Explain why alkanes are described as saturated hydrocarbons.

Edexcel GCSE Chemistry (1CH0) — 10.1 Crude oil, hydrocarbons and alkanes (Chem only) · Explain · 4 marks · View as Markdown

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

Alkanes are a homologous series of compounds found in crude oil and are widely used as fuels.

Model answer (4 marks)

Alkanes are hydrocarbons, containing only carbon and hydrogen atoms.
They are saturated because all the bonds between carbon atoms are single bonds.
Each carbon atom forms four bonds, so it is bonded to the maximum number of hydrogen atoms possible.
The general formula CₙH₂ₙ₊₂ shows the maximum hydrogen content for a given number of carbon atoms.

Examiner tips

  • Use the term "saturated" and explain it means only single C–C bonds. Show the general formula to justify the maximum hydrogen content. Mention that alkanes are hydrocarbons (C and H only).

Common mistakes

  • Confusing saturated with unsaturated or double bonds. Forgetting to state that alkanes contain only C and H. Using the wrong general formula (e.g., CₙHₙ).

Mark scheme (4 marks)

  1. Alkanes contain only carbon and hydrogen atoms (are hydrocarbons)
  2. Alkanes are described as saturated because they contain only single bonds (between carbon atoms)
  3. Each carbon atom forms four bonds in total / carbon is bonded to the maximum number of hydrogen atoms possible
  4. The general formula for alkanes is CₙH₂ₙ₊₂, showing the maximum hydrogen content for a given number of carbon atoms

Key terms in this question

saturated · hydrocarbon · alkane

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