Chem 1b exam 2
54. If the ratio of acid to base in a buffer is changed by a factor of 10, the pH changes by ± _____ .
1
53. If a strong acid is titrated with a strong base, the equivalence point occurs at a pH of ________.
7.00
55. A buffer made from an acid with a Ka equal to 1.0 ´ 10-8 will have a pH approximately equal to _______.
8.0
57. Why do salts containing basic anions have a greater solubility in water than predicted from calculations using Ksp values? Examples of such salts are CaCO3, PbF2, Ca3(PO4)2.
Basic anions react with water to form their conjugate acids, such as HCO3 - , HF, and HPO4 2- . The reactions reduce the concentration of the basic anion. Additional salt dissociates to replace the basic anions. 58. Why is the solubility of silver chloride greater in distilled water than in 0.100 M KCl? Answer: This is an application of Le Chatelier's principle. When a reactant or product is added to a system at equilibrium, the reaction proceeds in a direction that re-establishes the equilibrium. In this case, the chloride ion reacts with Ag+ to form AgCl(s), thereby reducing the amount of dissolved AgCl.
56. Hyperventilation can cause your blood pH to rise. One way to lower your blood pH is to breath into a paper bag, thus recycling the air you exhale. Why does this procedure lower your blood pH?
By breathing recycled air, you increase your CO2 intake. Carbon dioxide is an acidic oxide
53. Which is the stronger Brønsted acid, Fe(H2O)6 2+ or Fe(H2O)63+? Explain.
Fe(H2O)6 3+. When a proton dissociates from the oxygen atom, the oxygen is left with an extra electron. This negative charge is stabilized by the interaction of the oxygen with the iron cation. Since the Fe3+ is more positively charged than the Fe2+, it can more effectively stabilize the negative charge.
52. The buffer that controls the pH of blood is composed of a mixture of HCO3 - and ________.
H2CO3
52. Write a net ionic equation for the neutralization reaction of nitric acid and potassium hydroxide.
H3O + (aq) + OH- (aq) É 2 H2O(l)
14. Molecules or ions that can behave as either a Brønsted-Lowry acid or base are called a) amphiprotic. b) hydronium. c) polyprotic acids or bases. d) conjugate acids or bases. e) weak electrolytes.
a
16. What is the pH of a buffer that results when 0.50 mole of H3PO4 is mixed with 0.75 moles of NaOH and diluted with water to 1.00 L? (Ka1 = 7.5 ´ 10-3, Ka2 = 6.2 ´ 10-8, Ka3 = 3.6 ´ 10-13) a) 7.21 b) 7.45 c) 8.01 d) 8.23 e) 9.91
a
17. At 298 K, what is the H3O+ concentration of a solution with a OH- concentration of 2.88 *10-2 M? a) 3.47 ´ 10-13 M b) 3.47 ´ 10-6 M c) 2.88 ´ 10-2 M d) 3.47 ´ 101 M e) 2.88 ´ 1012 M
a
21. What is the H3O+ concentration of a solution with a pH of 10.55? a) 2.8 ´ 10-11 M b) 1.1 ´ 10-10 M c) 3.5 ´ 10-6 M d) 3.6 ´ 10-4 M e) 2.8 ´ 103 M
a
23. How many moles of NaOH must be added to 1.00 L of 0.400 M NH4+ to make a buffer with a pH of 9.00? (Ka for NH4+ = 5.6 ´ 10-10) a) 0.144 mol b) 0.163 mol c) 0.225 mol d) 0.256 mol e) 0.320 mol
a
26. Which of the following chemical reactions corresponds to the base ionization constant, Kb, for ammonia? a) NH3(aq) + H2O(l) É NH4+(aq) + OH-(aq) b) NH4+(aq) + H2O(l) É NH3(aq) + H3O+(aq) c) NH4+(aq) + OH-(aq) É NH3(aq) + H2O(l) d) NH3(aq) + OH-(aq) É NH2-(aq) + H2O(l) e) NH3(aq) + H3O+(aq) É NH4+(aq) + H2O(l)
a
27. Which one of the following conditions is true for a titration of a weak acid with a strong base? a) The equivalence point occurs at a pH greater than 7. b) The equivalence point occurs at a pH equal to 7. c) Equal volumes of acid and base are required to reach the equivalence point. d) A colored indicator with a pKa less than 7 should be used. e) The colored indicator should change color rapidly in the buffer region.
