plumiKa, pH and the ionic product of water: OCR A‑Level Chemistry A questions
OCR A-Level Chemistry A past-paper questions on 5.1.3.2 Ka, pH and the ionic product of water, 2016–2025, with mark schemes and examiner’s reports where available.
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Q19(a)(i)
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All 11 questions on Ka, pH and the ionic product of water, as a list
- June 2024, Paper 1, Q19(a)(i) (1 mark): Write the expression for the acid dissociation constant, Ka, of Cl CH2COOH. [1]
- 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 2023, Paper 1, Q20(a)(i) (2 marks): Calculate the pH of water at 40 °C. Give your answer to 2 decimal places. pH = [2]
- June 2023, Paper 1, Q20(a)(ii) (1 mark): Table 20.1 shows different Kw values at 25 °C and at 40 °C. A student suggests that water is neutral at these temperatures. Explain why this student is correct.
- November 2020, Paper 3, Q6(b) (4 marks): Ethanoic acid, CH3COOH, and methanesulfonic acid, CH3SO2OH, are both monobasic acids. The pKa values are shown in the table. Acid pKa Ethanoic acid CH3COOH 4.76
- 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)(i) (1 mark): Write the expression for the acid dissociation constant, Ka, of CH3COOH. [1]
- 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(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 3, Q5(a)(i) (1 mark): Thiols are weak acids. Write the expression for the acid dissociation constant, Ka, for butane-1-thiol. [1]
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