Alcohols form a homologous series. Describe four features of alcohols as a homologous series, and state the functional group present in all alcohols.

AQA A-Level Chemistry (7405) — 3.3.5 Alcohols · Describe · 5 marks · View as Markdown

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

Model answer (5 marks)

1. All alcohols contain the –OH functional group.
2. They form a homologous series, i.e. members differ only by a –CH₂– unit.
3. Successive members have the same functional group and therefore similar chemical properties.
4. The molecular formula of each member increases by CH₂ (e.g. C₁H₄O, C₂H₆O, C₃H₈O, C₄H₁₀O).
5. The first four members are methanol, ethanol, propanol and butanol.

Examiner tips

  • Use the exact wording – ‘–OH functional group’ and ‘homologous series’. Include the CH₂ increment and list the first four members. Keep the answer concise and numbered to show each point.
  • Make sure to state the functional group before the series description.

Mark scheme (5 marks)

  1. Alcohols contain/have the functional group –OH
  2. Alcohols are a homologous series / members of a homologous series with the same functional group
  3. Members of the series have similar chemical properties (to each other)
  4. Each successive member differs by one –CH₂– unit (or the molecular formula increases by CH₂ each time)
  5. The first four members are methanol, ethanol, propanol and butanol (all four named correctly)

Key terms in this question

homologous series · functional group · alcohols

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