Ethanol can be used as a fuel and is also found in alcoholic drinks. However, ethanol is toxic to the human body. Describe the oxidation of ethanol and explain why the products formed are harmful to health.

WJEC A-Level Chemistry (Wales) — 4.3 Alcohols and phenols · 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)

Ethanol is oxidised in the liver by alcohol dehydrogenase to ethanal (acetaldehyde).

The ethanal is then oxidised by aldehyde dehydrogenase to ethanoic acid (acetic acid).

Acetaldehyde is highly toxic; it causes hang‑over symptoms and damages cells by forming adducts with proteins and DNA.

Ethanoic acid lowers the pH of the blood, leading to acidosis and disrupting normal body chemistry.

Repeated oxidation of ethanol in the liver can damage liver cells, contributing to liver disease.

Examiner tips

  • Use the exact terms ‘ethanal’ and ‘ethanoic acid’ and mention the liver enzymes; link toxicity to hang‑over and acidosis.
  • Show the stepwise oxidation and explain the harmful effects of each product.

Mark scheme (5 marks)

  1. Ethanol is oxidised to ethanal (acetaldehyde)
  2. Ethanal is further oxidised to ethanoic acid
  3. Ethanal is toxic / responsible for hangover symptoms / damages cells
  4. Ethanoic acid lowers the pH of the blood / causes acidosis / disrupts body chemistry
  5. The liver is responsible for the oxidation of ethanol / the liver can be damaged by repeated oxidation of ethanol

Key terms in this question

oxidation · ethanol

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