Chemistry Test Acids and Bases 3 — Questions and Answers
Question 1: Which of the following salts produces a basic solution when dissolved in water?
- NaCl
- NH₄Cl
- Na₂CO₃ (Correct answer)
- KNO₃
Correct answer: Na₂CO₃
Na₂CO₃ is a salt of a strong base (NaOH) and a weak acid (H₂CO₃), so CO₃²⁻ hydrolyzes to produce OH⁻.
Question 2: The Henderson–Hasselbalch equation is used to:
- Calculate the Ka of a strong acid
- Determine the pH of a buffer solution (Correct answer)
- Find the boiling point of an acid solution
- Measure the ionic strength of a base
Correct answer: Determine the pH of a buffer solution
The Henderson–Hasselbalch equation, pH = pKa + log([A⁻]/[HA]), calculates the pH of buffer solutions.
Question 3: Which process describes autoionization of water?
- H₂O → H₂ + ½O₂
- 2H₂O ⇌ H₃O⁺ + OH⁻ (Correct answer)
- H₂O + CO₂ → H₂CO₃
- H₂O → OH⁻ + H⁺ (irreversible)
Correct answer: 2H₂O ⇌ H₃O⁺ + OH⁻
Water undergoes autoionization where two water molecules form hydronium and hydroxide ions in equilibrium.
Question 4: Which of the following is the strongest acid?
- HF (Ka = 6.8×10⁻⁴)
- HCN (Ka = 6.2×10⁻¹⁰)
- HNO₂ (Ka = 4.5×10⁻⁴)
- HClO₄ (completely dissociates) (Correct answer)
Correct answer: HClO₄ (completely dissociates)
HClO₄ (perchloric acid) is a strong acid that completely dissociates, making it stronger than any weak acid.
Question 5: What happens to the pH of a buffer when a small amount of strong acid is added?
- It drops sharply to 1
- It remains essentially unchanged (Correct answer)
- It rises slightly
- It becomes neutral (pH 7)
Correct answer: It remains essentially unchanged
The conjugate base component of the buffer neutralizes the added acid, keeping pH nearly constant.
Question 6: In a titration of a weak acid with a strong base, where is the equivalence point located?
- At pH 7
- Below pH 7
- Above pH 7 (Correct answer)
- It varies unpredictably
Correct answer: Above pH 7
At the equivalence point, the weak acid is fully converted to its conjugate base, which hydrolyzes to give a basic solution (pH > 7).
Question 7: Which of the following is an amphiprotic species?
- Cl⁻
- Na⁺
- HCO₃⁻ (Correct answer)
- SO₄²⁻
Correct answer: HCO₃⁻
HCO₃⁻ can donate a proton (acting as an acid) or accept a proton (acting as a base), making it amphiprotic.
Chemistry Test Acids and Bases 3
Which of the following salts produces a basic solution when dissolved in water?