AQA A-Level Chemistry: Carboxylic acids and derivatives (7405) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover section 3.3.9 Carboxylic acids and derivatives of the AQA AS and A-level Chemistry specification (7404/7405), version 1.2, July 2026, for exams from June 2016 onwards: 3.3.9.1 Carboxylic acids and esters, 3.3.9.2 Acylation and Required practical 10. The whole section is A-level only. It is examined on A-level Paper 2, and Paper 3 can test any content and any practical skill. Show your working in every calculation.

Learn the content first with the study guide and the revision notes. The course hub is AQA A-Level Chemistry, and the printable checklist lists every point. For the carbonate test and infrared evidence for acids, see the organic analysis practice.

Use Ar values: H = 1.0, C = 12.0, N = 14.0, O = 16.0, Na = 23.0, Cl = 35.5.

Questions

1. An ester has the structural formula CH₃CH₂COOCH₃.

(a) Name the ester. [1] (b) Name the carboxylic acid and the alcohol that react to make it. [2]

2. Propanoic acid is a weak acid.

(a) Write an equation for the reaction of propanoic acid with sodium carbonate. [2] (b) Explain what is meant by a weak acid. [1]

3. Methyl ethanoate is made by warming ethanoic acid with methanol.

(a) Write an equation for the reaction and name a suitable catalyst. [2] (b) 9.00 g of ethanoic acid reacts with excess methanol. 7.77 g of methyl ethanoate is obtained. Calculate the percentage yield. [3]

4. Methyl butanoate, CH₃CH₂CH₂COOCH₃, is hydrolysed.

(a) Give the organic products when it is heated under reflux with (i) dilute hydrochloric acid and (ii) sodium hydroxide solution. [2] (b) Explain why hydrolysis with sodium hydroxide goes to completion but hydrolysis with acid does not. [2]

5. Glyceryl trioctadecanoate, (C₁₇H₃₅COO)₃C₃H₅ (Mr = 890.0), is an animal fat. It is boiled with sodium hydroxide solution to make soap.

(a) Write an equation for the reaction. [2] (b) Calculate the maximum mass of sodium octadecanoate (Mr = 306.0) formed from 44.5 g of the fat. [3] (c) Calculate the minimum mass of sodium hydroxide needed. [1]

6. A vegetable oil contains glyceryl trihexadecanoate, (C₁₅H₃₁COO)₃C₃H₅ (Mr = 806.0).

(a) State what biodiesel is. [1] (b) Calculate the maximum mass of methyl hexadecanoate (Mr = 270.0) made from 403 g of this oil with methanol. [3]

7. Ethanoyl chloride reacts with methanol.

(a) Name the mechanism and outline it, describing each curly arrow and the intermediate. [4] (b) Name the organic product. [1]

8. Propanoyl chloride, CH₃CH₂COCl, reacts with ammonia and with ethylamine.

(a) Write an equation for the reaction with excess ammonia. [2] (b) Name the organic product with ethylamine and give its structural formula. [2] (c) Explain why two moles of ethylamine are used for each mole of propanoyl chloride. [1]

9. Write equations for the reactions of ethanoic anhydride with:

(a) water [1] (b) propan-1-ol [1] (c) excess methylamine. [1]

10. Aspirin, CH₃COOC₆H₄COOH (Mr = 180.0), is made from 2-hydroxybenzoic acid, HOC₆H₄COOH (Mr = 138.0). Ethanoic anhydride has Mr = 102.0 and ethanoyl chloride has Mr = 78.5.

(a) Write an equation for the reaction with ethanoic anhydride. [1] (b) Calculate the percentage atom economy for aspirin by the anhydride route and by the acyl chloride route. [3] (c) In a school preparation, 2.76 g of 2-hydroxybenzoic acid gives 2.52 g of aspirin. Calculate the percentage yield. [3] (d) Industry uses ethanoic anhydride even though its atom economy is lower. Give two reasons. [2]

11. This question is about Required practical 10. A student has crude aspirin containing small amounts of soluble and insoluble impurities.

