Deck 7: Acids and Bases

Question 1

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) CH₃OH(aq) + OH^-(aq)
Identify the strongest base.

A) CH₃OH
B) CH₃O^-
C) H₂O
D) NO₃^-
E) CN^-

Answer 1

CH₃O^-

Question 2

Which of the following is a conjugate acid-base pair?

A) H₃O⁺/OH^-
B) NH₄⁺/NH₃
C) Mg²⁺/Mg(OH)₂
D) HCl/OCl₂^-
E) H₃PO₄/PO₄^3-

Answer 2

NH₄⁺/NH₃

Question 3

Which of the following does not represent a conjugate acid-base pair?

A) H₃O⁺ and H₂O
B) HCN and NH₃
C) HF and F^-
D) C₅H₅NH⁺ and C₅H₅N
E) none of these

Answer 3

HCN and NH₃

Question 4

Identify the Brønsted acids and bases in the following equation (A = Brønsted acid, B = Brønsted base). HPO₄^2- + HSO₄^- H₂PO₄^- + SO₄^2-

A) A B B A
B) B A A B
C) A B A B
D) B B A A
E) B A B A

Question 5

The equilibrium constant for the reaction A^- + H⁺ HA
Is called

A) K_b
B)
C) K_wK_a
D)
E) K_a

Question 6

The conjugate base of a weak acid is

A) a strong base.
B) a strong acid.
C) a weak base.
D) a weak acid.
E) none of these

Question 7

The strong acid HA is added to water. Which of the following is the strongest base in the system?

A) A^-
B) HA
C) H₃O⁺
D) H₂A^-
E) H₂O

Question 8

The acids HC₂H₃O₂ and HF are both weak, but HF is a stronger acid than HC₂H₃O₂. HCl is a strong acid. Order the following according to base strength.

A) Cl^- > F^- > C₂H₃O₂^- > H₂O
B) C₂H₃O₂^- > F^- > H₂O > Cl^-
C) C₂H₃O₂^- > F^- > Cl^- > H₂O
D) F^- > C₂H₃O₂^- > H₂O > Cl^-
E) none of these

Question 9

Given that the K_a for HOCl is 3.5 * 10^-8, calculate the K value for the reaction of HOCl with OH^-.

A) 3.5 * 10^-22
B) 3.5 *10^-8
C) 2.9 * 10^-7
D) 3.5 * 10⁶
E) none of these

Question 10

Which reaction does not proceed far to the right?

A) HCN + OH^- $\rightarrow$ H₂O + CN^-
B) HCl + H₂O $\rightarrow$ H₃O⁺ + Cl^-
C)
D) H₃O⁺ + OH^- $\rightarrow$ 2H₂O
E)

Question 11

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 $\rightarrow$ SO₄^2- + H₃O⁺
B) HSO₄^- + H₂O $\rightarrow$ H₂SO₄ + OH^-
C) HSO₄^- + H₃O⁺ $\rightarrow$ SO₃ + 2H₂O
D) HSO₄^- + OH^- $\rightarrow$ H₂SO₄ + O^2-
E) none of these

Question 12

Which of the following represents a conjugate acid-base pair?

A) H₂PO₄^- and PO₄^3-
B) HNO₃ and NO₃^-
C) HCl and NaOH
D) HSO₄^- and SO₃^2-
E) none of these

Question 13

Which of the following is the equilibrium constant expression for the dissociation of the weak acid HOCl?

A)
B) K = [H⁺][OCl^-]
C)
D)
E) none of these

Question 14

In deciding which of two acids is the stronger, one must know

A) the pH of each acid solution only.
B) the concentration of each acid solution only.
C) the equilibrium constant of each acid only.
D) all of the these.
E) both the concentration and the equilibrium constant of each acid.

Question 15

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) CH₃OH(aq) + OH^-(aq)
Identify the strongest acid.

A) HNO₃
B) HCN
C) OH^-
D) H₂O
E) CH₃OH

Question 16

According to the Brønsted-Lowry definition, an acid is

A) a substance that can donate a proton to another species.
B) a substance that increases the hydroxide ion concentration in a solution.
C) a substance that can accept a proton from another species in solution.
D) an electron pair acceptor.
E) a substance that increases the hydrogen ion concentration in a solution.

Question 17

Which of the following reactions is associated with the definition of K_a?

