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Acid-base equilibria: Eduqas A‑Level Chemistry questions

Every Eduqas A-Level Chemistry exam question on PI5.2 Acid-base equilibria, 2016–2025, with its mark scheme and examiner’s report.

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1,513 questions

  1. Q9(c)(ii)

    June 2025 · Component 1

    4 marksPI5.2 Acid-base equilibria
    The whole paper ↗
    June 2025 Component 1, question 9(c)(ii): A weak acid can be used to make a buffer solution. A student takes a certain volume of ethanoic acid of initial concentration 0.200 mol dm–3. They add the same

  2. Q13(c)

    June 2025 · Component 1

    6 marksPI5.2 Acid-base equilibria
    The whole paper ↗
    June 2025 Component 1, question 13(c): The ionic product of water, Kw, varies with temperature as shown in the graph below. Kw / mol2 dm–6 7.0 × 10–13 6.0 × 10–13 5.0 × 10–13 4.0 × 10–13 3.0 × 10–13

  3. Q9(a)(i)

    June 2024 · Component 1

    2 marksPI5.2 Acid-base equilibria
    The whole paper ↗
    June 2024 Component 1, question 9(a)(i): Propanoic acid can be neutralised using aqueous sodium hydroxide. Calculate the pH of aqueous sodium hydroxide of concentration 0.500 mol dm–3. [2] pH =

  4. Q9(a)(ii)

    June 2024 · Component 1

    3 marksPI5.2 Acid-base equilibria
    The whole paper ↗
    June 2024 Component 1, question 9(a)(ii): 20.0 cm3 of 0.500 mol dm–3 aqueous sodium hydroxide is added to 40.0 cm3 of 0.500 mol dm–3 aqueous propanoic acid. Calculate the pH of the resulting solution. [

  5. Q11(c)

    June 2024 · Component 1

    4 marksPI5.2 Acid-base equilibria
    The whole paper ↗
    June 2024 Component 1, question 11(c): Peroxynitrous acid is a weak acid with a Ka of 1.6 × 10–7 mol dm–3. Nitric(V) acid is a strong acid. Calculate the change in pH when a 0.100 mol dm–3 solution o

  6. Q3(c)(i)

    June 2024 · Component 3

    3 marksPI5.2 Acid-base equilibria
    The whole paper ↗
    June 2024 Component 3, question 3(c)(i): Calculate the ratio of the concentration of sodium ethanoate to ethanoic acid in the buffer mixture. [3] (Ka for ethanoic acid = 1.78 × 10–5 mol dm–3 at 298 K)

  7. Q3(c)(ii)

    June 2024 · Component 3

    1 markPI5.2 Acid-base equilibria
    The whole paper ↗
    June 2024 Component 3, question 3(c)(ii): Calculate the volumes of sodium ethanoate and ethanoic acid used to prepare 1 dm3 of the buffer solution. [1] Volume of ethanoic acid = cm3 Volume of sodium eth

  8. Q3

    Autumn 2021 · Component 1

    1 markPI5.2 Acid-base equilibria
    The whole paper ↗
    Autumn 2021 Component 1, question 3: The strengths of many acids are recorded using their pKa values, where pKa = –log Ka. The pKa values of several acids are given below. State, giving a reason, w

  9. Q10(a)

    Autumn 2021 · Component 1

    1 markPI5.2 Acid-base equilibria
    The whole paper ↗
    Autumn 2021 Component 1, question 10(a): State what is meant by a buffer solution. [1]

  10. Q10(b)

    Autumn 2021 · Component 1

    1 markPI5.2 Acid-base equilibria
    The whole paper ↗
    Autumn 2021 Component 1, question 10(b): Give a use for a buffer. [1]

  11. Q10(c)(i)

    Autumn 2021 · Component 1

    4 marksPI5.2 Acid-base equilibria
    The whole paper ↗
    Autumn 2021 Component 1, question 10(c)(i): Find the pH of the buffer when the concentration of the sodium propanoate is equal to the concentration of the propanoic acid. [4] pH =

  12. Q10(c)(ii)

    Autumn 2021 · Component 1

    2 marksPI5.2 Acid-base equilibria
    The whole paper ↗
    Autumn 2021 Component 1, question 10(c)(ii): Find the value of Ka for propanoic acid. [2] Ka =

  13. Q10(c)(iii)

    Autumn 2021 · Component 1

    3 marksPI5.2 Acid-base equilibria
    The whole paper ↗
    Autumn 2021 Component 1, question 10(c)(iii): At a higher temperature a greater mass of sodium propanoate must be added to the propanoic acid to achieve the same pH. Explain what information this provides a