a
29. Sodium hydroxide (0.100 M) is used to titrate 25.0 mL of 0.250 M HNO2. What is the pH of a solution when the titration is 90.0% complete? (Ka for HNO2 = 4.5 ´ 10-4) a) 4.30 b) 4.74 c) 5.00 d) 5.39 e) 6.89
a
3. Acids that ionize extensively in solution are referred to as a) strong acids. b) weak acids. c) Arrhenius acids. d) Brønsted-Lowry acids. e) amphiprotic.
a
31. Hydrochloric acid is used to titrate 25.0 mL of 0.0100 M NH3. What is the pH after the addition of 40.0 mL of 0.0100 M HCl? (Kb for NH3 = 1.8 ´ 10-5) a) 2.64 b) 3.82 c) 4.12 d) 4.94 e) 5.00
a
33. What is the pH of a 0.050 M solution of formic acid? (Ka for HCO2H = 1.8 ´ 10-4) a) 2.54 b) 2.91 c) 3.21 d) 4.07 e) 5.99
a
4. What is the pH of a mixture containing 0.30 M HNO2 and 0.15 M NaNO2? (Ka for HNO2 = 4.5 ´ 10-4) a) 3.05 b) 4.05 c) 4.35 d) 4.65 e) 5.01
a
40. Which of the following chemical reactions corresponds to Kb2 for Na2SO3? a) HSO3-(aq) + H2O(l) É H2SO3(aq) + OH-(aq) b) SO32-(aq) + H3O+(aq) É HSO3-(aq) + H2O(l) c) H2SO3(aq) + OH-(aq) É HSO3-(aq) + H2O(l) d) HSO3-(aq) + OH-(aq) É SO32-(aq) + H2O(l) e) HSO3-(aq) + H3O+(aq) É H2SO3(aq) + H2O(l)
a
42. Calculate the molar solubility of CaCO3 in 0.050 M CaCl2. The Ksp for CaCO3 is 3.8 ´ 10-9. Assume that CO32- does not react appreciably with water. a) 7.6 ´ 10-8 mol/L b) 1.9 ´ 10-7 mol/L c) 6.2 ´ 10-5 mol/L d) 8.3 ´ 10-5 mol/L e) 5.0 ´ 10-2 mol/L
a
46. What is the pH of the solution which results from mixing 25 mL of 0.30 M NH3 and 75 mL of 0.10 HCl? (Ka for NH4+ = 5.7 ´ 10-10) a) 5.18 b) 6.54 c) 7.00 d) 8.82 e) 9.17
a
47. If you mix equal molar quantities of CH3CO2H (Ka = 1.8 ´ 10-5) and NaF (Kb = 1.4 ´ 10-11), the resulting solution will be a) acidic because Ka of CH3CO2H is greater than Kb of F-. b) acidic because Ka of CH3CO2H is greater than Ka of F-. c) basic because Ka of CH3CO2H is greater than Kb of F-. d) basic because Ka of CH3CO2H is greater than Ka of F-. e) neutral.
a
47. The concentration of Ca2+ in a solution is 4.7 ´ 10-4 M. What concentration of CO3 2- is required to just begin precipitating CaCO3? The Ksp for CaCO3 is 3.8 ´ 10-9 . a) 8.1 ´ 10-6 M b) 5.1 ´ 10-5 M c) 3.8 ´ 10-4 M d) 4.7 ´ 10-4 M e) 1.4 ´ 10-2 M
a
6. What is the pH of the solution that results from adding 15 mL of 0.50 M NaOH to 25 mL of 0.50 M HF? (Ka for HF = 7.2 ´ 10-4) a) 3.32 b) 3.49 c) 4.61 d) 7.53 e) 10.86
a
51. Some metal hydroxides can act as either Lewis acids or Brønsted bases. These metal hydroxides are called ________ substances.
