of starch, including corn, potatoes, and rice. b. Advantages of starch packing peanuts include that they are lightweight, compostable, and made from a renewable material. Disadvantages include that they will degrade if the package gets wet, they are made from what could be eaten as a food, and they are less “springy” than polystyrene foam peanuts.

c. Composting is a good option. Although some can be washed down the drain, this results in the starch needing to be removed later at a water treatment plant.

47. Answer: Shifting baselines is the idea that what we take as “normal” or as “the way we do things” shifts over time, and the previous norm is forgotten. a. What is “normal” for packaging has slowly shifted over time. Before the widespread use of plastics, foods were either sold in cardboard containers or in bulk, and you brought your own containers. Packaging became more prominent with the introduction of refrigeration in the 1940s when you could store food at home in your own freezer (as opposed to in an ice box). Plastic bottles for soft drinks overtook glass bottles in the 1970s. Plastic packaging also became more secure when tamper-evident caps were introduced. b. What is normal for our waterways also has shifted. Trash, garbage, manufacturing waste, and human excrement have always been a problem in lakes and in rivers that flow by cities. But with the advent of plastic, items began appearing in waterways that did not degrade over time. If the previous waste streams no longer flowed into waterways, slowly these waterways cleaned themselves over time. In contrast, plastic waste needs to be removed because it may break into smaller pieces, but for the most part will not biodegrade. As a result, it is “normal” for us now to see pieces of plastic along roadways, streets, fields, and beaches.

48. Answer: a. A plasticizer is a compound added to a hard or rigid plastic that makes it more pliable.in order to soften it. b. DEHP was added to PVC in order to make soft vinyl products such as boots, shower curtains, clothing items, and flexible tubing. c. DEHP has been banned for items that infants repeatedly put in their mouths, such as pacifiers. It has also been banned in some medical devices and children‘s toys. The use of DEHP remains controversial and different restrictions are in place in different countries.

Exploring Extensions 49.

Answer:

a. Check Table 12.3 in Chapter 12. Examples of functional groups not discussed in this chapter include ethers, aldehydes, and ketones. b. The structural formula for acetone is shown below. It contains the circled ketone functional

group..

50.

Answer: Cotton is formed from glucose; silk and wool are formed from amino acids. All are condensation polymers. Natural rubber is formed from isoprene (contains a C=C double bond, shown below) and is an addition polymer.

51. Answer: The weekly news magazine of the American Chemical Society, Chemical and Engineering News, has run articles about the plastic debris in the Pacific Ocean. So have Scientific American and Science. Reports of plastic debris are not a hoax. Furthermore, they have implications for marine and human health. A particularly useful journal issue is The Philosophical Proceedings of the Royal Society, July 27, 2009; 364 (1526), an issue themed on “Plastics, the Environment, and Human Health.” Some recent sources: http://plastic-pollution.org https://www.frontiersin.org/articles/10.3389/fmars.2019.00447/full https://www.nationalgeographic.com/environment/2019/03/un-environment-plastic-pollutionnegotiations/

52.

Answer: a. The two main properties are (1) stable over time of intended use and (2) non-toxic. Other factors to consider are low cost, lack of solubility in body fluids, lack of reactivity in body fluids, and the ease of implantation. b. Several different types of contact lenses are on the market and each uses a different type of polymer. Polymethyl methacrylate (PMMA), one of the earliest polymers used for rigid gas

permeable lenses, is structurally similar to Lucite and plexiglas. Silicone-acrylate materials now are more commonly used under trade names such as Kolfocon. Newer rigid gas permeable (RGP) polymers tend to contain fluorine. Manufacturers’ websites are good sources of information. Desirable properties include being nontoxic, permeable to oxygen, comfortable to wear, and inexpensive. Also desirable is the ability to conform to the shape of the eye and to be easily cleaned (if necessary).

53. Answer:

The cradle-to-grave life cycle of vinyl needs to be considered in answering this question. An additional factor is that vinyl often includes a plasticizer (typically a phthalate such as DEHP or DINP) that is added to the rigid PVC in order to soften it. With these factors in mind, risks include (1) those to the worker (occupational exposure to vinyl chloride, a carcinogenic monomer), (2) those to the consumer (from leaching of the plasticizer, which in a few cases carries health risks), and (3) those to the environment (disposal of a plastic that contains chlorine and can produce HCl if burned). The film and website “Blue Vinyl” tells of one person‘s research into the risks of PVC.

The benefits of vinyl include that it is a beautiful and an incredibly versatile plastic with many uses. These include vinyl siding for buildings, IV tubing and blood bags, clear or shiny plastic containers, plastic charge cards, vinyl hoses, “patent leather” belts and shoes, and PVC pipe for plumbing. Manufacturer and plastic industry websites describe the benefits.

54. Answer:

In 1965, Stephanie Kwolek created Kevlar, the first polymer in a series of synthetic fibers with exceptional strength and stiffness. She was interested in both chemistry and medicine and graduated from Carnegie-Mellon University. She later worked at the DuPont Company in polymer research, where she made her key discoveries. Although the fiber was initially of interest for use in radial tires, because of its stiffness and strength it found other uses as well, including bulletproof fabrics. Kevlar and its close chemical relatives are used today in boats, airplanes, ropes, cables, tennis racquets, sails, tires, and skis. Search the Internet for details, including the MIT and Chemical Heritage Foundation websites.Source: http://www.rsc.org/diversity/175-faces/all-faces/stephanie-kwolek/

55. Answer:

During polymerization, the electrons in the molecule rearrange, forming one double bond where previously there were two. Of the four electrons between carbons 1 and 2, two are

unchanged leaving a single bond after the reaction. The other two electrons end up elsewhere in the molecule. One goes to form the bond between one isoprene monomer and the next. The second electron moves between carbons 2 and 3. One pair of electrons in the C=C between carbons 3 and 4 similarly moves elsewhere, with one electron moving between carbons 2 and 3. The net result of this rearrangement is a C=C between carbons 2 and 3 and C–C between all other carbon atoms. 56. Answer: a. With its high molar mass, this polymer should not dissolve in water. Like many polymers, it would be expected to be an electrical insulator. With its methyl groups, it should be somewhat flammable (but the presence of silicon reduces the flammability and gives it good stability at high temperature). b. “Silly Putty” bounces, but it breaks when pulled sharply. When it is formed into a shape, it slowly loses this shape over time and flattens out. Ink will stick to Silly Putty and so it can “lift” images from newsprint. These properties are rather unique, and led to the popular acceptance of Silly Putty as a toy long before it was widely used for other products. Answers.com has great information about Silly Putty. c. Silicone rubber is used for flexible bakeware because of its resistance to high temperatures. It also is used in greases, caulking, and tubing.

57. Answer: a. Here is a quote from Heidi Schussele, NY Times, November 23, 2000, “Computer components have changed over the years, but aA PC today is composed of a variety of metals with increasingly larger percentages of plastics to make them lightweight.typically 40 percent steel, 30 percent to 40 percent plastic, 10 percent aluminum and 10 percent other metals, including copper, gold, silver, cadmium and platinum. A monitor adds glass and lead to the components. But in our experience, finding out what which polymers are in the 40% plastic is no easy task. The outer shell of the mouse is typically ABS (acrylonitrile butadiene styrene) plastic that is injection-molded. Keyboards and monitor cases are also ABS and sometimes polystyrene (high-impact polystyrene, HIPS). ” Curious to learn more, a member of the author team asked a colleague who is a polymer chemist. He responded with perhaps a bit more technical information than you want to know, but because it is an interesting response, we include it here: “Computer monitor shells and the like are usually composed of poly(styrene), however, some feature Apple has gone to poly(carbonate) for the shells of their computers and laptops. The textured grips on mice are probably some kinda type of poly(propylene) or a poly(ethylene-co-1-octene) like the materials that you find on the textured grip of a toothbrush. The ethylene/1-octene materials are relatively new, in that their synthesis was only achieved in the mid 1990's and they came to market in the late 1990's after a messy patent dispute between DOW and Exxon- Mobil. I think the The keyboards are mostly ABS materials with high styrene content, which provides the stiffness. As for the rest of the computer, the green circuit boards are actually made of an epoxy

thermoset and the circuitry is composed of a variety of metals including silver, gold, and copper. DOW makes a lot of these materials and markets them as DERs (Dow Epoxy Resins—imaginative marketing!). One of the issues with these epoxies derived from bisphenol A is that they are flammable. DOW mitigates the flammability by using a perbrominated bisphenol A, since the bromine will serve as a radical trap in the combustion reaction and prevent fire. That being said, the introduction of all of the bromine causes the material to become very brittle. This problem has been recently addressed by adding some block copolymers to the resin which make tubular micelles within the epoxy. These long, tubular structures can entangle like spaghetti and enhance the toughness of the polymer by 3-4 orders of magnitude.” b. The answer to this question is a moving target. The electronic parts of computers are still more widely recycled than the plastics they contain, which is commonly referred to as ‘urban mining‘ to recoup valuable metals. However, the options for plastics appear to be increasing. Some companies will take computers and recycle or reuse all of their components, including the plastics. These companies may charge extra for the monitors, because of the lead in the glass.

Sources: https://resource-recycling.com/e-scrap/2017/04/26/e-plastics-explained/ https://plastics.americanchemistry.com/Ten-Facts-About-Plastics-from-Electronics/

58. Answer: Search the internet to find reasons to support bottle bills. These include that they: (1) work to reduce waste that goes to the landfill, (2) conserve resources, especially those of energy, (3) create jobs, and (4) provide financial incentives for recycling. The reasons against bottle bills include that they: (1) are extra work and extra cost for the grocers and beverage companies, (2) duplicate existing curbside recycling programs, (3) are inconvenient for consumers, and (4) are outdated.

59. Answer: As you might suspect from the –ol ending, polyols are alcohols. The “poly” refers to the fact that they have multiple hydroxyl (–OH) groups. Many types of polyols exist, some with only two hydroxyl groups and others with many more. For example, in this chapter, you met ethylene glycol, a polyol with two hydroxyl groups (also called a diol). It served as one of the two monomers for PET. In Chapter 5 in the section on biofuelsSection 6.16 related to biofuels, you met ethylene glycol and propylene glycol, two polyols. In Chapterss 5 6 & and 11 both, in regards to fats and triglycerides, you will read about glycerol (glycerin), a polyol that contains three hydroxyl groups (also called a triol).

Polyols can serve as monomers for any condensation polymers such as polyesters (made from a “double acid” and a “double alcohol” (diol). An internet search for soybean plastics or soybean-based polymers should turn up many examples.

ANSWERS TO END-OF-CHAPTER QUESTIONS CHAPTER 10: BREWING AND CHEWING

Emphasizing Essentials

1. Answer:

For g/ml, 5

1x103 cm3

For mg/L, 5

1dm3

dm3

1dm3

For mg/m3, 5

) = 5 x 10-3 g/cm3

)x (

1x103 mg

1x103 dm3

x( 3

1 m3

)x (

) = 5 x 10 mg/L

1x103 mg 1g

) = 5 x 10 mg/m

2. Answer:

g dm

3 x(

1dm3 3

1x10 cm

3) (

1cm3 1g water

)(

1x103103 g 1 kg water

)(

1 mol NaCl 58.5 g NaCl

-2

) = 8.5 x 10 mol/kg

8.5 x 10-2 mol/kg x 0.52 oC = 0.044 oC, new boiling point is 100.044 oC To find how much salt:, 101 oC/0.52 oC = 1.94 mol/kg salt water

1kg water = 1 L water, so 1kg = 1 L, so 1.94 mol/L salt water, Use molar mass to find mass of salt needed:, (1.94 mol NaCl/1 L water)  x (58.5 g NaCl/1 mol NaCl) = 113 g NaCl needed.

3. Answer:

g mL

1000 mL 1000 mg )x( ) = 1 x 106 mg/L 1L 1g

In terms of how does a solute affect the density of water, their presence increases the density of the liquid water. Because of the nature of solutions, solid solutes in liquid solvents add mass while not adding appreciable volume, and so, density increases.