(a) Describe how the student should purify the aspirin by recrystallisation. [4] (b) Sample P melts sharply at the data value. Sample Q melts over a range of several degrees, starting below the data value. Explain what this shows. [2]

12. Compound X, C₄H₈O₂, is a neutral liquid with a sweet smell. 4.40 g of X is heated under reflux with sodium hydroxide solution. The products are sodium ethanoate and an alcohol Z. When Z is heated under reflux with excess acidified potassium dichromate(VI), ethanoic acid forms.

(a) Identify X and Z, explaining your reasoning. [3] (b) Calculate the amount, in moles, of sodium hydroxide that reacts with 4.40 g of X. [1] (c) Suggest a reagent that converts Z into X in a reaction that is not reversible. [1] (d) Outline how a pure sample of liquid X could be obtained after making it from ethanoic acid and Z. [3]

Answers

1. (a) Methyl propanoate [1] (b) Propanoic acid [1]; methanol [1] Examiner insight: the alcohol part is written first in the name, so swapping the two words names a different ester and scores nothing.

2. (a) 2CH₃CH₂COOH + Na₂CO₃ → 2CH₃CH₂COONa + CO₂ + H₂O: correct formulas [1]; balanced [1] (b) It only partially dissociates (ionises) in water [1] Examiner insight: “does not fully dissociate” earns the mark; “has a high pH” or “reacts slowly” does not.

3. (a) CH₃COOH + CH₃OH ⇌ CH₃COOCH₃ + H₂O [1]; concentrated sulfuric acid (an acid catalyst) [1] (b) Moles of ethanoic acid = 9.00 ÷ 60.0 = 0.150 mol [1] Theoretical mass = 0.150 × 74.0 = 11.1 g [1] Yield = 7.77 ÷ 11.1 × 100 = 70.0% [1] Examiner insight: an error in the moles step can still earn the later marks by error carried forward, provided the working is shown.

4. (a) (i) Butanoic acid and methanol [1] (ii) sodium butanoate and methanol [1] (b) Acid hydrolysis is reversible and reaches equilibrium [1]; in alkali the carboxylate ion forms, which does not react with methanol to re-form the ester [1] Examiner insight: naming butanoic acid as the product in alkali loses the mark; the product is the salt.

5. (a) (C₁₇H₃₅COO)₃C₃H₅ + 3NaOH → 3C₁₇H₃₅COONa + C₃H₅(OH)₃: products [1]; 3NaOH and 3 salt balanced [1] (b) Moles of fat = 44.5 ÷ 890.0 = 0.0500 mol [1] Moles of salt = 3 × 0.0500 = 0.150 mol [1] Mass = 0.150 × 306.0 = 45.9 g [1] (c) 0.150 × 40.0 = 6.00 g [1] Examiner insight: a 1 : 1 ratio is a method error, so the final mark is lost even if the rest of the arithmetic is correct.

6. (a) A mixture of methyl esters of long-chain carboxylic acids [1] (b) Moles of oil = 403 ÷ 806.0 = 0.500 mol [1] Moles of methyl ester = 3 × 0.500 = 1.50 mol [1] Mass = 1.50 × 270.0 = 405 g [1] Examiner insight: the product mass can exceed the oil mass, because methanol is also a reactant.

7. (a) Nucleophilic addition–elimination. Arrow from a lone pair on the methanol O to the δ+ carbonyl carbon [1]; arrow from the C=O bond onto the carbonyl O [1]; intermediate with O⁻ and a positive charge on the oxygen from methanol [1]; C=O re-forms, Cl⁻ leaves and H⁺ is lost from the O⁺ [1] (b) Methyl ethanoate [1] Examiner insight: each arrow must start from a lone pair or a bond, because the arrow shows where the electron pair comes from; arrows from an atom symbol or a charge are a common way to lose mechanism marks.

8. (a) CH₃CH₂COCl + 2NH₃ → CH₃CH₂CONH₂ + NH₄Cl: propanamide [1]; 2NH₃ and NH₄Cl [1] (b) N-ethylpropanamide [1]; CH₃CH₂CONHCH₂CH₃ [1] (c) The second molecule acts as a base and reacts with the HCl formed, giving CH₃CH₂NH₃⁺Cl⁻ [1] Examiner insight: when the question says excess ammonia, write the ammonium chloride product; leaving free HCl alongside excess base is chemically inconsistent and risks the balancing mark.