amphoteric
11. What is the conjugate acid of HPO42-(aq)? a) H3PO4 b) H2PO4- c) PO42- d) H3O+ e) OH
b
16. A solution is prepared by diluting 0.25 mol HNO3 to a volume of 750 mL. What is the pH of this solution? a) 0.33 b) 0.48 c) 0.60 d) 3.5 e) 4.2
b
19. If the ratio of base to acid in a buffer changes by a factor of 10, the pH of the buffer a) increases by 2. b) increases by 1. c) decreases by 1. d) decreases by 2. e) remains unchanged.
b
19. What is the pH of 0.094 M HCl at 25 °C? a) 0.094 b) 1.03 c) 4.90 d) 9.01 e) 12.97
b
21. A buffer is prepared by adding 250 mL of 0.300 M NaOH to 250 mL of 0.500 M weak acid, HA. If the pH of the buffer is 8.15, what is the pKa of the acid? a) 7.56 b) 7.97 c) 8.15 d) 8.37 e) 8.89
b
23. What is the OH- concentration of a solution with a pH of 3.75? a) 5.2 ´ 10-13 M b) 5.6 ´ 10-11 M c) 4.9 ´ 10-7 M d) 1.8 ´ 10-4 M e) 3.8 ´ 10-2 M
b
24. A buffer contains 0.50 mol CH3CO2H and 0.50 mol CH3CO2 diluted to with water to 1.0 L. How many moles of NaOH are required to increase the pH of the buffer to 5.00? (pKa for CH3CO2H = 4.74) a) 0.12 mol b) 0.15 mol c) 0.17 mol d) 0.26 mol e) 0.35 mol
b
26. Which one of the following conditions is met at the equivalence point of the titration of a monoprotic weak acid with a strong base? a) The volume of base added from the buret must equal the volume of acid titrated. b) The moles of based added from the buret equals the initial moles of acid. c) The molarity of the base equals the initial molarity of the weak acid. d) The percent ionization of the base must equal the percent ionization of the acid. e) The pH of the solution is equal to or less than 7.00.
b
29. Given the following acid dissociation constants, Ka (HF) = 7.2 ´ 10-4 Ka (HCN) = 4.0 ´ 10-10 determine the equilibrium constant for the reaction below. HCN(aq) + F-(aq) É CN-(aq) + HF(aq) a) 2.9 ´ 10-13 b) 5.6 ´ 10-7 c) 7.2 ´ 10-4 d) 1.8 ´ 106 e) 3.5 ´ 1012
b
33. Potassium hydrogen phthalate (molar mass = 204.2 g/mol) is used to standardize sodium hydroxide. If 22.10 mL of NaOH is required to titrate 0.6103 g KHP to the equivalence point, what is the concentration of the NaOH? HC8H4O4-(aq) + OH-(aq) É C8H4O42-(aq) + H2O(l) a) 0.06605 M b) 0.1352 M c) 0.1514 M d) 0.1617 M e) 0.2762 M
b
39. The solubility of PbCl2 is 0.016 mol/L. What is the value of Ksp for PbCl2? a) 4.1 ´ 10-6 b) 1.6 ´ 10-5 c) 2.6 ´ 10-4 d) 5.1 ´ 10-4 e) 4.8 ´ 10-2
b
41. What is the pH of 0.50 M H3PO4? (Ka1 = 7.5 ´ 10-3, Ka2 = 6.2 ´ 10-8 , Ka3 = 3.6 ´ 10-13) a) 0.97 b) 1.24 c) 2.67 d) 5.15 e) 6.33
b
44. All of the following compounds are acids containing chlorine. Which compound is the weakest acid? a) HCl b) HClO c) HClO2 d) HClO3 e) HClO4
b
46. At what pH will a solution 0.150 M Cu2+ begin to precipitate as Cu(OH)2? The Ksp for Cu(OH)2 is 1.6 ´ 10-19. a) 1.80 b) 5.01 c) 7.23 d) 8.99 e) 13.18
b
50. A solution contains 0.10 M Cl- and 0.10 M Br- . If Ag+ is added until AgCl just begins to precipitate, what are the concentrations of Ag+ and Br- ? (Ksp for AgCl = 1.8 ´ 10-10 , Ksp for AgBr = 3.3 ´ 10-13) a) [Ag+ ] = 1.8 ´ 10-9 M, [Br- ] = 3.3 ´ 10-12 M b) [Ag+ ] = 1.8 ´ 10-9 M, [Br- ] = 1.8 ´ 10-4 M c) [Ag+ ] = 3.3 ´ 10-12 M, [Br- ] = 1.0 ´ 10-1 M d) [Ag+ ] = 3.3 ´ 10-12 M, [Br- ] = 1.8 ´ 10-4 M e) [Ag+ ] = 1.8. ´ 10-9 M, [Br- ] = 1.8 ´ 10-3 M
b
6. All of the following are weak bases EXCEPT a) NH3 b) Ba(OH)2 c) CH3CO2-d) F e) HCO3-
b
8. In the following reaction HCO3-(aq) + NH3(aq) É CO32-(aq) + NH4+(aq) a) HCO3- is an acid and NH3(aq) is its conjugate base. b) HCO3- is an acid and CO32- is its conjugate base. c) NH3 is an acid and HCO32- is its conjugate base. d) NH3 is an acid and NH4+ is its conjugate base. e) NH4+ is an acid and CO32-is its conjugate base.
