Deck 15: Acidbase Equilibria: Proton Transfer in Biological Systems

Question 1

The base ionization constant K_b describes which of the following reactions for a weak base, B, in aqueous solution?

A)B +H⁺
BH⁺
B)B +H₃O⁺ BH⁺+ H₂O
C)B + H₂O BH^- + OH^-
D)B + OH^- BH^- + O^2-
E)BH⁺ + OH^- B + H₂O

Answer 1

B + H₂O BH^- + OH^-

Question 2

In the following reaction in aqueous solution, the base reactant is ________ and its conjugate acid product is ________.
HCOOH + C₅H₅N HCOO^- + C₅H₅NH⁺

A)HCOOH; HCOO^-
B)C₅H₅N; HCOO^-
C)HCOOH; C₅H₅NH⁺
D)C₅H₅N; C₅H₅NH⁺
E)C₅H₅N; OH^-

Answer 2

C₅H₅N; C₅H₅NH⁺

Question 3

Solutions of each of the hypothetical bases in the following table are prepared with an initial concentration of 0.100 M. Which of the four solutions will have the lowest pH and be least basic?

A)A
B)B
C)C
D)D
E)All will have the same pH because the concentrations are the same.

Answer 3

A

Question 4

Which sketch best represents the qualitative molecular view of an aqueous solution of sodium hydroxide? (Water molecules are not shown explicitly.)

A)
B)
C)
D)

Question 5

In the following reaction in aqueous solution, the acid reactant is ________ and its conjugate base product is ________.
CH₃NH₂ + HSO₄^- CH₃NH₃⁺ + SO₄^2-

A)CH₃NH₂; CH₃NH₃⁺
B)CH₃NH₂; SO₄^2-
C)HSO₄^-; CH₃NH₃⁺
D)HSO₄^-; SO₄^2-
E)HSO₄^-; H₃O⁺

Question 6

Which of the following is a strong acid?

A)HNO₃
B)H₂S
C)HNO₂
D)HCO₃^-
E)HOCl

Question 7

Which of the following is the conjugate acid of the hydrogen phosphate ion, HPO₄^2-?

A)H₃PO₄
B)H₂PO₄^-
C)HPO₄^2-
D)PO₄^3-
E)H₃O⁺

Question 8

Ammonia (NH₃) acts as a weak base in aqueous solution. What is the acid that reacts with this base when ammonia is dissolved in water?

A)None, there are no acids in pure water.
B)H₂O
C)NH₄⁺
D)trick question, because no acids are present, ammonia cannot act as a base
E)oxygen that always is dissolved in water

Question 9

The acid ionization equilibrium constant, K_a, describes the reaction (where HA is a generic weak acid) ________

A)HA +OH^- H₂O +A^-.
B)HA + H₂O H₃O⁺ + A^-.
C)HA + H₃O⁺ H₂A^- + H₂O.
D)HA + H₂A⁺ H₂A^-+ HA.
E)H₃O⁺ +A^- HA + H₂O.

Question 10

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

A)NH₃ and NH₄⁺
B)H₃O⁺ and OH^-
C)NH₂^- and NH₄⁺
D)H₂O and O^2-
E)NaF and F^-

Question 11

Which sketch best represents the qualitative molecular view of an aqueous solution of nitrous acid? (Water molecules are not shown explicitly.)

A)
B)
C)
D)

Question 12

Three acids found in foods are lactic acid (in milk products), oxalic acid (in rhubarb), and malic acid (in apples). The pK_a values are LA = 3.88, OA = 1.23, and MA = 3.40. Which list has these acids in order of decreasing acid strength?

A)LA > OA > MA
B)LA > MA > OA
C)OA > MA > LA
D)OA > LA > MA
E)MA > LA > OA

Question 13

Which of the following is the conjugate base of the hydrogen carbonate ion, HCO₃^-?

A)H₂CO₃
B)HCO₃^-
C)CO₃^2-
D)OH^-
E)H₃CO₃⁺

Question 14

Which one of the following is not a strong base?

A)lithium hydroxide, LiOH
B)sodium hydroxide, NaOH
C)potassium hydroxide, KOH
D)calcium hydroxide, Ca(OH)₂
E)ammonium hydroxide, NH₄OH

Question 15

Which one of the following is not a strong acid?

