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A-Level Chemistry May/June 2025 Q4(b)(iii): Construct an equation to describe the reaction of butanenitrile with NaOH(aq) in step 3.
A-Level Chemistry · Paper 9701/22 · May/June 2025 · Question 4(b)(iii) · [2 marks]
Construct an equation to describe the reaction of butanenitrile with NaOH(aq) in step 3.
A full-marks model answer with a mark-by-mark examiner breakdown is below.
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This question asks for the balanced chemical equation for the alkaline hydrolysis of butanenitrile.
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Identify Reactants: The reactants are butanenitrile (CH₃CH₂CH₂CN) and aqueous sodium hydroxide (NaOH). Hydrolysis reactions require water, so H₂O is also a reactant.
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Identify Products: The nitrile group (–CN) is hydrolysed to a carboxyl group (–COOH). However, in the presence of the alkali (NaOH), this acidic group is deprotonated to form the sodium salt, sodium butanoate (CH₃CH₂CH₂CO₂Na). The nitrogen atom from the nitrile group is converted to ammonia (NH₃).
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Construct and Balance the Equation:
CH₃CH₂CH₂CN + NaOH + H₂O → CH₃CH₂CH₂CO₂Na + NH₃
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Final Answer:
CH₃CH₂CH₂CN + NaOH + H₂O → CH₃CH₂CH₂CO₂Na + NH₃
How the marks are awarded
- M1 — Correctly identifying the organic product as sodium butanoate, CH₃CH₂CH₂CO₂Na. This demonstrates knowledge that alkaline hydrolysis of a nitrile produces a carboxylate salt.
- M2 — Providing a fully correct and balanced equation, including water as a reactant and ammonia as the inorganic product, alongside the correct reactants and the organic product from M1.
Common mistakes
- Writing the carboxylic acid (CH₃CH₂CH₂COOH) as the product instead of the sodium salt, forgetting that the alkaline conditions neutralise the acid.
- Omitting water (H₂O) as a reactant, which is essential for hydrolysis and results in an unbalanced equation.
- Incorrectly identifying the inorganic product, for example writing N₂ or just N.
- Miscounting the number of carbon atoms in the product; the carbon from the -CN group becomes part of the carboxylate group, so butanenitrile (4 carbons) gives butanoate (4 carbons).
Examiner tip: For hydrolysis reactions, always consider the pH of the medium to determine the final form of the organic product (acid or salt) and remember to include water as a reactant.
AI-generated model answer, grounded in the official Cambridge mark scheme and reviewed by the MarkScheme team. Mark your own answer to this question →
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