A student is given three organic compounds with the following molecular formulae: C₃H₈, C₄H₉OH, and C₂H₄. State the name of each compound and identify the homologous series to which each belongs.

Cambridge International IGCSE Chemistry (0620) — 11.2 Naming organic compounds · State · 4 marks · View as Markdown

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

Model answer (4 marks)

C₃H₈ – propane – alkanes
C₄H₉OH – butan‑1‑ol (butanol) – alcohols
C₂H₄ – ethene – alkenes

Examiner tips

  • Use the exact IUPAC/accepted names (propane, butan‑1‑ol, ethene).
  • Identify the correct homologous series (alkanes, alcohols, alkenes).
  • Keep answer concise – one line per compound.
  • Avoid extra words like ‘the’ or ‘compound’.

Common mistakes

  • Writing ‘butanol’ without the ‘‑1‑’ prefix or ‘ethene’ as ‘ethylene’.
  • Misidentifying C₂H₄ as an alkane instead of an alkene.
  • Using the wrong series name (e.g., calling C₃H₈ a cycloalkane).

Mark scheme (4 marks)

  1. C₃H₈ is named propane
  2. C₃H₈ belongs to the alkanes
  3. C₄H₉OH is named butan-1-ol (accept butanol)
  4. C₂H₄ is named ethene AND belongs to the alkenes

Key terms in this question

molecular formula · homologous series

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