Chapter 15 2 What is the percent dissociation of a benzoic acid solution

60) The pH of 0.255 M HCN is 4.95. What is the value of Ka for hydrocyanic acid?

A) 1.3 × 10–10

B) 4.9 × 10–10

C) 1.1 × 10–5

D) 4.4 × 10-5

61) The pH of 0.150 M CH3CO2H, acetic acid, is 2.78. What is the value of Ka for acetic acid?

A) 2.8 × 10-6

B) 1.9 × 10-5

C) 1.7 × 10–3

D) 1.1 × 10-2

62) What is the strongest monoprotic acid of the following set if all the acids are at 0.100 M concentration?

A) hydrofluoric acid with Ka = 3.5 × 10-4

B) benzoic acid with Ka = 6.5 × 10-5

C) acetic acid with Ka = 1.8 × 10-5

D) hypochlorous acid with Ka = 3.5 × 10-8

63) What is the hydronium ion concentration of a 0.100 M acetic acid solution with a Ka = 1.8 × 10-5? The

equation for the dissociation of acetic acid is:

CH3CO2H(aq) + H2O(l) ⇌ H3O+(aq) + CH3CO2–(aq).

A) 1.3 × 10-2 M

B) 4.2 × 10-2 M

C) 1.3 × 10–3 M

D) 4.2 × 10-3 M

64) What is the hydronium ion concentration of a 0.100 M hypochlorous acid solution with Ka = 3.5 ×

10-8? The equation for the dissociation of hypochlorous acid is:

HOCl(aq) + H2O(l) ⇌ H3O+(aq) + OCl–(aq).

A) 1.9 × 10-4

B) 5.9 × 10-4

C) 1.9 × 10–5

D) 5.9 × 10-5

65) Para-Aminobenzoic acid (PABA), p-H2NC6H4(COOH), is used in some sunscreens and hair

conditioning products. Calculate the pH of an aqueous solution with [PABA] = 0.030 M and Ka = 2.2 ×

10-5.

A) 1.52

B) 3.09

C) 4.66

D) 6.18

66) A tablet containing 500.0 mg of aspirin (acetylsalicylic acid or HC9H7O4) was dissolved in enough

water to make 100 mL of solution. Given that Ka = 3.0 × 10-4 for aspirin, what is the pH of the solution?

A) 1.57

B) 2.54

C) 3.52

D) 5.08

67) Benzoic acid (C6H5CO2H = HBz) solutions are sometimes used in experiments to determine the

molarity of a basic solution of unknown concentration. What is the pH of a 0.100 M solution of benzoic

acid if Ka = 6.5 × 10–5 and the equilibrium equation of interest is HBz(aq) + H2O(l) ⇌ H3O+(aq) + Bz–(aq).

A) 1.00

B) 2.59

C) 4.19

D) 5.19

68) Potassium hydrogen phthalate (molar mass = 204.2 g/mol) is one of the most commonly used acids for

standardizing solutions containing bases. KHP is a monoprotic weak acid with Ka = 3.91 × 10-6. Calculate

the pH of the solution that results when 0.40 g of KHP is dissolved in enough water to produce 25.0 mL

of solution.

A) 2.10

B) 3.26

C) 4.30

D) 5.41

69) Vinegar is a 5.0% solution by weight of acetic acid (CH3CO2H) in water. Given that Ka = 1.8 × 10-5 for

acetic acid and assuming the density of vinegar to be 1.00 g/cm3, what is the pH of this vinegar solution?

A) 2.00

B) 2.41

C) 2.87

D) 4.74

70) Vinegar is a 5.0% solution by weight of acetic acid (CH3CO2H) in water. Given that the pH for acetic

acid is 2.41, the Ka = 1.8 × 10–5 and assuming the density of vinegar to be 1.00 g/cm3, what is the percent

dissociation of acetic acid in vinegar?

A) 0.47%

B) 1.5%

C) 4.0%

D) 5.0%

71) What is the percent dissociation of a benzoic acid solution with pH = 2.59? The acid dissociation

constant for this monoprotic acid is 6.5 × 10-5.

