Brønsted–Lowry theory of acids and bases: past paper questions
Real questions on brønsted–lowry theory of acids and bases
The newest 20 of 278 written questions. Open one to see it on the real paper.
- 9701/41 · May/June 2026 · Q2a(i)[1]
Define pH mathematically. pH =
See it on the paper → - 9701/41 · May/June 2026 · Q2a(ii)[1]
Define K w mathematically. K w =
See it on the paper → - 9701/41 · May/June 2026 · Q2b(i)[1]
Calculate the concentration, in mol dm –3 , of H + (aq) in A. [H + ] in A = mol dm –3
See it on the paper → - 9701/41 · May/June 2026 · Q2b(ii)[1]
Calculate the value of K a of CH 3 CH 2 CH 2 COOH at 298 K. K a of CH 3 CH 2 CH 2 COOH =
See it on the paper → - 9701/41 · May/June 2026 · Q2c(i)[3]
Calculate the concentration of CH 3 CH 2 CH 2 COONa in C. (If you were unable to calculate an answer in 2(b)(ii), then use 3.00 × 10 –5 as the value of K a of CH 3 CH 2 CH 2 COOH. This is not the correct answer.) [CH 3 CH 2 CH 2 COONa] in C = mol dm –3
See it on the paper → - 9701/41 · May/June 2026 · Q2c(ii)[1]
Write an equation for the reaction when H 2 SO 4 (aq) is added to D.
See it on the paper → - 9701/41 · May/June 2026 · Q2c(iii)[1]
Write an equation for the reaction when KOH(aq) is added to D.
See it on the paper → - 9701/41 · May/June 2026 · Q2d[2]
Predict the relative acidities of 2,2-dichlorobutanoic acid, CH 3 CH 2 CCl 2 COOH, and butanoic acid, CH 3 CH 2 CH 2 COOH. Explain your answer. stronger acid explanation
See it on the paper → - 9701/21 · October/November 2025 · Q1c(ii)[1]
The oxidation state of the carbon atom in methanal is 0. Calculate the oxidation state of carbon in carbon dioxide.
See it on the paper → - 9701/41 · October/November 2025 · Q7a[4]
State the relative acidities of bromoethanoic acid, BrCH 2 COOH, chloroethanoic acid, Cl CH 2 COOH, ethanoic acid, CH 3 COOH and ethanol, CH 3 CH 2 OH. Explain your answer. most acidic least acidic
See it on the paper → - 9701/42 · October/November 2025 · Q3a(i)[1]
Define conjugate acid–base pair.
See it on the paper → - 9701/42 · October/November 2025 · Q3a(ii)[1]
Give the formulas of the conjugate acid and the conjugate base of the hydrogen phosphate ion, HPO 42– . conjugate acid of HPO 42–
See it on the paper → - 9701/42 · October/November 2025 · Q3b(i)[2]
Calculate the concentration of CH 3 CH 2 COOH in solution C. [CH 3 CH 2 COOH] = mol dm –3 (i)
See it on the paper → - 9701/42 · October/November 2025 · Q3b(ii)[1]
Calculate the concentration of hydroxide ions in solution C. [OH – ] = mol dm –3 (ii)
See it on the paper → - 9701/42 · October/November 2025 · Q3b(iii)[1]
Calculate the concentration of a solution of hydrochloric acid with the same pH as solution C. concentration = mol dm –3
See it on the paper → - 9701/42 · October/November 2025 · Q3c(i)[1]
Complete the sentence and write an equation for the reaction that occurs. Solution D acts as a buffer when is added to it.
See it on the paper → - 9701/42 · October/November 2025 · Q3c(ii)[1]
Complete the sentence and explain why solution D does not act as a buffer when the other solution is added. Solution D does not act as a buffer when is added to it. explanation
See it on the paper → - 9701/42 · October/November 2025 · Q8a[1]
Define isoelectric point.
See it on the paper → - 9701/42 · October/November 2025 · Q8b[2]
Draw the structures of asparagine and aspartic acid at pH 2. aspartic acid at pH 2 asparagine at pH 2
See it on the paper → - 9701/42 · October/November 2025 · Q8e[2]
Asparagine is hydrolysed with an excess of hot NaOH(aq). Draw the structure of the organic product of this reaction.
See it on the paper →
What examiners said
Most candidates realised that the suitable indicator was thymolphthalein, but very few could satisfactorily explain why. Very few candidates realised that potassium hydroxide is a strong alkali and, as it is used up in the reaction, the pH would fall from about 14 to 7 as equimolar amounts were used in the reaction and thymolphthalein was the only one of the three indicators which would change co...
— Examiner report, February/March 2025, 9701/52 Q2(b) (Cambridge)
Very few candidates noticed the fact that concentrated sulfuric acid was a catalyst and therefore the pH of the mixture would not (significantly) change. Thus, none of the indicators would change colour.
— Examiner report, February/March 2025, 9701/52 Q2(h) (Cambridge)
This definition was described accurately in most candidates answers. A common misconception was seen in weaker responses that described a weak acid as one that ‘did not completely dissolve’.
— Examiner report, October/November 2023, 9701/22 Q3(a)(ii) (Cambridge)
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