A) [Al(OH₂)₆]³⁺
Al(OH)(OH₂)₅²⁺ + H⁺
B) CN^- + H⁺ HCN
C) OCl^- + H₂O HOCl + OH^-
D) Al³⁺ + 6H₂O Al(OH₂)₆³⁺

Question 18

For the equilibrium that exists in an aqueous solution of nitrous acid (HNO₂, a weak acid), the equilibrium constant expression is

A)
B)
C)
D) K = [H⁺][NO₂^-]
E) none of these

Question 19

Which of the following species is not amphoteric?

A) H₂PO₄^-
B) HPO₄^2-
C) H₂O
D) HSO₄^-
E) All of these are amphoteric.

Question 20

The following acids are listed in order of decreasing acid strength in water. HI > HNO₂ > CH₃COOH > HClO > HCN
According to Brønsted-Lowry theory, which of the following ions is the weakest base?

A) ClO^-
B) NO₂^-
C) CH₃COO^-
D) I^-
E) CN^-

Question 21

Calculate the pH of a solution made by mixing equal volumes of a solution of HCl with a pH of 1.68 and a solution of HNO₃ with a pH of 2.39. (Assume the volumes are additive.)

A) 4.06
B) 2.03
C) 2.39
D) 1.90
E) 1.60

Question 22

How many moles of benzoic acid, a monoprotic acid with K_a = 6.4 *10^-5, must be dissolved in 500. mL of H₂O to produce a solution with pH = 2.50?

A) 1.6 *10^-1
B) 2.0 * 10^-2
C) 7.8 *10^-2
D) 0.50
E) none of these

Question 23

The pH of a solution is raised from 3 to 5. Which statement is false?

A) The final [OH^-] (at pH = 5) is 10^-9 M.
B) The [H⁺] decreases by a factor of 20.
C) The initial solution could be 0.001 M HNO₃.
D) The pOH decreases from 11 to 9.
E) The initial [H⁺] (at pH = 3) is 10^-3 M.

Question 24

A monoprotic weak acid, when dissolved in water, is 0.92% dissociated and produces a solution with pH = 3.42. Calculate K_a for the acid.

A) 1.4 * 10^-7
B) 2.8 * 10^-3
C) 3.5 * 10^-6
D) We need to know the initial concentration of the acid.
E) none of these

Question 25

At a particular temperature, the ion-product constant of water, K_w, is 4.4 *10^-15. What is the pH of pure water at this temperature?

A) 6.26
B) 7.00
C) 6.82
D) 6.36
E) 7.18

Question 26

In pure liquid ammonia, the equilibrium concentrations of both NH₄⁺ and NH₂^- are 3 *10^-14 M. Which of the following equations always holds for liquid ammonia solutions?

A) pNH₄⁺ = log [pNH₄⁺]
B) pNH₄⁺ = 27.0
C) pNH₄⁺ - pNH₂^- = 13.5
D) pNH₄⁺ = 27.0 - pNH₂^-
E) pNH₄⁺ + pNH₂^- = 13.5

Question 27

Calculate the pH of the following aqueous solutions. Choose your answer from the given pH ranges. 0.1 M NaCN (pK_a for HCN = 9.31)

A) pH 11.00-14.00
B) pH 3.00-5.99
C) pH 0.00-2.99
D) pH 6.00-8.99
E) pH 9.00-10.99

Question 28

Find the pH of a solution at 25°C in which [OH^-] = 2.5 * 10^-9 M.

A) 6.50
B) 8.60
C) 7.40
D) 2.50
E) 5.40

Question 29

Calculate the pH of a 1.9 M solution of HNO₃.

A) -0.64
B) -0.28
C) 14.28
D) 13.72
E) 0.28

Question 30

Calculate [H⁺] in a solution that has a pH of 9.7.

A) 1 *10^-1 M
B) 5 *10^-5 M
C) 10 M
D) 4 M
E) 2*10^-10 M

Question 31

For a neutral solution, it must be true that

A) pH = 7.00.
B) [H⁺] = [OH^-].
C) [H₂O] = 1 *10^-14
D) [H⁺] = 0 M.
E) At least two of these must be true.

Question 32

For nitrous acid, HNO₂, K_a = 4.0 * 10^-4. Calculate the pH of 0.27 M HNO₂.

A) 2.83
B) 1.98
C) 3.40
D) 0.57
E) 4.54

Question 33

What concentration of HF (K_a = 7.2 * 10^-4) has the same pH as that of 0.069 M HCl?

