plumiKw, pKw and the pH of strong bases: Edexcel International A Level Chemistry questions
Edexcel International A Level Chemistry past-paper questions on 14.1.4 Kw, pKw and the pH of strong bases, 2019–2025, with mark schemes and examiner’s reports where available.
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All 22 questions on Kw, pKw and the pH of strong bases, as a list
- June 2025, Unit 4, Q5 (1 mark): At 25 °C, the pH of pure water is 7.0 and at 75°C the pH is 6.4 . Why is the pH of pure water lower at 75 °C than at 25 °C? A there are more hydrogen ions than
- June 2025, Unit 4, Q6 (1 mark): A sodium hydroxide solution with pH = 12 is diluted by a factor of 100. What is the pH of the diluted solution? A 10 B 11 C 13 D 14 Use this space for any rough
- January 2025, Unit 4, Q11 (1 mark): What is the pH of a 0.100 mol dm–3 solution of sodium hydroxide at 283 K? [pKw = 14.53 at 283 K] A 13.00 B 13.53 C 14.43 D 14.53
- October 2024, Unit 4, Q8 (1 mark): The dissociation of water is an endothermic reaction. H2O(l) H+(aq) + OH–(aq) ΔH is positive [Kw = 1.0 × 10–14 mol2 dm–6 at 298 K Kw = 2.92 × 10–14 mol2 dm–6
- October 2024, Unit 4, Q17(a) (6 marks): Sulfuric acid reacts with sodium hydroxide solution as shown. H2SO4(aq) + 2NaOH(aq) → Na2SO4(aq) + 2H2O(l) Calculate the pH of the solution formed when 20.0 cm3
- June 2024, Unit 4, Q19(c) (5 marks): A student was given 50.0 cm3 of a solution of sodium hydroxide. The pH of this solution was 12.43. The student was asked to adjust the pH to 12.00, by dilution
- January 2024, Unit 4, Q7 (1 mark): At 50 °C, the ionic product of water, Kw, is 5.5 × 10–14 mol2 dm–6. At this temperature, water is A neutral with a pH of 7.0 B neutral with a pH of 6.6 C acidic
- January 2024, Unit 4, Q10 (1 mark): What is the pH of a 0.200 mol dm–3 solution of strontium hydroxide, Sr(OH)2? Kw = 1.00 × 10–14 mol2 dm–6 A 14.0 B 13.6 C 13.3 D 12.6
- October 2023, Unit 4, Q8 (1 mark): At 100 °C, pure water has a pH of 6, but at 25 °C it has a pH of 7. This is because A the dissociation of water is endothermic, so the concentration of hydrogen
- October 2023, Unit 4, Q9 (1 mark): Four beakers each contain equal volumes of four solutions. Beaker 1 contains 0.01 mol dm–3 NaOH Beaker 2 contains 0.01 mol dm–3 NH3 Beaker 3 contains 0.1 mol dm
- October 2023, Unit 4, Q18(a)(ii) (2 marks): The student deduced that the pH at Key point 4 must be less than 13. Use a calculation to justify the student’s deduction. You are not required to calculate the
- June 2023, Unit 4, Q16 (1 mark): What is the pH of the solution when 2.15 g of barium hydroxide is dissolved in 200 cm3 of deionised water? [molar mass of barium hydroxide = 171.3 g mol–1 Kw =
- January 2023, Unit 4, Q12(a) (1 mark): What is the pH of a saturated solution of magnesium hydroxide at 25 °C? (1) A 9.7 B 10.0 C 10.3 D 12.0
- January 2023, Unit 4, Q12(b) (1 mark): Saturated solutions of magnesium hydroxide at 25 °C and 100 °C are compared. How do the concentrations of hydroxide ions and the pH values of these solutions di
- January 2023, Unit 4, Q21(b)(ii) (5 marks): Calculate the pH of the titration mixture after the addition of 35.0 cm3 of sodium hydroxide solution. The value required cannot be obtained from the titration
- October 2022, Unit 4, Q8 (1 mark): What is the pH of a 0.050 mol dm−3 solution of barium hydroxide, Ba(OH)2 ? A 13.3 B 13.0 C 12.7 D 12.4
- June 2022, Unit 4, Q8 (1 mark): What is the pH of a 0.27 mol dm−3 aqueous solution of sodium hydroxide? [Kw = 1.0 × 10−14 mol2 dm−6 at 298 K] A 0.57 B 13.43 C 13.73 D 14.57 Use this space for
- January 2022, Unit 4, Q6 (1 mark): At 25 °C, the pH of pure water is 7.00 and at 100 °C, the pH of pure water is 6.14. What can be deduced from this information? Enthalpy change of Concentration
- October 2021, Unit 4, Q9 (1 mark): What is the pH of 0.010 mol dm−3 aqueous calcium hydroxide, Ca(OH)2(aq)? [pKw = 14] A 11.7 B 12.0 C 12.3 D 13.3 Use this space for any rough working. Anything y
- October 2020, Unit 4, Q18(a)(i) (2 marks): A solution of hydrochloric acid has a pH of 1.125. Calculate the concentration of hydrogen ions and of hydroxide ions, in mol dm−3, in this solution. [Kw = 1.00
- January 2020, Unit 4, Q12 (1 mark): A solution of sodium hydroxide of concentration 0.0080 mol dm–3 has a pH A between 7 and 9 B between 9 and 11 C between 11 and 13 D above 13 Use this space for
- January 2020, Unit 4, Q20(a)(iii) (3 marks): The students used 25.0 cm3 of sodium hydroxide solution with concentration 0.980 mol dm–3 for the hydrolysis. Calculate the pH of the reaction mixture when the
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