K/U Knowledge/Understanding T/i Thinking/Investigation C Communication A Application
CHAPTER
8
Knowledge
For each question, select the best answer from the four alternatives.
1. Which of the following is a characteristic of a base? (8.1) K/U
(a) tastes sour (b) feels slippery
(c) turns blue litmus pink (d) all of the above
2. According to the Arrhenius theory, bases in aqueous solution
(a) produce H1(aq)
(b) produce OH2(aq)
(c) accept H1(aq)
(d) accept OH2(aq) (8.1) K/U
3. Which of the following is a base according to the Brønsted–Lowry theory, but not according to the Arrhenius theory? (8.1) K/U
(a) ammonia, NH3(aq)
(b) sodium hydroxide, NaOH(aq) (c) phenol, HC6H5O(aq)
(d) hydrochloric acid, HCl(aq)
4. A conjugate acid–base pair consists of two entities that (a) differ by one oxygen atom
(b) differ by one hydrogen ion
(c) neutralize each other in aqueous solution (d) produce hydroxide ions in solution (8.1) K/U
5. Which of the following is the conjugate acid of water? (8.1) K/U
(a) H2O2(aq)
(b) OH2(aq)
(c) HCHO2(aq)
(d) H3O1(aq)
6. Which of the following is a property of a strong acid? (8.2) K/U
(a) Ka is small.
(b) It exists primarily in the form of molecules in solution.
(c) It ionizes completely in aqueous solution. (d) Its ionization equilibrium lies far to the left. 7. Determine the pH of a 0.032 mol/L solution of
NaOH(aq), a strong base. (8.2) K/U
(a) 2.49 (b) 3.20 (c) 11.51 (d) 14.00
RevieW
8. Which of the following substances is the first to be produced in the sulfuric acid manufacturing process? (8.3) K/U
(a) oleum, H2S2O7(aq)
(b) water, H2O(l)
(c) sulfur trioxide, SO3(g)
(d) sulfur dioxide, SO2(g)
9. Which of the following salts forms a basic solution when dissolved in water? (8.6) K/U
(a) potassium chloride, KCl(s) (b) sodium nitrate, NaNO3(s)
(c) potassium cyanide, KCN(s) (d) lithium sulfate, Li2SO4(s)
10. Which of the following terms describes substances that have different colours in solutions of different pH? (8.2, 8.7) K/U
(a) amphiprotic (b) indicators (c) polyprotic (d) electrolytes
11. Which of the following statements correctly describes the process of titration? (8.7) K/U
(a) The titrant is added slowly from a burette into the sample until the equivalence point is observed.
(b) The sample is added slowly from a burette into the titrant until the equivalence point is observed.
(c) The sample is added slowly from a burette into the titrant until the endpoint is observed.
(d) The titrant is added slowly from a burette into the sample until the endpoint is observed.
12. Which of the following best describes the components of a buffer solution? (8.8) K/U
(a) a weak acid and a strong base in water (b) a weak acid and its conjugate base in water (c) a strong acid and a weak base in water (d) a neutral salt in water
13. Which of the following statements correctly explains why weak acids, rather than strong acids, are used as food additives? (8.8) K/U
(a) Weak acids can only be used in low concentrations.
(b) Weak acids have a buffering effect. (c) Weak acids have a lower pH.
Indicate whether each statement is true or false. If you think the statement is false, rewrite it to make it true.