9. (a) (CH₃CO)₂O + H₂O → 2CH₃COOH [1] (b) (CH₃CO)₂O + CH₃CH₂CH₂OH → CH₃COOCH₂CH₂CH₃ + CH₃COOH [1] (c) (CH₃CO)₂O + 2CH₃NH₂ → CH₃CONHCH₃ + CH₃COO⁻CH₃NH₃⁺ [1] Examiner insight: the anhydride by-product is ethanoic acid (or its salt), never HCl; mixing up the two reagents’ by-products is a common slip.

10. (a) HOC₆H₄COOH + (CH₃CO)₂O → CH₃COOC₆H₄COOH + CH₃COOH [1] (b) Anhydride: 180.0 ÷ (138.0 + 102.0) × 100 = 75.0% [1] Acyl chloride: total reactant Mr = 138.0 + 78.5 = 216.5 [1]; 180.0 ÷ 216.5 × 100 = 83.1% [1] (c) Moles of 2-hydroxybenzoic acid = 2.76 ÷ 138.0 = 0.0200 mol [1] Theoretical mass of aspirin = 0.0200 × 180.0 = 3.60 g [1] Yield = 2.52 ÷ 3.60 × 100 = 70.0% [1] (d) Any two: the by-product is ethanoic acid, not corrosive, toxic hydrogen chloride [1]; the anhydride reacts less vigorously so the reaction is easier to control [1]; it is hydrolysed less readily by water so it is easier to store and handle Examiner insight: “safer” alone is too vague for a mark; name the hazard (HCl gas) or the property (less vigorous, less readily hydrolysed).

11. (a) Dissolve the crude solid in the minimum volume of hot solvent [1]; filter while hot to remove insoluble impurities [1]; cool so crystals form while soluble impurities stay in solution [1]; filter under reduced pressure, wash with a little cold solvent and dry [1] (b) P is pure [1]; Q contains impurities, which lower the melting point and widen the range [1] Examiner insight: “minimum volume” and “hot” must both appear; “dissolve in solvent” alone does not explain why crystals form on cooling.

12. (a) Sodium ethanoate shows X is an ester of ethanoic acid [1]; Z is oxidised to ethanoic acid, so Z is ethanol (a primary alcohol with two carbons) [1]; X is ethyl ethanoate, CH₃COOCH₂CH₃, which matches C₄H₈O₂ [1] (b) Mr of X = 88.0; 4.40 ÷ 88.0 = 0.0500 mol (1 : 1 with NaOH) [1] (c) Ethanoyl chloride or ethanoic anhydride [1] (d) Shake the distillate with sodium hydrogencarbonate solution in a separating funnel to remove acid, releasing pressure [1]; dry the organic layer with an anhydrous salt such as anhydrous sodium sulfate [1]; redistil and collect the fraction at the boiling point of X [1] Examiner insight: in identification questions, link each piece of evidence to a conclusion; a correct name given without reasoning cannot earn the reasoning marks.

Where marks are usually lost

• Naming esters with the acid part first.
• Giving the carboxylic acid, not its salt, as the product of alkaline hydrolysis.
• Writing esterification with a single arrow or without an acid catalyst.
• Using 1 : 1 instead of 1 : 3 for a triglyceride in soap or biodiesel calculations.
• Calling the mechanism “nucleophilic substitution” instead of nucleophilic addition–elimination.
• Curly arrows that start at atoms or charges, or a missing charge on the intermediate.
• Forgetting the second NH₃ or amine molecule in equations with excess reagent.
• Arguing that ethanoic anhydride is chosen for aspirin because of atom economy.
• Vague practical answers: no “minimum” volume or no sharp melting point.
• Omitting the step that removes acid (NaHCO₃ wash) when purifying an ester.

Next steps

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Official syllabus

AQA AS and A-level Chemistry specification (7404/7405), version 1.2, July 2026, for AS and A-level exams June 2016 onwards. Published by AQA. These questions cover section 3.3.9 and Required practical 10.