Ethanoic acid is a carboxylic acid. Explain what happens when ethanoic acid is added to sodium carbonate solution, and describe how the products of this reaction could be used to identify that a carboxylic acid was present.

WJEC A-Level Chemistry (Wales) — 2.7 Alcohols and carboxylic acids · Explain · 5 marks · View as Markdown

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

Vinegar contains ethanoic acid, which reacts with sodium carbonate solution. This reaction can be used as a test for carboxylic acids.

Model answer (5 marks)

Ethanoic acid reacts with sodium carbonate:

CH₃COOH + Na₂CO₃ → CH₃COONa + CO₂↑ + H₂O

The reaction releases carbon dioxide gas. The CO₂ is bubbled through limewater (Ca(OH)₂). The CO₂ reacts with the calcium hydroxide to give calcium carbonate:

CO₂ + Ca(OH)₂ → CaCO₃↓ + H₂O

The limewater turns milky, showing that CO₂ has been produced and confirming the presence of a carboxylic acid.

Examiner tips

  • Show the balanced equation first, then explain the CO₂ release and the limewater test.
  • Mention that the milky appearance is due to CaCO₃ precipitation. Use the term ‘milky’ or ‘cloudy’.
  • Link the CO₂ production directly to the carboxylic acid functional group.

Mark scheme (5 marks)

  1. Ethanoic acid reacts with sodium carbonate (solution)
  2. Carbon dioxide gas is produced / given off
  3. A salt (sodium ethanoate) and water are also formed
  4. The carbon dioxide gas is passed through / bubbled into limewater
  5. The limewater turns milky / cloudy, confirming carbon dioxide is present and therefore a carboxylic acid was present

Key terms in this question

carboxylic acid · sodium carbonate

Related

More Alcohols and carboxylic acids questions

▶ Try answering this question with AI marking (free) →