  14. Q7(b)

    Autumn 2020 · Component 1

    2 marksPI5.2 Acid-base equilibria
    The whole paper ↗
    Autumn 2020 Component 1, question 7(b): Find the pH of a solution of chloroethanoic acid of concentration 0.200 mol dm–3. [2] pH = ……… …………………

  15. Q7(c)(ii)

    Autumn 2020 · Component 1

    5 marksPI5.2 Acid-base equilibriaC2.1 Simple equilibria and acid-base reactions
    The whole paper ↗
    Autumn 2020 Component 1, question 7(c)(ii): Suggest three changes that should be made to this method, giving reasons for each. [5]

  16. Q9(d)(ii)

    Autumn 2020 · Component 1

    3 marksPI5.2 Acid-base equilibria
    The whole paper ↗
    Autumn 2020 Component 1, question 9(d)(ii): Use the pH to calculate the concentration of the initial methyllithium solution. You must show your working. [3] Concentration = ……… ………………… mol dm–3

  17. Q11(b)(iii)

    Autumn 2020 · Component 1

    3 marksPI5.2 Acid-base equilibria
    The whole paper ↗
    Autumn 2020 Component 1, question 11(b)(iii): At the end of the electrolysis process the solution contained a base and a salt. A student suggests that this could therefore be used as a buffer. Is the studen

  18. Q9(a)(i)

    June 2019 · Component 1

    1 markPI5.2 Acid-base equilibria
    The whole paper ↗
    June 2019 Component 1, question 9(a)(i): e are acids that can donate only one hydrogen ion in chemical reactions. Hydrochloric acid is a strong acid and ethanoic acid is a weak acid. (i) Define pH. [1]

  19. Q9(a)(ii)

    June 2019 · Component 1

    1 markPI5.2 Acid-base equilibria
    The whole paper ↗
    June 2019 Component 1, question 9(a)(ii): Write an expression for the acid dissociation constant, Ka, for ethanoic acid. [1]

