Carboxylic acids and alcohols can react together to form esters. Describe how an ester is formed from ethanoic acid and methanol, and explain two properties of esters that make them useful.

AQA A-Level Chemistry (7405) — 3.3.14 Organic synthesis (A-Level only) · Describe · 5 marks · View as Markdown

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

Esters are produced in a condensation reaction between a carboxylic acid and an alcohol. They are widely used in the food and perfume industries.

Model answer (5 marks)

Ethanoic acid reacts with methanol in a condensation reaction, losing a molecule of water. The product is methyl ethanoate. Esters have distinctive, pleasant, fruity odours, making them useful as flavourings or in perfumes. They are also good solvents, able to dissolve many substances such as paints or nail varnish.

Examiner tips

Use the word "condensation" and state "water is lost" to gain the first two marks.
Mention the exact product name "methyl ethanoate" for the third mark.
Give two properties – pleasant smell and good solvent – and link each to a real‑world use.
Use UK spelling (e.g. "colour").

Common mistakes

Writing the reaction as a simple addition without mentioning water loss.
Using the wrong ester name (e.g. "ethyl acetate") instead of "methyl ethanoate".
Failing to link the properties to their practical applications.

Mark scheme (5 marks)

Ethanoic acid and methanol react together (in a condensation reaction)
Water is lost / produced as a small molecule during the reaction
The ester produced is methyl ethanoate
Esters have distinctive / pleasant smells / fruity odours, making them useful as flavourings or in perfumes
Esters are good solvents (they dissolve other substances / used to dissolve paints or nail varnish)

Key terms in this question

ester · carboxylic acid · alcohol

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