A) 0.50%

B) 1.5%

C) 2.5%

D) 3.5%

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72) The percent dissociation of acetic acid changes as the concentration of the acid decreases. A 100-fold

decrease in acetic acid concentration results in a ________ fold ________ in the percent dissociation.

A) 10, increase

B) 10, decrease

C) 100, increase

D) 100, decrease

73) What is the second stepwise equilibrium constant expression for phosphoric acid H3PO4?

A) Ka2 = ([H3O+][H2PO4–])/([H3PO4])

B) Ka2 = ([H3O+]2[HPO42-])/([H3PO4])

C) Ka2 = ([H3O+]3[PO43–])/([H3PO4])

D) Ka2 = ([H3O+][HPO42–])/([H2PO4–])

74) Calculate the pH of a 0.020 M carbonic acid solution, H2CO3(aq), that has the stepwise dissociation

constants Ka1 = 4.3 × 10–7 and Ka2 = 5.6 × 10–11.

A) 1.70

B) 4.03

C) 6.37

D) 10.25

75) Calculate the pH of a 0.20 M H2SO3 solution that has the stepwise dissociation constants Ka1 = 1.5 ×

10-2 and Ka2 = 6.3 × 10-8.

A) 1.26

B) 1.32

C) 1.82

D) 2.52

76) Calculate the concentration of bicarbonate ion, HCO3–, in a 0.010 M H2CO3 solution that has the

26

stepwise dissociation constants Ka1 = 4.3 × 10-7 and Ka2 = 5.6 × 10–11.

A) 6.6 × 10-5 M

B) 4.3 × 10-7 M

C) 4.3 × 10–9 M

D) 5.6 × 10–11 M

77) What is the pH of a 0.10 M H2Se solution that has the stepwise dissociation constants Ka1 = 1.3 × 10-4

and Ka2 = 1.0 × 10–11?

A) 2.44

B) 3.89

C) 4.89

D) 5.50

78) What is the selenide ion concentration [Se2-] for a 0.100 M H2Se solution that has the stepwise

dissociation constants of Ka1 = 1.3 × 10-4 and Ka2 = 1.0 × 10–11?

A) 3.6 × 10-3 M

B) 1.3 × 10-4 M

C) 1.3 × 10–5 M

D) 1.0 × 10–11 M

79) Which of the following can be classified as a weak base?

A) CH3NH2

B) NH2OH

C) Both CH3NH2 and NH2OH

D) Neither CH3NH2 nor NH2OH

80) What is the pH of a 0.100 M NH3 solution that has Kb = 1.8 × 10-5? The equation for the dissociation of

NH3 is

NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH–(aq).

A) 1.87

B) 2.87

C) 11.13

D) 12.13

81) What is the pH of a 0.30 M pyridine solution that has a Kb = 1.9 × 10-9? The equation for the

dissociation of pyridine is

C5H5N(aq) + H2O(l) ⇌ C5H5NH+(aq) + OH–(aq).

A) 4.62

B) 8.72

C) 9.38

D) 10.38

82) Aniline, (C6H5NH2, Kb = 4.3 × 10–10 at 25°C) is an industrially important amine used in the making of

dyes. Determine the pH of an aniline solution made by dissolving 3.90 g of aniline in enough water to

make 100 mL of solution.

A) 4.87

B) 9.13

C) 9.74

D) 10.74

83) Determine the ammonia concentration of an aqueous solution that has a pH of 11.50. The equation for

the dissociation of NH3 (Kb = 1.8 × 10-5) is

NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH–(aq).

A) 2.5 M

B) 0.55 M

C) 5.7 × 10–3 M

D) 3.2 × 10-3 M

84) How many grams of pyridine are there in 100 mL of an aqueous solution that has a pH of 9.00? The

Kb for pyridine is 1.9 × 10-9 and the equation of interest is

C5H5N(aq) + H2O(l) ⇌ C5H5NH+(aq) + OH–(aq).

A) 0.053 g

B) 0.42 g

C) 0.79 g

D) 7.9 g

85) Ammonia NH3, has a base dissociation constant of 1.8 × 10-5. What is the conjugate acid of ammonia

and what is its acid dissociation constant?

