Ethanol can be oxidised to produce ethanoic acid. Describe two chemical properties of ethanoic acid that show it belongs to the carboxylic acid homologous series, and explain what is meant by the term homologous series.

AQA GCSE Chemistry (8462) — 4.7.2 Reactions of alkenes and alcohols (Chem only) · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

Ethanoic acid contains the –COOH functional group, which is the defining group of carboxylic acids.

1. It is a weak acid – it only partially ionises in water, giving a solution with pH < 7.
2. It reacts with carbonates (e.g. Na₂CO₃) to give CO₂ gas, a characteristic reaction of carboxylic acids.

A homologous series is a group of compounds that share the same functional group and therefore have similar chemical properties.

Examiner tips

  • Use the term –COOH to show the functional group. Show two distinct reactions/behaviours (acidic pH, carbonate reaction). Define homologous series clearly – same functional group, similar properties.

Common mistakes

  • Writing that ethanoic acid is a strong acid. Forgetting to mention the –COOH group. Using vague phrases like ‘has similar properties’ without linking to the functional group.

Mark scheme (4 marks)

  1. Ethanoic acid contains the functional group –COOH
  2. Ethanoic acid is a weak acid / reacts with carbonates to produce carbon dioxide / dissolves in water to produce an acidic solution / has a pH below 7
  3. A homologous series is a series of compounds with the same functional group
  4. Members of a homologous series have similar chemical properties

Key terms in this question

homologous series · ethanoic acid

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