Chem 102 Ch 15

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, Ka, for lactic acid.

1.4 × 10-4

What is the pH of a solution made from 46.20 mL of a 0.0500 M nitric acid solution diluted to 100.0 mL?

1.64

What is the pH of a 0.25 M NH4Cl solution (Ka = 5.68 × 10-10)?

4.92

58.Define a conjugate acid-base pair and provide an example.

A conjugate acid-base pair consists of two species that are related by a proton transfer from one to the other (for example, HF and F-).

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? Base Kb A 1.8 × 10-3 B 2.3 × 10-1 C 4.6 × 10-4 D 5.3 ×10-6

D 5.3 ×10-6

Four solutions have pH values of 3, 5, 8, and 10. Arrange these in order of increasing acidity, and identify those that are acidic, basic, and neutral.

Increasing acidity: 10 < 8 < 5 < 3 Acidic: 3 and 5 Basic: 8 and 10

Given the pKa values in the table, rank the order of strongest to weakest acid and the order of strongest to weakest conjugate bases. 58.Define a conjugate acid-base pair and provide an example. Acid pKaHA 4.00HB 7.00HC 10.00HD 11.00

The lower the pKa of an acid is, the stronger the acid will be. Thus, acid strength would be ordered as: HA > HB > HC > HD The stronger the acid is, the weaker its corresponding conjugate base. As a result, conjugate base strength would be ordered as: [D-] > [C-] > [B-] > [A-]

40.What is the pH of a 0.030 M solution of oxalic acid? Ka for oxalic acid is 5.9 × 10-2. a. 1.66 b. 1.37 c. 2.78 d. 12.67 e. 12.34

a. 1.66

What is the concentration of the acetate ion in a 1.00 M CH3COOH solution given the Ka of CH3COOH is 1.78 × 10-5? a. 4.20 × 10-3 M b. 0.996 M c. 1.00 M d. 2.84 × 10-4 M e. 5.62 × 10-5 M

a. 4.20 × 10-3 M

A 0.100 M solution of a monoprotic weak acid has a pH of 3.00. What is the pKa of this acid? a. 5.00 b. 0.999 c. 3.00 d. 9.99 e. 6.00

a. 5.00

10.Identify the weakest and strongest acids in this group: HCl, HBr, HI (The weakest acid is listed first in these answer options.) a. HCl < HI b. HCl < HBr c. HBr < HCl d. HBr < HI e. HI < HCl

a. HCl < HI

Which of the following is a strong acid?

a. HNO3

Which statement is correct? a. K2SO3 is a stronger base than KHSO3. b. K2CO3 is a weaker base than KHCO3. c. NaHSO3 is a stronger acid than NaHSO4. d. Na2HPO4 is a weaker base than NaH2PO4. e. All of these statements are correct.

a. K2SO3 is a stronger base than KHSO3.

Which of these is a conjugate acid-base pair? a. NH3 and NH4+ b. H3O+ and OH- c. NH2- and NH4+ d. H2O and O2- e. NaF and F-

a. NH3 and NH4+

Which molecule partially dissociates in water, meaning that only a small fraction of the molecules in the solution releases H+ ions?

acetic acid, CH3COOH

43.What is the hydronium ion concentration of a 0.200 M solution of methylamine? The Kb value for methylamine is 4.38 × 10-4. a. 9.14 × 10-3 b. 1.09 × 10-12 c. 5.24 × 10-14 d. 1.00 × 10-7 e. 1.91 × 10-1

b. 1.09 × 10-12

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, Ka, for lactic acid. a. 1.2 × 10-2 b. 1.4 × 10-4 c. 4.7 × 10-3 d. 1.8 × 10-4 e. 7.4 × 10-3

b. 1.4 × 10-4

25.If the pH of a solution decreases by 2 units (e.g., from 3 to 1), then the hydronium ion concentration changes by a factor of a. 2. b. 100. c. 1/2. d. 1/100. e. 1000.

b. 100

Sodium hypochlorite is a common ingredient in household bleach. What is the pH of this bleach if it contains 5% NaOCl by mass? (pKa of HOCl = 7.46; assume the density of the solution is 1 g/mL) a. 9 b. 11 c. 4 d. 8 e. 7

b. 11

What is the pH of a 0.500 M solution of trimethylamine (pKb = 4.13)? a. 2.22 b. 11.8 c. 0.00609 d. 4.42 e. 5.91

b. 11.8

The concentration of acetic acid (pKa = 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 × 10-3 d. 7.0 e. 5.35

b. 2.4

A solution with a pH of 2.50 has an [OH-] of a. 3.16 × 102. b. 3.16 × 10-12. c. 3.16 × 10-3. d. 3.16 × 1016. e. 3.16 × 1011.

b. 3.16 × 10-12.