A) NH4+, 1.9 × 109

B) NH4+, 1.8 × 10-5

C) NH4+, 5.6 × 10–10

D) NH2–, 5.6 × 10–10

86) Methylamine CH3NH2, has a base dissociation constant of 3.7 × 10-4. What is the conjugate acid of

methylamine and what is its acid dissociation constant?

A) CH3NH3+, 2.7 × 103

B) CH3NH3+, 3.7 × 10-4

C) CH3NH3+, 2.7 × 10–11

D) CH3NH2–, 2.7 × 10–11

87) Acetic acid CH3COOH, has an acid dissociation constant of 1.8 × 10-5. What is the conjugate base of

acetic acid and what is its base dissociation constant?

A) CH3C(OH)2+, 5.6 × 104

B) CH3C(OH)2+, 5.6 × 10–10

C) CH3COOH, 5.6 × 10–10

D) CH3CO2–, 5.6 × 10–10

88) Dihydrogen phosphate H2PO4–, has an acid dissociation constant of 6.2 × 10-7. What is the conjugate

base of H2PO4– and what is its base dissociation constant?

A) H3PO4, 1.6 × 106

B) H3PO4, 1.6 × 10-8

C) HPO42-, 1.6 × 106

D) HPO42-, 1.6 × 10-8

89) If you know Kb for ammonia, NH3, you can calculate the equilibrium constant, Ka, for the following

reaction:

NH4+ + H2O ⇌ NH3 + H3O+

using the equation:

A) Ka = Kw × Kb

B) Ka = Kw / Kb

C) Ka = 1 / Kb

D) Ka = Kb / Kw

90) If an equal number of moles of the weak acid HCN and the strong base KOH are added to water, is

the resulting solution acidic, basic, or neutral?

A) acidic

B) basic

C) neutral

D) There is insufficient information provided to answer this question.

91) Arrange the following 0.10 M aqueous solutions in order of increasing pH:

NaOH, HBr, NaCH3CO2, KBr, NH4Br.

A) HBr, KBr, NH4Br, NaCH3CO2, NaOH

B) NaOH, NaCH3CO2, NH4Br, KBr, HBr

C) NaOH, NaCH3CO2, KBr, NH4Br, HBr

D) HBr, NH4Br, KBr, NaCH3CO2, NaOH

92) Which one of the following salts, when dissolved in water, produces the solution with a pH closest to

7.00?

A) NH4Cl

B) BaO

C) NaHSO4

D) RbI

93) Calculate the pH of a 0.100 M NaCH3CO2 solution. Ka for acetic acid, CH3CO2H, is 1.8 × 10-5.

A) 2.87

B) 5.13

C) 8.87

D) 11.13

94) Calculate the pH of a of 0.100 M KBrO solution. Ka for hypobromous acid, HBrO, is 2.0 × 10-9.

A) 3.15

B) 4.85

C) 9.15

D) 10.85

95) Calculate the pH of a 0.100 M CH3NH3Cl solution. Kb for methylamine, CH3NH2, is 3.7 × 10–4.

A) 2.22

B) 5.78

C) 8.22

D) 11.78

96) Equal volumes of 0.10 M NH3 (Kb = 1.8 × 10-5) and 0.10 M HCN (Ka = 4.9 × 10–10) are mixed together.

Will the resulting solution be acidic, basic, or neutral?

A) acidic

B) basic

C) neutral

D) insufficient information to solve

97) What is the identity of M in the hydrate M(H2O)6n+ that has the 0.10 M solution with the lowest pH?

A) Li+

B) Na+

C) Mg2+

D) Al3+

98) What is the identity of M in the hydrate M(H2O)6n+ that has the 0.10 M solution with the highest pH?

A) Li+

B) Na+

C) Mg2+

D) Al3+

99) Identify the Lewis acid that acts as a reactant in the following reaction.

Fe(H2O)63+(aq) + 6 CN–(aq) → Fe(CN)63-(aq) + 6 H2O(l)

A) Fe3+

B) H2O

C) CN–

D) Fe(H2O)63+

100) Identify the Lewis acid that acts as a reactant in the following reaction.

