Methanol, ethanol, propanol and butanol are all members of the same homologous series. Explain what is meant by the term homologous series and describe two chemical properties that all members of this alcohol series share.

Edexcel GCSE Chemistry (1CH0) — 10.3 Alcohols and carboxylic acids (Chem only) · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

A homologous series is a family of compounds that have the same general formula or functional group. Each successive member differs by one CH₂ unit (one carbon and two hydrogen atoms). All alcohols in the series share the following chemical properties:
1. They all undergo complete combustion in oxygen/air to give CO₂ and H₂O.
2. They all react with sodium metal (or can be oxidised to give carboxylic acids) – for example, alcohols react with Na to form alkoxide salts and water.

Examiner tips

  • Use the definition of a homologous series – mention general formula/functional group and CH₂ increment.
  • State two properties that apply to all alcohols – combustion and reaction with Na (or oxidation).
  • Keep the answer concise and use exam‑specific terminology.

Mark scheme (4 marks)

  1. A homologous series is a family/group of compounds that share the same general formula (or functional group)
  2. Each successive member differs by CH₂ (one carbon and two hydrogen atoms)
  3. All alcohols undergo combustion (burn in oxygen/air to produce carbon dioxide and water)
  4. All alcohols react with sodium (or can be oxidised to form a carboxylic acid / undergo fermentation / react with carboxylic acids to form esters)

Key terms in this question

homologous series · alcohol

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