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Simple equilibria and acid-base reactions: WJEC A‑Level Chemistry questions

Every WJEC A-Level Chemistry exam question on 1.7 Simple equilibria and acid-base reactions, 2016–2025, with its mark scheme and examiner’s report.

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1,204 questions

  1. Q9(b)(ii)

    Summer 2025 · Unit 3

    2 marks1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2025 Unit 3, question 9(b)(ii): Calculate the pH of an aqueous solution of the strong acid HI of concentration 0.250 mol dm–3. [2] pH =

  2. Q12(e)(i)

    Summer 2025 · AS Unit 1

    2 marks1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2025 AS Unit 1, question 12(e)(i): Write an expression for the equilibrium constant, Kc, and give its unit, if any. [2] Kc = Unit

  3. Q12(e)(ii)

    Summer 2025 · AS Unit 1

    2 marks1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2025 AS Unit 1, question 12(e)(ii): The equilibrium constant, Kc, has a numerical value of 0.092 at a temperature of 1200 °C. If the equilibrium concentration of water is 0.77 mol dm–3, hydrogen i

  4. Q13(a)

    Summer 2025 · AS Unit 1

    6 marks1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2025 AS Unit 1, question 13(a): A student is given a white powder and told to prove that the powder is pure calcium carbonate by finding its relative formula mass. The relative formula mass ca

  5. Q13(b)(i)

    Summer 2025 · AS Unit 1

    1 mark1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2025 AS Unit 1, question 13(b)(i): State what is meant by a strong acid. [1]

  6. Q13(b)(ii)

    Summer 2025 · AS Unit 1

    2 marks1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2025 AS Unit 1, question 13(b)(ii): acid. State whether the second and third properties apply to a 1.00 mol dm–3 solution of ethanoic acid. Explain your answers. [2]

  7. Q13(d)

    Summer 2025 · AS Unit 1

    2 marks1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2025 AS Unit 1, question 13(d): Stagnant water has a potential for microbial growth. The bacteria legionella thrives in stagnant water that has a pH range of 5.5-8.1. Calculate the minimum hyd

  8. Q10(a)

    Summer 2024 · Unit 3

    2 marks1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2024 Unit 3, question 10(a): The pH of the initial stretch of Afon Goch was found to be 3.24. Calculate the concentration of H+ ions in this water. [2] [H+] = mol dm–3

  9. Q10(c)(i)

    Summer 2024 · AS Unit 1

    1 mark1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2024 AS Unit 1, question 10(c)(i): Calculate the hydrogen ion concentration of this solution. [1] [H+] = … …….. mol dm–3

  10. Q10(c)(ii)

    Summer 2024 · AS Unit 1

    3 marks1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2024 AS Unit 1, question 10(c)(ii): Since the pH meter had not been used for a while, the teacher wanted to check the accuracy of the reading. He asked the student to check this by titrating 25.0

  11. Q10(c)(iii)

    Summer 2024 · AS Unit 1

    1 mark1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2024 AS Unit 1, question 10(c)(iii): The student said that the reading on the pH meter was incorrect. Do you agree? Justify your answer by comparing your answers to parts (i) and (ii). [1]

  12. Q12(a)

    Summer 2024 · AS Unit 1

    6 marks1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2024 AS Unit 1, question 12(a): There are several stages in the industrial production of methanol from methane. The final stage involves an equilibrium where carbon dioxide is converted into m

  13. Q12(b)(i)

    Summer 2024 · AS Unit 1

    2 marks1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2024 AS Unit 1, question 12(b)(i): Write an expression for the equilibrium constant, Kc, and give its unit, if any. [2] Kc = Unit

  14. Q12(b)(ii)

    Summer 2024 · AS Unit 1

    2 marks1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2024 AS Unit 1, question 12(b)(ii): The equilibrium constant, Kc, has a numerical value of 0.350 at a temperature of 350 °C. If the equilibrium concentration of carbon monoxide is 0.725 mol dm–3 a

  15. Q13(a)

    Summer 2024 · AS Unit 1

    3 marks1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2024 AS Unit 1, question 13(a): Complete the table and calculate the mean titre at the phenolphthalein end-point (A) and the mean titre at the methyl orange end-point (B). [3] Mean titre A = …

  16. Q13(b)

    Summer 2024 · AS Unit 1

    1 mark1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2024 AS Unit 1, question 13(b): solution into the conical flask. [1] … ……..