4. Answer: Answers will vary, but should account for various concentrations of salt and replication of tests, while making sure to hold a control variable and use repeated trials.

5. Answer:

Recall for gases,

𝑃1 =

𝑃2

𝑇1

𝑇2

or P T = P T 1 2

2 1

and for good practice with gases, it is best to express

temperature in Kelvin, and so, recall K = oC + 273.

(1 atm)(x) = (2 atm)(373 K), x = 746 K, or 473 oC

With a 100 oC increase in temperature, the reaction rate would double 10 times. (100/10 = 10). At 2 atm, the rate of reaction would be over 1000 times the original rate at 1 atm. (210 = 1024). This emphasizes how pressure cookers cook food so much faster than an open pot of boiling water.

6. Answer: a. 2 cups of water (L):, 2 cups ×

1 quart 4 cups

1L = 0.47 L water 1.06 quarts

2 cups water x (1 quart/4 cups)(1L/1.06 quarts) = 0.47 L water b. 2 teaspoons of salt, NaCl (kg): 2 tsp ×

g 1 cm3 1 kg × 2.16 3 NaCl × = 2.1 x 10−2 kg NaCl cm 0.2029 tsp 1000 g

2 teaspoons salt x (1 cm3/0.2029 teaspoons) x (2.16 g/cm3 NaCl) x (1kg/1000 g) = 2.1x10-2 kg NaCl c. 3 hours at 300 oF (seconds and oC): 3h ×

60 min 1h

60 s = 10,800 s 1 min

3 hrs x (60 min/1 hr) x (60s/1 m in) = 10,800 seconds 9/5 oC + 32 = oF, (300 oF- 32) x (5/9) = 148 oC

7. Answer: How strongly molecules stick together via intermolecular forces determine how easily they will transition from the solid or liquid phase to the gas phase. To be considered volatile, these molecules must make this transition fairly easily and so not be held to tightly to their other molecules. Weaker intermolecular forces among molecules tend to come from non-polar features in the molecule as well as the molecule being compact and not made of many branched, but single long chains of nonpolar groups. Small molecular masses can also be a factor, but recall non-polar versus polar molecules tend to be the bigger factor. Numerous molecules that have properties of smells and/or tastes have a small rings of nonpolar groups. See examples below:

Lemon

Almond

Thyme

8. Answer: The browning of cut fruit is the result of a reaction of an enzyme, polyphenol oxidase, which is exposed when the fruit is cut, and oxygen from the air. It is an oxidation process much like the formation of rust on iron structures. These products create an unpleasant sour taste and are arguably a defense mechanism so that the fruit is not eaten by animals or even invaded by germs. This is not the same process as carmelization and the Maillard reaction which occur at high temperature and with no moisture present.

9. Answer: Oxygen prefers to react with the acidic vitamin C before reacting with the polyphenol oxidase in fruit, and so, the browning product from the oxidase reaction does not form. This the juice of lemons, limes, or even cranberries, which contain high amounts of vitamin C, when squeezed on fruits are effective at preventing the browning process.

10. Answer: There are a variety of variables and aspects that can cause a cake too fall. Essentially, though if the flour protein network that is in the batter (usually gluten) has not had time to set and provide the structure for the cake, it will collapse. Most often, this results from not having enough temperature and time to the baking process for the cake.

Concentrating on Concepts

11. Answer:

Answers may vary. However, at both the residential and commercial level, the harvesting of sea salt begins with sea water and the process of evaporation. As water evaporates from whatever size sample – 1 L at home or small ponds, say from the San Francisco Bay area – the salt concentration naturally increases. When the amount of water diminishes enough, salt crystals begin to form and can be raked up and harvested. Depending on the sample of seawater, other chloride salts, such as calcium and magnesium can be present. With certain brine rinse solutions, these can be washed away and a sea salt

purity can be as high as 99.8%!

12. Answer: All green plants (and so including vegetables) contain chlorophyll, which also includes a magnesium atom attached to it. This gives them their characteristic color. When exposed to heat (or acid) long enough, the magnesium is replaced by hydrogen atoms. This change in composition alters the color property and these vegetables turn from bright green to a more dull, olive green. In terms of texture, long exposure to heat and acid breaks down the fibrous, crunchy structural molecules of the vegetable and they become softer.

13. Answer: Pure to a chemist, at least, would mean nothing else present but the actual compound described. In the case of table salt, this would be only solid sodium chloride is present, NaCl. Ironically, the term sea salt does not mean a specific chemical compound. Because of the sea source of the salt. The salt mixture itself can vary from source to source. Sodium chloride, though, is still the primary component of interest. However, this also means that the idea of purity on the food label differs somewhat from what a chemist in a lab would mean by a pure substance. The FDA in the United States regulates that all food products labeled as table salt must be at least 97.5% pure sodium chloride. If you return to the answer to Qquestion #11, you can see that is threshold is usually exceeded in the harvesting and processing phases.

14. Answer: Heated and usually boiling water is used to make a cup of tea. In order to extract the molecules from the tea leaves, sufficient heating of the water solvent is necessary. Recall that achieving the boiling point of a liquid is actually more related to overcoming the external, atmospheric pressure rather than just merely heating to a particular temperature. Water boils at a lower temperature when the atmospheric pressure is lower, such as at higher altitudes. These lower temperatures may not be sufficient for extracting all the molecules one might enjoy from tea leaves, and so, the brewed tea may not be a flavorful.

15. Answer: As you may have learned in other chapters, as atmospheric pressure decreases, the temperature at which water boils also decreases. That temperature at Mt. Everest can be as low at 70 oC. The problem, then, becomes what temperature it takes to set the components of the egg. The yolk takes about 70 oC and the

white takes about 80 oC. If the water temperature on Mt. Everest reaches 80 oC, one is in luck and is likely to have a good boiled egg. Just remember if the water does reach that temperature, it still needs a longer time in the water than most recipes posted, which assume an atmospheric pressure of 1 atm (sea level).

The other option to more certainly cook the egg is to use a pressure cooker. As described in this chapter, the pressure cooker increases the immediate atmospheric pressure around the cooking environment and lead to higher temperature water boiling.

16. Answer: Baking soda and baking powder are both used in baking recipes. They are different mixtures, but both produce the same result. They are leavening agents. Baking soda is a solid base salt, NaHCO3. Baking powder is solid mixture of baking soda and a solid acid of some sort, usually, cream of tartar, an acid salt, KHC4H4O6. Both leavening agents react to produce carbon dioxide, CO2, gas which is what causes the airy texture in many baked goods. Baking soda is used with the other ingredients include some significant acid already, like vinegar or buttermilk. The reaction with vinegar is: HCO 3-(aq) + HC2H3O2(aq)  C2H3O2-(aq) + H2O(l) + CO2(g). InN baking powder, once the mixture is in contact with a water solvent, as is the case in many baking recipes, the two acid and base components react: HCO 3-(aq) + HC4H4O6-(aq)  C4H4O6-(aq) + H2O(l) + CO2(g). Baking powder is often used in batters that do not have acid in them already.

17. Answer: Drinking alcohol (ethanol) is a substance that more readily evaporates than water. Usually, much, but not all, of any alcohol put in a dish that is cooked evaporates. The amount of this removal, though, does vary with cooking method and cooking times. Beer is usually about 5-6% alcohol. If a bread batter made with beer is cooked for about 1 hour, then about 25% of the original amount of alcohol may remain. That would be about 1.1-1.5% alcohol of the original beer remaining. Longer cooking times to the bread would decrease that amount even more.

18. Answer: The terms “strong” and “weak” are terms used to describe the chemical properties of an acid (or base). In this case, these describe the degree to which a molecule of a particular acid dissociates in water. Strong acids mean that nearly every molecule of the acid donates its proton when places in water, e.g. hydrochloric acid is a strong acid: HCl + H2O  Cl- + H3O+. For weak acids, only some of their molecules dissociate and donate the protons. For these substances there remains some undissociated

molecules and is represented with an equilibrium reaction, e.g. acetic acid is a weak acid: HC2H3O2 + H2O ;⫘ C2H3O2- + H3O+.

The terms “concentrated” and “dilute” do not refer to the nature of the acid itself, but to the relative amount of the acid in the water solvent. These terms are independent of the particular acid, so that a solution could be a dilute strong acid solution, e.g. 0.001 M HCl(aq), or a concentrated weak acid solution, 18 M HC2H3O2(aq).

19. Answer: Microwave radiation causes changing electric fields. Because water is polar, is responds to the changing negative and positive conditions, alternating between repulsions and attractions that ultimately increases the motion of the water molecules. It is this motion (friction) that heats up the food. Other polar molecules are likely to respond in this manner. Among the three molecules listed, only ammonia (NH3) is polar and is likely to respond like water to microwaves.

20. Answer: Capsaicin is the common name for the chemical responsible for the chemical heat in peppers. Its molecular structure is:It has a chemical formula, and molecules structure:

Drinking water is not useful to cool the heat because capsaicin is insoluble in water. It is mostly a nonpolar molecule. The water merely spreads the capsaicin more around your mouth and across your tongue. Drinking milk or beverages with more fat that can dissolve the capsaicin may be more beneficial for washing down the heat.

21. Answer: Sulfur containing compounds react with silver to from silver sulfide, a black solid:

Ag(s) + S(s)  Ag2S(s).

The black is the “tarnish” on the silver. Usually this tarnish has to been removed (which also removes some of the silver of the cookware) or the reaction of the tarnish can be reversed and the elemental silver returns to the cookware. In the presence of a hot baking soda solution, aluminum reacts with silver sulfide to form elemental silver and aluminum sulfide:

3Ag2S(s) + 2Al(s)  6Ag(s) + Al2S3(s)

Exploring Extensions

22. Answer: Answers may vary depending on the flavors selected, but should focus on some aspects of the molecules that are in common, such as does the molecules have a ring structure, are their ester (-RCOOR-) groups present, etc. For example the flavor molecules for pineapple and are shown below. One can see the characteristic esterCOO group in each of these molecules. That accounts for some aspect of flavor characteristic, but clearly the other components are part of the experience as well, as pineapple and pear may have some slight similarity of taste, they also are clearly distinct tasting from one another to most people.

Allyl hexanoate (from pineapple)

ethyl decadienoate (from pear)

23. Answer: Flavor tripping is nickname concept in the culinary world for deceiving the other senses for what you are about to taste. For example, most people see and touch a lemon wedge and are ready for a very sour taste, but after eating a miracle berry, the raw lemon wedge taste like the sweetest lemonade. Miracle berries contain a particular molecule called miraculin that is a glycoprotein. This glycoprotein interacts with particular receptors on your tongue, the ones that detects sour, and blocks them for detecting the sour part. The lemon tastes sweet.

This concept of blocking flavors might be interesting because it could make things that are perfectly nutritious but taste dreadful more palatable, which could expand diet options for feeding a growing world population.

24. Answers: Answers will vary for (a), but are likely to focus on the types of ingredients, whether theh food is whole or natural or processed. Answers for (b) will also vary, but may focus on food miles, energy needed to make the food consumed, or whether or not it was meat versus vegetables.

25. Answer: A food mile is a measure of the energy needed just to transport a particular food item from the point of production to the point of consumption. For example, to someone in the Midwestern part of the United States, obtaining a pineapple will use more food miles than obtaining an ear of corn. Pineapples are grown far from the Midwest, but corn is grown directly there.

We can reduce food miles by eating foods that are produced relatively close to where we consume them – the “eat locally” movement. Another options is connected to the flavor tripping notion from Qquestion 23. If we can make local, nutritious foods that does naturally taste goodare more palatable, we may have more options for eating locally!

No matter your option of the importance of reducing food miles, the concept of energy use and its ongoing availability is a factor in this analysis.

26. Answer: Answers will vary, but should focus on the amounts of both wet and dry ingredients, and particularly the amount of eggs, butter, and/or milk as well as the ratio to baking soda or baking powder.

