Describe what happens during the incomplete combustion of an alkane, and explain why the products formed are harmful.

Pearson Edexcel International GCSE Chemistry (4CH1) — 4.3 Alkanes · Describe · 4 marks · View as Markdown

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

Alkanes are the most common hydrocarbons found in crude oil and are widely used as fuels. When alkanes burn, the products formed depend on the amount of oxygen available.

Model answer (4 marks)

Incomplete combustion occurs when there is not enough oxygen for the alkane to react fully. The reaction then produces mainly carbon monoxide (CO) and small amounts of unburnt carbon (soot). Carbon monoxide is poisonous because it binds to haemoglobin more strongly than oxygen, preventing oxygen transport in the blood. The soot particles are harmful as they can penetrate the lungs, causing respiratory problems and contribute to global dimming by scattering sunlight.

Examiner tips

  • Use the word ‘incomplete combustion’ and state the lack of oxygen first.
  • Mention CO and soot as the main products.
  • Explain CO’s toxicity by its affinity for haemoglobin.
  • Link soot to health and environmental effects.

Common mistakes

  • Confusing complete with incomplete combustion.
  • Failing to mention CO or soot.
  • Not explaining why CO is harmful.

Mark scheme (4 marks)

  1. Incomplete combustion occurs when there is insufficient oxygen
  2. Carbon monoxide is produced during incomplete combustion
  3. Carbon monoxide is toxic / harmful to humans
  4. Carbon particulates are also produced and cause global dimming / health problems

Key terms in this question

incomplete combustion · alkane

Related

More Alkanes questions

▶ Try answering this question with AI marking (free) →