A) 6.6 M
B) 5.0 *10^-6 M
C) 1.0 * 10^-2 M
D) 0.069 M
E) 0.15 M

Question 34

The pH of a 0.013 M weak acid solution is 5.27. Calculate K_a for this acid.

A) 1.9 *10^-9
B) 2.2 * 10^-9
C) 5.4* 10^-6
D) 2.6*10^-16
E) 4.2*10^-8

Question 35

HCl gas is in a 1.21-L cylinder at 0.870 atm and 28.0° C. This gas is dissolved in 750.0 mL of water. Calculate the pH of this solution (assume no volume change).

A) 0.950
B) 2.52
C) 1.25
D) 1.37
E) none of these

Question 36

Calculate the pH of a 0.040 M perchloric acid (HClO₄) solution.

A) 1.40
B) 2.10
C) 12.60
D) 11.90
E) none of these

Question 37

As water is heated, its pH decreases. This means that

A) [OH^-] > [H⁺].
B) [H⁺] > [OH^-].
C) the water is no longer neutral.
D) Two of these are correct.
E) None of these is correct.

Question 38

Which of the following indicates the most acidic solution?

A) pOH = 5.9
B) [H⁺] = 0.3 M
C) [H⁺] = 1.0 *10^-4 M
D) [OH^-] = 0.5 M
E) pH = 1.2

Question 39

The pH of a 0.6 M solution of a weak acid is 4.0. What percent of the acid has ionized?

A) 0.02%
B) 7%
C) 4%
D) 0.06%
E) 2%

Question 40

Solid calcium hydroxide is dissolved in water until the pH of the solution is 10.94. What is the hydroxide ion concentration [OH^-] of the solution?

A) 3.06 M
B) 1.1 *10^-11 M
C) 1.0 *10^-14 M
D) 8.7 *10^-4 M
E) none of these

Question 41

The pK_a of HOCl is 7.5. Calculate the pH of a 0.5 M solution of HOCl.

A) 0.3
B) 6.5
C) 7.5
D) 10.1
E) 3.9

Question 42

A 0.050 M aqueous solution of a weak monoprotic acid is 1.2% ionized at equilibrium at 25° C. Calculate K_a for this acid.

A) 7.3 * 10^-33
B) 29
C) 3.4 *10^-2
D) 6.4 *10^-8
E) none of these

Question 43

Calculate the pOH of a 0.70 M solution of acetic acid (K_a = 1.8 *10^-5) at 25°C.

A) 2.72
B) 9.26
C) 4.90
D) 11.55
E) 2.45

Question 44

Calculate the pH of the following aqueous solutions. Choose your answer from the given pH ranges. 0.1 M methylamine (pK_b = 3.36)

A) pH 11.00-14.00
B) pH 6.00-8.99
C) pH 3.00-5.99
D) pH 0.00-2.99
E) pH 9.00-10.99

Question 45

Calculate the pH of a 0.10 M solution of HOCl, K_a = 3.5 * 10^-8.

A) 8.46
B) 4.23
C) 1.00
D) 3.73
E) 3.23

Question 46

Which of the following reactions is associated with the definition of K_b?

A) [Al(OH₂)₆]³⁺ Al(OH)(OH₂)₅²⁺ + H⁺
B) OCl^- + H₂O HOCl + OH^-
C) Al³⁺ + 6H₂O Al(OH₂)₆³⁺
D) CN^- + H⁺ HCN

Question 47

The pH of a 0.100 M solution of an aqueous weak acid (HA) is 3.20. What is K_a for the weak acid?

A) 4.0 * 10^-6
B) 6.3*10^-4
C) 7.2 *10^-5
D) 3.2
E) none of these

Question 48

A 0.240 M solution of the salt NaA has pH = 8.40. Calculate K_a for the acid HA.

A) 2.63 * 10^-11
B) 3.80 * 10^-4
C) 1.05 * 10^-5
D) 6.60 *10^-17
E) none of these

Question 49

If an acid, HA, is 10.0% dissociated in a 1.0 M solution, what is K_a for this acid?

A) 6.3 * 10^-2
B) 9.1 * 10^-2
C) 8.1 * 10^-1
D) 1.1 * 10^-2
E) none of these

Question 50

The pH of a 0.22 M solution of a weak monoprotic acid, HA, is 2.74. Calculate K_a for this acid.

