Lesson 12.2.2

12.2.2 Weak acids, Ka and pKa Quiz: Pearson Edexcel Chemistry, Unit 12

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 12.2.2, Weak acids, Ka and pKa: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 12: Acid-base Equilibria, written with Revision Ninja.

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The 20 questions

  1. How does a weak acid behave when dissolved in aqueous solution?

    • Completely dissociates
    • Fully ionises
    • Does not dissociate
    • Partially dissociates

  2. Which expression is the correct acid dissociation constant Ka for the equilibrium HA dissociating into H+ and A-?

    • Ka = ([H+] + [A-]) / [HA]
    • Ka = [H+][A-] / [HA]
    • Ka = [H+][HA] / [A-]
    • Ka = [HA] / ([H+][A-])

  3. What is pKa defined as?

    • pKa = -log10(Ka)
    • pKa = 10^-Ka
    • pKa = 1/Ka
    • pKa = log10(Ka) + 14

  4. What does a lower pKa value indicate about an acid?

    • Weaker acid
    • Stronger acid
    • Lower Ka
    • Higher pH

  5. Which of these is a weak acid?

    • Ethanoic acid
    • Hydrobromic acid
    • Hydrochloric acid
    • Nitric acid

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

    • 1.00 x 10^-7 mol2 dm-6
    • 1.00 x 10^-14 mol2 dm-6
    • 1.00 x 10^-14 mol dm-3
    • 7.00 x 10^-14 mol2 dm-6

  7. Which expression correctly defines pH?

    • pH = -log10[H+]
    • pH = log10[H+]
    • pH = -[H+] / 14
    • pH = 10^-[H+]

  8. What is the pH of a 0.0100 mol dm-3 solution of hydrochloric acid, which is fully dissociated?

    • 12.00
    • 1.00
    • 2.00
    • 10.00

  9. A weak acid has Ka = 1.8 x 10^-5 mol dm-3. Assuming the dissociation is small, what is the approximate pH of a 0.100 mol dm-3 solution?

    • 1.00
    • 3.37
    • 4.74
    • 2.87

  10. A 0.100 mol dm-3 weak monobasic acid has pH 2.87. Which value is the best estimate of its Ka?

    • 2.9 x 10^-3 mol dm-3
    • 1.8 x 10^-3 mol dm-3
    • 1.8 x 10^-7 mol dm-3
    • 1.8 x 10^-5 mol dm-3

  11. What is the pKa of an acid with Ka = 6.3 x 10^-5 mol dm-3?

    • 3.20
    • 4.20
    • 5.20
    • 4.80

  12. The pKa of a weak acid is 4.00. What is its Ka?

    • 1.0 x 10^4 mol dm-3
    • 1.0 x 10^-4 mol dm-3
    • 4.0 x 10^-4 mol dm-3
    • 1.0 x 10^-10 mol dm-3

  13. A 0.50 mol dm-3 solution of a weak monobasic acid has Ka = 2.0 x 10^-4 mol dm-3. What is its pH?

    • 1.70
    • 2.00
    • 3.70
    • 4.00

  14. If a weak acid solution is diluted 100-fold, by how much does its pH rise?

    • More than 2
    • Exactly 2
    • Less than 2
    • Exactly 100

  15. A weak monobasic acid HA has Ka = 1.6 x 10^-5 mol dm-3. What is the pH of a 0.20 mol dm-3 solution?

    • 3.20
    • 2.20
    • 4.80
    • 2.75

  16. A 0.80 g sample of a weak monobasic acid (Mr = 80.0) is dissolved to make 500 cm3 of solution, and its pH is 3.00. Assuming [HA] is approximately 0.0200 mol dm-3, what is Ka?

    • 5.0 x 10^-5 mol dm-3
    • 1.5 x 10^-4 mol dm-3
    • 5.0 x 10^-3 mol dm-3
    • 2.0 x 10^-6 mol dm-3

  17. What is the pH of a 0.0010 mol dm-3 solution of sodium hydroxide at 298 K?

    • 14.00
    • 3.00
    • 11.00
    • 7.00

  18. At 350 K, Kw for water is 2.5 x 10^-14 mol2 dm-6. What is the pH of pure water at this temperature?

    • 7.60
    • 7.00
    • 6.80
    • 6.60

  19. Which assumption is made when calculating the pH of a weak acid solution?

    • Dissociation is negligible
    • Dissociation is complete
    • Concentration reaches zero
    • Water dissociation dominates

  20. What is the pH of a 0.10 mol dm-3 hydrochloric acid solution?

    • 1.00
    • 2.87
    • 7.00
    • 13.00

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