Butanoic acid reacts with methanol to form an ester and water. Explain why this reaction is described as a condensation reaction, name the ester formed, and state the role of the concentrated sulfuric acid used in this reaction.

AQA A-Level Chemistry (7405) — 3.3.9 Carboxylic acids and derivatives (A-Level only) · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (5 marks)

A condensation reaction is one in which a small molecule is removed when two larger molecules combine. In this case the carboxylic acid and the alcohol join to give the ester and water is lost.
The ester formed is methyl butanoate.
Concentrated sulphuric acid is used as a catalyst – it is not consumed and is unchanged at the end of the reaction.

Examiner tips

  • Use the term ‘condensation reaction’ and mention the loss of water.
  • State the ester name correctly – methyl butanoate.
  • Explain that the acid is a catalyst and is not used up.
  • Keep the answer concise – 5 marks only.

Common mistakes

  • Saying the acid is a reagent rather than a catalyst.
  • Giving the wrong ester name (e.g. butyl butanoate).
  • Omitting that water is the small molecule removed.

Mark scheme (5 marks)

  1. A condensation reaction produces a small molecule (water) when the two reactants join together
  2. The two reactants (carboxylic acid and alcohol) join together to form the ester (a larger molecule)
  3. The ester formed is methyl butanoate
  4. Concentrated sulfuric acid acts as a catalyst
  5. The catalyst is not used up / remains unchanged at the end of the reaction

Key terms in this question

condensation reaction · ester

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