A) 3.3 * 10^-6
B) 1.5 *10^-5
C) 5.5 * 10^-10
D) 2.2 * 10^-4
E) 1.8* 10^-3

Question 51

Which of the following aqueous solutions will have the highest pH? For NH₃, K_b = 1.8 * 10^-5; for C₂H₃O₂^-, K_b = 5.6 *10^-10.

A) 2.0 M NH₃
B) 2.0 M HCl
C) 2.0 M NaOH
D) 2.0 M HC₂H₃O₂
E) All these solutions will have the same pH.

Question 52

In a solution prepared by dissolving 0.100 mol of propionic acid in enough water to make 1.00 L of solution, the pH is observed to be 1.35. What is K_a for propionic acid (HC₃H₅O₂)?

A) 4.5 * 10^-2
B) 2.0 * 10^-2
C) 5.0 * 10^-12
D) 3.6 * 10^-2
E) none of these

Question 53

Calculate [H⁺] in a 0.012 M solution of HCN, K_a = 6.2 *10^-10.

A) 3.0 *10^-7 M
B) 3.7 * 10^-9 M
C) 6.2 *10^-10 M
D) 2.7 * 10^-6 M
E) 2.3 * 10^-4 M

Question 54

A 2.5 M solution of a weak acid is 0.52% ionized. What is K_a for this acid?

A) 1.3 * 10^-2
B) 6.8* 10^-5
C) 0.11
D) 1.1* 10^-5
E) none of these

Question 55

Which of the following reactions is associated with the definition of K_b?

A) CN^- + H⁺ HCN
B) Cr³⁺ + 6H₂O Cr(OH₂)₆³⁺
C) Zn(OH₂)₆²⁺ [Zn(OH₂)₅OH]⁺ + H⁺
D) F^- + H₂O HF + OH^-
E) none of these

Question 56

Calculate the pH of a 0.02 M solution of KOH.

A) 1.7
B) We cannot calculate the answer unless a volume is given.
C) 12.3
D) 2.0
E) 12.0

Question 57

Calculate the pOH of a 0.10 M solution of Ba(OH)₂.

A) 13.30
B) 0.70
C) 13.00
D) 1.00
E) none of these

Question 58

How much water should be added to 10.0 mL of 12.0 M HCl so that it has the same pH as 0.90 M acetic acid (K_a = 1.8*0 10^-5)? (Assume the volumes are additive.)

A) 30 mL
B) 3 L
C) 30 L
D) 300 L
E) 300 mL

Question 59

Calculate the pH of a solution made by a mixture of the following acids: 0.40 M HC₂H₃O₂ (K_a = 1.8 *10^-5), 0.10 M HOCl (K_a = 3.5 *10^-8), and 0.20 M HCN (K_a = 6.2 *10^-10).

A) 2.57
B) 3.92
C) 4.95
D) 4.23
E) 3.49

Question 60

The pH of a solution made of 0.100 mol of a weak monoprotic acid HA in 1.000 L of solution is 1.470. Calculate K_a for this acid.

A) 29.5
B) 0
C) 0.100
D) 0.0174
E) 0.0339

Question 61

Calculate [H⁺] in a 1.0 M solution of Na₂CO₃ (for H₂CO₃, K_a1 = 4.3 * 10^-7 and K_a2 = 5.6 * 10^-11).

A) 6.6 *10^-4 M
B) 7.5 *10^-13 M
C) 7.5 * 10^-6 M
D) 1.3 * 10^-2 M
E) none of these

Question 62

A 0.10-mol sample of a diprotic acid, H₂A, is dissolved in 250 mL of water. K_a1 for this acid is 1.0 * 10^-5 and K_a2 is 1.0 *10^-10. Calculate the concentration of A^2- in this solution.

A) 2.0 * 10^-3 M
B) 4.0 * 10^-6 M
C) 0.40 M
D) 1.0 * 10^-10 M
E) 1.0 * 10^-5 M

Question 63

A 2.58-g sample of NaOH(s) is added to enough water to make 600.0 mL of solution at 25°C. What is the pH of this solution?

A) 10.03
B) 0.97
C) 13.03
D) 14.63
E) 12.59

Question 64

The pH of a 2.1 *10^-3 M solution of a weak base is 9.87. Calculate K_b for this base.

A) 2.6 * 10^-6
B) 1.2 * 10^-4
C) 6.4 *10^-8
D) 8.7 *10^-18
E) none of these

Question 65

Calculate the pH of a 0.048 M solution of KOH.