A)nitric acid, HNO₃
B)sulfuric acid, H₂SO₄
C)carbonic acid, H₂CO₃
D)hydrochloric acid, HCl
E)perchloric acid, HClO₄

Question 16

Which one of the following is not a conjugate acid-base pair?

A)NH₃ and NH₂^-
B)HNO₃ and HNO₂
C)HI and I^-
D)H₂PO₄^- and HPO₄^2-
E)H₂O and OH^-

Question 17

Which one of the following is a strong acid?

A)nitrous acid, HNO₂
B)sulfurous acid, H₂SO₃
C)carbonic acid, H₂CO₃
D)hydrofluoric acid, HF
E)perchloric acid, HClO₄

Question 18

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

A)NaF and F^-
B)HNO₃ and HNO₂
C)HI and I^-
D)NH₄⁺ and NH₂^-
E)H₂O and H₂O₂

Question 19

In the following reaction in aqueous solution, the acid reactant is ________ and its conjugate base product is ________.
CH₃COOH +NH₃ CH₃COO^-+NH₄⁺

A)CH₃COOH; CH₃COO^-
B)CH₃COOH; NH₄⁺
C)NH₃; CH₃COO^-
D)NH₃; NH₄⁺
E)CH₃COOH; H₃O⁺

Question 20

Which one of the following is not a conjugate acid-base pair?

A)NH₃ and NH₄⁺
B)H₃O⁺ and OH^-
C)H₂PO₄^- and HPO₄^2-
D)HS^- and H₂S
E)NH₃ and NH₂^-

Question 21

A substance that can act as both an acid and base is ________

A)amphibious.
B)amphiprotic.
C)bacidic.
D)androgynous.
E)acibasic.

Question 22

When [H⁺] = 1.0 $\times$ 10^-7 M in water at 25 ^$\circ$ C, then ________

A)pH = 1.
B)pH = 10^-7.
C)[OH^-] = 1.0 $\times$ 10^-7 M.
D)[OH^-] = 1.0 $\times$ 10⁷ M.
E)[OH^-] = 0 M.

Question 23

Which one A-D is not related to the water autoionization constant, K_w?

A)[H₃O⁺] [OH^-]
B)1.0 $\times$ 10^-14 at 25 ^$\circ$ C
C)2 H₂O H₃O⁺ + OH^-
D)pH = 7 at 25 ^$\circ$ C
E)A-D are all related to K_w.

Question 24

Sometimes liquid ammonia, NH₃, is used as a solvent rather than water. Which expression defines the ammonia autoionization counterpart of K_w?

A)[H₃O⁺][OH^-]
B)[NH₃][NH₄⁺]
C)[NH₂^-][NH₄⁺]
D)[H₃O⁺][NH₂^-]
E)[NH₄⁺][OH^-]

Question 25

What is the actual concentration of the molecular form of HF in a 1.0 M HF solution given that K_a of HF is 6.8 $\times$ 10^-4?

A)2.6 $\times$ 10^-2 M
B)0.97 M
C)1.59 M
D)6.8 $\times$ 10^-4 M
E)1.0 M

Question 26

Use the following acid ionization constants to identify the correct decreasing order of base strengths for the conjugate bases.
HF $\quad$ $\quad$$\quad$ K_a = 7.2 $\times$ 10^-4
HNO₂ $\quad$ $\quad$ K_a = 4.5 $\times$ 10^-4
HCN $\quad$ $\quad$ K_a = 6.2 $\times$ 10^-10

A)CN^- > NO₂^- > F^-
B)NO₂^- > F^- > CN^-
C)F^- > CN^- > NO₂^-
D)F^- > NO₂^- > CN^-
E)NO₂^- > CN^- > F^-

Question 27

Three common weak bases are phosphate (P; PO₄^3-, pK_b = 1.3), carbonate (C; CO₃^2-, pK_b = 3.7), and acetate (A; CH₃COO^-, pK_b = 9.3). Which response has these bases listed in order of increasing strength?