Co(H2O)63+(aq) + 6 NH3(aq) → Co(NH3)63+(aq) + 6 H2O(l)

A) Co(H2O)63+

B) Co3+

C) NH3

D) H2O

101) For Cu2+ and CO2, which will behave as a Lewis acid toward OH– in water?

A) only Cu2+

B) only CO2

C) Cu2+ and CO2

D) neither Cu2+ nor CO2

102) Which one of the following is expected to be the strongest Lewis acid?

A) Fe

B) Fe+

C) Fe2+

D) Fe3+

103) Which of the following species cannot act as a Lewis base?

A) O2-

B) CH4

C) H2O

D) NH3

In the following reaction the unshaded spheres represent H atoms.

104) Identify the Br∅nsted-Lowry acids.

A) (1) and (3)

B) (1) and (4)

C) (2) and (3)

D) (2) and (4)

105) Identify the Br∅nsted-Lowry bases.

A) (1) and (3)

B) (1) and (4)

C) (2) and (3)

D) (2) and (4)

In the following reaction the unshaded spheres represent H atoms.

106) Identify the Br∅nsted-Lowry acids.

A) (1) and (3)

B) (1) and (4)

C) (2) and (3)

D) (2) and (4)

107) Identify the Br∅nsted-Lowry bases.

A) (1) and (3)

B) (1) and (4)

C) (2) and (3)

D) (2) and (4)

In the following reaction the unshaded spheres represent H atoms.

108) Identify the Br∅nsted-Lowry acid/base conjugate pairs.

A) (1)/(2) and (3)/(4)

B) (1)/(3) and (2)/(4)

C) (1)/(4) and (2)/(3)

In the following reaction the unshaded spheres represent H atoms.

109) Identify the Br∅nsted-Lowry acid/base conjugate pairs.

A) (1)/(2) and (3)/(4)

B) (1)/(3) and (2)/(4)

C) (1)/(4) and (2)/(3)

The following pictures represent aqueous solutions of three acids HA (A = X, Y, or Z); water molecules

have been omitted for clarity.

110) Arrange the three acids in order of increasing acid strength.

A) HZ < HY < HX

B) HY < HZ < HX

C) HZ < HX < HY

D) HX < HZ < HY

111) Which acid, if any, is a strong acid?

A) All are strong acids.

B) HX and HZ

C) HY

D) None are strong acids.

112) Which acid has the smallest value of Ka?

A) HX

B) HY

C) HZ

D) All have the same Ka value.

113) Which acid has the lowest percent dissociation?

A) HX

B) HY

C) HZ

D) All have the same percent dissociation.

114) Which acid solution has the lowest pH?

A) HX

B) HY

C) HZ

D) All have the same pH.

115) Which of the above pictures represents a solution of a weak diprotic acid H2A for which Ka1 >> Ka2?

(Water molecules have been omitted for clarity.)

A) picture (a)

B) picture (b)

C) picture (c)

D) picture (d)

116) Which of the above pictures represents a solution of a diprotic acid H2A for which Ka1 = ∞ and Ka2

is exceptionally small. (Water molecules have been omitted for clarity.)

A) picture (a)

B) picture (b)

C) picture (c)

D) picture (d)

40

The following pictures represent equal volumes of aqueous solutions of three acids HA (A = X, Y, or Z);

water molecules have been omitted for clarity.

117) Arrange the acids in order of increasing acid strength.

A) HZ < HY < HX

B) HY < HZ < HX

C) HZ < HX < HY

D) HX < HZ < HY

118) Arrange the acids in order of increasing value of Ka.

A) Ka(HZ) < Ka(HY) < Ka(HX)

B) Ka(HY) < Ka(HZ) < Ka(HX)

C) Ka(HZ) < Ka(HX) < Ka(HY)

D) Ka(HX) < Ka(HZ) < Ka(HY)

119) Arrange the acids in order of increasing value of percent dissociation.

A) HZ < HY < HX

B) HY < HZ < HX

C) HZ < HX < HY

D) HX < HZ < HY

120) Arrange the acids in order of increasing pH.