14. A weak acid completely ionizes in solution. (8.2) K/U
15. The autoionization of water involves the transfer of a proton from one water molecule to another to produce a hydroxide ion and a hydronium ion. (8.2) K/U
16. The hydrogen ion concentration of a solution with a pH of 3.0 is 3.33 3 1023 mol/L. (8.2) K/U
17. A strong acid exists primarily in the form of molecules in solution. (8.2) K/U
18. A diprotic acid has 2 ionizable hydrogen atoms. (8.4) K/U
19. The reaction of a weak acid with a strong base produces a neutral salt. (8.6) K/U
20. The endpoint in a titration is the point at which an indicator starts to change colour permanently. (8.7) K/U
21. The endpoint of a strong acid–strong base titration occurs at a pH near 5. (8.7) K/U
22. The colour of an acid–base indicator depends on the pH of the solution. (8.7) K/U
23. A buffer solution can absorb any amount of acid or base without a significant change in pH. (8.8) K/U
24. The sour taste of citric acid enhances fruit flavours. (8.9) K/U
Match each term in the first list ((a) to (k)) with the most appropriate definition in the second list ((i) to (xi)). 25. (a) conjugate acid
(b) sample (c) weak (d) concentrated (e) Ka (f) polyprotic (g) strong acid (h) organic acid (i) dilute (j) acid titrant (k) monoprotic
(i) containing relatively few entities per unit volume (ii) used to titrate a base
(iii) only partially ionized in water (iv) acid ionization constant
(v) having only one ionizable hydrogen atom (vi) entity formed when a base gains a hydrogen ion (vii) the solution in the flask during a titration (viii) an acid based on the elements C, H, and O (ix) having 2 or more ionizable hydrogen atoms (x) an acid that ionizes almost completely in water (xi) containing many entities per unit volume
(8.1, 8.2, 8.4, 8.7) K/U
Write a short answer to each question.
26. How did Arrhenius describe acids and bases? (8.1) K/U
27. Identify whether water behaves as an acid or a base in each of the following reactions: (8.1) K/U
(a) H3PO4(aq) 1 H2O(l) m
H2PO42(aq) 1 H3O1(aq)
(b) NH3(aq) 1 H2O(l) m NH41(aq) 1 OH2(aq)
(c) HBr(aq) 1 H2O(l) m Br2(aq) 1 H3O1(aq)
(d) CN2(aq) 1 H
2O(l) m HCN(aq) 1 OH2(aq)
28. Identify the conjugate acid–base pairs in each of the reactions shown in question 27. (8.1) K/U
29. Write the name and formula for (a) the conjugate base of HF (b) the conjugate acid of H2O
(c) the conjugate base of H2O
(d) the conjugate acid of NH3 (8.1) K/U
30. Write equations to show how the hydrogen sulfate ion, HSO42(aq), is amphiprotic. (8.1) K/U
31. Calculate the pH of each of the following strong acid or base solutions: (8.2) T/i
(a) 0.004 mol/L hydrochloric acid
(b) a 3.5 3 1028 mol/L solution of potassium
hydroxide
(c) 7.3 3 1026 mol/L nitric acid, HNO 3(aq)
(d) 0.25 mol/L hydrobromic acid, HBr(aq) (e) a 0.45 mol/L solution of sodium hydroxide (f) a 6.1 3 1025 mol/L solution of barium hydroxide,
Ba(OH)2(aq)
(g) a 0.006 mol/L solution of potassium hydroxide, KOH(aq)
32. Write the equation used to calculate pOH from pH. (8.2) K/U
33. Write the chemical equation that represents the autoionization of water. (8.2) K/U
34. What is the hydroxide ion concentration of a solution with a pH of 8.0? (8.2) K/U
35. What is the difference between a strong acid and a weak acid? (8.2) K/U
36. Would you expect hydrochloric acid to have a large or small Ka? Explain. (8.2) K/U
37. Calculate the Ka value of a 0.1000 mol/L solution of
44. Describe a solution for which each of the following mathematical expressions would be true. Give an example in each case. [HA(aq)initial] and [A2(aq) initial]
represent the initial concentrations of an acid and its conjugate base. (8.2, 8.4) K/U T/i
(a) [OH2(aq)] 5 [A2(aq) initial]
(b) [H1(aq)] 5 2 [HA(aq) initial]
45. Calculate the percentage ionization of 0.050 mol/L hydrofluoric acid, HF(aq). (Ka 5 6.6 3 1024)
(8.4) K/U T/i
46. Determine the concentrations of the ions present in a beverage that contains 0.050 mol/L carbonic acid, H2CO3(aq). (Use information from Table 4 in
Section 8.4.) (8.4) K/U T/i
47. Methanoic acid (formic acid) is a colourless solution used in making textiles. Calculate the value of Ka
for a 0.100 mol/L methanoic acid solution in which [H1(aq)] 5 1.34 3 1023. (8.4) K/U
48. Calculate the pH of 0.10 mol/L ethanoic acid, HC2H3O2(aq). (Ka 5 1.8 3 1025) (8.4) T/i
49. Will an aqueous solution of each of the following salts will be acidic, basic, or neutral? (8.6) T/i
(a) sodium nitrate, NaNO3(s)
(b) ammonium bromide, NH4Br(s)
(c) sodium fluoride, NaF(s)
50. An acid–base titration starts at pH 3.4 and reaches an endpoint at pH 8.5. Describe the type of sample and titrant being used in the titration. (8.7) K/U T/i