54.What is the Ka for nitrous acid, given that the pKb for the nitrite ion is 10.61? a. 1.38 × 104 b. 4.07 × 10-4 c. 1.90 × 10-5 d. 5.60 × 10-6 e. 4.30 × 10-7

b. 4.07 × 10-4

Identify the weakest and strongest acids in this group: CH4, SiH4, SnH4 (The weakest acid is listed first in these answer options.) a. CH4 < SiH4 b. CH4 < SnH4 c. SiH4 < SnH4 d. SiH4 < SnH4 e. SnH4 < CH4

b. CH4 < SnH4

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. No acids are present, so ammonia cannot act as a base. e. oxygen

b. H2O

Identify the weakest and strongest acids in this group: H2Te, H 2S, H2Se (The weakest acid is listed first in these answer options.) a. H2Se < H2S b. H2S < H2Te c. H2S < H2Se d. H2Te < H2Se e. H2Te < H2S

b. H2S < H2Te

The acid ionization equilibrium constant, Ka, 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

b. HA + H2O H3O+ + A-

36.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.

b. HF, because its concentration is larger.

52.How would you calculate Kb for the formate ion, given that the Ka for formic acid is 1.8 × 10-4? a. Kb = Ka × Kw b. Kb = Kw / Ka c. Kb = Ka / Kw d. Kb = Kw + Ka e. Kb = Kw - Ka

b. Kb = Kw / Ka

When pure water autoionizes, which ions are produced? a. O2-, OH-, H3O+, and H2O+ b. OH- and H3O+ c. O2- and H4O2+ d. H+ and OH- e. 2H+ and O2-

b. OH- and H3O+

A substance that can act as both an acid and base is a. amphibious. b. amphiprotic. c. bacidic. d. androgynous. e. acibasic.

b. amphiprotic.

39.In evaluating the pH of an aqueous weak acid solution, ________ can usually be ignored. a. the concentration of the weak acid b. the concentration of hydronium ions 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

b. the concentration of hydronium ions produced by the autoionization of water

31.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 × 10-4 b. 6.4 × 10-4 c. 1.8 × 10-4 d. 1.9 × 10-5 e. 3.5 × 10-8

c. 1.8 × 10-4

The hydronium ion concentration of a dilute solution of vinegar is 1.5 × 10-5. What is the pH of this solution? a. 5.7 b. -4.8 c. 4.8 d. -5.7 e. 7.0

c. 4.8

What is the pH of a 0.029 M solution of potassium benzoate? The Ka value for benzoic acid is 6.46 × 10-5. a. 11.14 b. 5.67 c. 8.33 d. 2.86 e. 7.45

c. 8.33

What is the pH of a 0.35 M solution of sodium azide? The Ka value for hydrazoic acid is 1.9 × 10-5. a. 11.41 b. 4.87 c. 9.13 d. 2.59 e. 12.47

c. 9.13

What is the conjugate base of the hydrogen carbonate ion, HCO3-? a. H2CO3 b. HCO3- c. CO32- d. OH- e. H3CO3+

c. CO32-

49.Which of the following salts produces a neutral solution when dissolved in water? a. KF b. Mg(NO2)2 c. NaClO4 d. CaCO3 e. All of these salts produce a neutral solution when dissolved in water.

c. NaClO4

Three acids found in food are lactic acid (in milk products), oxalic acid (in rhubarb), and malic acid (in apples). The pKa values are LA = 3.88, OA = 1.23, and MA = 3.40. Which answer option puts these acids in the correct 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

c. OA > MA > LA

22.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.

c. [H3O+] = [OH-].

When [H+] = 1.0 × 10-7 M in water at 25°C, then a. pH = 1. b. pH = 10-7. c. [OH-] = 1.0 × 10-7 M. d. [OH-] = 1.0 × 107 M. e. [OH-] = 0 M.

c. [OH-] = 1.0 × 10-7 M.