  17. Q13(c)

    Summer 2024 · AS Unit 1

    1 mark1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2024 AS Unit 1, question 13(c): The percentage error due to the burette in the first titration with phenolphthalein is just over 1%. Suggest what the student could have changed in the method t

  18. Q13(d)

    Summer 2024 · AS Unit 1

    1 mark1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2024 AS Unit 1, question 13(d): Despite having a larger percentage error due to the burette, suggest a reason why mean titre A could be more accurate than mean titre B. [1]

  19. Q13(e)(i)

    Summer 2024 · AS Unit 1

    1 mark1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2024 AS Unit 1, question 13(e)(i): The equation for the reaction taking place in the phenolphthalein titration is as follows. CO32– H+ HCO3– + Mean titre A is the volume needed to convert all the

  20. Q13(e)(ii)

    Summer 2024 · AS Unit 1

    2 marks1.7 Simple equilibria and acid-base reactions
    The whole paper ↗
    Summer 2024 AS Unit 1, question 13(e)(ii): The equation for the reaction taking place in the methyl orange titration is as follows. HCO3– H+ + CO2 + H2O Mean titre B is the volume needed to convert all t
All 72 questions on Simple equilibria and acid-base reactions, as a list
  1. Summer 2025, Unit 3, Q9(b)(ii) (2 marks): Calculate the pH of an aqueous solution of the strong acid HI of concentration 0.250 mol dm–3. [2] pH =
  2. Summer 2025, AS Unit 1, Q12(e)(i) (2 marks): Write an expression for the equilibrium constant, Kc, and give its unit, if any. [2] Kc = Unit
  3. Summer 2025, AS Unit 1, Q12(e)(ii) (2 marks): The equilibrium constant, Kc, has a numerical value of 0.092 at a temperature of 1200 °C. If the equilibrium concentration of water is 0.77 mol dm–3, hydrogen i
  4. Summer 2025, AS Unit 1, Q13(a) (6 marks): A student is given a white powder and told to prove that the powder is pure calcium carbonate by finding its relative formula mass. The relative formula mass ca
  5. Summer 2025, AS Unit 1, Q13(b)(i) (1 mark): State what is meant by a strong acid. [1]
  6. Summer 2025, AS Unit 1, Q13(b)(ii) (2 marks): acid. State whether the second and third properties apply to a 1.00 mol dm–3 solution of ethanoic acid. Explain your answers. [2]
  7. Summer 2025, AS Unit 1, Q13(d) (2 marks): Stagnant water has a potential for microbial growth. The bacteria legionella thrives in stagnant water that has a pH range of 5.5-8.1. Calculate the minimum hyd
  8. Summer 2024, Unit 3, Q10(a) (2 marks): The pH of the initial stretch of Afon Goch was found to be 3.24. Calculate the concentration of H+ ions in this water. [2] [H+] = mol dm–3
  9. Summer 2024, AS Unit 1, Q10(c)(i) (1 mark): Calculate the hydrogen ion concentration of this solution. [1] [H+] = … …….. mol dm–3
  10. Summer 2024, AS Unit 1, Q10(c)(ii) (3 marks): Since the pH meter had not been used for a while, the teacher wanted to check the accuracy of the reading. He asked the student to check this by titrating 25.0
  11. Summer 2024, AS Unit 1, Q10(c)(iii) (1 mark): The student said that the reading on the pH meter was incorrect. Do you agree? Justify your answer by comparing your answers to parts (i) and (ii). [1]
  12. Summer 2024, AS Unit 1, Q12(a) (6 marks): There are several stages in the industrial production of methanol from methane. The final stage involves an equilibrium where carbon dioxide is converted into m