  20. Q9(a)(iii)

    June 2019 · Component 1

    6 marksPI5.2 Acid-base equilibria
    The whole paper ↗
    June 2019 Component 1, question 9(a)(iii): A student makes the following statements: • when the concentration of any monobasic acid is doubled, the concentration of H+ ions is also doubled; this applies
All 32 questions on Acid-base equilibria, as a list
  1. June 2025, Component 1, Q9(c)(ii) (4 marks): A weak acid can be used to make a buffer solution. A student takes a certain volume of ethanoic acid of initial concentration 0.200 mol dm–3. They add the same
  2. June 2025, Component 1, Q13(c) (6 marks): The ionic product of water, Kw, varies with temperature as shown in the graph below. Kw / mol2 dm–6 7.0 × 10–13 6.0 × 10–13 5.0 × 10–13 4.0 × 10–13 3.0 × 10–13
  3. June 2024, Component 1, Q9(a)(i) (2 marks): Propanoic acid can be neutralised using aqueous sodium hydroxide. Calculate the pH of aqueous sodium hydroxide of concentration 0.500 mol dm–3. [2] pH =
  4. June 2024, Component 1, Q9(a)(ii) (3 marks): 20.0 cm3 of 0.500 mol dm–3 aqueous sodium hydroxide is added to 40.0 cm3 of 0.500 mol dm–3 aqueous propanoic acid. Calculate the pH of the resulting solution. [
  5. June 2024, Component 1, Q11(c) (4 marks): Peroxynitrous acid is a weak acid with a Ka of 1.6 × 10–7 mol dm–3. Nitric(V) acid is a strong acid. Calculate the change in pH when a 0.100 mol dm–3 solution o
  6. June 2024, Component 3, Q3(c)(i) (3 marks): Calculate the ratio of the concentration of sodium ethanoate to ethanoic acid in the buffer mixture. [3] (Ka for ethanoic acid = 1.78 × 10–5 mol dm–3 at 298 K)
  7. June 2024, Component 3, Q3(c)(ii) (1 mark): Calculate the volumes of sodium ethanoate and ethanoic acid used to prepare 1 dm3 of the buffer solution. [1] Volume of ethanoic acid = cm3 Volume of sodium eth
  8. Autumn 2021, Component 1, Q3 (1 mark): The strengths of many acids are recorded using their pKa values, where pKa = –log Ka. The pKa values of several acids are given below. State, giving a reason, w
  9. Autumn 2021, Component 1, Q10(a) (1 mark): State what is meant by a buffer solution. [1]
  10. Autumn 2021, Component 1, Q10(b) (1 mark): Give a use for a buffer. [1]
  11. Autumn 2021, Component 1, Q10(c)(i) (4 marks): Find the pH of the buffer when the concentration of the sodium propanoate is equal to the concentration of the propanoic acid. [4] pH =
  12. Autumn 2021, Component 1, Q10(c)(ii) (2 marks): Find the value of Ka for propanoic acid. [2] Ka =
  13. Autumn 2021, Component 1, Q10(c)(iii) (3 marks): At a higher temperature a greater mass of sodium propanoate must be added to the propanoic acid to achieve the same pH. Explain what information this provides a
  14. Autumn 2020, Component 1, Q7(b) (2 marks): Find the pH of a solution of chloroethanoic acid of concentration 0.200 mol dm–3. [2] pH = ……… …………………
  15. Autumn 2020, Component 1, Q7(c)(ii) (5 marks): Suggest three changes that should be made to this method, giving reasons for each. [5]
  16. Autumn 2020, Component 1, Q9(d)(ii) (3 marks): Use the pH to calculate the concentration of the initial methyllithium solution. You must show your working. [3] Concentration = ……… ………………… mol dm–3
  17. Autumn 2020, Component 1, Q11(b)(iii) (3 marks): At the end of the electrolysis process the solution contained a base and a salt. A student suggests that this could therefore be used as a buffer. Is the studen
  18. June 2019, Component 1, Q9(a)(i) (1 mark): e are acids that can donate only one hydrogen ion in chemical reactions. Hydrochloric acid is a strong acid and ethanoic acid is a weak acid. (i) Define pH. [1]
  19. June 2019, Component 1, Q9(a)(ii) (1 mark): Write an expression for the acid dissociation constant, Ka, for ethanoic acid. [1]
  20. June 2019, Component 1, Q9(a)(iii) (6 marks): A student makes the following statements: • when the concentration of any monobasic acid is doubled, the concentration of H+ ions is also doubled; this applies
  21. June 2019, Component 3, Q2(a)(i) (4 marks): Plot the titration curve on the grid, clearly labelling the axes. [4]
  22. June 2019, Component 3, Q2(a)(ii) (6 marks): Use information from the titration curve in answering parts I-III. I. Calculate the concentration, in mol dm–3, of the aqueous ethanoic acid. [3] Concentration
  23. June 2019, Component 3, Q2(b) (1 mark): State the colour obtained if a few drops of the acid-base indicator methyl red are added to a sodium ethanoate solution. Give a reason for your answer. [1] pH M
  24. June 2019, Component 3, Q2(c) (4 marks): Aqueous propanoic acid and sodium propanoate can form a buffer solution. A student requires a buffer of pH 4.46 for an experiment. He adds solid sodium propanoa
  25. June 2018, Component 1, Q3 (1 mark): State what is meant by a buffer solution. [1]
  26. June 2018, Component 1, Q13(d)(ii) (2 marks): The acidic solution is neutralised using aqueous sodium hydroxide of concentration 2.00 mol dm–3. Calculate the pH of this sodium hydroxide solution. [2] [ionic
  27. June 2018, Component 3, Q5(c)(i) (3 marks): Calculate the pH of the aqueous solution of the weak carboxylic acid X at 298 K. [3] (Ka for carboxylic acid X is 1.32 × 10–5 mol dm–3 at 298 K) pH =
  28. June 2018, Component 3, Q5(c)(ii) (5 marks): Sketch a curve to show the variation in pH when 50.0 cm3 of 0.0200 mol dm–3 sodium hydroxide solution is gradually added to 25.0 cm3 of the solution of carboxyl
  29. June 2017, Component 1, Q9 (2 marks): Suggest a pH value for a dilute solution of ammonium chloride, giving a reason for your answer. [2]
  30. June 2017, Component 1, Q13(b) (6 marks): Explain how an indicator works and give reasons why two different indicators are used to identify the end-points for neutralisation of sodium hydroxide and sodi
  31. June 2017, Component 1, Q13(c)(i) (2 marks): Calculate the pH of 0.100 mol dm–3 ethanoic acid. [2] (Ka for ethanoic acid = 1.76 × 10−5 mol dm−3) pH =
  32. June 2017, Component 1, Q13(c)(ii) (2 marks): Suggest how the equivalence point for the titration of a weak acid and a weak base such as sodium carbonate can be found experimentally. [2]

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