Chemistry Acid-Base Equilibrium Practice Problems

Acid-Base Equilibrium Practice Problems

1. The conjugate acid of HAsO₄²⁻ is:
   Answer: C. H₂AsO₄⁻
2. Which of the following tests could be used to distinguish between 1.0 M HCl and 1.0 M NaOH?
   Answer: C. II and III only
3. Consider the following Brønsted-Lowry equilibrium:
   C₆H₅NH₂(aq) + H₂O(l) ⇌ C₆H₅NH₃⁺(aq) + OH⁻(aq)
   The substances acting as acids and bases from left to right are:
   Answer: C. Base, acid, acid, base
4. Which of the following are amphiprotic?
   I. H₂O, II. NH₄⁺, III. HCO₃⁻
   Answer: B. I and III only
5. Which of the following represents the equilibrium expression for the ionization of water?
   Answer: A.
6. Which of the following will have the lowest electrical conductivity?
   Answer: D. 1.00 M H₃PO₄
7. Water acts as an acid when it reacts with which of the following?
   Answer: C. I, II and IV only
8. In a solution of 0.10 M H₂SO₄, the ions present in order of decreasing concentration are:
   Answer: [H₃O⁺] > [SO₄²⁻] > [HSO₄⁻] > [OH⁻]
9. Consider the following equilibrium:
   2 CrO₄²⁻(aq) + 2 H₃O⁺(aq) ⇌ Cr₂O₇²⁻(aq) + 3 H₂O(l) (yellow ⇌ orange)
   An unknown solution is added to an orange equilibrium sample until the sample turns yellow. The unknown solution could be:
   Answer: B. NaOH
10. Consider the following equilibrium:
    2 H₂O(l) + energy ⇌ H₃O⁺(aq) + OH⁻(aq)
    The temperature is increased and a new equilibrium is established. The new equilibrium can be described by:
    Answer: A. pH = pOH and Kw > 1.0 × 10⁻¹⁴
11. The relationship:
    Answer: A. Kₐ for H₃P₂O₇⁻
12. Write the base ionization constant expression for:
    Answer: B
13. Consider the following equilibrium at 25°C:
    Correct Answer: B
14. What is the pH of the solution formed when 0.040 mol NaOH is added to 1.00 L of 0.050 M HCl?
    Correct Answer: C
15. Calculate the pH in a 0.020 M solution of Sr(OH)₂.
    Correct Answer: D
16. Calculate the value of K_b for HPO₄²⁻.
    Closest answer: B
17. What is the [H₃O⁺] in a solution with a pOH = 5.20?
    Correct Answer: B

Reaction Analysis

1. The two reactants in an acid-base reaction are HNO₂(aq) and HCO₃⁻(aq)
   a. Write the equation for the above reaction:
   HNO₂(aq) + HCO₃⁻(aq) ⇌ NO₂⁻(aq) + H₂CO₃(aq)
   b. Write the formulas for a conjugate acid-base pair for the above reaction:
   HNO₂ (acid) / NO₂⁻ (base)
2. Consider the following equilibria:
   a) HOCN, b) CH₃COOH
   c. Consider the following reaction:
   Products are favored because equilibrium favors the side with the weaker acid and weaker base. HOCN is a stronger acid than HClO.
3. Calculation:
   HCl: 0.0600 × 0.55 = 0.0330 mol
   NaOH: 0.0750 × 1.3 = 0.0975 mol
   0.0975 − 0.0330 = 0.0645 mol OH⁻
   60.0 mL + 75.0 mL = 135.0 mL = 0.1350 L
   [OH⁻] = 0.0645 / 0.1350 = 0.478 M
   pOH = -log(0.478) = 0.321 → pH = 13.68