A) 12.68
B) 11.32
C) 1.32
D) 2.68
E) none of these

Question 66

Calculate the pH of a solution made by mixing equal volumes of a solution of NaOH with a pH of 11.40 and a solution of KOH with a pH of 10.30. (Assume the volumes are additive.)

A) 11.13
B) 1.10
C) 10.85
D) 21.70
E) none of these

Question 67

Calculate the pH of a 0.50 M NH₃ (K_b = 1.8 *10^-5) solution.

A) 4.78
B) 2.52
C) 7.00
D) 13.72
E) none of these

Question 68

Calculate the percentage of pyridine (C₅H₅N) that forms pyridinium ion, C₅H₅NH⁺, in a 0.10 M aqueous solution of pyridine (K_b = 1.7 * 10^-9).

A) 0.77%
B) 0.060%
C) 0.0060%
D) 1.6%
E) 0.013%

Question 69

Consider two separate solutions of equal concentration. The first solution contains sodium hydroxide, and the second solution contains barium hydroxide. Which solution has the lower pH?

A) The barium hydroxide solution.
B) The sodium hydroxide solution.
C) We need to know the concentrations to answer this question.
D) The pH's of the two solutions are equal.
E) We need to know the volumes to answer this question.

Question 70

What is [OH^-] in a 0.50 M pyridine (C₅H₅N; K_b = 1.7 * 10^-9) solution?

A) 1.8 * 10^-9 M
B) 2.9 *10^-5 M
C) 0.50 M
D) 3.3 *10^-10 M
E) none of these

Question 71

Calculate the pH of a 0.05 M solution of ascorbic acid (K_a1 = 7.9 *10^-5; K_a2 = 1.6 * 10^-12).

A) 5.4
B) 3.1
C) 6.5
D) 1.3
E) 2.7

Question 72

The conjugate acid and conjugate base of bicarbonate ion, HCO₃^-, are, respectively,

A) H₃O⁺ and OH^-
B) H₂CO₃ and OH^-
C) H₃O⁺ and CO₃^2-
D) H₂CO₃ and CO₃^2-
E) CO₃^2- and OH^-

Question 73

What is the pH in a solution of 1.0 M H₂A (K_a1 = 1.0 *10^-6; K_a2 = 1.0 *10^-14)?

A) 10.00
B) 3.00
C) 4.00
D) 13.00
E) 7.00

Question 74

The pH of a 0.132 M solution of a weak base is 10.88 at 25°C. Calculate the pH of a 0.0392 M solution of the base at 25°C.

A) 10.61
B) 11.40
C) 3.23
D) 3.39
E) 10.35

Question 75

Calculate the pH of a 5.0 M solution of aniline (C₆H₅NH₂; K_b = 3.8 *10^-10).

A) 9.64
B) 9.30
C) 4.36
D) -0.070
E) none of these

Question 76

What is the equilibrium constant for the following reaction? NH₄⁺ + OH^- NH₃ + H₂O

A)
B)
C)
D)
E)

Question 77

Calculate the pH of a solution that is 7.22 *10^-4 M C₆H₅NH₂. K_b is 3.8 *10^-10.

A) 6.28
B) 7.72
C) 6.50
D) 7.50
E) none of these

Question 78

Of the bases NaOH, H₂O, CN^-, SO₄^2-, and HPO₄^2-, which is the weakest? (K_a for HCN is 6.2 *10^-10; K_a for HSO₄^- is 1.2 *10^-2; and K_a3 for H₃PO₄, is 4.8*10^-13)

A) CN^-
B) HPO₄^2-
C) SO₄^2-
D) NaOH
E) H₂O

Question 79

Which of the following species is present in the greatest concentration in a 0.100 M H₂SO₄ solution in H₂O?

A) H₂SO₄
B) H₃O⁺
C) All species are in equilibrium and therefore have the same concentration.
D) HSO₄^-
E) SO₄^2-

Question 80

The dihydrogenphosphate ion, H₂PO₄^-, has both a conjugate acid and a conjugate base. These are, respectively,

A) H₂PO₄^- and HPO₄^2-
B) HPO₄^2- and H₃PO₄
C) HPO₄^2- and PO₄^3-
D) H₃PO₄ and PO₄^3-
E) H₃PO₄ and HPO₄^2-