b
9. The conjugate acid of OH- is a) H3O+ b) H2O c) OH d) O2- e) H
b
1. According to the Brønsted-Lowry definition, an acid a) increases the H3O+ concentration in a solution. b) increases the OH- concentration in a solution. c) is a proton donor. d) is a proton acceptor. e) has a lone pair of electrons that can bond to a proton.
c
14. What is the pH of the buffer that results when 15.0 g of NaH2PO4 is mixed with 12.0 g Na2HPO4 and diluted with water to 0.500 L? (Ka1 = 7.5 ´ 10-3, Ka2 = 6.2 ´ 10-8,Ka3 = 3.6 ´ 10-13) a) 1.95 b) 4.74 c) 7.04 d) 9.25 e) 12.27
c
18. Which one of the following solutions will have a pH of 3.0? a) 3.0 M HCl b) 3.0 M NH3 c) 0.0010 M HBr d) 0.0010 M CH3CO2H e) 0.0010 M NaOH
c
20. The Ka for hypochlorous acid, HClO, is 3.5 ´ 10-8 . To make a buffer of pH = 7.20 using this acid, what [ClO-]/[HClO] ratio is necessary? a) 0.23 b) 0.34 c) 0.55 d) 1.8 e) 2.94
c
22. What is the OH- concentration of a solution with a pH of 12.81? a) 1.6 ´ 10-13 M b) 2.7 ´ 10-8 M c) 6.5 ´ 10-2 M d) 1.2 ´ 100 M e) 1.3 ´ 101 M
c
24. A solution with a pH of 2.00 is diluted from 1.0 L to 2.0 L. What is the pH of the diluted solution? a) 1.00 b) 1.70 c) 2.30 d) 3.00 e) 4.30
c
25. What volume of 0.500 M NaOH should be added to 750.0 mL of 0.250 M HCO3- to make a buffer with a pH of 10.00? (pKa for HCO3- = 10.32) a) 60.7 mL b) 82.1 mL c) 121 mL d) 375 mL e) 455 mL
c
28. A volume of 25.0 mL of 0.100 M CH3CO2H is titrated with 0.100 M NaOH. What is the pH after the addition of 12.5 mL of NaOH? (Ka for CH3CO2H = 1.8 ´ 10-5) a) 1.34 b) 2.87 c) 4.74 d) 5.12 e) 5.87
c
30. Given the following equilibrium constants, Ka (HNO2) = 4.5 ´ 10-4 Kb (NH3) = 1.8 ´ 10-5 Kw = 1.00 ´ 10-14 determine the equilibrium constant for the reaction below. HNO2(aq) + NH3(aq) É NO2-(aq) + NH4+(aq) a) 2.5 ´ 10-13 b) 8.1 ´ 10-9 c) 8.1 ´ 105 d) 4.0 ´ 1012 e) 2.5 ´ 1015
c
31. What is the H3O+ concentration of 0.25 M NH4Cl? (Ka for NH4+ = 5.6 ´ 10-10) a) 1.4 ´ 10-10 M b) 5.9 ´ 10-6 M c) 1.2 ´ 10-5 M d) 2.4 ´ 10-5 M e) 9.5 ´ 10-5 M
c
34. A 25.0 mL sample of vinegar is titrated with 0.0950 M NaOH. If the titration requires 35.8 mL of NaOH, what is the concentration of acetic acid in the vinegar? a) 0.0663 M b) 0.0971 M c) 0.136 M d) 0.329 M e) 0.727 M
c
36. Benzoic acid has a pKa value of 4.20. What is the value of Kb for sodium benzoate? a) 1.0 ´ 10-14 b) 2.4 ´ 10-14 c) 1.6 ´ 10-10 d) 6.3 ´ 10-5 e) 2.8 ´ 10-3
