Ethanoic acid is a carboxylic acid found in vinegar. Describe the reaction of ethanoic acid with sodium carbonate solution, and explain why ethanoic acid is described as a weak acid.

Cambridge International IGCSE Chemistry (0620) — 11.7 Carboxylic acids · Describe and Explain · 4 marks · View as Markdown

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

Ethanoic acid, CH₃COOH, is a carboxylic acid. It reacts with sodium carbonate solution and only partially dissociates in aqueous solution.

Model answer (4 marks)

Ethanoic acid reacts with sodium carbonate according to the equation
CH₃COOH + Na₂CO₃ → 2 NaCH₃COO + CO₂ + H₂O
The reaction produces the salt sodium ethanoate, carbon dioxide gas (effervescence) and water.
Ethanoic acid is a weak acid because it only partially dissociates in aqueous solution, so only a small fraction of the molecules give up a proton to form CH₃COO⁻ and H⁺.

Examiner tips

  • Write the balanced equation and mention CO₂ effervescence and water. Explain weak acid by stating partial dissociation. Use the exact terms ‘sodium ethanoate’ and ‘partial dissociation’.
  • common_mistakes
  • :
  • Forgetting to include CO₂ or water in the equation. Describing ethanoic acid as a strong acid or claiming complete dissociation. Using vague terms like ‘reacts’ without specifying the products.

Mark scheme (4 marks)

  1. Ethanoic acid reacts with sodium carbonate to produce a salt (sodium ethanoate)
  2. Carbon dioxide gas is produced / effervescence / bubbling observed
  3. Water is also produced in the reaction
  4. Ethanoic acid is a weak acid because it only partially dissociates / ionises in aqueous solution

Key terms in this question

carboxylic acid · weak acid · sodium carbonate

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