A)P < C < A
B)C < P < A
C)A < C < P
D)C < A < P
E)P < A < C

Question 28

A cup of coffee has a hydroxide ion concentration of 1.0 $\times$ 10^-10 M. What is the pH of this coffee?

A)1.0 $\times$ 10^-4
B)4
C)10
D)7
E)(-10)

Question 29

Which statement A-D is not correct? Pure water at 25 ^$\circ$ C has ________

A)K_w = 1.0 $\times$ 10^-14.
B)pOH = 7.
C)[H₃O⁺] = [OH^-].
D)pH = 7.
E)A-D are all correct.

Question 30

When [H⁺] = 4.0 $\times$ 10^-9 M in water at 25 ^$\circ$ C, then ________

A)pH = 9.40.
B)pH = 7.00.
C)pH = -8.40.
D)pH = 8.40.
E)pH = -9.40.

Question 31

Pure water at any temperature has ________

A)a pH less than 7.
B)a pOH more than 7.
C)[H₃O⁺] =[OH^-].
D)pH = 7.
E)no hydronium ions in it.

Question 32

A solution with a pOH of 4.3 has a [H⁺] of ________

A)6.8 $\times$ 10^-9 M.
B)3.2 $\times$ 10^-4 M.
C)4.8 $\times$ 10^-5 M.
D)2.0 $\times$ 10^-10 M.
E)4.3 M.

Question 33

The pH of a popular soft drink is 3.4; what is its hydronium ion concentration?

A)5.0 $\times$ 10^-4 M
B)4.0 $\times$ 10^-4 M
C)2.5 $\times$ 10³ M
D)1.0 $\times$ 10^-7 M
E)5.0 $\times$ 10^-5 M

Question 34

Which expression defines the autoionization constant for water, K_w?

A)[H₃O⁺][OH^-]
B)[H₂O][H₃O⁺]
C)[OH^-][H₂O]
D)[H₄O²⁺][O^2-]
E)[H₂O][H₂O]

Question 35

A solution with a pH of 9.50 has a pOH of ________

A)9.50.
B)0.50.
C)4.50.
D)23.5.
E)19.0.

Question 36

When pure water autoionizes, which ions are produced?

A)O^2-, OH^-, H₃O⁺, and H₂O⁺
B)OH^- and H₃O⁺
C)O^2- and H₄O²⁺
D)H⁺ and OH^-
E)2H⁺ and O^2-

Question 37

Three acids found in foods are lactic acid (in milk products), oxalic acid (in rhubarb), and malic acid (in apples). The pK_a values are LA = 3.88, OA = 1.23, and MA = 3.40. Which list has the conjugate bases of these acids in order of decreasing strength?

A)lactate > oxalate > malate
B)oxalate > malate > lactate
C)lactate > malate > oxalate
D)oxalate > lactate > malate
E)malate > lactate > oxalate

Question 38

A solution with a pOH of 6.92 has an [OH^-] concentration of ________

A)1.20 $\times$ 10^-7 M.
B)9.2 $\times$ 10^-6 M.
C)6.8 $\times$ 10^-6 M.
D)7.08 M.
E)6.92 M.

Question 39

A solution with a pH of 2.50 has an [OH^-] of ________

A)3.16 $\times$ 10².
B)3.16 $\times$ 10^-12.
C)3.16 $\times$ 10^-3.
D)3.16 $\times$ 10¹⁶.
E)3.16 $\times$ 10¹¹.

Question 40

The hydronium ion concentration of a dilute solution of vinegar is 1.45 $\times$ 10^-5. What is the pH of this solution?

A)5.7
B)(-4.8)
C)4.8
D)(-5.7)
E)7.0

Question 41

The concentration of acetic acid (pK_a = 4.75) in vinegar is about 1.0 M. With this information, what do you predict the pH of vinegar to be?

A)4.75
B)2.4
C)4.0 $\times$ 10^-3
D)7.0
E)5.35

Question 42

What is the pOH of a 0.125 M solution of hydroxylamine? The K_b value for hydroxylamine is 1.1 $\times$ 10^-8.

A)4.43
B)3.47
C)5.57
D)10.53
E)9.57

Question 43

In evaluating the pH of an aqueous weak acid solution, ________ usually can be ignored.