c
38. The pH of 1.5 M formic acid, HCO2H, is 1.78. What is the pKa for this acid? a) 1.86 b) 2.43 c) 3.73 d) 5.14 e) 6.92
c
41. The Ksp for PbSO4 is 1.8 ´ 10-8. What is the concentration of SO42- in a saturated solution ofPbSO4? a) 9.0 ´ 10-9 M b) 1.8 ´ 10-8 M c) 1.3 ´ 10-4 M d) 1.9 ´ 10-4 M e) 1.7 ´ 10-3 M
c
43. Of the following salts, which one forms a 0.1 M solution with the lowest pH? a) CaCO3 b) KBr c) NH4Cl d) NaCN e) K3PO4
c
45. What is the molar solubility of Fe3+ in a solution that is buffered at a pH of 4.00? The Ksp for Fe(OH)3 is 6.3 ´ 10-38. a) 6.3 ´ 10-23 mol/L b) 2.3 ´ 10-9 mol/L c) 6.3 ´ 10-8 mol/L d) 2.3 ´ 10-6 mol/L e) 1.4 ´ 10-4 mol/L
c
45. What is the pH of the solution which results from mixing 25 mL of 0.20 M CH3CO2H and 25 mL of 0.20 M NaOH? (Ka for CH3CO2H = 1.8 ´ 10-5) a) 5.13 b) 7.00 c) 8.87 d) 9.02 e) 10.43
c
5. All of the following are weak acids EXCEPT a) HF b) CH3CO2H c) HBr d) NH4+ e) HCN
c
49. When a Lewis acid combines with a Lewis base, the base supplies both electrons to the bond. This type of chemical bond is called a ________ covalent bond.
coordinate
1. We have a solution of benzoic acid, C6H5CO2H. What is the effect of adding sodium hydroxide to this solution? 1. The pH increases. 2. The concentration of C6H5CO2H decreases. 3. The concentration of H3O+ increases. a) 1 only b) 2 only c) 3 only d) 1 and 2 e) 2 and 3
d
12. What is the pH of the buffer that results when 3.0 g of NH3 and 3.0 g of NH4Cl are diluted with water to a volume of 250 mL? (Ka for NH4+ = 5.6 ´ 10-10) a) 8.25 b) 8.75 c) 9.25 d) 9.75 e) 10.25
d
12. Which acid is a potentially dangerous component of rhubarb leaves? a) hydrochloric b) phosphoric c) acetic d) oxalic e) selenic
d
15. At 10 °C, the water ionization constant, Kw, is 2.9 * 10-15. What is the H3O+ concentration in neutral water at this temperature? a) 2.9 *10-15 M b)1.4*10-15 M c) 3.8 * 10-8 M d) 5.4 * 10-8 M e) 1.0 * 10-7 M
d
15. If you add 3.2 g NaF to 225 mL of 0.25 M HF, what is the pH of the resulting solution? (Ka for HF = 7.2 ´ 10-4) a) 2.32 b) 3.01 c) 3.14 d) 3.27 e) 3.40
d
2. According to the Brønsted-Lowry definition, a base a) increases the H3O+ concentration in a solution. b) increases the OH- concentration in a solution. c) is a proton donor. d) is a proton acceptor. e) has a lone pair of electrons that can bond to a proton.