Predictions to different outcomes of the baked goods will also vary, but should focus on sweetness, texture, and crispness.

27. Answer: The Maillard reaction only takes place when there is no measurable water in the cooking environment. On a hot grill, meat will brown because the grill temperatures cause the water on the surface of the meat to evaporate. The meat can then “brown” on the surface. Done properly, this browning seared the surface of the meat and locks moisture inside the meat so that it does not dry out. (With moisture, though, the inside will not brown.) Food items do not brown in boiling water because of the abundance of water in the environment, and food only cooks in the microwave if water is present. Recall earlier questions about how a microwave cooks food.

28. Answer: The taste of the different oils really comes down to its source and the results flavor chemicals of that source. Olive oil tastes differentt than from coconut and canola oils because olives are the source of olive oil and coconuts are the source of coconut oil (. (cCanola oil comes from rapeseed).) The state of the oil at room temperature has to do with its amount of saturated fatty acids. Coconut oil has more saturated fatty acids than either olive or canola oil. Coconut oil is a solid at room temperature whereas olive and canola oils are liquids. This higher amount of saturated fatty acids also means that coconut oil can hold higher temperatures before decomposing and, for health purposes, then, is preferred to lower saturated fatty acid oils for frying and sautéing.

29. Answer: Answers may vary, but a couple common and one more modern and unique ways to brew coffee are: a) Drip coffee makers – here water is drawn up a small tube where it is heated and “showers down on the coffee grounds. As it does so, the coffee oil and other ingredients are extracted from the grounds and fall together with the hot water into a glass reservoir. Repeating this process over and over the grounds, is meant to ensure maximum extraction of the flavor and caffeine ingredients from the grounds. Drip makers vary in cost, but can be as cheap as $25 USD. b) Percolators work by driving boiling water up through a tube that then runs down over the coffee grounds, not unlike the drip coffee maker mentioned in (a). However, the percolator then continues to resend the liquid coffee mixture up and over the grounds. This can be ideal for creating a particular strength to your coffee, but it can also be more susceptible to over-extraction, and making a bitter cup of joe. Percolators can run between $20-$40 USD. c) The Clover Coffee maker still relies on physical extraction of the flavorful chemicals from coffee grounds, however, this equipment uses a series of pumps and pistons to move the temperature-controlled water across the grounds and extracts to form the coffee in

about 40 seconds. Clover Coffee makers currently run at a cost of more than $10,000 USD.

30. Answer: a. Teflon is actually long chain polymer of repeating units of the monomer, C2F4. It is mostly non-reactive due to the strong carbon to fluorine bonds. Even though the Teflon contains fluorine, a highly electronegative element, the arrangement of the fluorine atoms in the polymer cancel each other out and the polymer is nonpolar, making it not want to interact with water. Since nearly all the foods we consume contain some degree of water, cooking with Teflon still allows the heat to transmit but does not cause the food to stick, because the Teflon repels the water in the food. b. Ultimately, the side of Teflon that will “stick” to the pan has to chemically altered in order to get it to bind to the other pan materials. This is done by breaking many of the carbon to fluorine bonds on the side that will stick and making it more chemically conducive to binding to the other pan materials.

31. Answer: Gelatin, the primary component in Jell-O, is a protein that provides structure to the liquid mixture, such that once cooled and/or some water evaporates, the web-like structure of the gelatin molecules allow the material to hold a relatively solid shape. (This is similar to how gluten provides structures for many baked breads and goods.)

Pineapples, kiwi, and papaya fruits contain an enzyme called bromelain, which catalyzes the breakdown of the gelatin protein molecules into its smaller components, its amino acids. These smaller building blocks, when broken apart, cannot provide enough structure to allow the liquid and the Jell-O mixture does not solidify. (Ironically, extracts of these fruits are used as digestive aids, to help us when our bodies are not able to do an effective enough job of breaking down the proteins we consume.)

32. Answer: Essentially, ice cream is both an emulsion (of water and fats, with ingredients that link the two together, traditionally an egg yolk, like in mayonnaise) and a foam (some air is trapped in the solid). In order to get the milk fat liquid emulsions mixture to form, in traditional home ice cream makers, a ice-salt-water mixture was used to surround a canister containing the ice cream mixture. The ice-salt-water mixture created a colder surroundings that just ice and because water is present the surface area of the mixture and thus the contact options for heat transfer from the ice cream mixture to the canister increases. Thus, the liquid ice cream mixture after a short amount of time freezes. For more detailed information try the Thermodynamics of Ice Cream website: https://blog.thermoworks.com/desserts/ice-cream-made-with-

dry-ice/. by David J. Vosen: http://david-vosen.squarespace.com/directions-data-tables/ (accessed September 9, 2016).

33. Answer: Dropping food on the floor does not necessarily make food inedible, but it does come into contact with whatever may be on the floor – dirt, germs, pet hair, etc – and it takes less than five seconds to transfer whatever may be in contact. If the floor that the food was dropped on was clean, however, the food is likely to show no microbial activity as a result of being dropped. More information can be found at the WedMD site: http://www.webmd.com/a-to-z-guides/features/5-second-rule-rules-sometimes-, (accessed September 9, 2016)

34. Answer: Asparagus contains asparagusic acid, which is a sulfur containing acid. When asparagus is digested and its chemical metabolized, new sulfur-containing compounds are formed. In many people, the sulfur containing products of metabolism (such as dimethyl sufide) are malodorous. There are debates as to why some people claim they do not smell this characteristic smell in their own urine after eating asparagus. Scientists are split on the reasons. One camp says they just don‘t produce the malodorous compounds and the other camps says everyone produces the compounds, some people just are not able to detect the scent of those compounds. For more information, go to the Smithsonian.com website: http://www.smithsonianmag.com/science-nature/why-asparagus-makes-your-urine-smell-49961252/?noist (accessed September 9, 2016).

ANSWERS TO END-OF-CHAPTER QUESTIONS CHAPTER 11: NUTRITION

Emphasizing Essentials 1. Answer: Malnutrition is caused by a diet lacking the proper mix of nutrients, even though the energy content of the food eaten may be adequate. Undernourishment is caused by insufficient energy content of the food eaten.

2. Answer: Processed foods have been altered from their natural state in order to extend their shelf life or protect consumers from serious illness, such as those contracted in past generations by drinking raw milk or from improper canning of vegetables. Processing techniques include canning, cooking, freezing, and adding chemical preservatives. Examples may include: baking chocolate (processed), a can of vegetables (processed), milk (processed unless it is directly from the cow), vegetable juice (processed), bologna (processed), orange juice (depends on the type), candy bar (processed), and soft drink (processed). 3. Answer: a. The three different types of macronutrients are fats, carbohydrates, and proteins. b. Fats are the highest in energy content, almost a factor of two higher than carbohydrates and proteins (which are similar in energy content). 4. Answer: Water is a reactant and a product in metabolic reactions. By its evaporation, it also helps to keep you cool. It serves to transport nutrients and to rid the body of unwanted side products. It keeps you (and your cells) hydrated! Water is the solvent for many chemicals needed by the body, including sugars and electrolytes. 5. Answer: The pie chart indicates more carbohydrate is present than would be found in steak, and more protein than would be found in chocolate chip cookies. Of the choices given, the pie chart is likely to be a representation of peanut butter, which has a high oil content. (See Table 11.1 for confirmation.) 6. Answer: a. Chocolate chip cookies, white bread, and cooked black beans are the top three foods on the list ranked in decreasing order by percentage of carbohydrates. b. Tuna fish, sirloin steak, and peanut butter are the top three foods on the list ranked in decreasing order by percentage of protein. c. Peanut butter and chocolate chip cookies.

7. Answer:

18 oz  0.28 = 5.0 oz of protein 18 oz  0.15 = 2.7 oz of fat 18 oz  0.57 = 10.3 oz of water 8. Answer: Fatty acids are smaller molecules than fat molecules, roughly one-third smaller (depending on the particular fat and fatty acid). The reason for the size difference is that fats are triglycerides synthesized from three fatty acids and the 3-carbon “triple” alcohol glycerol. Fatty acids contain the carboxylic acid functional group; in contrast, fats contain the ester functional group. In terms of the role in your diet, you consume fats from many of the foods you eat, both animal and plantbased. In contrast, your foods do not contain fatty acids because these are pretty unappealing to eat alone or in combination with other foods. 9. Answer: a. Here is the structural formula for lactic acid:.

b. As a fatty acid, lactic acid would be saturated because the hydrocarbon chain contains only single bonds between the carbon atoms. c. No, lactic acid is not a fatty acid. Although it has the carboxylic acid group characteristic of a fatty acid, it lacks the long hydrocarbon chain (12–24 carbon atoms). Lactic acid also has a hydroxyl group (—–OH) that is not found in fatty acids.

10. Answer: Unsaturated fats contain one or more C=C bonds in the hydrocarbon chains that were part of the fatty acids from which they were synthesized. In contrast, all the carbon-carbon bonds in saturated fats are single bonds; that is, these carbon atoms are fully “saturated” with hydrogen atoms. Both unsaturated and saturated fats play the important role in your diet of providing an energy source. Intake of saturated fats, however, is linked with a higher prevalence of cardiovascular disease. 11. Answer: a. flaxseed oil

b. safflower oil c. safflower oil d. coconut oil

12. Answer: a. Trans fats are a type of unsaturated fat. They differ from saturated fats because of the C=C bond(s) that they contain. However, trans fats also differ from other unsaturated fats in the way in which the H atoms are arranged around the C=C bond. Here is the difference:

b. Trans fats and saturated fats tend to be solids at room temperature because their long hydrocarbon tails pack well together. Cis unsaturated fats have kinks in their hydrocarbon tails, breaking up the interactions between adjacent chains, and therefore tend to be liquids at room temperature. c. Trans fats are similar to saturated fats in that both raise the levels of “bad” cholesterol in the bloodstream. Unsaturated fats that are cis are, in general, more healthy.

13. Answer: a. Milk (lactose is “milk sugar”) b. Many fruits contain fructose (“fruit sugar”). So does honey. c. Sucrose (“table sugar”) originates from both beets and sugarcane. d. Starch is a primary component of potatoes, rice, tapioca, taro root, wheat, and corn.

14. Answer: a. A monosaccharide is a “single sugar,” that is, a carbohydrate containing only one ring. Examples are glucose and fructose. b. A disaccharide is a “double sugar” and has two monosaccharide rings joined analogous to joining two monomer units. For example, sucrose is formed from the condensation of molecules of α-glucose and β-fructose. c. Polysaccharides are condensation polymers that are formed by joining many monosaccharides. Examples include starch, glycogen, and cellulose. 15. Answer: Both starch and cellulose are polymers in which the monomer is glucose. But the glucose units are hooked together in a different manner. Our bodies possess an enzyme that can digest starch. In contrast, we lack the enzyme that would enable us to digest cellulose. In essence, we can derive nutritional value from a potato but not from a piece of paper.

16. Answer: a. C6(H2O)6. By grouping water as a unit, this chemical formula emphasizes the idea that carbohydrates are “carbon plus water.” However, this idea is not correct in that fructose contains no water molecules as such. b. Here is a structural formula for one of the isomers of fructose, α-D-glucose.

c. Like the isomers of sucrose, each isomer of fructose has a slightly different fit with the taste receptor sites in your tongue. As a result, the different isomers each have a somewhat different taste. 17. Answer: See Section 11.4 and Figure 11.11 for the chemical structures of fructose and glucose. Observe that the chemical structure of fructose is based on a five-membered ring composed of 4 C atoms and 1 O atom. In contrast, the chemical structure of glucose is based on a six-member ring composed of 5 C atoms and 1 O atom. Glucose has one —–CH2OH side chain, and fructose has two.

