Acid-Base Reactions Quiz

Grade 11 · Science · Quiz

10 questions covering pH calculations, acid-base theories, strong vs. weak acids, neutralization, and buffers.

Questions

1. What is the pH of a solution with [H⁺] = 0.001 mol/L?

   1. 1
   2. 2
   3. 3
   4. 4
   Show answer

   Answer: 3

   pH = −log(0.001) = −log(10⁻³) = 3.

2. A solution has pH = 9. What is the [H⁺]?

   1. 1 × 10⁻⁷ mol/L
   2. 1 × 10⁻⁹ mol/L
   3. 9 mol/L
   4. 0.9 mol/L
   Show answer

   Answer: 1 × 10⁻⁹ mol/L

   [H⁺] = 10⁻pH = 10⁻⁹ mol/L.

3. Which of the following is classified as a weak acid?

   1. HCl
   2. HNO₃
   3. HBr
   4. CH₃COOH (acetic acid)
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   Answer: CH₃COOH (acetic acid)

   Acetic acid partially dissociates in water (Ka ≈ 1.8 × 10⁻⁵). HCl, HNO₃, and HBr are all strong acids.

4. In a titration, the equivalence point is reached when:

   1. Indicator changes color
   2. Moles of acid equal moles of base
   3. pH reaches 7
   4. Temperature peaks
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   Answer: Moles of acid equal moles of base

   The equivalence point is when stoichiometric amounts of acid and base have reacted. The endpoint (indicator color change) is close but not identical.

5. Ammonia (NH₃) acts as a Brønsted-Lowry base because it:

   1. Produces OH⁻ directly
   2. Accepts a proton (H⁺) from water
   3. Donates an electron pair
   4. Dissociates completely
   Show answer

   Answer: Accepts a proton (H⁺) from water

   NH₃ + H₂O → NH₄⁺ + OH⁻. Ammonia accepts H⁺ from water, acting as a Brønsted-Lowry base.

6. What does a buffer solution do?

   1. Neutralizes all acids completely
   2. Resists changes in pH when small amounts of acid or base are added
   3. Turns universal indicator blue
   4. Raises pH to exactly 7
   Show answer

   Answer: Resists changes in pH when small amounts of acid or base are added

   Buffers contain a weak acid and its conjugate base; they absorb added H⁺ or OH⁻ without a large pH change.

7. A solution has pOH = 4. What is its pH at 25°C?

   1. 4
   2. 7
   3. 10
   4. 14
   Show answer

   Answer: 10

   pH + pOH = 14 at 25°C. pH = 14 − 4 = 10. This is a basic solution.

8. Which definition of acid and base applies even in non-aqueous and gaseous systems?

   1. Arrhenius
   2. Brønsted-Lowry
   3. Lewis
   4. Svante
   Show answer

   Answer: Lewis

   Lewis theory (electron pair donor/acceptor) is the most general — it applies in non-aqueous solvents and gaseous reactions where no proton transfer occurs.

9. What salt is formed when sulfuric acid (H₂SO₄) reacts with potassium hydroxide (KOH)?

   1. KCl
   2. K₂SO₄
   3. KHSO₄ only
   4. K₂O
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   Answer: K₂SO₄

   H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O. Two moles of KOH are needed to fully neutralize diprotic H₂SO₄.

10. The conjugate base of H₂CO₃ (carbonic acid) is:

    1. CO₃²⁻
    2. HCO₃⁻
    3. H₃CO₃⁺
    4. H₂O
    Show answer

    Answer: HCO₃⁻

    When H₂CO₃ donates one proton it becomes HCO₃⁻ (bicarbonate) — its conjugate base after losing one H⁺.

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