51. Consider the titration that gives the titration curve shown in Figure 1.
38. Copy Table 1 into your notebook and fill in the missing information. (8.2) K/U T/i
Table 1 Characteristics of Four Solutions
Solution pH pOH [H1(aq)] [OH–(aq)]
Acidic, basic, or neutral? A 6.88 B 8.4 3 10–14 mol/L C 3.11 D 1.0 3 10–7 mol/L
39. What is the pH of a substance with a pOH of 7.6? (8.2) K/U T/i
40. Calculate the hydroxide ion concentration of each of the following solutions at 25 °C. Identify each solution as neutral, acidic, or basic. (8.2) K/U T/i
(a) [H1(aq)] 5 1.0 3 1027 mol/L
(b) [H1(aq)] 5 8.3 3 1026 mol/L
(c) [H1(aq)] 5 1.0 3 10212 mol/L
(d) [H1(aq)] 5 5.4 3 1025 mol/L
41. What is the hydroxide ion concentration of a solution with a pH of 4.0? (8.2) K/U T/i
42. State whether the ionization of each of the following favours the reactants or the products: (8.2) T/i
(a) H2SO4
(b) HCO32
(c) HF
43. Use the information in Table 2 to answer the following questions. (8.2) K/U T/i
Table 2 Kw Values at Various Temperatures
Temperature (°C) Kw 0 1.14 3 10–15 25 1.00 3 10–14 35 2.09 3 10–14 40 2.92 3 10–14 50 5.47 3 10–14
(a) Is the autoionization of water exothermic or endothermic? Explain your answer.
(b) Calculate [H1(aq)] and [OH2(aq)] in a neutral
solution at 50 °C.
Figure 1
5
pH
10 15 20 25
Titration of a Weak Acid with a Strong Base
Volume of base (mL)
Copy the titration curve into your notebook. On your curve, indicate the points that correspond to the following: (8.7) T/i
(a) the stoichiometric (equivalence) point
(b) the region corresponding to the buffering action of the weak acid
52. If the pH of a solution is 4.8, what is the colour of each of the following indicators in this solution? (8.7) T/i
(a) phenolphthalein (b) bromocresol green (c) phenol red
53. Sodium lactate is the sodium salt of lactic acid. What is the pH of a solution that contains 0.75 mol/L lactic acid, HC3H5O3(aq) (Ka 5 1.4 3 1024), and 0.25 mol/L
sodium lactate, NaC3H5O3(aq)? (8.8) T/i
54. Calculate the volume of 0.10 mol/L sodium methanoate solution that must be added to 1.00 L of 0.1 mol/L methanoic acid to give a buffer solution with a pH of 3.5. (The pKa value for methanoic acid is 3.75.) (8.8) T/i
55. A buffer solution contains aqueous ammonia and ammonium chloride. K/U
(a) Write an equation for the equilibrium system. (b) In which direction does the equilibrium shift if
hydrochloric acid is added? Why?
