Esters are formed in a condensation reaction between a carboxylic acid and an alcohol. Describe the formation of an ester, including the type of reaction, the functional groups involved, and two uses of esters.

Pearson Edexcel International GCSE Chemistry (4CH1) — 4.7 Esters · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

An ester is formed by a condensation reaction between a carboxylic acid and an alcohol.
The carboxylic acid contains the –COOH functional group and the alcohol contains the –OH functional group.
During the reaction a molecule of water is removed and the ester functional group –COO– is produced.
Esters are used in perfumes and flavourings.

Examiner tips

  • Use the word ‘condensation’ and mention water loss; include the –COOH and –OH groups; state the –COO– group; give a specific use such as perfumes or flavourings.
  • Structure your answer in four clear points to match the 4 marks.

Common mistakes

  • Omitting the water loss or calling it a ‘synthesis’ instead of ‘condensation’
  • Not naming the –COOH and –OH groups explicitly
  • Giving a use that is not typical for esters, e.g. ‘fuel’ instead of perfumes/flavourings

Mark scheme (4 marks)

  1. An ester is formed by a condensation reaction between a carboxylic acid and an alcohol
  2. The carboxylic acid contains the functional group –COOH and the alcohol contains the functional group –OH
  3. The ester contains the functional group –COO–
  4. Esters are used in perfumes and/or flavourings

Key terms in this question

ester · condensation reaction · carboxylic acid · alcohol · functional group

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