A)the concentration of the weak acid
B)the concentration of hydronium ion produced by the autoionization of water
C)the reaction of the weak acid with water
D)the concentration of the ionized hydronium ion
E)the concentration of the conjugate base

Question 44

The acidic ingredient in vinegar is acetic acid. The pH of vinegar is around 2.4, and the molar concentration of acetic acid in vinegar is around 0.85 M. Based on this information, determine the value of the acid ionization constant, K_a, for acetic acid.

A)2.5 $\times$ 10^-5
B)5.0 $\times$ 10^-5
C)4.7 $\times$ 10^-3
D)1.9 $\times$ 10^-5
E)7.4 $\times$ 10^-3

Question 45

What is the actual concentration of molecular NH₃ in a 0.200 M solution of ammonia? The K_b value for ammonia is 1.80 $\times$ 10^-5.

A)0.200 M
B)0.198 M
C)1.80 $\times$ 10^-5 M
D)1.90 $\times$ 10^-3 M
E)3.6 $\times$ 10^-6 M

Question 46

Diethylamine ((CH₃CH₂) NH₂) is a weakly basic compound. Calculate the K_b for diethylamine if a 0.127 M solution is 9.61% ionized.

A)1.8 $\times$ 10^-5
B)4.4 $\times$ 10^-4
C)5.6 $\times$ 10^-4
D)1.3 $\times$ 10^-3
E)3.8 $\times$ 10^-10

Question 47

What is the concentration of the acetate ion in a 1.00 M CH₃COOH solution given that the K_a of CH₃COOH is 1.8 $\times$ 10^-5?

A)4.20 $\times$ 10^-3 M
B)0.996 M
C)1.00 M
D)2.84 $\times$ 10^-4 M
E)5.62 $\times$ 10^-5 M

Question 48

Methylamine (CH₃NH₂) is a weakly basic compound. Calculate the K_b for methylamine if a 0.253 M solution is 4.07% ionized.

A)2.29 $\times$ 10³
B)4.37 $\times$ 10^-4
C)5.72
D)4.24 $\times$ 10^-2
E)4.19 $\times$ 10^-4

Question 49

What is the concentration of ammonium ion in a 0.150 M solution of ammonia? The K_b value for ammonia is 1.80 $\times$ 10^-5.

A)0.146 M
B)0.148 M
C)2.34 $\times$ 10^-5 M
D)1.63 $\times$ 10^-3 M
E)4.20 $\times$ 10^-3 M

Question 50

When values of K_a are small (e.g., 1 $\times$ 10^-5) and concentrations of weak acids [HA] are relatively large (e.g., 0.10 M), the hydronium ion concentration of the solution can be calculated using which expression?

A)[H⁺] = K_a
B)[H⁺] = K_a[HA]
C)[H⁺] = (K_a[HA])^1/2
D)[H⁺] = K_aK_b[HA]
E)[H=⁺] = K_a[HA]/[A^-]

Question 51

What is the concentration of [OH^-] in a 0.20 M solution of ammonia? The K_b value for ammonia is 1.8 $\times$ 10^-5.

A)3.6 $\times$ 10^-6 M
B)1.8 $\times$ 10^-5 M
C)0.20 M
D)1.9 $\times$ 10^-3 M
E)4.2 $\times$ 10^-4 M

Question 52

What is the pH of a 0.500 M solution of trimethylamine (pK_b = 4.13)?

A)2.22
B)11.8
C)0.00609
D)4.42
E)5.91

Question 53

What is the pH of a 0.030 M solution of oxalic acid? K_a for oxalic acid is 5.9 $\times$ 10^-2.

A)1.66
B)1.37
C)2.78
D)12.67
E)12.34

Question 54

Lactic acid is a major component of Ringer's solution, which is used as an intravenous fluid to maintain fluid balance in trauma patients. The pH of a 0.100 M lactic acid solution is around 2.44. Based on this information, determine the value of the acid ionization constant, K_a, for lactic acid.

A)1.2 $\times$ 10^-2
B)1.4 $\times$ 10^-4
C)4.7 $\times$ 10^-3
D)1.8 $\times$ 10^-4
E)7.4 $\times$ 10^-3

Question 55

What is the hydronium ion concentration of a 0.010 M solution of acetic acid? K_a for acetic acid is 1.8 $\times$ 10^-5.