d
20. What is the pH of 1.3 ´ 10-5 M NaOH at 25 °C? a) 1.30 b) 4.89 c) 7.69 d) 9.11 e) 11.58
d
27. Which of the following is the strongest acid? a) acetic acid, Ka = 1.8 ´ 10-5 b) benzoic acid, Ka = 6.3 ´ 10-5 c) dihydrogen phosphate ion, Ka = 6.2 ´ 10-8 d) formic acid, Ka = 1.8 ´ 10-4 e) hydrocyanic acid, Ka = 4.0 ´ 10-10
d
3. What is the pH of a solution of 0.25 M acetic acid and 0.25 M sodium acetate? (Ka for CH3CO2H = 1.8 ´ 10-5) a) 0.60 b) 2.12 c) 2.67 d) 4.74 e) 5.32
d
30. Hydrochloric acid (0.0200 M) is used to titrate 50.0 mL of 0.0100 M NH3. What is the pH at the equivalence point? (Kb for NH3 = 1.8 ´ 10-5) a) 1.92 b) 3.44 c) 4.79 d) 5.72 e) 8.81
d
32. What is the OH- concentration of 0.33 M NaF? (Kb for F- = 1.4 ´ 10-11) a) 4.6 ´ 10-12 M b) 4.2 ´ 10-11 M c) 6.5 ´ 10-7 M d) 2.1 ´ 10-6 M e) 3.7 ´ 10-6 M
d
35. A solution is made by diluting 0.60 mol NaClO to a volume of 2.0 L. What is the pH of the solution? (Kb for ClO- = 2.9 ´ 10-7) a) 3.53 b) 7.06 c) 9.52 d) 10.47 e) 12.91
d
35. An impure sample of sodium carbonate, Na2CO3, is titrated with 0.100 M HCl according to the reaction below. 2 HCl(aq) + Na2CO3(aq) É CO2(g) + H2O(l) + 2 NaCl(aq) What is the percent of Na2CO3 in a 0.500 g sample if the titration requires 37.3 mL of HCl? The molar mass of Na2CO3 is 106.0 g/mol. a) 0.746% b) 12.7% c) 24.5% d) 39.5% e) 74.6%
d
37. The pH of 0.010 M trimethylamine is 10.88. What is the value of Kb for this base? a) 1.3 ´ 10-11 b) 9.8 ´ 10-8 c) 4.8 ´ 10-7 d) 6.2 ´ 10-5 e) 7.6 ´ 10-4
d
38. The solubility of BaSO4 is 1.05 ´ 10-5 mol/L. What is the value of Ksp for BaSO4? a) 3.24 ´ 10-3 b) 6.48 ´ 10-3 c) 2.10 ´ 10-5 d) 1.10 ´ 10-10 e) 2.20 ´ 10-10
d
42. Of the following salts, which one forms a 0.1 M solution with the highest pH? a) KCl b) NH4Cl c) FeCl3 d) KNO2 e) Ca(NO3)2
d
43. What is the molar solubility of Ag2CrO4 in 0.20 M K2CrO4? The value of Ksp for Ag2CrO4 is 9.0 ´ 10-12. a) 4.5 ´ 10-11 mol/L b) 1.3 ´ 10-10 mol/L c) 3.6 ´ 10-8 mol/L d) 6.7 ´ 10-6 mol/L e) 1.3 ´ 10-4 mol/L
d
48. Of the following list of molecules and ions, which are Lewis acids: NH3, Cl-, Al3+, BH3? a) NH3 only b) Al3+ only c) NH3 and Cld) Al3+ and BH3 e) Cl- and BH3
d
48. What mass of Na2SO4 (molar mass = 142.0 g/mol) must be added to 225 mL of 0.33 M Ag+ to initiate precipitation of Ag2SO4? The Ksp for Ag2SO4 is 1.7 ´ 10-5 . Assume no volume change occurs upon addition of Na2SO4. a) 3.5 ´ 10-5 g b) 1.6 ´ 10-4 g c) 1.6 ´ 10-3 g d) 5.0 ´ 10-3 g e) 7.3 ´ 10-3 g
d
5. What is the pH of the solution that results from adding 25 mL of 0.33 M HCl to 25 mL of 0.58 M NH3? (Kb for NH3 = 1.8 ´ 10-5) a) 3.87 b) 4.62 c) 8.99 d) 9.13 e) 9.38
d
7. In the following reaction H2S(aq) + H2O(l) <> HS-(aq) + H3O+(aq) a) H2O is an acid and H2S is its conjugate base. b) H2S is an acid and H2O is its conjugate base. c) H2O is an acid and H3O+ is its conjugate base. d) H2S is an acid and HS- is its conjugate base. e) H3O+ is an acid and HS- is its conjugate base.
