Ethanol can be produced by fermentation using yeast and glucose. The ethanol produced can then be separated from the fermentation mixture. Describe the process of fermentation and explain why the conditions used must be carefully controlled.

Eduqas A-Level Chemistry — 2.4 Organic compounds · Describe and Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

Yeast contains enzymes that convert glucose into ethanol and carbon dioxide.
The reaction occurs in the absence of oxygen – anaerobic conditions.
The temperature must be kept at an optimum, usually around 25–35 °C.
If the temperature rises too high the enzymes become denatured, so fermentation stops.
After fermentation, distillation is used to separate and purify the ethanol from the mixture.

Examiner tips

  • Use the exact terms "enzymes", "anaerobic", "optimum temperature", "denatured", "distillation".
  • Show the sequence: yeast → enzymes → glucose → ethanol + CO₂, then distillation.
  • Mention the temperature range to demonstrate understanding of control.
  • Keep the answer concise and directly linked to the mark scheme points.

Common mistakes

  • Confusing aerobic with anaerobic conditions.
  • Forgetting to mention the temperature range or enzyme denaturation.
  • Using the word "boiling" instead of "distillation" for separation.

Mark scheme (5 marks)

  1. Yeast contains enzymes that break down / convert glucose into ethanol and carbon dioxide
  2. The process takes place in the absence of oxygen / anaerobic conditions
  3. Temperature must be kept at an optimum / warm temperature (around 25–35 °C)
  4. If temperature is too high, enzymes are denatured / destroyed and fermentation stops
  5. Distillation is used to separate / purify the ethanol from the fermentation mixture

Key terms in this question

fermentation

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