  13. Summer 2024, AS Unit 1, Q12(b)(i) (2 marks): Write an expression for the equilibrium constant, Kc, and give its unit, if any. [2] Kc = Unit
  14. Summer 2024, AS Unit 1, Q12(b)(ii) (2 marks): The equilibrium constant, Kc, has a numerical value of 0.350 at a temperature of 350 °C. If the equilibrium concentration of carbon monoxide is 0.725 mol dm–3 a
  15. Summer 2024, AS Unit 1, Q13(a) (3 marks): Complete the table and calculate the mean titre at the phenolphthalein end-point (A) and the mean titre at the methyl orange end-point (B). [3] Mean titre A = …
  16. Summer 2024, AS Unit 1, Q13(b) (1 mark): solution into the conical flask. [1] … ……..
  17. Summer 2024, AS Unit 1, Q13(c) (1 mark): The percentage error due to the burette in the first titration with phenolphthalein is just over 1%. Suggest what the student could have changed in the method t
  18. Summer 2024, AS Unit 1, Q13(d) (1 mark): Despite having a larger percentage error due to the burette, suggest a reason why mean titre A could be more accurate than mean titre B. [1]
  19. Summer 2024, AS Unit 1, Q13(e)(i) (1 mark): The equation for the reaction taking place in the phenolphthalein titration is as follows. CO32– H+ HCO3– + Mean titre A is the volume needed to convert all the
  20. Summer 2024, AS Unit 1, Q13(e)(ii) (2 marks): The equation for the reaction taking place in the methyl orange titration is as follows. HCO3– H+ + CO2 + H2O Mean titre B is the volume needed to convert all t
  21. Summer 2023, AS Unit 1, Q9(a) (1 mark): Over 180 million tonnes of ammonia are manufactured each year. The main use of ammonia is in the production of salts such as ammonium sulfate, which is used as
  22. Summer 2023, AS Unit 1, Q9(c)(i) (1 mark): State Le Chatelier’s principle. [1]
  23. Summer 2023, AS Unit 1, Q9(c)(ii) (2 marks): A student looked at curves A and B and said that the forward reaction is exothermic. Is he correct? Justify your answer by using Le Chatelier’s principle. [2]
  24. Summer 2023, AS Unit 1, Q9(c)(iii) (2 marks): On the graph, draw a curve that represents the reaction at 850 °C but with a catalyst added to the reaction mixture. Label this curve C. Explain the shape of th
  25. Summer 2023, AS Unit 1, Q9(d) (1 mark): Calculate its pH. [1] pH =
  26. Summer 2023, AS Unit 1, Q11(a)(i) (1 mark): Before starting the titration, the student rinses the burette with silver nitrate solution. Suggest why he does this. [1]
  27. Summer 2023, AS Unit 1, Q11(a)(ii) (1 mark): Suggest why the student dilutes the seawater. [1]
  28. Summer 2023, AS Unit 1, Q11(a)(iv) (2 marks): Describe and explain one action the student might take just before the endpoint of the titration, to ensure that the volume of silver nitrate added at the endpo
  29. Summer 2022, Unit 3, Q10(b) (2 marks): Calculate the concentration of the HA solution. [2] Concentration = mol dm–3
  30. Summer 2022, AS Unit 1, Q9(c)(i) (2 marks): the forward reaction is endothermic or exothermic. [2]
  31. Summer 2022, AS Unit 1, Q9(c)(ii) (2 marks): the forward reaction involves an increase or decrease in the number of moles of gas. [2]
  32. Summer 2022, AS Unit 1, Q11(b)(ii) (1 mark): A solution of arsenous acid has a pH of 5.11. Calculate the hydrogen ion concentration of this solution. [1] [H+] = mol dm–3
  33. Summer 2022, AS Unit 1, Q12(b) (1 mark): State why he adds an indicator to this solution. [1]