18. Answer: The relative sweetness value of sucrose is 100 and the relative sweetness value of sucralose is 600. Since sucralose is approximately six times sweeter than sucrose, it should only take 1/6 of the amount of sucralose to match sucrose‘s sweetness. One-sixth of 1 g is about 0.17 g, so it should take 0.17 g of sucralose to be equivalent to sucrose. 19. Answer: The “amino” in amino acid indicates that there is amine functional group present. The “acid” indicates there is an acidic functional group, in this case, a carboxylic acid. 20. Answer: The amide functional group, formed by the reaction of a carboxylic acid and an amine, is shaded in blue in Equations 11.3a and b4. It also is reproduced in the answer of the next question. a. The functional groups in an amino acid, the building block of proteins, are the carboxylic acid group and the amine group. In contrast, nylons are typically made from two monomers. One has two carboxylic acid groups and the other has two amine groups. Here are two examples from Chapter 9, adipic acid (a “double” carboxylic acid) and hexamethylenediamine (a “double” amine):.

b. The differences between proteins are striking! Consider, for example, how hemoglobin in the bloodstream differs from hair which in turn differs from muscle fiber. The properties and functions of the many proteins in your body differ widely. Proteins are able to take on such different characteristics because they are formed from amino acids that have different side chains (the “R groups”). In essence, these side chains give proteins their different “personalities.” In contrast, most nylons are fairly similar to each other. All are strong fibers, waterproof, and reasonably heat- resistant. The reason for the similarities is that the monomers show only a small amount of variation. Although the nylon monomers may differ in the number of carbon atoms and how they are bonded, they still are chemically quite similar.

21. Answer: Analogous to Eequation 11.34:

22. Answer: Essential amino acids are those required in our bodies for protein synthesis that must be obtained from the diet because the body cannot synthesize them. 23. Answer: Phenylketonuria (PKU) is a disease in which people lack the enzyme necessary to metabolize phenylalanine, an amino acid. Without the enzyme, phenylalanine accumulates in the body and eventually causes problems in brain development. People who are phenylketonurics must carefully limit their intake of foods rich in proteins. Although aspartame is a sweetener, it is a dipeptide of aspartic acid and phenylalanine, as shown in Figure 11.18. Sucralose, with a chemical structure not related to amino acids, does not pose any risk to people with this disease.

24. Answer: The elements shaded in the diagram (sodium, magnesium, phosphorus, sulfur, chlorine, potassium, and calcium) are all macrominerals required in our diets. You may recognize the role that calcium and magnesium play in building strong bones and teeth; similarly, the role that sodium and potassium play as electrolytes in our bloodstream. 25. Answer: The two methods are increasing crop yields (for example, fertilizers) and devoting more land to agriculture (for example, deforestation).

26. Answer: Both what you eat and how much you eat affect your health. Some examples connect to common sense. For instance example, excessive food intake correlates with obesity; a diet rich in sugars and fats is high in calories and thus is not a wise choice for those whose activity level does not require it. Less obvious is the effect of food choices on ecosystems and water use. As this chapter points out, eating beef that is corn-fed and then sent to slaughter connects to both local degradation of the land (corn usually is grown with relatively high use of herbicides and fertilizers) and regional deterioration of the water ways (in the U.S., check the effluent of the Mississippi River into the “Dead Zone” in the Gulf of Mexico). Other examples of how your food choices affect the health of a region include (1) the effects of irrigation (depletion of aquifers, rivers drying up downstream), (2) the loss of forests when creating farmland, and (3) the type of energy used to plant, grow, and harvest a particular crop and the waste products of this energy. 27. Answer: Several answers are possible. For example, food production may diminish water quality through the amount of: (1) water required for irrigation that may deplete aquifers, causing more salty water to seep in, (2) fertilizers used, which may run off into waterways providing excess nutrients that promote algal blooms, (3) herbicides and insecticides used that may contaminate local streams and rivers, and (4) draining of wetlands that serve as natural filters for water.

28. Answer: In the case of beef, it usually requires grain to feed the animals. In turn, the grain requires land, water, fertilizer, and energy to produce. Depending on the individual farmer‘s practices, it also requires varying amounts of land to pasture or graze the animals. Raising pigs and chickens also requires land and water, although in general less because these animals also can eat food wastes and insects. 29. Answer: a. Reactive nitrogen refers to the chemical species of nitrogen that cycle relatively quickly through the biosphere and interconvert via several pathways. b. Atmospheric nitrogen gas (N2) is an unreactive form of nitrogen. c. A natural source of reactive nitrogen is nitrogen-fixing bacteria in soils. An unnatural source of reactive nitrogen is synthetic fertilizers from the Haber-Bosch process.

Concentrating on Concepts 30. Answer: Answers will vary, based on student‘s food consumption and overall diet comparison to Figure 11.2.. 31. Answer: To a chemist, all food is composed of chemical compounds (“chemicals”). These include fats, carbohydrates, proteins, minerals, and water. As a result, it is impossible to go on a “chemicalfree” diet. Admittedly, though, the term “chemicals” is commonly taken to mean “added chemicals” or perhaps even “bad chemicals.” An “all organic” diet is possible, though, and most organic foods strictly limit which chemicals can be used in raising the crops and can be added during food processing. 32. Answer: a. True only in some circumstances. Compared to animal fats, plant oils (e.g., olive oil and canola oil) tend to be lower in saturated fat. However, a few oils, notably palm oil and coconut oil, are higher in saturated fat. b. True. All edible oils and fats become rancid over time if exposed to the oxygen in the air. Fats go rancid more slowly than oils, though, because fats are more highly saturated, that is, fats have fewer C=C bonds. c. False. Our diet must provide some fat because our bodies cannot synthesize all of the essential fatty acids (notably linoleic and linolenic acid). 33. Answer: In terms of food chemistry, hydrogenation is the process of “adding hydrogen” to an unsaturated molecule to make it saturated (or more highly saturated). On a molecular level, in hydrogenation a molecule of H2 is “added” to a C=C double bond to form two new C–H bonds. Partial hydrogenation is the case in which some of the C=C bonds are hydrogenated, but not all of them. The manufacturers are required to report this, as these are two different chemical substances (i.e., partially hydrogenated soybean oil is different from soybean oil). These substances have different properties and different effects on your health. 34. Answer: Trans fats both increase the “bad” cholesterol and decrease the “good cholesterol.” In essence, this is a double whammy.

35. Answer: The process of hydrogenating an oil to “add H atoms” converts some of the C=C double bonds in the oil to C-C single bonds. This is desirable in that it improves the shelf-life of the product (and sometimes the spreadability as well). However, hydrogenation produces trans fats as a sideproduct, a drawback, because trans fats both increase the “bad” cholesterol and decrease the “good” cholesterol. Interesterification also reduces the number of C=C double bonds but accomplishes this in a way that does not produce trans fat. 36. Answer: a. The process of interesterification used sodium hydroxide, a strong base. The use of NaOH raised worker health concerns and also presented a disposal hazard. b. The solution, developed by Novozyme and Archer Daniels Midland Company, was to use a process that used enzymes instead of the sodium hydroxide catalyst. c. This addresses green chemistry principle #3: It is better to use and generate substances that are not toxic. 37. Answer: Based only on the percent of saturated fat in coconut oil relative to the butterfat in cream, this is not a good plan. Coconut oil is 87% saturated fat, but butterfat is only 63% saturated fat. However, if a person uses a smaller quantity of the non-dairy creamer than of cream, his or her total amount of saturated fat consumption may be reduced. 38. Answer: While it may be advantageous to limit the amount of sugars and fats that you consume, limiting the proteins that you eat generally is not a concern. Furthermore, sugars are all sweet so any other sweet compound can substitute for them. In contrast, proteins are so varied in flavor and texture that one substitute would not be sufficient. Even so, meat-like protein substitutes are on the market derived from plant proteins like soy or gluten. People desiring the texture of meat without consuming animal protein will purchase them, but they are very often not a low fat or calorie alternative.

39. Answer:

According to Table 11.1, peanut butter is a good source of protein but is high in fat/oil, which in this case is peanut oil. On the positive side, unless the peanut butter has been hydrogenated, peanut oil is largely unsaturated, as shown in Figure 11.7.

40. Answer: The fast food meal described contains 1230 Calories. According to Table 11.7, the average energy content of fat is 9 Cal/g. The 16.5 grams of saturated fat contribute 149 Calories to the meal‘s total Calories, or 12%. The meal exceeds the guidelines.

41. Answer: a.

1.5 g fat 

9 Cal

 10 Calories fromfat

g fat 17 g carbohydrate 

4 Cal

 70 Calories from carbohydrate g carbohydrate 4 Cal 3 g protein  10 Caloriesfromprotein g protein

The total number of Calories is 90 Calories per slice of bread. 10 Cal 100  11% b. The percent Calories from fat is 90 Cal Note: To one significant figure, this would be 10%, something worth keeping an eye on, but that we have not emphasized in this textbook. c. One slice of whole wheat bread qualifies as a nutritious food because it provides a serving of whole grains with few additional calories from sugars and fats. Remember that if one slice of bread counts for one serving, then a sandwich counts as two servings.

42. Answer: Many possibilities exist for answering this question, starting with the seeds used to grow the crop. These need to be harvested, dried, packaged, shipped to the grower, and planted. Similarly, preparing the soil is likely to require energy from fossil fuels. To be prepared for planting, the soil may need to be tilled, possibly fertilized, watered, and weeded. Once the agricultural crop is ripe, it needs to be harvested, perhaps washed, dried, or packaged and then shipped either to market or to a processing plant. Any or all of these steps may require fossil fuels, depending on the particular crop and soil type. Eating locally may reduce the amount of fossil fuels used in

shipping the crop to market, but not necessarily if the crop is first shipped to a distant processing plant before going to market.

43. Answer: a. Carbohydrates b. Possibilities include corn, sugarcane, and tapioca. c. Digesting the starch to make glucose, fermentation of the glucose to produce ethanol, and distillation of the ethanol. See Section 65.15 for more details. d. One controversy involves the energy costs. The energy gained by burning ethanol in an engine may be less than the energy inputs to produce it. Another controversy involves the environmental costs of growing corn and cutting down forests to produce sugarcane.

44. Answer: a. Triglycerides (fats), especially oils. b. Possibilities include soybean oil, rapeseed oil, and palm oil. Used cooking oil also works. c. Converting the oil (a triglyceride) to fatty acid esters by reacting it with a catalytic amount of sodium hydroxide. d. Like ethanol, one controversy involves the environmental costs of producing palm oil, especially in Malaysia. Additionally, there may be costs to the local communities that supply the palm oil, depending on land and labor practices. See Section 5.17 for more details. Exploring Extensions 45. Answer: Answers will vary, but could include eating lower calorie food, eating a greater variety of food, buying locally -grown food, and eating less resource-intensive food such as red meats.

46. Answer: Although the fat in avocados varies by type of avocado, primarily it is monounsaturated fat. The

fatty acid from which this fat is synthesized is oleic acid (see Section 11.2). Monounsaturated fats are more “heart healthy” than saturated fats, promoting healthy cholesterol levels. Similarly, olive oil (touted for its health benefits) is high in monounsaturated fat (see Figure 11.7).

47. Answer: Assumptions made in your estimate might include: (1) the number of days a year you drink soft drinks (non-diet), (2) the volume you drink or the packets of sugar you add to coffee or tea, and (3) the type of soft drink and grams of sugar it contains.

