Ethanol can be produced by two different industrial methods: fermentation of glucose and the hydration of ethene. Describe both methods and explain one advantage of using fermentation over hydration of ethene to produce ethanol.

Edexcel GCSE Chemistry (1CH0) — 10.3 Alcohols and carboxylic acids (Chem only) · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

Fermentation: glucose is converted to ethanol (and CO₂) by yeast or enzymes at around room temperature or a moderate temperature.
Hydration of ethene: ethene reacts with steam in the presence of an acid catalyst (e.g. phosphoric acid) at high temperature and pressure to give ethanol.
Advantage of fermentation: it uses a renewable resource – glucose or sugar from plants or crops – whereas hydration uses ethene derived from crude oil, a finite, non‑renewable resource. This makes fermentation more sustainable in the long term.

Examiner tips

  • Use the exact terms ‘fermentation’, ‘yeast’, ‘glucose’, ‘ethene’, ‘acid catalyst’, ‘high temperature and pressure’, ‘renewable resource’, ‘finite/non‑renewable’
  • Show the link between renewable raw material and sustainability to justify the advantage
  • Keep the answer concise – 4 marks only

Common mistakes

  • Confusing the conditions for hydration (e.g. using low temperature instead of high temperature and pressure)
  • Failing to mention the acid catalyst in the hydration step
  • Not explicitly stating that glucose comes from plants or crops

Mark scheme (4 marks)

  1. Fermentation: glucose is converted to ethanol (and carbon dioxide) by yeast / enzymes (at around room temperature / moderate temperature)
  2. Hydration of ethene: ethene reacts with steam (in the presence of an acid catalyst / phosphoric acid catalyst) at high temperature and pressure to form ethanol
  3. One advantage of fermentation: uses a renewable resource / raw material (glucose / sugar from plants / crops) whereas hydration uses ethene from crude oil (a finite/non-renewable resource)
  4. Explanation of advantage is linked to context: crude oil is a finite/non-renewable resource OR glucose/sugar crops can be regrown/replenished, making fermentation more sustainable long-term

Key terms in this question

fermentation · hydration · ethanol · ethene

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