56. What is the conjugate base of citric acid? (8.9) T/i
57. Summarize the use of citric acid as an additive in the food industry. (8.9) K/U
Understanding
58. Explain why nitric acid, HNO3(aq), is an Arrhenius
acid. (8.1) K/U
59. Explain why ammonia, NH3, is a base according to
the Brønsted–Lowry theory, but not according to the Arrhenius theory. (8.1) K/U
60. Explain why water, H2O(l), is not included in the
equilibrium constant equation for an acid ionizing in water. (8.1) K/U
61. Two monoprotic acids have Ka values of 1.0 3 1024
and 1.0 3 1026, respectively. Which acid produces a
1.0 mol/L solution with the highest pH? Why? (8.1) K/U
62. Why does doubling the concentration of a
hydrochloric acid solution not cause the pH of the solution to decrease by a factor of two? (8.2) K/U
63. Show that the pH of pure water at 25 °C is 7. (8.2) K/U
64. Explain how a sample of an acid can be both weak and concentrated. (8.2) K/U
65. In the production of sulfuric acid, increased pressure favours the forward reaction, forming more products. Use Le Châtelier’s principle to explain why. (8.3) K/U
66. Which acid has the larger percentage ionization: hydrofluoric acid or ethanoic acid. Explain. (8.4) K/U
67. Rank Ka1, Ka2, and Ka3 for a triprotic acid, H3A(aq),
in order of decreasing magnitude. Justify your order. (8.4) K/U
68. Does water act as a diprotic acid? Explain. (8.4) T/i
69. An acid, HA(aq), is a very weak acid. (8.4) K/U
(a) How does the strength of the conjugate base, A2(aq), compare to that of water?
(b) How do the relative concentrations of H1(aq)
and HA(aq) compare at equilibrium?
70. Explain why aqueous solutions of salts may be either acidic, basic, or neutral. (8.6) K/U
71. Create a flow chart or concept map that can be used to determine the type of solution (acidic, basic, or neutral) that will form when different types of salts are dissolved in water. (8.6) K/U C
72. Consider the titration of 100.0 mL of 0.200 mol/L ethanoic acid, HC2H3O2(aq) (Ka 5 1.8 3 1025), by
0.100 mol/L potassium hydroxide solution, KOH(aq). Calculate the pH of the resulting solution after each of the following volumes of potassium hydroxide solution has been added: (8.7) T/i
(a) 0.0 mL (d) 150.0 mL (b) 50.0 mL (e) 200.0 mL (c) 100.0 mL (f) 250.0 mL
73. Describe how you would choose an indicator for the titration of a strong acid with a strong base. (8.7) T/i
74. Which is the better indicator for the titration of a weak acid with a strong base: methyl yellow or thymol blue? Why? (Use Figure 10 in Section 8.7.) (8.7) T/i
75. Use equations to show how a buffer system works. (8.8) K/U T/i C
76. Would a solution made from combining hydrochloric acid and sodium chloride make a good buffer? Explain your answer. (8.8) T/i
77. A solution is 0.40 mol/L hydrazine, H2NNH2(aq)
(Kb 5 1.7 3 1026), and 0.80 mol/L hydrazinium
nitrate, H2NNH3NO3(aq). (8.8) T/i
(a) Calculate the pH of the solution.
(b) Describe, using words or chemical equilibrium equations, what happens when hydrochloric acid and sodium hydroxide are added to two different samples of the original solution.
