Chemistry Test Acids and Bases 2 — Questions and Answers
Question 1: Which of the following best describes a Lewis acid?
- A proton donor
- A proton acceptor
- An electron pair acceptor (Correct answer)
- An electron pair donor
Correct answer: An electron pair acceptor
A Lewis acid accepts an electron pair from a Lewis base to form a coordinate covalent bond.
Question 2: What is the conjugate base of H₂SO₄?
- SO₄²⁻
- HSO₄⁻ (Correct answer)
- H₃SO₄⁺
- S²⁻
Correct answer: HSO₄⁻
H₂SO₄ loses one proton to form HSO₄⁻, its conjugate base.
Question 3: A buffer solution resists changes in pH because it contains:
- A strong acid and its salt
- A weak acid and its conjugate base (Correct answer)
- Two strong acids
- A strong base and water
Correct answer: A weak acid and its conjugate base
A buffer contains a weak acid and its conjugate base, which can neutralize added acids or bases.
Question 4: At 25°C, what is the pOH of a solution with [OH⁻] = 1×10⁻³ M?
- 11
- 3 (Correct answer)
- 7
- 1
Correct answer: 3
pOH = -log[OH⁻] = -log(1×10⁻³) = 3.
Question 5: Which indicator would be most appropriate for titrating a strong acid with a strong base?
- Methyl orange (pH 3.1–4.4)
- Phenolphthalein (pH 8.2–10)
- Either methyl orange or phenolphthalein (Correct answer)
- Congo red (pH 3–5)
Correct answer: Either methyl orange or phenolphthalein
Strong acid–strong base titrations have a steep equivalence point, so both methyl orange and phenolphthalein are suitable.
Question 6: Acetic acid (CH₃COOH) has a Ka of 1.8×10⁻⁵. What does this indicate?
- It is a strong acid that fully dissociates
- It is a weak acid that partially dissociates (Correct answer)
- It has a neutral pH in solution
- It cannot act as a proton donor
Correct answer: It is a weak acid that partially dissociates
A small Ka value indicates weak acid behavior with only partial dissociation in water.
Question 7: When NH₃ reacts with water, it acts as a base by:
- Donating a proton to water
- Accepting a proton from water (Correct answer)
- Releasing OH⁻ directly
- Forming a Lewis acid complex
Correct answer: Accepting a proton from water
NH₃ accepts a proton from water to form NH₄⁺ and OH⁻, acting as a Brønsted–Lowry base.
Chemistry Test Acids and Bases 2
Which of the following best describes a Lewis acid?