plumipH of strong and weak acids and bases: OCR A‑Level Chemistry A questions
OCR A-Level Chemistry A past-paper questions on 5.1.3.3 pH of strong and weak acids and bases, 2016–2025, with mark schemes and examiner’s reports where available.
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Q19(a)
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All 25 questions on pH of strong and weak acids and bases, as a list
- June 2025, Paper 1, Q19(a) (1 mark): Nitric acid, HNO3, is a strong monobasic acid. Calculate the pH of 0.150 mol dm–3 HNO3. Give your answer to 2 decimal places. pH = [1]
- June 2025, Paper 1, Q19(b)(i) (2 marks): Nitrous acid, HNO2, is a weak monobasic acid. Predict whether the pH of 0.150 mol dm–3 HNO2 is higher, lower or the same as the pH of 0.150 mol dm–3 nitric acid
- June 2025, Paper 3, Q2(c) (5 marks): Barium hydroxide, Ba(OH)2, is an alkali. A student is supplied with a solution of Ba(OH)2 with a concentration of 46.80 g dm–3 at 25 °C. The student dilutes 20.
- June 2024, Paper 1, Q19(a)(ii) (1 mark): The expression for the acid dissociation constant, Ka, of Cl CH2COOH can be simplified to: [H+]2 Ka = [Cl CH2COOH] Expression 19.1 State one approximation that
- June 2024, Paper 1, Q19(a)(iii) (3 marks): A student carries out an experiment to determine the pKa value of a solution of Cl CH2COOH. The concentration of Cl CH2COOH is 0.090 mol dm–3. • • The pH of Cl
- June 2024, Paper 3, Q1(a) (2 marks): What is the pH of 1.00 dm3 of 0.400 mol dm–3 of NaOH(aq) at 298 K? pH = [2]
- June 2024, Paper 3, Q1(b) (1 mark): Water is added to 10.0 cm3 of 0.750 mol dm–3 HCl (aq) to produce 100 cm3 of diluted HCl (aq). What is the pH of the diluted HCl (aq)? Give your answer to 2 deci
- June 2023, Paper 1, Q10 (1 mark): What is the percentage dissociation of a 0.015 mol dm–3 solution of methanoic acid, HCOOH (Ka = 1.60 × 10–4 mol dm–3)? A 0.016% B 1.1% C 1.82% D 10.3% Your answ
- June 2023, Paper 1, Q20(b) (5 marks): A student reacts strontium metal with water to make a 250.0 cm3 solution of aqueous strontium hydroxide, Sr(OH)2. The solution contains 0.145 g of strontium hyd
- June 2023, Paper 3, Q2(b) (3 marks): A student investigates the rate of a reaction that is 1st order with respect to hydrochloric acid, HCl (aq). The student carries out a reaction using 0.680 mol
- June 2022, Paper 1, Q21(b)(i) (5 marks): Determine the mass of barium oxide that was used. Give your answer to 3 significant figures. mass of barium oxide = g [5]
- June 2022, Paper 3, Q6(c)(ii) (3 marks): The student dissolves 0.150 mol of vitamin C in water and makes the solution up to 250 cm3 in a volumetric flask. Calculate the pH of this solution of vitamin C
- November 2021, Paper 1, Q10 (1 mark): An aqueous solution of ethanoic acid, CH3COOH, has a concentration of 0.50 mol dm–3. pKa for CH3COOH = 4.76 at 25 °C. What is the pH of the ethanoic acid soluti
- November 2021, Paper 1, Q22(a) (2 marks): Sodium hydroxide, NaOH, is a strong base. Calculate the pH of 0.140 mol dm–3 NaOH(aq) at 298 K. Give your answer to 2 decimal places. pH = [2]
- November 2021, Paper 3, Q5(b)(i) (2 marks): Calculate the pH of 0.125 mol dm–3 hydrazoic acid. Give your answer to 2 decimal places. pH = [2]
- November 2020, Paper 1, Q11 (1 mark): 20 cm3 of 0.10 mol dm−3 hydrochloric acid is added to 10 cm3 of 0.10 mol dm−3 sodium hydroxide. What is the pH of the resulting mixture? A 1.00 B 1.18 C 1.30 D
- November 2020, Paper 1, Q18(c)(i) (2 marks): The student measures the pH of CH3COOH(aq) as 2.72. Show that the concentration of the CH3COOH(aq) is 0.204 mol dm−3. [2]
- June 2019, Paper 1, Q20(a) (2 marks): Calculate the pH of 0.0800 mol dm−3 C2H5COOH(aq). Give your answer to 2 decimal places. pH = [2]
- June 2019, Paper 1, Q20(b)(ii) (4 marks): Calculate the pH of the final solution. Give your answer to 2 decimal places. pH = [4]
- June 2019, Paper 1, Q20(c) (1 mark): The student calculates the pH of 0.0800 mol dm−3 HIO3(aq). The student assumes that the equilibrium concentration of HIO3(aq) is the same as the initial concent
- June 2019, Paper 3, Q4(a)(iv) (5 marks): A student measures the pH of the contents in a bottle of Dettol® as 5.14. The label on the bottle shows the percentage of chloroxylenol in Dettol® as 4.80% i.e.
- June 2018, Paper 1, Q19(a)(ii) (3 marks): Calculate the pKa value of CH3COOH. Give your answer to two decimal places. pKa = [3]
- June 2018, Paper 1, Q19(a)(iii) (1 mark): Determine the percentage dissociation of ethanoic acid in the vinegar. Give your answer to three significant figures. percentage dissociation = % [1]
- June 2018, Paper 1, Q19(b) (4 marks): Many solid drain cleaners are based on sodium hydroxide, NaOH. • A student dissolves 1.26 g of a drain cleaner in water and makes up the solution to 100.0 cm3.
- June 2017, Paper 1, Q21(a) (3 marks): A student uses a pH meter to measure the pH of a solution of CH3COOH at 25 °C. The measured pH is 2.440. Calculate the concentration of ethanoic acid in the sol
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