Lesson 5.1.3

5.1.3 Acids, bases and buffers Quiz: OCR Chemistry, Unit 4

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 5.1.3, Acids, bases and buffers: 20 multiple choice questions for the OCR Chemistry (H432), Unit 4: Physical chemistry and transition elements, written with Revision Ninja.

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The 20 questions

  1. According to the Brønsted–Lowry theory, what is an acid?

    • Electron donor
    • Hydroxide donor
    • Proton acceptor
    • Proton donor

  2. What is the conjugate base of hydrogen sulfate ion, HSO4-?

    • H3SO4+
    • H2SO4
    • HSO3-
    • SO4^2-

  3. Which of the following is a dibasic acid?

    • Sulfuric acid, H2SO4
    • Hydrochloric acid, HCl
    • Phosphoric acid, H3PO4
    • Ethanoic acid, CH3COOH

  4. What are the units of the acid dissociation constant Ka for a weak acid HA <=> H+ + A-?

    • mol dm^-3
    • No units
    • mol^-1 dm^3
    • mol^2 dm^-6

  5. The relationship between pKa and Ka is which of the following?

    • pKa = 1/Ka
    • pKa = 10^-Ka
    • pKa = -log Ka
    • pKa = Ka^2

  6. What is the value of the ionic product of water, Kw, at 298 K?

    • 1.0 x 10^14 mol^2 dm^-6
    • 1.0 x 10^-14 mol dm^-3
    • 1.0 x 10^-14 mol^2 dm^-6
    • 1.0 x 10^-7 mol^2 dm^-6

  7. What is the pH of 0.050 mol dm^-3 hydrochloric acid, a strong monobasic acid?

    • 1.30
    • 2.70
    • 12.70
    • 0.050

  8. What is the pH of 0.010 mol dm^-3 sodium hydroxide solution at 298 K?

    • 14.0
    • 12.0
    • 2.0
    • 10.0

  9. A solution has pH 4.5. What is the hydrogen ion concentration?

    • 2.2 x 10^-4 mol dm^-3
    • 4.5 x 10^-4 mol dm^-3
    • 3.2 x 10^-5 mol dm^-3
    • 4.5 x 10^-5 mol dm^-3

  10. What is the pH of a 0.10 mol dm^-3 solution of ethanoic acid, with Ka = 1.8 x 10^-5 mol dm^-3, using the weak acid approximation?

    • 2.87
    • 1.00
    • 4.74
    • 5.37

  11. A 0.20 mol dm^-3 weak monobasic acid has pH 2.70. Using the weak acid approximation, what is Ka?

    • 2.0 x 10^-5 mol dm^-3
    • 1.0 x 10^-5 mol dm^-3
    • 2.0 x 10^-3 mol dm^-3
    • 4.0 x 10^-6 mol dm^-3

  12. An ethanoic acid / sodium ethanoate buffer has equal concentrations of acid and salt, and Ka = 1.8 x 10^-5 mol dm^-3. What is its pH?

    • 9.26
    • 2.87
    • 4.74
    • 7.00

  13. A buffer contains 0.10 mol dm^-3 ethanoic acid and 0.40 mol dm^-3 sodium ethanoate, with pKa = 4.74. What is its pH?

    • 5.34
    • 4.14
    • 4.74
    • 3.94

  14. Which indicator is suitable for a strong acid-weak base titration?

    • Litmus
    • Thymol blue
    • Methyl orange
    • Phenolphthalein

  15. Which assumption fails in [H+] = √(Ka × c) as weak acid strength increases?

    • Kw remains constant
    • [H+]eq ≈ [A-]eq
    • [HA]eq ≈ [HA]initial
    • Ka remains constant

  16. Which species in an acidic buffer reacts with added hydroxide ions?

    • Conjugate base
    • Sodium ions
    • Weak acid
    • Water molecules

  17. What happens to pH when a small amount of alkali is added to a buffer?

    • Remains completely unchanged
    • Increases slightly
    • Decreases slightly
    • Increases significantly

  18. What is the normal pH range of human arterial blood controlled by buffer systems?

    • 7.35 to 7.45
    • 7.55 to 7.75
    • 6.80 to 7.00
    • 7.00 to 7.20

  19. Why is the equivalence point above pH 7 for a weak acid-strong base titration?

    • Indicator changes early
    • Cation hydrolyses water
    • Acid fully dissociates
    • Anion hydrolyses water

  20. What is the conjugate acid of ammonia, NH3?

    • NH4+
    • N2H4
    • NH4OH
    • NH2-

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