A)1.8 $\times$ 10^-3
B)1.8 $\times$ 10^-5
C)1.0 $\times$ 10^-2
D)1.8 $\times$ 10^-7
E)4.2 $\times$ 10^-4

Question 56

Formic acid is a weak acid naturally occurring in certain species of ants. Calculate the acid ionization constant for formic acid if a 0.213 M solution is 2.86% ionized. The abbreviated structural formula for formic acid is HCOOH.

A)7.2 $\times$ 10^-4
B)6.4 $\times$ 10^-4
C)1.8 $\times$ 10^-4
D)1.9 $\times$ 10^-5
E)3.5 $\times$ 10^-8

Question 57

A 0.100 M solution of a monoprotic weak acid has a pH of 3.00. What is the pK_a of this acid?

A)5.00
B)0.999
C)3.00
D)9.99
E)6.00

Question 58

Boric acid frequently is used as an eyewash to treat eye infections. The pH of a 0.050 M solution of boric acid is 5.28. What is the value of the boric acid ionization constant, K_a?

A)5.25 $\times$ 10^-6
B)5.51 $\times$ 10^-10
C)5.43 $\times$ 10^-8
D)5.79 $\times$ 10^-4
E)5.33 $\times$ 10^-12

Question 59

Butanoic acid contributes to the rancid odor of spoiled butter. Calculate the acid ionization constant for butanoic acid if a 0.155 M solution is 1.15% ionized. The abbreviated structural formula for butanoic acid is CH₃CH₂CH₂COOH.

A)5.1 $\times$ 10^-3
B)1.8 $\times$ 10^-3
C)1.2 $\times$ 10^-2
D)2.1 $\times$ 10^-5
E)1.5 $\times$ 10^-5

Question 60

The first disinfectant used by Joseph Lister was called carbolic acid. This substance now is known as phenol, C₆H₅OH (pK_a = 10.0). What is the pH of a 0.10 M solution of phenol?

A)3.5
B)10.0
C)6.5
D)5.5
E)4.5

Question 61

Sodium hypochlorite is a common ingredient in household bleach. What is the pH of this bleach if it contains 5% NaOCl by mass? (pK_a of HOCl = 7.46)

A)9
B)11
C)4
D)8
E)7

Question 62

The degree of ionization of a strong acid is ________

A)dependent on the concentration of the acid.
B)between 1 and 10%.
C)between 10 and 100%.
D)100%.
E)dependent on which strong acid it is.

Question 63

Identify the weakest and strongest acids in the group below. The weakest acid is listed first in the responses. HCl, H₂S, PH₃

A)HCl < H₂S
B)HCl < PH₃
C)H₂S < HCl
D)H₂S < PH₃
E)PH₃ < HCl

Question 64

In each of the following, the stronger acid is identified and an explanation is given. All except one are correct statements. Which one is not correct?

A)HCl > HF because the HF bond energy is larger than the HCl bond energy.
B)HCO₃^- > H₂CO₃ because the negative charge stabilizes the loss of a proton.
C)CCl₃COOH > CH₃COOH because electronegative substituents stabilize the conjugate base.
D)HBrO₃ > HBrO₂ because of the additional electronegative oxygen atom.
E)ClOH > BrOH because Cl is more electronegative than Br.

Question 65

Identify the weakest and strongest acids in the group below. The weakest acid is listed first in the responses. H₂O, H₂S, H₂Se

A)H₂Se < H₂S
B)H₂Se < H₂O
C)H₂S < H₂Se
D)H₂O < H₂Se
E)H₂O < H₂S

Question 66

What is the hydronium ion concentration of a 0.200 M solution of methylamine? The K_b value for methylamine is 4.38 $\times$ 10^-4.

A)9.14 $\times$ 10^-3
B)1.09 $\times$ 10^-12
C)5.24 $\times$ 10^-14
D)1.00 $\times$ 10^-7
E)1.91 $\times$ 10^-1

Question 67

Which one of the following statements is not correct?

