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CAIE A Level Chemistry 9701

Equilibria questions

Exam-style questions on Equilibria, ordered from foundation to challenge. Pick one, write your answer the way you would in the exam, and it comes back marked against the mark scheme, point by point.

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Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.

  1. Explain4 marksStandardExplain how the carbonic acid / hydrogencarbonate buffer system controls pH in human blood. Include chemical equations in your explanation.
  2. Describe5 marksStandardEthanoic acid, CH3COOH, is a weak acid. In aqueous solution it partially dissociates according to the equation CH3COOH(aq) + H2O(l) ⇌ CH3COO-(aq) + H3O+(aq) State what is meant by the terms conjugate acid and conjugate…
  3. Compare5 marksStandardA student has two beakers. Beaker A contains 0.1 mol dm⁻³ hydrochloric acid, HCl. Beaker B contains 0.1 mol dm⁻³ ethanoic acid, CH3COOH. The student adds a few drops of universal indicator to each beaker. Compare the…
  4. Compare5 marksStandardA student prepares a buffer solution by mixing equal volumes of 0.10 mol dm⁻³ ethanoic acid and 0.10 mol dm⁻³ sodium ethanoate. Compare the buffer solution with pure water in terms of how each responds to the addition…
  5. Suggest4 marksStandardA student wants to prepare a buffer solution with a pH close to 9.2 using aqueous ammonia, NH3(aq), and solid ammonium chloride, NH4Cl. Suggest how the student could make this buffer solution and explain how it…
  6. Describe5 marksStandardA student adds aqueous ammonia, NH3 (a weak base), to aqueous hydrochloric acid, HCl (a strong acid). Describe what happens in terms of the Brønsted–Lowry theory of acids and bases. In your answer, state which species…
  7. Compare5 marksStandardTwo separate gas-phase reactions are at equilibrium in closed containers at constant temperature. Reaction 1: N2(g) + 3H2(g) ⇌ 2NH3(g), Δ H = -92.4\ kJ mol^-1 Reaction 2: H2(g) + I2(g) ⇌ 2HI(g), Δ H = +9.6\ kJ mol^-1…
  8. Compare5 marksStandardA student shakes a mixture of water and hexane with two different solutes, P and Q, separately. Solute P is polar and solute Q is non-polar. Compare the values of the partition coefficient, Kpc, of P and Q in the…
  9. Explain4 marksStandardA buffer solution is made by mixing aqueous ethanoic acid, CH3COOH, with aqueous sodium ethanoate, CH3COONa. Explain how this buffer solution controls the pH when small amounts of a strong acid and of a strong base are…
  10. Compare5 marksStandardThe following equilibrium is established in a closed vessel: SO2(g) + NO2(g) ⇌ SO3(g) + NO(g) Compare the equilibrium constant in terms of concentrations, Kc, with the equilibrium constant in terms of partial…
  11. Explain4 marksStandardA student has three dilute aqueous solutions: solution X: ce0.1 mol dm^-3 HCl solution Y: ce0.1 mol dm^-3 CH3COOH solution Z: ce0.1 mol dm^-3 NaOH The student measures the pH of each solution using a pH meter. The…
  12. Describe5 marksStandardA chemist carries out the reaction between hydrogen and iodine in a sealed flask at 450 °C. H2(g) + I2(g) ⇌ 2HI(g) The flask is sealed so that no gas can enter or leave. After some time, the amounts of all three gases…
  13. Suggest4 marksStandardAgricultural soil is often treated with lime (CaCO3) to raise its pH. The carbonate–hydrogencarbonate buffer system in the soil is represented by: ceCO3^2-(aq) + H2O(l) <= HCO3^-(aq) + OH^-(aq) A soil scientist adds a…
  14. Compare5 marksStandardA buffer solution can be prepared by mixing a weak acid with its conjugate base. An example is the ethanoic acid / sodium ethanoate buffer. The bicarbonate buffer system in blood uses carbonic acid, H2CO3, and…
  15. Explain4 marksStandardA student investigates the distribution of solute X between water and an organic solvent Y at constant temperature. Explain what is meant by the term partition coefficient, and discuss how the polarities of the solute…
  16. Compare5 marksStandardTwo beakers contain equal volumes and equal concentrations of hydrochloric acid, HCl, and ethanoic acid, CH3COOH. Small pieces of magnesium ribbon are added to each. State and compare the observations made, and explain…
  17. Suggest4 marksStandardA student places a mixture of hydrogen and iodine vapour in a sealed flask and heats the flask to 450 °C. The gases reach a dynamic equilibrium. H2(g) + I2(g) ⇌ 2HI(g) (a) Suggest what is meant by a dynamic…
  18. Compare5 marksStandardAmmonia is manufactured by the Haber process: N2(g) + 3H2(g) ⇌ 2NH3(g) The reaction is at dynamic equilibrium in a closed system at constant temperature. A small amount of ammonia gas is added to the equilibrium…
  19. Suggest4 marksStandardIn a closed flask, iodine reacts reversibly with propanone to form an organic product. The forward reaction is exothermic. The system reaches dynamic equilibrium at a fixed temperature. Suggest and explain how…
  20. Compare5 marksStandardA student has two aqueous solutions, P and Q, each of concentration 0.10 mol dm^-3. Solution P has a pH of 1.0 when measured with a pH meter. Solution Q has a pH of 2.9. Both solutions react with excess magnesium…
  21. Explain4 marksStandardThe synthesis of methanol from carbon monoxide and hydrogen is a reversible reaction that can reach dynamic equilibrium: CO(g) + 2H2(g) ⇌ CH3OH(g) Δ H = -90\ kJ mol^-1 Explain what is meant by dynamic equilibrium and…
