CHEM134 Practice Exam 10 Aqueous
Ionic Equilibria Practice Exam
Questions And Correct Answers
(Verified Answers) Plus Rationales
2026 Q&A | Instant Download Pdf
1. Which statement best describes an aqueous ionic equilibrium?
A. A reaction that proceeds completely to products in water
B. A reaction in which no ions are present in solution
C. A dynamic balance between opposing ionic processes in aqueous
solution
D. A reaction that occurs only between gases
Answer: C
Rationale: Aqueous ionic equilibrium occurs when forward and
reverse processes continue simultaneously at equal rates. The
concentrations of the participating species remain essentially constant
at equilibrium, even though microscopic reactions continue.
2. What is the equilibrium expression for the ionization of a weak
acid HA in water?
A. Ka = [HA]/[H₃O⁺][A⁻]
B. Ka = [H₃O⁺][A⁻]/[HA]
C. Ka = [HA][H₂O]/[H₃O⁺][A⁻]
D. Ka = [H₃O⁺]/[HA][A⁻]
Answer: B
Rationale: For HA + H₂O ⇌ H₃O⁺ + A⁻, liquid water is omitted from
,the equilibrium expression because it is a pure liquid with essentially
constant activity. Therefore, Ka equals the product of the hydronium
and conjugate-base concentrations divided by the weak-acid
concentration.
3. Which species is the conjugate base of H₂CO₃?
A. H₃CO₃⁺
B. CO₃²⁻
C. HCO₃⁻
D. HCO₃⁻
Answer: D
Rationale: A conjugate base forms when an acid loses one proton.
When H₂CO₃ donates one H⁺, it becomes HCO₃⁻. Carbonate, CO₃²⁻, is
the conjugate base formed after HCO₃⁻ loses a second proton.
4. A weak acid has Ka = 1.0 × 10⁻⁵. What does this value indicate?
A. The acid ionizes only partially in water
B. The acid ionizes completely in water
C. The acid cannot react with water
D. The acid is stronger than every acid with Ka > 1.0 × 10⁻⁵
Answer: A
Rationale: A relatively small Ka indicates that the equilibrium favors
the unionized acid rather than its ions. Therefore, only a fraction of
the weak-acid molecules ionize in aqueous solution. Larger Ka values
correspond to stronger acids.
5. Which equation represents the ionization of a weak base B in
water?
A. B + H₂O → BH⁺ + OH⁻
B. B + H⁺ → BH⁻
,C. B + H₂O ⇌ BH⁺ + OH⁻
D. B + OH⁻ ⇌ BH⁺ + H₂O
Answer: C
Rationale: A weak base accepts a proton from water, producing its
conjugate acid, BH⁺, and hydroxide ion. Because the reaction is
incomplete, an equilibrium arrow is appropriate.
6. What is the relationship between Ka and Kb for a conjugate acid-
base pair at 25°C?
A. Ka + Kb = Kw
B. Ka − Kb = Kw
C. Ka/Kb = Kw
D. KaKb = Kw
Answer: D
Rationale: For conjugate acid-base pairs, the acid ionization constant
and base ionization constant are related through the water ion-product
constant. At 25°C, KaKb = Kw = 1.0 × 10⁻¹⁴.
7. Which solution is expected to have the greatest concentration of
H₃O⁺?
A. pH 2.0
B. pH 5.0
C. pH 7.0
D. pH 1.0
Answer: D
Rationale: Lower pH corresponds to greater hydronium concentration.
A pH of 1.0 corresponds to [H₃O⁺] = 1.0 × 10⁻¹ M, which is greater
than the hydronium concentration at pH 2, 5, or 7.
8. What is the pH of a solution with [H₃O⁺] = 1.0 × 10⁻⁴ M?
, A. 2.00
B. 3.00
C. 4.00
D. 10.00
Answer: C
Rationale: pH is calculated as −log[H₃O⁺]. Therefore, pH = −log(1.0 ×
10⁻⁴) = 4.00.
9. What is the hydroxide concentration of a solution at 25°C with
pOH = 3.00?
A. 3.00 M
B. 1.0 × 10⁻³ M
C. 1.0 × 10⁻¹¹ M
D. 1.0 × 10⁻³ M
Answer: D
Rationale: pOH = −log[OH⁻], so [OH⁻] = 10⁻pOH. A pOH of 3.00
therefore corresponds to [OH⁻] = 1.0 × 10⁻³ M.
10. At 25°C, a neutral aqueous solution has:
A. [H₃O⁺] = 1.0 × 10⁻⁷ M
B. [OH⁻] = 1.0 × 10⁻¹⁴ M
C. pH = 14
D. [H₃O⁺] = [OH⁻] = 1.0 × 10⁻⁷ M
Answer: D
Rationale: In neutral water at 25°C, hydronium and hydroxide
concentrations are equal. Their common concentration is 1.0 × 10⁻⁷
M, corresponding to pH 7.00 and pOH 7.00.