d
7. Which of the following combinations would be the best to buffer the pH to 7.0? a) H3PO4 and H2PO4-, Ka = 7.5 ´ 10-3 b) HNO2 and NO2-, Ka = 4.5 ´ 10-4 c) CH3CO2H and CH3COO-, Ka = 18 ´ 10-5 d) H2PO4- and HPO42-, Ka = 6.2 ´ 10-8 e) NH4+ and NH3, Ka = 5.7 ´ 10-10
d
10. The conjugate base of NH3 is a) OHb) H2O c) H3O+ d) NH4+ e) NH2-
e
11. All of the following statements concerning buffers are true EXCEPT a) buffers are resistant to changes in pH upon the addition of strong acids. b) buffers are resistant to changes in pH when diluted with water. c) the pH of a buffer is close to the pKa of the weak acid from which it is made. d) buffers contain appreciable quantities of a weak acid and its conjugate base. e) buffers are used as colored indicators in acid-base titrations.
e
13. All of the following ions are amphiprotic EXCEPT a) HPO42- b) H2PO4- c) HCO3- d) HS- e) CH3CO2-
e
13. What is the pH of the buffer that results when 18.0 g of NaCH3CO2 is mixed with 125 mL of 1.00 M CH3CO2H and diluted with water to 1.00 L? (Ka for CH3CO2H = 1.8 ´ 10-5) a) 2.44 b) 3.87 c) 4.14 d) 4.74 e) 4.99
e
17. What is the pH of a buffer that results when 25 g NaHCO3 is mixed with 100.0 mL of 2.00 M NaOH and diluted with water to 225 mL? (Ka for HCO3- = 4.8 ´ 10-11) a) 7.88 b) 9.36 c) 10.05 d) 10.27 e) 10.63
e
18. How many grams of solid KF (molar mass = 58.1 g/mol) should be added to 1.00 L of 0.250 M HF to make a buffer of pH = 3.143? (Ka for HF = 7.20 ´ 10-4) a) 3.54 g b) 3.98 g c) 6.98 g d) 10.1 g e) 14.5 g
e
182 49. The following anions can be separated by precipitation as silver salts: Cl- , Br- , I- , CrO4 2- . If Ag+ is added to a solution containing the four anions, each at a concentration of 0.10 M, in what order would they precipitate? Compound Ksp AgCl 1.8 ´ 10-10 Ag2CrO4 9.0 ´ 10-12 AgBr 3.3 ´ 10-13 AgI 1.5 ´ 10-16 a) AgCl ® Ag2CrO4 ® AgBr ® AgI b) AgI ® AgBr ® Ag2CrO4 ® AgCl c) Ag2CrO4 ® AgCl ® AgBr ® AgI d) Ag2CrO4 ® AgI ® AgBr ® AgCl e) AgI ® AgBr ® AgCl ® Ag2CrO4
e
2. We have a solution of ammonia. What is the effect of adding ammonium chloride to this solution? 1. The pH increases. 2. The concentration of NH3 increases. 3. The concentration of H3O+ increases a) 1 only b) 2 only c) 3 only d) 1 and 2 e) 2 and 3
e
22. A buffer is composed of 0.250 mol H2PO4- and 0.250 mol HPO42- diluted with water to a volume of 1.00 L. The pH of the buffer is 7.208. How many moles of HCl must be added to reduce the pH to 6.208? a) 0.0455 mol b) 0.063 mol c) 0.125 mol d) 0.187 mol e) 0.205 mol
e
25. Which of the following chemical reactions corresponds to the acid ionization constant, Ka, for hydrogen carbonate ion (HCO3-)? a) HCO3-(aq) + OH-(aq) É CO32-(aq) + H2O(l) b) HCO3-(aq) + H3O+(aq) É H2CO3(aq) + H2O(l) c) HCO3-(aq) + H3O+(aq) É CO2(g) + 2 H2O(l) d) HCO3-(aq) É CO2(g) + OH-(aq) e) HCO3-(aq) + H2O(l) É CO32-(aq) + H3O+(aq)
