CHAPTER 14 Acids and Bases - Tamkang University

1 CHAPTER 14 Acids and Bases 1. For the equilibrium that exists in an aqueous solution of nitrous acid (HNO2, a weak acid ), the equilibrium constant expression is: [H+][NO2 ]. a) K= [HNO2]. [H+][N][O]2. b) K= [HNO2]. c) K = [H+][NO2 ]. [H+]2[NO2 ]. d) K = [HNO ]. 2. e) none of these [H+][NO2 ]. ANS: a) K = [HNO ] PAGE: 2. 2. Which of the following is a conjugate acid / base pair? a) HCl/OCl- b) H2SO4/SO42- c) NH4+/NH3. d) H3O+/OH- e) none of these ANS: c) NH4+/NH3 PAGE: 3. The equilibrium constant for the reaction A + H+ HA. is called: a) Ka b) Kb 1. c) Ka Kw d) Kb e) KwKa 1. ANS: c) Ka PAGE: 321 Houghton Mifflin Company. All rights reserved. CHAPTER 14 Acids and Bases 4. For the stepwise dissociation of aqueous H3PO4, which of the following is not a conjugate acid base pair? a) HPO42 and PO43.

2 B) H3PO4 and H2PO4 . c) H2PO4 and HPO42 . d) H2PO4 and PO43 . e) H3O+ and H2O. ANS: d) H2PO4 and PO43 PAGE: ,7. 5. What is the equilibrium constant for the following reaction? N3 + H3O+ HN3 + H2O. The Ka value for HN3 = 10 5. a) 10 10. b) 10 9. c) 10 5. d) 104. e) 109. ANS: d) 104 PAGE: 6. The hydrogen sulfate or bisulfate ion HSO4 can act as either an acid or a base in water solution. In which of the following equations does HSO4 act as an acid ? a) HSO4 + H2O H2SO4 + OH . b) HSO4 + H3O+ SO3 + 2H2O. c) HSO4 + OH H2SO4 + O2 . d) HSO4 + H2O SO42 + H3O+. e) none of these ANS: d) HSO4 + H2O SO42 + H3O+ PAGE: ,2. 322 Houghton Mifflin Company. All rights reserved. CHAPTER 14 Acids and Bases 7. Using the following Ka values, indicate the correct order of base strength. HNO2 Ka = 10 4. HF Ka = 10 4.

3 HCN Ka = 10 10. a) CN > NO2 > F > H2O > Cl . b) Cl > H2O > F > NO2 > CN . c) CN > F > NO2 > Cl > H2O. d) H2O > CN > NO2 > F > Cl . e) none of these ANS: a) CN > NO2 > F > H2O > Cl PAGE: 8. At 0 C, the ion-product constant of water, Kw, is 10 15. The pH of pure water at 0 C is: a) b) c) d) e) none of these ANS: d) PAGE: ,3. 9. The equilibrium constants (Ka) for HCN and HF in H2O at 25 C are 10 10 and 10 4, respectively. The relative order of base strengths is: a) F > H2O > CN . b) H2O > F > CN . c) CN > F > H2O. d) F > CN > H2O. e) none of these ANS: c) CN > F > H2O PAGE: Houghton Mifflin Company. All rights reserved. 323. CHAPTER 14 Acids and Bases 10. Given the following Acids and Ka values: HClO4 HOAc HCN HF. 1 107 10 5 10 10 10 4. which shows the conjugate Bases listed by increasing strength?

4 A) CN , F , OAc , ClO4 . b) CN , OAc , F , ClO4 . c) CN , ClO4 , F , OAc . d) ClO4 , OAc , CN , F . e) ClO4 , F , OAc , CN . ANS: e) ClO4 , F , OAc , CN PAGE: 11. The conjugate base of a weak acid is a) a strong base b) a weak base c) a strong acid d) a weak acid e) none of these ANS: b) a weak base PAGE: 12. Which of the following is the equilibrium constant expression for the dissociation of the weak acid HOCl? [H+][OCl ]. a) K= [HOCl]. b) K = [H+][OCl ]. [HOCl]. c) K = [H+][OCl ]. [H+][O2 ][Cl ]. d) K= [HOCl]. e) none of these [H+][OCl ]. ANS: a) K= [HOCl] PAGE: ,2. 13 14. The following three equations represent equilibria that lie far to the right. HNO3(aq) + CN (aq) HCN(aq) + NO3 (aq). HCN(aq) + OH (aq) H2O(l) + CN (aq). H2O(l) + CH3O (aq) CH2OH(aq) + OH (aq). 324 Houghton Mifflin Company.

5 All rights reserved. CHAPTER 14 Acids and Bases 13. Identify the strongest acid . a) HCN. b) HNO3. c) H2O. d) OH . e) CH3OH. ANS: b) HNO3 PAGE: 14. Identify the strongest base . a) CH3O . b) CH3OH. c) CN . d) H2O. e) NO3 . ANS: a) CH3O PAGE: 15. Given that the Ka for HOCl is x 10-8, calculate the K value for the reaction of HOCl with OH-. a) x 106. b) x 10-8. c) x 10-22. d) x 10-7. e) none of these ANS: a) x 106 PAGE: ,6,8. 16. Calculate the [H+] in a solution that has a pH of a) M. b) M. c) 10 3 M. d) 10 12 M. e) none of these ANS: d) 10 12 M PAGE: 17. Calculate the [H+] in a solution that has a pH of a) M. b) M. c) 10 3 M. d) 10 12 M. e) none of these ANS: c) 10 3 M PAGE: Houghton Mifflin Company. All rights reserved. 325. CHAPTER 14 Acids and Bases 18. The pH of a solution at 25 C in which [OH ] = 10 5 M is: a) b) c) d) e) none of these ANS: c) PAGE: 19.