48. Answer: a. Although Sunkist orange soda has the highest ratio of the number of grams of sugar to the number of Calories (0.274), Dr Pepper (0.267) and Delmonte Pineapple Cup (0.260) rank a close second and third. b. Some people are surprised at the high sugar content of soft drinks. They may also be surprised to know that Twinkies and Snickers bars have less sugar per gram than soft drinks. Some people may not have realized that Altoids mints contain sugar. c. In the case of soft drinks, it is hard to predict because the sugar depends on the manufacturer. In general, though, soft drinks are sweetened with high-fructose corn syrup so the types of sugar are likely to be the same. The fruit and fruit juice are expected to differ from the Dr. Pepper because fruits and fruit juices do not contain high-fructose corn syrup. Rather, they typically contain fructose, glucose, and several other sugars. d. Starch filler compounds could account for the other 1 g of carbohydrates. 49. Answer: a. There are zero Calories in a packet of Splenda. b. Splenda is made from sucrose by selectively replacing three of the ——OH groups with ——Cl groups to produce a molecule that is 600 times sweeter than sucrose. It is made from sugar but is an entirely different chemical compound. 50. Answer: a. With its long hydrocarbon tail, vitamin K is expected to be fat-soluble. b. An important role of vitamin K is in blood clotting, but the vitamin plays other roles as well, including in the kidneys and bones.

c. Although many foods contain vitamin K, including dark green leafy vegetables, egg yolks, liver and cheese, there is another reason why we have adequate supplies in our bodies. Bacteria in our large intestine synthesize it for us.

51. Answer: a. As you can see from the pie charts, soybeans are higher in protein (~35%) than wheat (~13%). Soybeans can be used to produce many different food products, including soy milk, textured vegetable protein, and tofu. b. People in some cultures, particularly in Asian countries, are accustomed to obtaining their protein from soy. The taste of soy-based beverages or other foods is familiar and in widespread use, which would increase its appeal and acceptance. 52. Answer: One way in which these connect is water use. Raising crops depends on long-term rainfall patterns which in turn is a function of climate. A second way in which these connect is energy use. Fossil fuels are burned as we grow, process, package, and transport foods. Burning fossil fuels releases carbon dioxide, a greenhouse gas. A third way in in which these connect is land use. As we drain wetlands and cut down forests to plant crops, we remove areas that effectively have sequestered carbon for perhaps thousands of years.

53. Answer: For updates of U.S. ethanol production, the Renewable Fuels Association web page is a useful place to start (http://www.ethanolrfa.org/pages/statistics#A, accessed July 2016). Ethanol is produced primarily from corn in the United States. Keep an eye out for any evidence that cellulosic ethanol (such as switchgrass or another non-food feedstock) has begun commercial production. Look for new estimates and carefully assess the assumptions behind these estimates. Finally, the Triple Bottom Line judges whether a business operation has benefits to the economy, the environment, and to the society. These benefits (or lack thereof) are relevant to U.S. ethanol production.

ANSWERS TO END-OF-CHAPTER QUESTIONS CHAPTER 12: HEALTH AND MEDICINE

Emphasizing Essentials 1. Answer: a. Biochemists study the chemical and physical basis of events in biology. b. Organic chemists study the chemistry of carbon compounds.

2. Answer: a. As the K < 1, this means that the reactant (here, glucose) is favored over the product (here, fructose). b. For a system at equilibrium, the ratio of K 

[fructose]

0.74. As we know the concentration of

[glucose]

glucose, we can solve for the concentration of fructose using the formula:

[fructose] 0.74 0.22 mM [fructose] 0.74 0.22 mM [fructose] 0.16 mM

3. Answer: a. For this reaction at equilibrium,

. If we suddenly decrease the amount of A by half, some of

substance B will convert back into A in order to return to equilibrium. b. For this reaction at equilibrium,

. If we suddenly double the amounts of both A and B, the

sample will still be at equilibrium as the increase is balanced in both reactants and products.

4. Answer: In the figure, the AB complex is in the position of the reactants leading to A free and B free as products.

[A free][B free] K [AB complex]

5. Answer: a. Sodium nitrite (NaNO2) would serve as a good salt to prepare a buffer solution with nitrous acid. b. If a base (OH-) were added to the NaNO2/HNO2 buffer, the acid (HNO2) would react with it. c. The pH would be slightly higher than its initial value; in contrast, if water were added, the pH would not change.

6. Answer: a.

pH = pKa + log pH = pKa + log

[conj. bBase] [wk acid] [formate]

[formic m. aAcid] [0.1 M]

pH = pKa = 3.8 + log

[0.05 M]

= 4.1 [0.1M] pH = 3.8 + log = 4.1

[0.05M]

[NH3]

pH = pKa + log

[NH 4 Cl]

pH = 9.3 + log

[0.1M] [0.2M]

= 9.0 c. C. pH = pKa + log

[acetate]

[acetic . acid]

log

pH = 4.8 + (log

[0.1M] ) [ 0.1M]

= 4.8 7. Answer: There are 5 different isomers. Shown belowHere are the structural formulas and line-angle drawings. The hydrogen atoms on the structural formulas have been omitted for clarity.

C C C C C C

8. Answer: For the chemical formula C4H9OH, four isomers exist that contain an -—OH group. Shown belowHere areare the structural formulass for each isomer. The hydrogen atoms have been omitted for clarity.

9. Answer:

contains the

10. Answer:

contains the

functional group and is an ether.

functional group and is a carboxylic acid.

functional group and is a ketone.

functional group and is an amide.

functional group and is an ester.

One-carbon examples exist for alcohol, aldehydes, and carboxylic acids. The other functional groups require more than one C atom. a. Alcohol. The simplest compound is methanol, CH3OH. b. Aldehyde. The simplest compound is methanal (commonly called formaldehyde), CH2O. c. Carboxylic acid. The simplest compound is methanoic acid (commonly called formic acid), HCO2H. d. Ester. The simplest compound has 2 carbon atoms: HCOOCH3. It is called methyl methanoate or methyl formate (but these names may be beyond the scope of your study). e. Ether. The simplest compound is dimethyl ether, CH3OCH3. f. Ketone. The simplest compound is dimethyl ketone (commonly called acetone), CH3COCH3.

11. Answer: a. The compound is an alcohol (ethanol). An isomer with a different functional group is an ether.

b. The compound is an aldehyde (propanal). An isomer with a different functional group is a ketone.

c. The compound is an ester (propyl formate). An isomer with a different functional group is a carboxylic acid.

12. Answer: a. The chemical formula is C5H9N3. b. The amine functional group, –NH2, is present in histamine.

c. The molecule‘s most polar region will be around the amine group. This can easily take on a proton in water and (particularly when charged) will be the principal part of the molecule that interacts with polar water molecules.

13. Answer: In examining the structure of estradiol, the steroid core has many hydrophobic elements and very few polar groups. Overall, the molecule will be predominantly hydrophobic and prefer hydrophobic organic solvents to water. 14. Answer: a. H C N b. C O

is the molecule of one carbon, one oxygen, and as few hydrogen atoms as possible though it shows both carbon and oxygen forming nonstandard numbers bonds for both atoms. For a molecule that has one carbon making four bonds, one oxygen making two bonds, and a minimal number of hydrogen atoms:

15. Answer: a. This compound cannot exist in chiral forms. The central carbon atom is bonded to two equivalent – —CH3 groups. b. This compound can exist in chiral forms. The four groups attached to the central carbon atom are all different. c. This compound can exist in chiral forms. The four groups attached to the central carbon atom are all different. d. This compound cannot exist in chiral forms. The central carbon atom is bonded to two equivalent – —CH3 groups. 16. Answer: a. This compound can exist in chiral forms because there are four different groups attached to the central carbon atom.

b. This compound cannot exist in chiral forms because there are two equivalent groups, ( –H, a hydrogen atom) attached to the central carbon atom. c. This compound can exist in chiral forms because there are four different groups attached to the central carbon atom. d. This compound can exist in chiral forms because there are four different groups attached to the central carbon atom. 17. Answer: Hormones are chemical signals produced in the body to regulate many physiological events, such as the metabolism of food (insulin), our response to sudden or dangerous events (adrenaline), and many others. Receptors are the proteins that bind to these hormones to transfer the information in that chemical signal. A chemical without a switch to flip will not serve a purpose. Similarly, a protein receptor without a chemical to activate it will be passive. 18. Answer: Answers will vary. Nonpolar amino acids include valine, leucine, isoleucine. All nonpolar amino acids will have side chains of only carbon and hydrogen elements without enough electronegativity difference to make polar bonds. 19. Answer: While all amino acids have a carboxylic acid functional group, they are not all acidic. Only aspartic and glutamic acids are categorized as acidic amino acids. The side chains include carboxylic acids.

20. Answer:

21. Answer:

a. n-propanol, CH3CH2CH2OH

b. isopropanol, (CH3)2CHOH

c. t-butanol, (CH3)3COH

22. Answer: Morphine contains alcohol, ether, and amine groups. Meperidine contains ester and amine groups. Because each compound contains more than one functional group, neither can be assigned to a unique class of compounds. 23. Answer: A pharmacophore is the three-dimensional arrangement of atoms, or groups of atoms, responsible for the biological activity of a drug molecule. 24. Answer: Sulfanilamide has the same basic shape and contains similar functional groups in the same regions as para-aminobenzoic acid, so it replaces the nutrient in some biologically important process. Without the key nutrient, the bacteria die. Concentrating on Concepts 25. Answer: The equilibrium constant only shows you whether the reactants or products are at a lower energy level. That constant does not provide any information about the barrier in between the two. To be more technical, the equilibrium constant provides information about the realm of thermodynamics rather than kinetics. 26. Answer: For each graph, the student should show a slowed transition with a midpoint at the point where the pH is equal to the pKa of the weak acid as shown in Ttable 12.1. a. transition at pH = 4.8 b. transition at pH = 9.3

c. two transitions must be evident, one at pH = 6.3 and 10.3. 27. Answer: a. Four single bonds, 1 triple bond

b. Six single bonds, 1 double bond

c. C6H5COOH (benzoic acid) has this structure. O C OH

The carbon atom in the carboxylic acid group is attached to one oxygen atom with a double bond, to the oxygen atom in the OH group with a single bond, and to the carbon atom in the ring with a single bond. The carbon atoms in the ring use single and double bonds to attach to other carbon atoms in the ring. Each carbon atom in the ring also shares a single bond with a hydrogen atom (not shown) with the exception of the ring carbon that is bonded to the carbon in the carboxylic acid group. 28. Answer: Only three isomers are shown here; some structures are duplicates. #1 and #5 are different representations of the same isomer. #2, #3, and #4 are all representations of the same isomer. #6 is an isomer different from #1 and #5, and from numbers #2–4.

29. Answer:

30. Answer: a. The chemical formula is C16H21N3. b. Both compounds have nitrogen-containing rings, but they are not the same size rings. The major structural similarity is the presence of the

CH2 CH2N

group, which is likely the part

of each molecule that competes to attach to the receptor site. 31. Answer: Functional groups are able to make the ionic bonds, hydrogen bonds, and other categories of energetic interactions that provide stability and specificity to the interaction of substrate to an enzyme. 32. Answer: To be specific enough for biochemical binding, functional groups must be pointed in the correct directions. Enzymes are very good at discriminating between chiral molecules.

33. Answer: a. The cellular membrane if primarily composed of lipids. b. Glycogen is a polymer of glucose, specifically a polysaccharide or, more commonly, a carbohydrate. c. Enzymes are protein-based catalysts. 34. Answer: Enzymes decrease the barrier against a process, but do not change the end points.

35. Answer: The messengers of the chemical communication system are hormones manufactured for that specific purpose in certain cells. The hormones travel from the cell where they are made through the bloodstream to receptor sites found on the plasma membrane of the target cells. 36. Answer: The analogy compares the receptor site on the surface of a cell to a lock that can only be opened by a unique key. Drug molecules can only bind to receptor sites that match the molecule‘s geometry. 37. Answer: Student answers will vary. Example answers include things simple pliable objects such as clay that we are able to mold around an object to fit match the required interaction and create a strong, yet malleable match. 38. Answer: a. Aspirin produces a physiological response in the body. b. Antibiotics kill or inhibit the growth of bacteria that cause infections.

c. Morphine produces a physiological response in the body. d. Estrogen, a hormone, produces a physiological response in the body. e. Penicillin kills or inhibits the growth of bacteria that cause infections. 39. Answer: Section 12.10 discusses many of the tests that we can use to detect effective versus ineffective or harmful responses to drugs including tests on specific proteins in isolation, model mammalian cells, and model test animals. 40. Answer: a. The codeine structure has two ether groups, an alcohol group, and an amine group:

. b. No, comparison of only two drugs is not enough evidence to draw general conclusions about the role structural changes play in determining drug effectiveness and addictiveness.

