Methanol (CH₃OH) and ethanol (C₂H₅OH) are both members of the alcohol homologous series. Explain why ethanol has a higher boiling point than methanol.

WJEC GCSE Chemistry (Wales) — 2.6 Carbon chemistry / organic chemistry · Explain · 4 marks · View as Markdown

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

Methanol has a boiling point of 65 °C and ethanol has a boiling point of 78 °C. Both are alcohols that are liquids at room temperature.

Model answer (4 marks)

Ethanol has a larger molecule and greater molecular mass than methanol.
The forces between ethanol molecules are stronger than those between methanol molecules.
More energy is needed to overcome the forces between ethanol molecules.
Therefore ethanol has a higher boiling point.

Examiner tips

  • Use the word ‘therefore’ to link the reasoning to the conclusion.
  • Mention both molecular mass and intermolecular forces as the two key factors.
  • Show the logical sequence: larger mass → stronger forces → more energy → higher BP.
  • Keep each point brief and to the point.

Mark scheme (4 marks)

  1. Ethanol has a larger molecule / greater molecular mass than methanol
  2. The forces between ethanol molecules are stronger than those between methanol molecules
  3. More energy is needed to overcome the forces between ethanol molecules
  4. Therefore ethanol has a higher boiling point

Key terms in this question

boiling point · homologous series

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