Analysis and Application
78. Hemoglobin (abbreviated to Hb) is a protein that is responsible for transporting oxygen in the blood of mammals. The binding of oxygen to hemoglobin is pH dependent. The relevant equilibrium reaction is HbH4411aq2 1 4 O21g2 m Hb1O2241aq2 1 4 H11aq2
Use Le Châtelier’s principle to answer the following questions: (8.2) K/U T/i
(a) What form of hemoglobin, HbH4 41(aq) or
Hb(O2)4(aq), is favoured in the lungs? What
(b) For the following volumes of sodium hydroxide solution added, list the major entities present after the hydroxide ions react completely: (i) 0 mL NaOH(aq) added
(ii) between 0 and 100 mL NaOH(aq) added (iii) 100 mL NaOH(aq) added
(iv) between 100 and 200 mL NaOH(aq) added (v) 200 mL NaOH(aq) added
(vi) more than 200 mL NaOH(aq) added (c) When 50.0 mL of sodium hydroxide solution
has been added, the pH is 4.0. When 150 mL of sodium hydroxide solution has been added, the pH is 8.0. Determine the values of Ka1 and Ka2 for
the diprotic acid.
82. A natural indicator is an indicator that is either a naturally occurring substance or produced from a naturally occurring substance. Summarize the procedure for an investigation designed to determine the pH range of a homemade indicator. The indicator may be made from cabbage juice, turmeric, or hydrangea flowers. (8.7) T/i C A
83. Write a procedure for a colour change trick using acids, bases, and indicators. (8.7) T/i C A
84. Write a procedure for preparing an acidic buffer solution. (8.8) T/i C A
85. Design an investigation to determine the buffering capacity of a buffer solution. (8.8) T/i C A
86. Table 3 lists four solids and four solutions that are available to you. What combinations of reactants would you use to prepare buffers with each of the following pH values? (8.8) T/i
(a) 3.0 (c) 5.0
(b) 4.0 (d) 7.0
Table 3 Available Reactants
Solids Solutions Ka of acid
potassium fluoride 5.0 mol/L hydrofluoric acid 6.6 3 10 24 sodium ethanoate 1.0 mol/L ethanoic acid 1.8 3 10 25 sodium
benzoate 2.6 mol/L benzoic acid 6.3 3 10
25 potassium dihydrogen phosphate 1.0 mol/L phosphoric acid, H3PO4(aq) 7.1 3 10–3
87. Create a concept map linking the main ideas in this chapter. Use “acid–base equilibria” as the central concept. Include the key terms introduced in this chapter. (8.1, 8.2, 8.4, 8.5, 8.6, 8.7, 8.8) K/U T/i C
(b) When a person hyperventilates, the concentration of carbon dioxide in the blood falls. How does this affect the oxygen-binding equilibrium? How does breathing into a paper bag help?
(c) When a person has suffered a cardiac arrest, injection of a sodium hydrogen carbonate solution is given. Why is this necessary? (Hint: [CO2(aq)]
in blood increases during cardiac arrest.)
79. Vitamin C (ascorbic acid) is a weak diprotic acid with the molecular formula C6H8O6 (Ka1 5 7.9 3 1025;
Ka2 5 1.6 3 10212). (8.4) T/i A
(a) Determine [H1(aq)] and the pH of a solution
made by dissolving a 0.500 g tablet of vitamin C in 250 mL of water.
(b) Stomach fluids have a pH < 1.0 due to the presence of hydrochloric acid. What fraction of the vitamin in a 0.500 g tablet will ionize if the volume of fluid in the stomach is 200 mL? 80. Fossil fuels contain trace amounts of nitrogen
and sulfur. Burning fossil fuels therefore produces nitrogen dioxide and sulfur dioxide, which may be released into the atmosphere. (8.6) K/U A
(a) Write the chemical reactions showing how these oxides react with water in the atmosphere. Will acidic or basic solutions be produced?
(b) The solutions formed may fall as precipitation and be washed into rivers and lakes. Lakes on lime. stone bedrock are less affected by these solutions than are many other lakes. Explain why this may be the case.