The pH of an aqueous ammonium nitrate (NH4NO3) solution is ________ because ________. a. 7; ammonium nitrate is a simple salt b. above 7; nitrate is a weak base c. below 7; ammonium is a weak acid d. about 7; ammonium is a weak acid but produces ammonia, and these two

c. below 7; ammonium is a weak acid

Which of the following is a weak acid? a. nitric acid, HNO3 b. sulfuric acid, H2SO4 c. carbonic acid, H2CO3 d. hydrochloric acid, HCl e. perchloric acid, HClO4

c. carbonic acid,

35.The degree of ionization of a weak acid a. does not depend on the concentration of the acid. b. depends on which weak acid it is. c. is consistent with Le Châtelier's Principle. d. is greater than 50% but less than 100%.

c. is consistent with Le Châtelier's Principle.

Three acids found in food are lactic acid (in milk products), oxalic acid (in rhubarb), and malic acid (in apples). The pKa 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

c. lactate > malate > oxalate

The pH of an ammonia solution is 11.3, and the solution has a concentration of 0.20 M. The pKb of ammonia is 4.75. What is the percent ionization of ammonia? a. 2.0% b. 2.3% c. 1.2% d. 1.0% e. 5.4%

d. 1.0%

Diethylamine ((CH3CH2) NH2) is a weakly basic compound. Calculate the Kb for diethylamine if a 0.127 M solution is 9.61% ionized. a. 1.8 × 10-5 b. 4.4 × 10-4 c. 5.6 × 10-4 d. 1.3 × 10-3

d. 1.3 × 10-3

What is the concentration of ammonium ion in a 0.150 M solution of ammonia? The Kb value for ammonia is 1.80 × 10-5. a. 0.146 M b. 0.148 M c. 2.34 × 10-5 M d. 1.63 × 10-3 M e. 4.20 × 10-3 M

d. 1.63 × 10-3 M

What is the concentration of [OH-] in a 0.20 M solution of ammonia? The Kb value for ammonia is 1.8 × 10-5. a. 3.6 × 10-6 M b. 1.8 × 10-5 M c. 0.20 M d. 1.9 × 10-3 M e. 4.2 × 10-4 M

d. 1.9 × 10-3 M

A solution with a pOH of 4.3 has a [H+] of a. 6.8 × 10-9 M. b. 3.2 × 10-4 M. c. 4.8 × 10-5 M. d. 2.0 × 10-10 M. e. 4.3 M.

d. 2.0 × 10-10 M.

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-

d. C5H5N; C5H5NH+

Aqueous solutions of ________ are acidic. a. NaF b. CsCN c. MgCl2 d. NH4I e. KI

d. NH4I

Solutions of sodium salts of the acids in the following table are prepared with an initial concentration of 0.500 M. Which solution will have the highest pH and be the least acidic? a. NaA b. NaB c. NaC d. NaD e. All will have the same pH because the concentrations are the same.

d. NaD

What is Kb1 for the citrate ion, given that the Ka1 for citric acid is 8.40 × 10-4? a. 2.40 × 10-12 b. 6.23 × 10-8 c. 6.17 × 10-10 d. 4.80 × 10-11 e. 1.19 × 10-11

e. 1.19 × 10-11

Which of these is a conjugate acid-base pair? a. NH3 and NH2- b. HNO3 and NO2- c. HI and I- d. H2PO4- and HPO42- e. All are conjugate acid-base pairs.

e. All are conjugate acid-base pairs.

Pure water at 25°C has a. Kw = 1.0 × 10-14. b. pOH = 7. c. [H3O+] = [OH-]. d. pH = 7. e. All of these answers are correct.

e. All of these answers are correct.

Which of the following salts produces a basic solution when dissolved in water? a. Na2S b. Na2CO3 c. NaClO2 d. NaNO2 e. All of these salts produce a basic solution when dissolved in water.

e. All of these salts produce a basic solution when dissolved in water.

Identify the weakest and strongest acids in the group: HOCl, HOBr, HOI (The weakest acid is listed first in these answer options.) a. HOBr < HOCl b. HOBr < HOI c. HOCl < HOBr d. HOCl < HOI e. HOI < HOCl

e. HOI < HOCl

47.Which of the following salts forms aqueous solutions with a pH of 7? a. Na2S b. NaBr c. NaClO2 d. NaNO2 e. Na2CO3

e. Na2CO3

The weak acid HY will be weaker 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. e. the Y group contains Br rather than Cl, which is in the Z group.

e. the Y group contains Br rather than Cl, which is in the Z group.

The concentration of acetic acid in vinegar is about 1.0 M, and the pH is about 2.4. With this information, what do you expect the pKa of vinegar to be?

pKa = 4.75