  34. Summer 2022, AS Unit 1, Q12(c) (1 mark): Suggest why he was told to carry out a rough titration first. [1]
  35. Summer 2022, AS Unit 1, Q12(d) (1 mark): State what you understand by the term ‘concordant titres’. [1]
  36. Summer 2022, AS Unit 1, Q12(e) (3 marks): Some of the student’s results are shown below: Mass of weighing bottle + carbonate / g 13.73 Mass of weighing bottle / g 12.48 Titration Rough 1 2 3 Final readi
  37. Summer 2022, AS Unit 1, Q12(f)(i) (2 marks): [2] number of moles =
  38. Summer 2019, AS Unit 1, Q11(c) (4 marks): The equation for the reaction between calcium carbonate and hydrochloric acid is as follows. CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2O(l) + CO2(g) Use this and the st
  39. Summer 2019, AS Unit 1, Q11(d) (1 mark): Comment on the validity of the mean titre calculated. [1]
  40. Summer 2019, AS Unit 1, Q11(e) (2 marks): Another student follows the same procedure but filters the solution before the reaction is complete. State what effect, if any, this would have on the value of
  41. Summer 2019, AS Unit 1, Q13(a)(i) (1 mark): Chemical equilibria are often described as dynamic equilibria. Explain the term dynamic equilibrium. [1]
  42. Summer 2019, AS Unit 1, Q13(a)(ii) (2 marks): Use Le Chatelier’s principle to explain why the pale green colour disappears if sodium hydroxide solution is added. [2]
  43. Summer 2018, Unit 4, Q8(b)(i) (1 mark): Write a statement that links the mole ratio of HF : CH2Cl2 with the yield of difluoromethane. [1]
  44. Summer 2018, Unit 4, Q8(c)(i) (1 mark): Suggest, giving a reason, whether a high or low pressure should be used in stage 1 [1]
  45. Summer 2018, Unit 4, Q8(c)(ii) (1 mark): Suggest, giving a reason, whether a high or low temperature should be used in stage 2 [1]
  46. Summer 2018, AS Unit 1, Q8(e) (1 mark): Hydrazine acts as a base in a similar way to ammonia. Suggest an equation for the equilibrium formed when hydrazine dissolves in water. [1]
  47. Summer 2018, AS Unit 1, Q9(b)(i) (1 mark): Suggest why she did not need to measure the volume of water accurately. [1]
  48. Summer 2018, AS Unit 1, Q9(b)(ii) (1 mark): Suggest why she heated the flask for 5 to 10 minutes. [1]
  49. Summer 2018, AS Unit 1, Q9(c) (2 marks): The student used the results from three titrations to calculate a mean titre. Some of her results are shown below. Titration 1 2 3 Final reading / cm3 26.90 26.
  50. Summer 2018, AS Unit 1, Q9(d) (2 marks): Ascorbic acid can decompose upon exposure to air. If this reaction occurred before the titration was completed, state how it might affect the titration results.
  51. Summer 2018, AS Unit 1, Q9(e) (3 marks): The equation for the reaction between ascorbic acid and sodium hydroxide is given below. C6H8O6 + NaOH C6H7O6Na + H2O Mr 176 The percentage of ascorbic acid is
  52. Summer 2018, AS Unit 1, Q9(f)(i) (2 marks): [2] pH =
  53. Summer 2018, AS Unit 1, Q10(a)(i) (4 marks): A student said that the equilibrium must lie to the left because the concentrations of nitrogen and hydrogen are greater than that of ammonia. Is he correct? Ju
  54. Summer 2018, AS Unit 1, Q10(a)(ii) (2 marks): When the temperature is increased the equilibrium yield of NH3 decreases. The student said that the reaction is endothermic. Is he correct? Justify your answer