41. Answer: The drug ()-dopa is effective because the molecule fits in the receptor site, but the nonsuperimposable mirror image form, (+)-dopa, does not. This is ()-dopa with the chiral carbon atom marked in red. Note that there are four different groups attached to the starred carbon atom.

Exploring Extensions 42. Answer: Lysine and aspartic acid are able to change charge with pH. Lysine‘s side chain will act like a base and pick up a proton to make a positively -charged side -chain. Aspartic acid can lose a proton from it‘s side chain to make a negatively-charged side -chain. For both of these a pH buffer may help these side -chains to stay at a predictable charge state.

43. Answer: a. There are 6(4) + 6(1) or 30 electrons available. Here is the structural formula of a possible linear isomer for benzene:

b. Here is the condensed structural formula: CH2=C=CH– CH=C=CH2 c. First, check to see if all of the structures correctly represent C6H6 and that each carbon has four bonds. If these conditions are met, the structures with double bonds should differ only in the placement of the lone C–C single bond. However, structures including carbon-carbon triple bonds can also be drawn; these would be distinctly different.

44. Answer: Thalidomide‘s two optical isomers have very different effects in the body. One isomer treats nausea and the other produces mutations in babies born to women who take the drug early in pregnancy. Unfortunately, the body can convert each isomer into the other. When the German maker of thalidomide applied to the FDA for approval to market the drug in the US in late 1960, their application was rejected repeatedly due to a lack of data proving the safety of the drug. In 1998, the FDA approved thalidomide for the treatment of skin lesions caused by leprosy, provided patients are not pregnant and take precautionary measures to avoid becoming pregnant while on the medication. 45. Answer: Lactose, maltose, and sucrose are very similar, but with slight differences structurally (see images below). While each is the same size of sugar, the differences in structure would make them (in the lock-and-key analogy) not fit in the same active site. An individual could have the enzymes that match maltose and sucrose, but lack the one to handle lactose.

46. Answer: Student answers will vary, but the molecule of the month archive includes a number of metabolic enzymes—all necessary to convert degrade, digest, or store the molecules that we consume. The enzymes include hexokinase which is unique for its shape shifting to lock water out of the active site and ATP synthase which uses a remarkable mechanical rotation to harvest energy. 47. Answer: Information on Presidential Green Chemistry Challenge Awards are collected online. The companies were collaborated to develop a novel synthesis incorporating an evolved enzyme. The prior synthetic route required high-pressure, expensive metals, and a costly purification step that now can be eliminated. This matches our understanding of the utility of enzymes as biological replacements for organic synthetic steps. If selected correctly, they can do the reaction at lower temperature and with less solvent waste. See the EPA award site for more information: https://www.epa.gov/greenchemistry/presidential-green-chemistry-challenge-winners. (accessed July 2016). 48. Answer: As a class of molecules, steroids are highly hydrophobic. The steroid core is a large molecule with primarily carbon and hydrogen. In contrast, our blood is primarily water. This means that the steroid molecules will not dissolve well in our blood. Carrier molecules could bind steroids and block the hydrophobic regions from interaction with water to stabilize them. 49. Answer: Here is the structure of RU-486:.

Students should note the distinctive steroid framework in this molecule. This topic will obviously lead to highly politicized websites and a careful set of search terms will be required to get an unbiased source of information. For more information, see the The FDA source: is the most obvious source (http://www.fda.gov/drugs/drugsafety/postmarketdrugsafetyinformationforpatientsandproviders/ucm1 11323.htm. Another online , accessed September 2013), but good resources for this reportthis drug also include review articles available for free public access on pubmed.org, such as is: http://www.ncbi.nlm.nih.gov/pubmed/9418681. (accessed September 2013). An important part of the report should note that although commonly used, aspirin has significant side effects and was never subjected to the FDA standards applied today. Perhaps it should not be the most reassuring of comparisons.

50. Answer: Research done on the Internet will likely lead to several sources of information about cyclosporine, its discovery, and its use. The National Kidney Foundation website has information about this drug, as it is widely used to help prevent rejection after kidney transplant. To learn more about the discovery of cyclosporine, check out http://www.davidmoore.org.uk/Sec04_01.htm.http://www.world-offungi.org/Mostly_Medical/Harriet_Upton/Harriet_Upton.htm or http://www.emedicine.com/med/topic3497.htm. (accessed October 2010)

To learn more about the designing of analog drugs, visit this site: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5770353/..

51. Answer: The life of Dorothy Crowfoot Hodgkin (1910-1994) is documented in several biographies. An interesting website is: http://www.sdsc.edu/ScienceWomen/hodgkin.html (accessed July 2016). Dorothy was born in Cairo, Egypt, where her father was in the Ministry of Education and administered archaeological sites. Her mother was a self-taught botanist. Dorothy was well-educated at Oxford and together with her mentor, J. D. Bernal, first applied X-ray diffraction to crystals of biological substances, including pepsin, penicillin, cholesterol, and later insulin. Hodgkin was elected

a Fellow of the Royal Society in 1947 after publishing the structure of penicillin and was awarded the Nobel Prize in Chemistry in 1964 for solving the structures of important biomolecules, such as vitamin B-12. In the words of colleague Max Perutz (Nobelist for his solution of the hemoglobin molecule structure), she was “a great chemist, a saintly, gentle and tolerant lover of people, and a devoted protagonist of peace.” 52. Answer: The structure of Cipro (ciprofloxacin):

This compound contains three amine groups with various substitutions, one ketone group, one carboxylic acid group, a benzene ring, and a cyclopropyl group. 53. Answer: Expiration dates are the last date that the pharmaceutical company can ensure 100% potency and safety of the drug. If a drug isn’t at full potency, it can cause damage by not fully treating a disorder. According to the FDA, testing is done to show stability of a drug during the approval stage. It looks at strength, quality, and purity over time.

54. Answer: Drugs are considered to be unsafe by the FDA unless proven otherwise through clinical trials. Manufacturing of the drug is then also carefully monitored and specific details are included in the packaging. The FDA also follows the drug after its release to note any issues. The opposite is true for supplements. They are considered safe until proven otherwise. Source: https://www.cancer.org/treatment/treatments-and-side-effects/complementary-and-alternativemedicine/dietary-supplements/fda-regulations.html

ANSWERS TO END-OF-CHAPTER QUESTIONS CHAPTER 13: GENES AND LIFE

Emphasizing Essentials

1. Answer: Traits that are determined by an individual‘s DNA include hair and eye color, fingerprints, and the shape of your earlobes (attached or hanging). Several other answers are possible for this question. Some traits, such as body type, will result from diet and environment as well as your genes. 2. Answer: Farming and medicine are the most obvious industries that have changed, as seen throughout this chapter, but other options are available. Plastics and recycling are also changing due to new methods for making materials with enzymes. Proposed answers can include the fuel industry with increasing biofuels development. 3. Answer: A genome is made up of all the genetic information in a cell while a gene is a small subsection of the genome that codes for a single protein. 4. Answer: a. The base adenine has an amine group (—NH2) in addition to a number of other nitrogen atoms bonded to carbons. b. The sugar deoxyribose has several hydroxyl groups (—OH) and an ether (—O—). c. The deoxyribose molecule is a carbohydrate comprised of carbon, oxygen, and hydrogen atoms, while adenine contains carbon, nitrogen, and hydrogen. 5. Answer: a. A nucleotide links a nitrogen-containing base, a sugar, and a phosphate group. b. Covalent bonds hold the units together. 6. Answer: At pH ~8 in the mitochondria, only two species of phosphate ions will dominate the equilibrium. HPO4 2– will be ~85% and H2 PO4 – will be ~15% of the phosphate ions.

7. Answer: Similarities: All four bases have nitrogen atoms within their ring structures and can participate in hydrogen bonding interactions. Also, the rings contain several double bonds. Differences: The bases differ in the number of rings they contain and the number of hydrogen bond interactions they can form. Adenine and guanine both contain two rings. Cytosine and thymine have one ring each. Guanine and cytosine form three hydrogen bonds while adenine and thymine form two hydrogen bonds.

8. Answer:

9. Answer: a. Nucleotides polymerize to form DNA when the phosphate group from one nucleotide reacts with the hydroxyl group on another nucleotide. The nucleotide shown has two hydroxyl groups. The one closer to the phosphate group is the correct site for polymerization, similar to DNA. The second hydroxyl group results in the significant chemical instability seen in this DNA-related polymer.

b. In the name DNA, the D stands for the deoxyribose in deoxyribonucleic acid. The name for the polymer built with ribose instead is RNA for ribonucleic acid.

10. Answer: a. DNA stands for deoxyribonucleic acid with the D for deoxyribose, N for nucleic, and A for Acid. b. The name highlights the deoxyribose sugar, the acidic nature of the phosphate groups, and the fact that DNA is a chain of nucleotides.

c. The name does not highlight the amines important in the bases. Nor does the name suggest the polymer nature of DNA, in contrast to polyamides or polyesters. 11. Answer: a. The hydrogen atoms that can hydrogen bond with water molecules are those covalently bonded to nitrogen atoms within the ring. b. The difference in electronegativity between H and N is large enough to establish a polar covalent bond. The hydrogen end of this bond is partially positive, allowing it to form a hydrogen bond with partially negative atoms, such as the oxygen atom in water molecules. H and C do not have enough of an electronegativity difference to create a hydrogen bond. c. The oxygen atoms as well as both nitrogen atoms have lone pairs available to hydrogen bond, though not all of these will hydrogen bond in the double-helix form of DNA. 12. Answer: Sequences are always read in one direction. On paper we read each sequence from left to right to determine which amino acid it codes for. Chemically, the directionality comes from the specific order of bonds connecting the alternating sugars and phosphates in the backbone. Although the second sequence in this question is simply the reverse of the first base sequence, it would code for a different amino acid. (ATG codes for methionine; GTA codes for valine). 13. Answer: a. The complementary base sequence is ATAGATC. b. Your answer should have two lines between each A and T and three lines between each C and G in the sequence:.

14. Answer: a. Below is the general formula for an amino acid, where R represents a side chain that is different in each of the 20 amino acids:.

b. The functional groups are —COOH, the carboxylic acid group, and —NH2, the amine group.

15. Answer: Each codon consists of a three-nucleotide sequence that is specific for an amino acid or the start/stop of protein synthesis. All of the codons together make up the code for translating a sequence of DNA into the amino acid sequence of a protein. 16. Answer: a. All amino acids must follow the same general structure (see image below). Only the R group varies between acidic, basic, and neutral amino acids. Correct example R groups for each category include:

Acidic = glutamic acid (–CH2CH2COOH) Basic = lysine (–CH2CH2CH2CH2NH2) Polar neutral = serine (–CH2OH) b. All three categories can make hydrogen bonds, but only acidic and basic amino acids can also make ionic bonds. c. Acidic amino acids have carboxylic acids within their R-groups, while basic amino acids often have amine groups. Neutral amino acids may contain hydroxyl groups or amides in their side chains. 17. Answer: The primary structure is the sequence of amino acids comprising the protein chain. The secondary structure describes the arrangement and local interactions of short segments of the protein chain. The protein‘s tertiary structure, or overall shape, is formed when residues far apart in sequence interact to bring them close in space.

18. Answer: Only a minor change in the amino acid composition of human hemoglobin leads to sicklecell anemia. In the hemoglobin S chain, a nonpolar valine replaces a specific charged glutamic acid in the sequence. This seemingly innocuous change in the protein‘s primary structure dramatically affects the shape of the protein. The tertiary structure must change to accommodate the change in its side chain; the nonpolar valine cannot positively interact with water or other polar groups in the same ways as glutamic acid. The change in protein shape leads to sickled red blood cells (under certain conditions) and a number of health problems.

