Ethanol is an alcohol that can be produced by fermentation. Describe what is meant by fermentation and explain why ethanol is considered a useful product of this process.

WJEC A-Level Chemistry (Wales) — 2.7 Alcohols and carboxylic acids · Describe and Explain · 5 marks · View as Markdown

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

Ethanol can be made by fermenting sugar solutions using yeast. It is used as a fuel and as a solvent in many everyday products.

Model answer (5 marks)

Fermentation is the breakdown of sugars by yeast.
The reaction produces ethanol and carbon dioxide.
It occurs without oxygen – it is an anaerobic process.
Ethanol is useful as a fuel, for example in cars or as a biofuel.
Ethanol is also a useful solvent, for example in perfumes, cleaning products and medicines.

Examiner tips

  • Use the word ‘anaerobic’ to show understanding of the process. Mention both products (ethanol and CO₂) to gain full marks. Give at least one example of each use (fuel and solvent).

Common mistakes

  • Forgetting that fermentation is anaerobic. Only naming one use of ethanol. Not specifying that yeast is the catalyst.”

Mark scheme (5 marks)

  1. Fermentation is the breakdown of sugars by yeast
  2. Fermentation produces ethanol and carbon dioxide
  3. The process occurs without oxygen / is anaerobic
  4. Ethanol is useful as a fuel (e.g. in cars / as a biofuel)
  5. Ethanol is useful as a solvent (e.g. in perfumes / cleaning products / medicines)

Key terms in this question

fermentation · ethanol

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