6 Consider the reaction HNO2(aq) + H2O(l) H3O+(aq) + NO (aq). Which species is the conjugate base ? a) HNO2(aq). b) H2O(l). c) H3O+(aq). d) NO (aq). e) Two of these ANS: e) Two of these PAGE: 20. In which of the following reactions does the H2PO4- ion act as an acid ? a) H3PO4 + H2O H3O+ + H2PO4 . b) H2PO4 + H2O H3O+ + HPO42- c) H2PO4 + OH H3PO4 + O2- d) The ion cannot act as an acid . e) Two of these ANS: b) H2PO4 + H2O H3O+ + HPO42- PAGE: 21. In deciding which of two Acids is the stronger, one must know: a) the concentration of each acid solution b) the pH of each acid solution c) the equilibrium constant of each acid d) all of these e) both a and c must be known ANS: c) the equilibrium constant of each acid PAGE: 22. Which of the following is not true for a solution at 25 C that has a hydroxide concentration of 10 6 M?

7 A) Kw = 1 10 14. b) The solution is acidic. c) The solution is basic. d) The [H] is 4 10 9 M. e) The Kw is independent of what the solution contains. ANS: c) The solution is basic. PAGE: 326 Houghton Mifflin Company. All rights reserved. CHAPTER 14 Acids and Bases 23. Calculate the [H+] in a solution that has a pH of a) 10 10 M. b) 10 5 M. c) 10 9 M. d) 10 9 M. e) 10 10 M. ANS: a) 10 10 M PAGE: 24. Calculate the pH of M HNO3(aq). a) b) c) d) e) ANS: a) PAGE: 25. Solid calcium hydroxide is dissolved in water until the pH of the solution is The hydroxide ion concentration [OH ] of the solution is: a) 10 11 M. b) M. c) 10 4 M. d) 10 14 M. e) none of these ANS: c) 10 4 M PAGE: 26. As water is heated, its pH decreases. This means that a) the water is no longer neutral b) [H+] > [OH-]. c) [OH-] > [H+].

8 D) a and b are correct e) none of these ANS: e) none of these PAGE: 27. Which of the following indicates the most basic solution? a) [H+] = 1 10 10 M. b) pOH = c) [OH ] = 7 10 5 M. d) pH = e) At least two of the solutions are equally basic. ANS: a) [H+] = 1 10 10 M PAGE: Houghton Mifflin Company. All rights reserved. 327. CHAPTER 14 Acids and Bases 28. Calculate the pOH of a M solution of HCl. a) b) c) d) e) none of these ANS: c) PAGE: 29. Calculate the pH of a M strong acid solution. a) b) c) d) e) none of these ANS: b) PAGE: 30. For nitrous acid , HNO2, Ka = 10 4. Calculate the pH of M HNO2. a) b) c) d) e) none of these ANS: a) PAGE: 31. For weak acid , HX, Ka = 10 6. Calculate the pH of a M solution of HX. a) b) c) d) e) none of these ANS: b) PAGE: 32. Acetic acid (HC2H3O2) is a weak acid (Ka = 10 5).

9 Calculate the pH of a M. HC2H3O2 solution. a) b) c) d) e) ANS: c) PAGE: 328 Houghton Mifflin Company. All rights reserved. CHAPTER 14 Acids and Bases 33. Determine the molarity of a solution of the weak acid HClO2 (Ka = 10 2) if it has a pH of a) M. b) M. c) M. d) M. e) M. ANS: a) M PAGE: 34 35. The following questions refer to a solution that contains M hydrofluoric acid , HF. (Ka = 10 4), and M hydrocyanic acid , HCN (Ka = 10 10). 34. What is the pH of this mixture of weak Acids ? a) b) c) d) e) ANS: b) PAGE: 35. Determine the [CN ] at equilibrium. a) 10 5 M. b) 10 7 M. c) 10 8 M. d) 10 10 M. e) none of these ANS: c) 10 8 M PAGE: 36. How many moles of benzoic acid , a monoprotic acid with Ka = 10 5, must be dissolved in 500. mL of H2O to produce a solution with pH = a) 10 1. b) 10 2. c) 10 2.

10 D) e) none of these ANS: c) 10 2 PAGE: Houghton Mifflin Company. All rights reserved. 329. CHAPTER 14 Acids and Bases 37. Calculate the [H+] in a M solution of HCN, Ka = 10 10. a) 10 7 M. b) 10 6 M. c) 10 3 M. d) 10 10 M. e) none of these ANS: b) 10 6 M PAGE: 38. In a solution prepared by dissolving mole of propionic acid in enough water to make L of solution, the pH is observed to be The Ka for propionic acid (HC3H5O2) is: a) 10 2. b) 10 2. c) 10 2. d) 10 12. e) none of these ANS: b) 10 2 PAGE: 39. A solution of M weak acid is ionized. What is the Ka value of this acid ? a) x 10-5. b) x 10-5. c) d) x 10-2. e) none of these ANS: a) x 10-5 PAGE: 40. A solution of M formic acid (HCOOH) is ionized. What is the Ka of formic acid ? a) 10 8. b) 10 4. c) 10 6. d) 10 2. e) need more data ANS: b) 10 4 PAGE: 330 Houghton Mifflin Company.