19. Answer: Both selective breeding and genetic engineering are techniques to create a plant with certain desired traits. Selective breeding results in a plant with a mixture of traits from both parents while genetic engineering transfers only specific traits to the final plant. Also, selective breeding requires the parents to be similar enough to breed while genetic engineering can take traits from a wide array of organisms.

20. Answer: Enzymes have many benefits over traditional organic synthesis reactions. The ability to bind and coordinate reactants as well as the control they exert over the reaction process means that they can often do the same transformation (1) with fewer toxic chemicals so less harmful waste is produced, (2) at a lower temperatures so that less energy is required for the reaction, and (3) while keeping them enzyme reusable for later transformations.

Concentrating on Concepts 21. Answer: The steps for both actually have a number of parallels. Both require a source that is grown in the lab or in the animal and at least some purification steps before the final medicine.

22. Answer: a. The phosphates and sugars combine to form the backbone of the DNA molecule. In Figure 132.4, these can be found along the left. b. The nitrogen bases hang off the backbone, never connecting to each other. In the figure, these are found along the right. c. In Figure 132.6 the backbone is represented with ribbons that use “s” and “p” to represent the alternating sugar and phosphate groups. The nitrogen bases are shown as colored hexagons hanging off these two ribbons. The sculpture at the beginning of the chapter represents the backbones with the silver coils without distinguishing sugars from phosphate. The bases between the coils are represented with colored plastic pieces for each type of base. 23. Answer: Adenine-thymine base pairs are less stable than cytosine-guanine base pairs because they have fewer hydrogen bonds holding them together.

24. Answer: a. In the electromagnetic spectrum, X-rays have high energies and short wavelengths. They are similar to gamma rays. b. A beam of X-rays is directed at an unknown substance. The nuclei in the substance scatter the X-rays. A detector measures the intensity and pattern of scattered X-rays. If the atoms in the substance are arranged in a regular pattern, the diffracted X-rays can be used to calculate the distance between atoms. c. One reason is that salts, such as sodium chloride, easily form crystals. In contrast, nucleic acids and proteins are much larger and do not easily form crystals. Another reason is that when nucleic acids and proteins do crystallize, their X-ray diffraction patterns are far more complex and difficult to interpret. 25. Answer: DNA can guide the synthesis of its own complement through the hydrogen bonding of the nucleotides. An A will associate with a T, a C with a G, etc.,, but only in the correct orientation. In addition, this association though will not mean that the covalent bonds between the sugar-phosphate backbone forms correctly though. The enzymes of DNA replication are necessary to coordinate the nucleotides and the template strand of DNA together along the predicted hydrogen bonds AND accelerate the formation of covalent bonds between them. 26. Answer: The two DNA strands are complementary, meaning that the sequence on one strand can be reconstructed from the other. If a single strand breaks, the other strand can be used by repair

enzymes to correctly replace any lost nucleotides and reassemble the backbone. If both strands break, the information on how to repair the break is lost and the correct sequence of DNA will be permanently altered.

27. Answer: The design of DNA is universal, so a generally DNA-damaging agent has a high chance of damaging the DNA in other species, including humans as well as bacteria. The risks involved with such drugs outweigh any potential benefits. 28. Answer: Many amino acids are represented by more than one DNA codon. For example, GTT, GTC, GTA, or GTG all translate to valine. If an error in the base sequence of DNA did not change the meaning of the codon, the protein would contain the correct amino acid. This redundancy makes the genome more resilient to change. 29. Answer: Having the same four bases and same codons allows genes from one organism to be translated by almost any other organism into the same protein. Without this, genetic transfer would require a complex translation of a gene before insertion into another organism. This universal translation is necessary for a simple organism such as bacteria to produce a mammalian protein such as insulin.

30. Answer: Reasons for the low public concern include: (1) insulin treatment is not new and have been seen to be safe before it was generated by genetically engineered bacteria, and (2) genetically engineered bacteria are kept within laboratories and industrial facilities and are therefore easier to control while plants spread more easily. 31. Answer: a. Transgenic organisms are plants and animals whose genome contains genes from one or more other species. b. (1) Traditional selective breeding methods blend the genes of both parents and require many generations to create a crop with the desired trait. Because they are not able to target a single trait, the results are unpredictable and take time. In addition, novel traits are not an option. (2) Genetic engineering transfers a single gene to get a specific targeted response and new trait options can come from any organism. As one downside, genetic transfer raises many public concerns about allergies from unexpected products. (3) Ionizing radiation is used to induce a mutation in the organism of interest. It can produce interesting and new traits when a source for that trait is not available. Because the mutation is a random process though, the results can take time and be paired with other undesirable traits. Exploring Extensions

32. Answer: Multiple answers are possible given the rate of new releases from both companies. Eli Lilly was involved in isolating insulin from animal sources to be the first to mass produce animal insulin for treatments. The company continues to work actively in drug development including treatments for type 2 diabetes as well as Alzheimer‘s disease, cardiovascular disease, and different types of cancers. They continue to work directly on the development and production of pharmaceuticals although technical advances make these very unlikely to start at the slaughterhouse. Genentech pioneered the genetic technologies necessary to produce human insulin in E. coli for mass production. The company continues to work in multiple areas of drug development including asthma, cancers, and multiple sclerosis. Though not a term used in the text, students may note that Genentech products are often presented as “biologics”. This means that they are biological molecules (often a mixture of molecules) rather than chemically synthesized organic molecules.

33. Answer: Rosalind Franklin was born in 1920, the daughter of a prominent London banking family. All of the children in the family were given encouragement to pursue an education. Both her undergraduate and graduate degrees were from Cambridge University. During World War II, she suspended her graduate research to contribute to the war effort by studying the properties of coal and graphite. After the war, she completed her PhD in physical chemistry and joined a prominent laboratory in Paris where she was introduced to the technique of X-ray crystallography. She soon became an expert in the field, moved back to London in 1951 to work at King‘s College, and in 1952 produced X-ray photographs of DNA. Before publishing the images, she showed them to Maurice Wilkins, another scientist studying DNA. Without Franklin‘s knowledge, Wilkins shared the photographs with James Watson, a molecular biologist who was working with Frances Crick to describe the structure of DNA. The X-ray data changed Watson and Crick‘s hypothesis about the structure, and they published a paper describing DNA as a double helix in 1953. Watson, Crick, and Wilkins shared the Nobel Prize for Physiology or Medicine in 1962, but Franklin did not live to be considered for the prize. Franklin died of ovarian cancer in 1958. For more information, good references are: http://www.sdsc.edu/ScienceWomen/franklin.html and Chemical Achievers: The Human Face of the Chemical Science, a publication of the Chemical Heritage Foundation, Philadelphia, PA, 1997. 34. Answer: The most popular explanation for the persistence of the sickle-cell trait is that carrying the trait protects against death from malaria. Certainly, the regions and climates

where the trait is historically common overlap closely with the regions affected by malaria. The reason that the trait provides resistance to malaria is not fully understood. 35. Answer: a. Fold.It is a game that combines the ability of computers to rapidly sample multiple interactions to find the most stable potential folding shapes of a protein with the power of human pattern recognition to accept, reject, or bias different shapes. This combination means that the computer can do the difficult math of testing multiple small changes in interaction energy while the human can keep the computer from going down the incorrect (though mathematically feasible) pathway. In addition, Fold.It compares and combines the best answers generated by its many users to determine the most accurate structure. b. Answers can vary as the laboratory behind the program continues to put out results. Initial work from Fold.It showed that humans could generate folded shapes for proteins that matched previously (and experimentally) determined folded shapes. More recently, Fold.It players have found previously unknown structures for viral enzymes and designed changes in an enzyme to increase its ability to perform a valuable chemical reaction. 36. Answer: Patenting GM plants will give distinct advantages to industrialized nations who have the funds to conduct further research on GM organisms. The patenting process may be advantageous because (1) it provides financial incentive to perform the extremely expensive research required and (2) it increases the control and decreases the spread of artificial GM crops. The process may be a disadvantage as it (1) prevents the creative and traditional breeding process by farmers and smaller scale plant breeders and (2) halts further research by academic scientists into a specific gene. Also, more importantly, patenting may make the technology too expensive for the underdeveloped nations that many GM crops are being developed to help. 37. Answer: With well-chosen parents, a dog with more strengths and fewer problems can result from breeding, while cloning can only produce the same dog. Excepting cases of inbreeding, breeding will create a dog with unique mixtures of traits from each parent and therefore creates opportunities for an improved overall breed. In contrast, cloning produces an identical dog containing identical genetic traits. 38. Answer: a. EAn excellent sources of information specific to the EU include: https://www.efsa.europa.eu/en/topics/topic/gmo https://www.liebertpub.com/doi/full/10.1089/blr.2019.29135.rbk https://www.futurity.org/genetically-modified-crops-eu-2053912-2/ is http://www.gmo-compass.org/eng/home/. Examples include rapeseed, soybean, carnations, and corn. New traits include herbicide tolerance and insect resistance. Some have been

approved for import and processing; very few have been accepted for cultivation. Typically, those allowed were cultivated before the onset of regulations. b. Examples of biotech milestonestimeline: 1973: The first genetically engineered bacteria producing a human protein is created. 1997: Two scientists at Harvard University, Walter Gilbert and Allan Maxam created a method for sequencing DNA using chemicals instead of enzymes. This technique was an important start to identifying DNA sequences efficiently. 1980: The U.S. Supreme Court ruled that genetically engineered organisms can be patented. The ruling allowed Exxon to patent an oil-eating microorganism. More importantly, it opened the door for commercialization of genetic engineered technologies. 1980: Kary Mullis and others at Cetus Corporation in Berkeley, California, created a method for copying target sequences of DNA outside of cells. The technique is now commonly used in labs across the globe to copy, alter, or create DNA sequences. 1982: Genentech, Inc. received FDA approval for the first genetically engineered drug – human insulin protein produced by bacteria. A full timeline of biotech can be found online: https://www.biotechnology.amgen.com/timeline.html https://geneticliteracyproject.org/2017/07/18/biotechnology-timeline-humans-manipulatinggenes-since-dawn-civilization/ 39. Answer: All outlines should include the scientific principle chosen and a description of how the principle will be embellished to create the science fiction story. The term “pseudoscience” refers to knowledge or practice that appears to be scientific but does not follow the scientific method. 40. Answer: Gene therapy involves introducing normal genes into patients lacking them. It would allow us to treat a specific subset of diseases caused by clear genetic alterations. For even a small subset of medical conditions, high-risk clinical trials have seen both disappointing results as well as some promise. Other diseases might be amenable to treatment with gene therapy, but developing appropriate protocols is costly, both in time and money. The Human Gene Therapy Subcommittee of the Recombinant DNA Advisory Committee of the National Institutes of Health must give approval to all proposed uses of gene therapy. Example histories: The first person treated was a four-year-old girl suffering from severe combined immunodeficiency disease (SCID) in which a genetic defect prevents the formation of a specific enzyme necessary for the health of white blood cells. Children with SCID have extremely weak immune systems and often die before adulthood. Initial results showed promise, but in January 2003, the FDA temporarily halted all gene therapy trials

using retroviral vectors in blood stem cells after two children developed a leukemia-like condition. (It should be noted that tThe first case of leukemia development in a child participating in a clinical trial occurred in 2002.) More recently gene therapy has been used with far more success to treat neural degenerative disorders and blindness. Here, the key to this success is that the genes were more carefully controlled and more specifically placed. At the time of this writing, long-term effects are still unknown in these studies. See Science 2009, 326, 818–823 (https://science.sciencemag.org/content/326/5954/818) (2009) and http://sciencenow.sciencemag.org/cgi/content/full/2009/1024/1 for more information.

