Ethanoic acid reacts with propanol to form an ester. Describe what is meant by an ester and explain how it is formed in this reaction, including the name of the ester produced and the type of reaction that occurs.

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

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

Model answer (5 marks)

An ester is a compound formed when a carboxylic acid reacts with an alcohol, giving a –COO– linkage.

In this case ethanoic acid (CH₃COOH) reacts with propanol (CH₃CH₂CH₂OH). The –OH of the acid and the –OH of the alcohol combine, releasing a molecule of water – a condensation reaction.

The product is propyl ethanoate (CH₃COOCH₂CH₂CH₃), an ester used as a flavouring or solvent.

Examiner tips

  • Use the term ‘ester’ and describe the –COO– linkage; mention water loss; give the IUPAC name; state it’s a condensation reaction.
  • Include the functional group description and a brief note on uses to hit all points.

Common mistakes

  • Calling the product ‘ethyl propionate’ (wrong order of groups); forgetting that water is released; not naming the ester correctly; using ‘acyl chloride’ instead of ester.”

Mark scheme (5 marks)

  1. An ester is the product of a reaction between a carboxylic acid and an alcohol
  2. The reaction is a condensation reaction
  3. Water is lost / released / produced during the reaction
  4. The ester produced is propyl ethanoate
  5. The functional group of the ester / esters contain the –COOH functional group from the carboxylic acid combined with the alcohol, forming a –COO– linkage / esters have a characteristic smell / are used as flavourings or solvents

Key terms in this question

ester

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