81. When a diprotic acid, H2A(aq), is titrated with
sodium hydroxide, NaOH(aq), the resulting graph is
Figure 2
pH
Volume of NaOH(aq) added (mL) Titration of a Diprotic Acid with Sodium Hydroxide Solution
essentially two titration curves (Figure 2). (8.7) T/i
97. Research factors that are responsible for acid rain. Present your findings in the form of a mystery story or investigative report. Begin with the observed results of acid rain and then use detective work to determine the culprits responsible. T/i C A
98. How does the concept of pH apply to the process of home canning of foods? Prepare a brochure that could be used to educate the general public about safe canning methods and why they are used. T/i C A
99. How is limestone used to moderate the effects of acid precipitation on lakes and streams? Prepare a slideshow that could be used at a visitors’ centre in a natural area for educating the public about environmental issues. T/i C A
100. Use Internet resources to research Svante Arrhenius’s role in the history of chemistry. Make a poster that presents your information in a creative, visual way. C A
101. Research the topic of acid indigestion or acid reflux, and the medicines manufactured to reduce the symptoms. What are the properties of these medicines, and how to they work? Present your findings in a format that a doctor could share with patients. T/i C A
102. Research medicines that include a buffer. Why are buffers added? Present your answer as though you were a chemist working for a pharmaceutical company and you must convince company officials of the benefits of adding a buffer to a new medication under development. T/i C A
103. Use your knowledge of acid–base chemistry to evaluate the effectiveness of the ingredients in toothpastes in preventing tooth decay. Start by researching the ingredients and identify which ones are intended to prevent tooth decay. Share your findings in the form of a pamphlet or electronic communication aimed at consumers choosing a toothpaste. T/i C A
104. List at least four occupations in which people need to measure pH on a regular basis. For each occupation, describe the techniques used to measure pH and how the pH measurements are used. C A
105. Sodium hydroxide is a strong base that is used to clear clogged drains. Hydrochloric acid is a strong acid used to clean stone and metal surfaces. Conduct research to identify two more bases and two more acids used for household purposes or hobbies. Prepare an informational pamphlet that can be distributed to homeowners explaining the safe use and disposal of the four substances you find. C A
106. Conduct research to determine the minerals used by farmers to maintain soil pH within an acceptable range and how these substances function. Present the results of your findings in either a poster or pamphlet. T/i C A
evaluation
88. Evaluate the cost-effectiveness of the active ingredient in four different antacids. Locate four brands at a drugstore and record the cost of each package and the quantity of antacid per package. Calculate the cost of a single dose from each package. Prepare a spreadsheet to summarize the information. (8.1) T/i C A
89. A chemistry student is selecting an appropriate indicator to use for the titration of 0.10 mol/L sodium borate, NaB4O7(aq), with 0.10 mol/L hydrochloric
acid, HCl(aq). The pH at the equivalence point for this titration is 5.22. Is phenolphthalein an appropriate choice? Explain your answer and, if appropriate, recommend a better choice. (8.7) T/i A
90. Is a titration of a weak acid with a weak base feasible? Give your reasons. If you feel that the titration could be done, what type of titration curve would you expect to see? (8.7) T/i A
Reflect on Your Learning
91. Think about the various examples of acids and bases that were discussed in this chapter. Do you think there may be more examples of acids and bases in the substances you use every day? How could you explore this possibility? What equipment would you use to search for examples of acids and bases? K/U T/i A
92. How did your study of pH indicators change how you think about substances that change colour? For example, if you observe an item that loses its colour (becomes colourless), how could you explain this change? How does this relate to your thinking about how stain removers might work? K/U T/i A
93. How has your understanding of the role of acids, bases, and buffers in food changed since you began studying this chapter? K/U T/i A
Research
94. Many recently published books and documents are printed on paper that has a high acid content. This paper deteriorates quite quickly. Research the methods used to save existing books and prevent them from deteriorating. Present your research in a poster. K/U T/i A
95. Use Internet research to collect information about the Arabic discovery of the alkali hydroxides. Use an innovative way to communicate what you learn to other chemistry students. T/i C
96. The Richter scale is used to measure the strength of earthquakes. Construct a Venn diagram comparing and contrasting the Richter scale with the pH scale. T/i C A
