Ethanol can be produced by fermentation of sugar solutions using yeast, or by hydration of ethene. Explain why fermentation is considered a more sustainable method of producing ethanol than hydration of ethene. In your answer, refer to the feedstock used in each process.

AQA A-Level Chemistry (7405) — 3.3.7 Optical isomerism (A-Level only) · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

Fermentation uses sugar or glucose, a renewable biological feedstock.
Hydration of ethene uses ethene, a feedstock derived from crude oil.
Crude oil is a finite, non‑renewable resource.
The sugar used in fermentation can be regrown or replaced, making it renewable.
Therefore fermentation is more sustainable because its feedstock will not run out and can be continually replaced.

Examiner tips

  • Use the exact phrases from the mark scheme – e.g. "renewable biological feedstock" and "finite, non‑renewable resource".
  • Show the logical sequence: feedstock type → source → renewability → sustainability.

Common mistakes

  • Confusing ethene with ethanol in the feedstock description.
  • Using vague terms like "natural" instead of "renewable" or "finite".

Mark scheme (5 marks)

  1. Fermentation uses sugar / glucose / a renewable / biological feedstock (1 mark)
  2. Hydration of ethene uses ethene / a feedstock derived from crude oil (1 mark)
  3. Crude oil is a finite / non-renewable resource (1 mark)
  4. Sugar / the feedstock for fermentation can be regrown / replaced / is renewable (1 mark)
  5. Therefore fermentation is more sustainable because its feedstock will not run out / can be continually replaced (1 mark)

Key terms in this question

fermentation · feedstock

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