11. Which species is amphiprotic?
Ionic Equilibria Practice Exam
Questions And Correct Answers
(Verified Answers) Plus Rationales
2026 Q&A | Instant Download Pdf
1. Which statement best describes an aqueous ionic equilibrium?
A. A reaction that proceeds completely to products in water
B. A reaction in which no ions are present in solution
C. A dynamic balance between opposing ionic processes in aqueous
solution
D. A reaction that occurs only between gases
Answer: C
Rationale: Aqueous ionic equilibrium occurs when forward and
reverse processes continue simultaneously at equal rates. The
concentrations of the participating species remain essentially constant
at equilibrium, even though microscopic reactions continue.
2. What is the equilibrium expression for the ionization of a weak
acid HA in water?
A. Ka = [HA]/[H₃O⁺][A⁻]
B. Ka = [H₃O⁺][A⁻]/[HA]
C. Ka = [HA][H₂O]/[H₃O⁺][A⁻]
D. Ka = [H₃O⁺]/[HA][A⁻]
Answer: B
Rationale: For HA + H₂O ⇌ H₃O⁺ + A⁻, liquid water is omitted from
,the equilibrium expression because it is a pure liquid with essentially
constant activity. Therefore, Ka equals the product of the hydronium
and conjugate-base concentrations divided by the weak-acid
concentration.
3. Which species is the conjugate base of H₂CO₃?
A. H₃CO₃⁺
B. CO₃²⁻
C. HCO₃⁻
D. HCO₃⁻
Answer: D
Rationale: A conjugate base forms when an acid loses one proton.
When H₂CO₃ donates one H⁺, it becomes HCO₃⁻. Carbonate, CO₃²⁻, is
the conjugate base formed after HCO₃⁻ loses a second proton.
4. A weak acid has Ka = 1.0 × 10⁻⁵. What does this value indicate?
A. The acid ionizes only partially in water
B. The acid ionizes completely in water
C. The acid cannot react with water
D. The acid is stronger than every acid with Ka > 1.0 × 10⁻⁵
Answer: A
Rationale: A relatively small Ka indicates that the equilibrium favors
the unionized acid rather than its ions. Therefore, only a fraction of
the weak-acid molecules ionize in aqueous solution. Larger Ka values
correspond to stronger acids.
5. Which equation represents the ionization of a weak base B in
water?
A. B + H₂O → BH⁺ + OH⁻
B. B + H⁺ → BH⁻
,C. B + H₂O ⇌ BH⁺ + OH⁻
D. B + OH⁻ ⇌ BH⁺ + H₂O
Answer: C
Rationale: A weak base accepts a proton from water, producing its
conjugate acid, BH⁺, and hydroxide ion. Because the reaction is
incomplete, an equilibrium arrow is appropriate.
6. What is the relationship between Ka and Kb for a conjugate acid-
base pair at 25°C?
A. Ka + Kb = Kw
B. Ka − Kb = Kw
C. Ka/Kb = Kw
D. KaKb = Kw
Answer: D
Rationale: For conjugate acid-base pairs, the acid ionization constant
and base ionization constant are related through the water ion-product
constant. At 25°C, KaKb = Kw = 1.0 × 10⁻¹⁴.
7. Which solution is expected to have the greatest concentration of
H₃O⁺?
A. pH 2.0
B. pH 5.0
C. pH 7.0
D. pH 1.0
Answer: D
Rationale: Lower pH corresponds to greater hydronium concentration.
A pH of 1.0 corresponds to [H₃O⁺] = 1.0 × 10⁻¹ M, which is greater
than the hydronium concentration at pH 2, 5, or 7.
8. What is the pH of a solution with [H₃O⁺] = 1.0 × 10⁻⁴ M?
, A. 2.00
B. 3.00
C. 4.00
D. 10.00
Answer: C
Rationale: pH is calculated as −log[H₃O⁺]. Therefore, pH = −log(1.0 ×
10⁻⁴) = 4.00.
9. What is the hydroxide concentration of a solution at 25°C with
pOH = 3.00?
A. 3.00 M
B. 1.0 × 10⁻³ M
C. 1.0 × 10⁻¹¹ M
D. 1.0 × 10⁻³ M
Answer: D
Rationale: pOH = −log[OH⁻], so [OH⁻] = 10⁻pOH. A pOH of 3.00
therefore corresponds to [OH⁻] = 1.0 × 10⁻³ M.
10. At 25°C, a neutral aqueous solution has:
A. [H₃O⁺] = 1.0 × 10⁻⁷ M
B. [OH⁻] = 1.0 × 10⁻¹⁴ M
C. pH = 14
D. [H₃O⁺] = [OH⁻] = 1.0 × 10⁻⁷ M
Answer: D
Rationale: In neutral water at 25°C, hydronium and hydroxide
concentrations are equal. Their common concentration is 1.0 × 10⁻⁷
M, corresponding to pH 7.00 and pOH 7.00.
11. Which species is amphiprotic?