  22. Suggest4 marksStandardA student measures the pH of two solutions of equal concentration, 0.1 mol dm^-3 hydrochloric acid and 0.1 mol dm^-3 ethanoic acid. The pH of the hydrochloric acid is 1.0 and the pH of the ethanoic acid is 2.9. Suggest…
  23. Explain4 marksStandardA sealed flask contains a mixture of N2O4(g) and NO2(g) at a constant temperature. The mixture is left until it reaches dynamic equilibrium: N2O4(g) ⇌ 2NO2(g) A small amount of a solid catalyst is then added to the…
  24. Suggest4 marksStandardAmmonia, NH3, is commonly used as a cleaning agent in aqueous solution. Suggest why ammonia solution is described as a weak alkali.
  25. Explain4 marksStandardA student measures the pH of separate 0.1 mol dm⁻³ solutions of hydrochloric acid, HCl, and ethanoic acid, CH3COOH, using a pH meter. The pH of the hydrochloric acid is 1.0, while the pH of the ethanoic acid is 2.9…
  26. Explain5 marksChallengeFour species are placed in separate beakers of water: HCl, NH3, CH3COOH, NaOH For each species, state whether it acts as a Brønsted–Lowry acid or base in water, and explain your reasoning in terms of proton transfer.
  27. Describe7 marksChallengeA student is studying buffer solutions and solubility equilibria. (a) Describe how a buffer solution can be prepared using ethanoic acid and sodium ethanoate. Include an equation to show how this buffer resists a…
  28. Explain5 marksChallengeIn the blood, carbon dioxide dissolves and reacts with water to form carbonic acid, H2CO3, which partially dissociates: H2CO3(aq) ⇌ H+(aq) + HCO3-(aq) (a) Identify the conjugate acid–base pair in this equilibrium. (b)…
  29. Explain7 marksChallengeA 1.0 dm³ closed vessel contains the following equilibrium at a fixed temperature: 2SO2(g) + O2(g) ⇌ 2SO3(g) The total pressure in the vessel is increased by forcing more nitrogen gas into the vessel at constant…
  30. Compare7 marksChallengeTwo separate gas-phase equilibria are set up in closed containers. In container 1, PCl5(g) ⇌ PCl3(g) + Cl2(g). In container 2, N2O4(g) ⇌ 2NO2(g). Both systems are allowed to reach dynamic equilibrium at the same…
  31. Suggest6 marksChallengeEthanol and ethanoic acid react reversibly in the presence of a strong acid catalyst: CH3CH2OH(l) + CH3COOH(l) ⇌ CH3COOCH2CH3(l) + H2O(l) In an experiment, equal amounts of ethanol and ethanoic acid are mixed in a…
  32. Describe5 marksChallengeTwo separate beakers contain equal volumes of dilute hydrochloric acid, HCl, and dilute ethanoic acid, CH3COOH, of the same concentration. A strip of magnesium ribbon is added to each beaker. Describe the differences…
  33. Compare7 marksChallengeA student has two aqueous solutions of acids of the same concentration (0.1 mol dm⁻³). One is hydrochloric acid, HCl, and the other is ethanoic acid, CH3COOH. The student measures the pH of each solution with a pH…
  34. Suggest6 marksChallengeA student has two solutions of equal concentration: one of sodium hydroxide and one of ammonia. Suggest, with reasons, two ways in which the behaviour of these two solutions would differ.
  35. Explain5 marksChallengeThe reaction between sulfur dioxide and oxygen is reversible: 2SO2(g) + O2(g) ⇌ 2SO3(g) (a) Explain what is meant by a dynamic equilibrium and why a closed system is needed. (b) The reaction is carried out in a closed…
  36. Describe5 marksChallengeLead(II) chloride is sparingly soluble in water. Its solubility equilibrium is represented by the equation cePbCl2(s) <= Pb^2+(aq) + 2Cl^-(aq) Describe how the solubility product, Ksp, is defined for this equilibrium…
  37. Explain7 marksChallengeTwo beakers each contain 100 cm³ of an aqueous solution of a different acid. Beaker A contains ethanoic acid, CH3COOH, and beaker B contains hydrochloric acid, HCl. Both solutions have the same concentration and the…
  38. Explain7 marksChallengeHuman blood plasma contains dissolved CO2, hydrogencarbonate ions, HCO3-, and carbonic acid, H2CO3. The equilibrium below helps to maintain the pH of blood at about 7.4. H2CO3(aq) ⇌ H+ (aq) + HCO3- (aq) (a) State what…
  39. Describe7 marksChallengeThe formation of methanol from carbon monoxide and hydrogen is a reversible reaction that reaches dynamic equilibrium. CO(g) + 2H2(g) ⇌ CH3OH(g) The forward reaction is exothermic. Describe the meaning of dynamic…
  40. Describe5 marksChallengeThe reaction SO2(g) + 1/2O2(g) ⇌ SO3(g) is exothermic in the forward direction. A mixture of sulfur dioxide and oxygen is sealed in a rigid container and allowed to reach dynamic equilibrium at a fixed temperature. A…
  41. Describe7 marksChallengeFour 0.10 mol dm^-3 aqueous solutions are prepared: hydrochloric acid (HCl), ethanoic acid (CH3COOH), sodium hydroxide (NaOH), and ammonia (NH3). A student measures the pH of each solution using a pH meter and also…
  42. Describe7 marksChallengeA student investigates the distribution of a non-polar organic compound, J, between water and an organic solvent, T, at 298 K. At equilibrium, the concentration of J in water is 0.020 mol dm^-3 and in T is 0.080 mol…
  43. Suggest6 marksChallengeA farmer adds a sparingly soluble calcium compound to acidic soil to raise its pH. The compound reacts with hydrogen ions, and the resulting solution contains both a weak acid and its conjugate base, so it acts as a…