e
28. Which of the following weak acids has the strongest conjugate base? a) acetic acid, Ka = 1.8 ´ 10-5 b) benzoic acid, Ka = 6.3 ´ 10-5 c) dihydrogen phosphate ion, Ka = 6.2 ´ 10-8 d) formic acid, Ka = 1.8 ´ 10-4 e) hydrocyanic acid, Ka = 4.0 ´ 10-10
e
32. Sodium hydroxide is used to titrate 50.0 mL of 0.100 M benzoic acid. What is the pH after the addition of 50 mL of 0.200 M NaOH? (Ka for benzoic acid = 6.3 ´ 10-5) a) 7.30 b) 9.18 c) 11.84 d) 12.27 e) 12.70
e
34. What is the pH of a 0.75 M solution of sodium cyanide, NaCN? (Kb for CN- =2.5 ´ 10-5) a) 2.36 b) 4.33 c) 9.58 d) 10.04 e) 11.64
e
37. Which is the best-colored indicator to use in the titration of NH4+ with NaOH? Why? Indicator pKa Bromocresol green 4.7 Phenol red 7.8 Phenolphthalein 9.0 a) Bromocresol green. The pH at the equivalence point is less than 7.0. b) Bromocresol green. The pKa values of the acid and indicator are similar. c) Phenol Red. The equivalence point of an acid-base titration occurs at a pH of 7.0. d) Phenol Red. The pKa values of the acid and the indicator are similar. e) Phenolphthalein. The pH at the equivalence point is greater than 7.0.
e
39. Which of the following chemical reactions corresponds to Ka2 for phosphoric acid? a) HPO42-(aq) + H2O(l) É PO43-(aq) + H3O+(aq) b) PO43-(aq) + H2O(l) É HPO42-(aq) + OH-(aq) c) H3PO4(aq) + H2O(l) É H2PO4-(aq) + H3O+(aq) d) H3PO4(aq) + 2 H2O(l) É HPO42-(aq) + 2 H3O+(aq) e) H2PO4-(aq) + H2O(l) É HPO42-(aq) + H3O+(aq)
e
4. All of the following are strong acids EXCEPT a) HCl b) HNO3 c) HClO4 d) H2SO4 e) H3PO4
e
40. The Ksp for BaF2 is 1.7 ´ 10-6. What is the concentration of Ba2+ in a saturated solution of BaF2? a) 5.7 ´ 10-7 M b) 1.7 ´ 10-6 M c) 1.0 ´ 10-2 M d) 1.3 ´ 10-3 M e) 7.5 ´ 10-3 M
e
44. Only 1.06 g of Ca(NO3)2 will dissolve per liter of a solution that is buffered to a pH of 13.00. What is the value of Ksp for Ca(OH)2? The molar mass of Ca(NO3)2 is 164.1 g/mol. a)1.8 ´ 10-10 M b) 4.2 ´ 10-7 M c) 1.1 ´ 10-6 M d) 4.2 ´ 10-5 M e) 6.5 ´ 10-5 M
e
51. Consider the reaction Ni(OH)2(s) + 4 CN- (aq) É Ni(CN)4 2- (aq) + 2 OH- (aq) K = 2.8 ´ 1014 If Ksp for Ni(OH)2 is 2.8 ´ 10-16, what is the value of the formation constant, Kform, for the reaction below? Ni2+(aq) + 4 CN- (aq) É Ni(CN)4 2- (aq) a) 1.0 ´ 10-30 b) 7.8 ´ 10-2 c) 1.3 ´ 101 d) 2.8 ´ 102 e) 1.0 ´ 1030
e
8. Which of the following combinations would be the best to buffer the pH to 9.0? a) H3PO4 and H2PO4-, Ka = 7.5 ´ 10-3 b) HNO2 and NO2-, Ka = 4.5 ´ 10-4 c) CH3CO2H and CH3COO-, Ka = 18 ´ 10-5 d) H2PO4- and HPO42-, Ka = 6.2 ´ 10-8 e) NH4+ and NH3, Ka = 5.7 ´ 10-10
e
9. All of the following will produce a buffer solution EXCEPT a) NH4Cl and NH3. b) HCN and KCN. c) NaHCO3 and Na2CO3. d) NaH2PO4 and Na2HPO4. e) NaOH and NaCl.
e
50. A Brønsted acid is known as a ________ donor.
proton