  55. Summer 2017, Unit 3, Q9(c)(i) (2 marks): Explain why the use of a catalyst is essential in industrial processes involving exothermic equilibria such as stage 1 [2]
  56. Summer 2017, Unit 3, Q9(c)(ii) (4 marks): A student attempted to perform stage 2 using a temperature of 450 K and a pressure of 5 atm. He obtained only a small yield. Suggest how the yield could be impr
  57. Summer 2017, Unit 3, Q10(e)(i) (1 mark): The pH of a dilute solution of nitric acid is measured using a pH probe and has a value of 0.3. Calculate the concentration of this solution. [1] Concentration
  58. Summer 2017, Unit 3, Q10(e)(ii) (2 marks): An alternative way of measuring the concentration of the solution is by titration against a standard solution of sodium hydrogencarbonate of concentration 0.500
  59. Summer 2017, Unit 4, Q9(d)(ii) (3 marks): The esterification of 2-aminobenzoic acid is a reversible reaction and eventually the mixture will reach equilibrium. Use the information below to suggest why t
  60. Summer 2017, AS Unit 1, Q7(b)(i) (1 mark): Calculate the mean titre that should be used to determine the concentration of the hydrochloric acid. [1] Mean titre = cm3
  61. Summer 2017, AS Unit 1, Q7(b)(ii) (1 mark): The burette used in the titrations has an uncertainty for each reading of ± 0.05 cm3. Estimate the maximum percentage error in the titre in titration 4 Show you
  62. Summer 2017, AS Unit 1, Q7(b)(iii) (2 marks): Apart from errors in reading the burette, suggest one reason why incorrect titres may have been obtained when carrying out the titrations. Explain the effect of
  63. Summer 2017, AS Unit 1, Q7(c)(i) (3 marks): the number of moles that reacted with the fertiliser. [3] n(NaOH) = mol
  64. Summer 2017, AS Unit 1, Q8(b) (2 marks): Sulfur dioxide can react with oxygen and water to form sulfuric acid. Although sulfuric acid is a strong acid, it does not have to be a concentrated acid. Expla
  65. Summer 2017, AS Unit 1, Q8(c)(i) (2 marks): A student was given an aqueous solution of an acid HX and was asked to find out if it was a strong or weak acid. 25.0 cm3 of the acid HX required 15.90 cm3 of 0
  66. Summer 2017, AS Unit 1, Q8(c)(ii) (2 marks): A teacher measured the pH of the aqueous solution and found it to be 2.10. She told the student that the acid in the solution must be a strong one. Is she corre
  67. Summer 2017, AS Unit 1, Q8(d)(i) (2 marks): State and explain what you would observe on adding water to the equilibrium mixture. [2]
  68. Summer 2017, AS Unit 1, Q8(d)(ii) (2 marks): State and explain what you would observe on heating the equilibrium mixture. [2]
  69. Summer 2016, AS Unit 1, Q7(a) (1 mark): Write the expression for the equilibrium constant in terms of concentration, Kc, for this reaction. [1]
  70. Summer 2016, AS Unit 1, Q7(b) (2 marks): The equilibrium constant, Kc , for this reaction has a value of 46.0 at a certain temperature. Calculate the equilibrium concentration of hydrogen at this tempe
  71. Summer 2016, AS Unit 1, Q10(e) (3 marks): Solid magnesium hexafluorosilicate hydrolyses rapidly when added to water. One equation for this reaction is as follows. MgSiF6(s) + 2H2O(l) Mg2+(aq) + 6F–(aq)
  72. Summer 2016, AS Unit 1, Q11(c) (6 marks): Ammonium sulfate can be prepared in the laboratory by neutralising aqueous sulfuric acid with ammonia solution in an acid-base titration. 2NH3(aq) + H2SO4(aq) (

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