A)HIO is a stronger acid than HClO.
B)HClO is a stronger acid than HBrO.
C)HClO₃ is a stronger acid than HClO₂.
D)HPO₄^2- is a weaker acid than H₂PO₄^-.
E)H₂SO₄ is a stronger acid than H₂SO₃.

Question 68

What is the pH of a 0.200 M solution of methylamine? The K_b value for methylamine is 4.38 $\times$ 10^-4.

A)2.04
B)(-1.33)
C)10.53
D)15.33
E)11.96

Question 69

The analysis label on a 500 mL bottle of Fiji natural artesian water reports pH = 7.5 and 140 mg of bicarbonates, HCO₃^-. Calculate the pH expected as a result of the bicarbonates to see if these two numbers are consistent with each other. (K_b = 2.4 $\times$ 10^-8 for HCO₃^-)

A)7.5
B)5.0
C)9.6
D)4.4
E)9.0

Question 70

The degree of ionization of a weak acid ________
I. varies with the concentration of the acid.
II. depends on which weak acid it is.
III. is 100%.
IV. is greater than 50% but less than 100%.

A)I only
B)II only
C)III only
D)both I and II
E)IV only

Question 71

The pH of an aniline solution is 8.91, and the solution has a concentration of 0.17 M. The pK_b of aniline is 9.42. What is the percent ionization of aniline?

A)1.2%
B)0.50%
C)2.1 $\times$ 10^-3%
D)4.7 $\times$ 10^-3%
E)6.3 $\times$ 10^-5%

Question 72

A solution of the weak acid HF and a solution of the strong acid HCl have the same pH. Which solution will require the most sodium hydroxide, NaOH, to neutralize?

A)HCl, because it is a strong acid and dissociates completely.
B)HF, because its concentration is larger.
C)Both will require the same amount because the concentrations are equal.
D)Both will require the same amount because the H₃O⁺concentrations are the same.
E)HCl, because the stronger acid has the higher concentration.

Question 73

Identify the weakest and strongest acids in the group below. The weakest acid is listed first in the responses. H₂Te, H₂S, H₂Se

A)H₂Se < H₂S
B)H₂S < H₂Te
C)H₂S < H₂Se
D)H₂Te < H₂Se
E)H₂Te < H₂S

Question 74

Which ending to the statement is not correct? The weak acid HY will be stronger than the weak acid HZ if ________

A)more Lewis resonance structures can be written for the Y group than for the Z group.
B)Y is more electronegative than Z.
C)the Y group has more oxygen atoms than the Z group.
D)the H-Y bond is weaker than the H-Z bond and other things are about the same.
E)the Y group contains Br rather than Cl, which is in the Z group.

Question 75

The pH of vinegar is 2.4, and the acetic acid in vinegar has a concentration of about 0.85 M. The pK_a of acetic acid is 4.75. What is the percent ionization of acetic acid in vinegar?

A)2.8%
B)4.7%
C)0.47%
D)0.21%
E)0.021%

Question 76

The pH of an ammonia solution is 11.6, and the solution has a concentration of about 0.20 M. The pK_b of ammonia is 4.75. What is the percent ionization of ammonia?

A)2.0%
B)2.3%
C)1.2%
D)0.95%
E)5.4%

Question 77

Identify the weakest and strongest acids in the group below. The weakest acid is listed first in the responses. HOCl, HOBr, HOI

A)HOBr < HOCl
B)HOBr < HOI
C)HOCl < HOBr
D)HOCl < HOI
E)HOI < HOCl

Question 78

Vitamin C, which is ascorbic acid, is a diprotic acid with = 5.00 and = 11.3. What is the pH of a 0.125 M solution of ascorbic acid?

A)2.95
B)3.05
C)5.00
D)6.10
E)3.54

Question 79

The degree of ionization ________

A)increases with increasing concentration of a weak acid.
B)decreases with increasing concentration of a weak acid.
C)does not change with changing concentration of a weak acid.
D)is not related to the concentration of a weak acid.
E)is independent of the composition of the weak acid.

Question 80

Identify the weakest and strongest acids in the group below. The weakest acid is listed first in the responses. HCl, HBr, HI

A)HCl < HI
B)HCl < HBr
C)HBr < HCl
D)HBr < HI
E)HI < HCl