41. Answer: Many examples will be found for discussion. Interesting sources for starting research include: https://www.nature.com/scitable/topicpage/genetically-modified-organisms-gmos-transgeniccrops-and-732/ https://www.accessdata.fda.gov/scripts/fdcc/index.cfm?set=Biocon http://sitn.hms.harvard.edu/flash/2015/how-to-make-a-gmo/ http://www.gmo-compass.org/eng/home/, http://www.greenpeace.org, and http://www.fda.gov/NewsEvents/Testimony/ucm115032.htm. Many students may be particularly interested in the use of genetic engineering in combination with the use of adult stem cells. News briefs from Science, Nature, The New York Times, and others may be particularly useful here.

42. Answer: This question draws upon Zambia‘s refusal of GM food aid in 2002. The list of advantages will vary depending on the type of genetic modification. The GM food may provide higher nutrient value than a non-GM food and may be easier to grow in your environment. As disadvantages, the prejudice against GM food may lead your people to reject the food or the use of the GM corn for new crops may risk local ecosystems.

ANSWERS TO END-OF-CHAPTER QUESTIONS CHAPTER 14: WHO KILLED DR. THOMPSON? A FORENSIC MYSTERY

Emphasizing Essentials 1. Answer: a. Class K (wet-chemical, such as aqueous potassium carbonate that includes a detergent) b. Class C (carbon dioxide or dry-chemical such as ammonium phosphate or sodium bicarbonate) c. Class A (water only)

2. Answer: The heats (enthalpies) of combustion for ethanol and acetone are -1371 kJ/mol and -1785 kJ/mol, respectively. In comparison, toluene and dichloromethane had values of -3900 kJ/mol and 605 kJ/mol, respectively. These values indicate how much heat will be evolved from their combustion in the presence of oxygen. Accordingly, the most heat will be generated from the combustion of toluene, followed by acetone, ethanol, and dichloromethane.

3. Answer: Ester, alkene, and nitrile (“cyano”) functional groups.

4. Answer: Light microscopes are often used in criminal forensic investigations to examine hair and vegetable fibers, paint chips, wood, pollen, diatoms, and blood crust. In addition, this technique is also widely used to examine rifling marks on bullets as well as ejector marks and firing pin impressions on cartridge casings. Electron microscopy can also be used for the above specimens, but is usually used to investigate the morphology and composition of gun powder residues. 5. Answer: Mmany possible examples, such as: accidentally stepping in a pool of blood in a dimly lit house, inadvertently remove or smear fingerprints when opening doors to secure the scene, or may knock something over as they move through the scene. They may also be tempted to pick up gauze, latex gloves, etc. left by emergency medical personnel or to “tidy up” before more personnel arrive. They may also not wear protective outer clothing and therefore may leave fibers from their own clothing in the crime scene.

6. Answer: i) Determining that CFCs contributed to the ozone hole required a thorough forensic investigation; ii) Ongoing investigations to determine whether global climate change is from natural and/or anthropogenic sources;

iii) Case studies of water pollution in Ch. 58; for instance, determining that there were high levels of lead in Flint, MI drinking water, and the ongoing investigation of where this came from and who was responsible for this oversight.

7. Answer: There are many possible answers to this open-ended question. The popular T.V. show "The First 48" offers a realistic depiction of the process involved during the early stages of a crime investigation. The textbook "The Science of Crime Scenes" by Max Houck, Frank Crispino, and Terry McAdam (Elsevier, 2012) is also a great resource to identify the many steps used during crime scene investigations. One possibility is: first responder surveys the scene, and calls for medical attention that is provided with minimal contamination of the crime scene. The scene is then secured to prevent unauthorized people from entering and contaminating/adulterating it. Suspects, witnesses, bystanders, victims/family/friends, and medical personnel are all identified at the scene. The scene is then preserved by documenting the condition as it was upon arrival. Once the lead investigator arrives, the first responder can then 'release the scene'. The first responder verbally relates all details about his actions that began the moment he/she arrived at the scene, sharing photos, sketches, and anything else pertaining to the case. The lead investigator then coordinates activities at the crime scene, communicating with other relevant professionals, and leading the crime scene team. The team consists of a medical examiner, latent print expert, photographer, and other experts relevant to the specific situation (forensic anthropologist, etc.). Once evidence is carefully collected, it is transported to a crime lab(s), where it is analyzed by trained professionals. Investigators then follow up with those people found at the crime scene to identify possible suspects. 8. Answer: many Many possible examples, such as: no sign of forced entry, or the entry is forced beyond what would be required to gain access; only one specific item was stolen; no search for any valuables in an apparent burglary, or no items have been stolen; excessive ransacking, or too careful of specific items (some items set aside to protect them); victim is posed to suggest or cover up a sexual assault; survivor of an attack has minor wounds only on the side of the body opposite their own handedness (self-inflicted); wounds are consistent with being self-inflicted 9. Answer: All three components are critical in order to extract the maximum amount of information from any crime scene by well-trained personnel. For example, recognize: search patterns are often used when trying to recognize the presence of physical evidence; recover: reagents such as luminol are sensitive to the presence of blood and is used to recover invisible traces of latent blood stains; record: sketching and photography are used to record crime scenes. If only one of these three are not properly carried out, such as proper recording of crime scene details, then the jury will disregard the evidence and reasonable doubt will be introduced.

10. Answer:

The order of places where, and the persons with whom, physical evidence was located from the time it was collected to its submission at trial. 11. Answer: Based on the evidence found at the crime scene, first responders and lead investigators are able to formulate an initial hypothesis regarding the likely circumstances surrounding the crime. However, it should be noted that the lack of physical evidence could jeopardize the entire criminal procedure. Hence, the collection of evidence from a scene should not be considered within the context of supporting one hypothesis over others. The crime scene can only be processed once, so it is best to collect an excess of evidence that would support more than one possible hypothesis.

Concentrating on Concepts

12. Answer: any Any solvents that have a flash point less than 25 ºC would ignite in contact with a match. These include: diethyl ether, acetone, tetrahydrofuran, hexanes, ethanol, acetonitrile, and toluene.

13. Answer: If 1 keV = 1.6 × 10-16 J, then 2 keV = (2)(1.6 × 10-16 J) = 3.2 × 10-16 J E = hc/λ; hence, λ = hc/E. Therefore, λ = (6.626 × 10-34 J.s)(3.0 × 108 m/s) / (3.2 × 10-16 J) = 6.2 × 10-10 m or 6.2 Å.

14. Answer: 2,500 nm to 25,000 nm

15. Answer: Locard's Exchange Principle states that physical evidence represents two-way sharing of materials between human beings and their environment, irregardless if it occurs through criminal intent or innocent means. Three examples are fingerprints or saliva transferred from a suspect to an object found at the crime scene, or paint transferred from a vehicle to a victim during a hit-and-run accident.

16. Answer: This can be solved by taking the natural log (ln) of both sides of the equation: 2n = 1,000,000. That is, n ln (2) = ln (1,000,000) or n = ln (1,000,000) / ln (2). This will equal 19.9 or 20 cycles.

17. Answer: It is possible to detect and recover fingerprints from porous surfaces by using a number of developing agents (e.g., organic powder, iodine, benzoflavone) and subsequent fingerprint detection using UVA light. 18. Answer: The spectrum shows the presence of alkyl C-H groups (strong C-H stretching peaks around 3000 cm-1 and C-H bending peaks around 1380-1400 cm-1) a C=O carbonyl group (peak around 1700 cm1 ), and perhaps an ester C-O peak (1170 cm-1). The absence of a medium-strong, broad peak around 3500 cm-1 indicates that an alcohol or carboxylic acid –OH is not present. You are not able to determine the concentration of functional groups based on their peak heights; IR spectroscopy is only used to determine whether certain functional groups are present.

19. Answer: No. All of these compounds would show the presence of C-H, C=O, C-O, and O-H groups. In order to distinguish between these compounds, mass spectrometry or nuclear magnetic resonance (NMR) spectroscopy would need to be performed.

20. Answer: The order of boiling points is: pentane (36 ℃) < heptane (99 ℃), cyclohexane (101 ℃), octane (125 ℃), and 2,3-dimethyloctane (156 ℃). Hence, since all of these compounds are nonpolar ("like retains like"), the order of elution will be governed by the above order of increasing boiling points. 21. Answer: a. When the swab is inserted into the instrument, it exposes it to high temperatures to ionize the residue collected from a traveler's hand or baggage. The ions are separated based on their mass by passing through a gas chromatograph/mass spectrometer. A detector responds to the various ions that pass from the column and software is specifically designed to respond to nitrates (NO 3-) that are a major component of explosives. For instance, nitroglycerin has the following chemical structure:

b. The detection limits for nitrates using these instruments is quite low, often several hundred ppm. Hence, there have been reports of 'false positives' at airports, from travelers that applied hand lotions or creams that contain glycerin.

c. The likelihood of testing positive for explosive residue decreases if these products are applied long in advance of passing through security. Other products that may result in a positive test include: cosmetics, hair products, baby wipes, hand soaps, etc. that contain glycerin, lawn fertilizers that contain nitrates, munitions, accelerants, fireworks and other pyrotechnics, and certain medications (e.g., nitroglycerine and other nitrate-containing formulations). 22. Answer: Yes. Depending on the alloy comprising the gun, various acid mixtures may be applied to the surface, which will etch the metal and reveal the serial number that lies beneath the scratch marks. 23. Answer: in In addition to fingerprints, earprints (e.g., left behind in a crime scene by someone listening through a door), or recognizing people by their gait—the way they walk.

Exploring Extensions

24. Answer: The mass of an electron is 9.1 x 10-31 kg; by plugging in these values into the equation, the best resolution would be 1.2 x 10-11 m. This corresponds to 0.012 nm or 0.12 Å.

25. Answer: a. Students will draw their own structure.

b. Luminol reacts with the iron in hemoglobin. When luminol is sprayed on an area, trace amounts of an activating oxidizing agent cause luminol to emit a blue glow that can be seen in a dark room. c. The oxidizing agent is typically a solution of hydrogen peroxide (H2O2) and an alcohol. Luminol reacts with the hydroxide ion (–-OH) of the alcohol to form a dianion (having a 2- charge); the oxygen produced from the hydrogen peroxide then reacts with the luminol dianion resulting in an unstable product that emits a photon of light. 26. Answer: a. Not necessarily. Luminol also exhibits bright chemiluminescence upon contact with other substances such as some paints, varnishes, fruit and vegetable juices, and iron-containing compounds. b. Although luminol may have an effect on the typing of bloodstains using conventional serological testing, it has been found that luminol does not interfere with DNA analyses. 27. Answer: Answers will vary; common myths found in the popular media include: very fast (immediate) results from evidence analysis, improper evidence collection techniques, crime labs fully equipped with every instrument, forensic scientists interrogate witnesses and perform their own investigations, crime scenes are contaminated by open access to media, etc. 28. Answer: Some possible examples: i) The amount of blood (or lack thereof) found in O.J.'s Ford Bronco, ii) the presence of EDTA (an anti-coagulating substance used by crime labs) on blood found on O.J.'s sock and gate of Nicole Brown Simpson's residence, iii) the glove found at the crime scene did not fit O.J. during the trial, iv) evidence was collected and not properly recorded and taken directly to the crime lab for processing (some evidence was kept in the trunk of the lead investigator's car overnight). 29. Answer: Visual inspection of the tungsten filament can be used to determine whether headlights were illuminated. The tungsten filament inside sealed headlights gets extremely hot when headlights are turned on. After a crash with an impact speed of > 20 km/h, a hot filament will be significantly deformed, whereas a cold filament will resemble a spring with little/no deformation observed. Often, the glass bulb will shatter during impact, which will allow oxygen to react with the hot filament. This will result in a yellowishwhite powder that will coat the surface of the filament, which is readily observable by using scanning electron microscopy. Furthermore, small glass particles and grains will implode into the bulb, which will adhere to the filament as it cools down. In contrast, a cold filament will not react with oxygen and will remain clean and shiny. Glass particulates will not adhere to a cold filament. 30. Answer: Yes. Any examination that includes the collection of data and drawing conclusions to describe a likely cause of a past event may be considered a forensic investigation.