About Carboxylic acids in A Level Chemistry
Carboxylic acids is one of the 18 main topics in our A Level Chemistry (Cambridge (CAIE) 9701) question bank, and about 5% of its real questions come from it. Tayyari Karo has 33 real questions on this topic from 2021 to 2026, from Paper 1, Paper 2, Paper 4; 25 are multiple choice and marked instantly, and the rest are structured questions with a model answer. By difficulty: 18 medium, 13 hard, 2 easy.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
Try 6 real questions
These are real past-paper questions. Think of your answer first, then open the explanation.
May/June 2026 · Paper 1 · Carboxylic acids
Which reaction has ethanoic acid as one of the products?
- CH3CN is heated with dilute alkali under reflux.
- CH3CH2CN is heated with dilute acid under reflux.
- CH3COOCH3 is heated with dilute alkali under reflux.
- CH3COOCH2CH2CH3 is heated with dilute acid under reflux.
Show answer and explanation
Answer: D. CH3COOCH2CH2CH3 is heated with dilute acid under reflux.
Acid hydrolysis of the propyl ester gives ethanoic acid and propan-1-ol. Alkaline hydrolysis gives the carboxylate salt, and the nitriles give other products.
May/June 2025 · Paper 1 · Carboxylic acids
P is a compound that burns in excess O2 to give only CO2 and H2O. 2.20 g of P contains 1.20 g carbon and 0.20 g hydrogen. When P is added to sodium carbonate solution, bubbles of gas are seen. What is P?
- CH3CHO
- CH3CO2H
- CH3COCH2CH2OH
- CH3CH2CH2CO2H
Show answer and explanation
Answer: D. CH3CH2CH2CO2H
Mass of O = 2.20−1.20−0.20 = 0.80 g, giving mole ratio C:H:O = 0.10:0.20:0.05 = 2:4:1, so molecular formula C4H8O2; effervescence with Na2CO3 shows a carboxylic acid, i.e. CH3CH2CH2CO2H.
October/November 2025 · Paper 1 · Carboxylic acids
Three mixtures are heated under reflux: 1 CH3CH2CHO + NaBH4(aq); 2 CH3CH2CH2OH + Na(s); 3 CH3CH2CN + NaOH(aq). Which mixtures will produce sodium propanoate as one product?
- 1, 2 and 3
- 1 and 2 only
- 2 and 3 only
- 3 only
Show answer and explanation
Answer: D. 3 only
NaBH4 reduces the aldehyde to an alcohol (mixture 1, no sodium propanoate); Na metal with an alcohol forms sodium alkoxide, not a carboxylate salt (mixture 2); alkaline hydrolysis of the nitrile CH3CH2CN with NaOH(aq) gives sodium propanoate directly (mixture 3 only).
May/June 2023 · Paper 1 · Carboxylic acids
Which method could produce butanoic acid?
- an acid-base reaction involving CH3CH2CH2CO2Na
- the hydrolysis of CH3CH2CH2CH2CN
- the acidic hydrolysis of CH3CH2COOCH2CH2CH3
- the oxidation of CH3CH2CH2OH
Show answer and explanation
Answer: A. an acid-base reaction involving CH3CH2CH2CO2Na
Reacting sodium butanoate (CH3CH2CH2CO2Na) with a stronger acid displaces butanoic acid; hydrolysing CH3CH2CH2CH2CN (pentanenitrile) gives pentanoic acid, hydrolysing CH3CH2COOCH2CH2CH3 gives propanoic acid, and oxidising propan-1-ol gives propanoic acid — not butanoic acid.
May/June 2022 · Paper 1 · Carboxylic acids
How many esters have the molecular formula C4H8O2?
- 2
- 3
- 4
- 5
Show answer and explanation
Answer: C. 4
The four esters with formula C4H8O2 are: HCO2CH2CH2CH3, HCO2CH(CH3)2, CH3CO2CH2CH3, and CH3CH2CO2CH3.
May/June 2021 · Paper 1 · Carboxylic acids
The compound cetyl palmitate, C15H31CO2C16H33, is a waxy solid. Cetyl palmitate is heated under reflux with an excess of aqueous sodium hydroxide. Which products will be formed?
- C15H31ONa and C16H33CO2Na
- C15H31CO2Na and C16H33ONa
- C15H31OH and C16H33CO2Na
- C15H31CO2Na and C16H33OH
Show answer and explanation
Answer: D. C15H31CO2Na and C16H33OH
Alkaline hydrolysis (saponification) of the ester C15H31CO2C16H33 cleaves the C(=O)–O bond, giving the sodium salt of the acyl (acid) side, C15H31CO2Na (sodium palmitate), and the free alcohol C16H33OH (cetyl alcohol) — alcohols are not acidic enough to be converted to their sodium salt by aqueous NaOH.
