Carboxylic acids are a homologous series of organic compounds. Describe the key features of carboxylic acids and explain what happens when ethanoic acid reacts with sodium carbonate solution.

AQA A-Level Chemistry (7405) — 3.3.9 Carboxylic acids and derivatives (A-Level only) · 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)

Carboxylic acids contain the functional group –COOH.
The first four members of the series are methanoic acid, ethanoic acid, propanoic acid and butanoic acid.
They dissolve in water to give acidic solutions.
When ethanoic acid reacts with sodium carbonate:

CH₃COOH + Na₂CO₃ → CH₃COONa + NaOH + CO₂↑

A salt (sodium ethanoate) is formed and carbon dioxide gas is released, giving effervescence.

Examiner tips

  • Use the exact functional‑group term –COOH; list the first four acids in order; state that they give acidic solutions; write the balanced equation showing the salt and CO₂; mention effervescence to show gas evolution.
  • Keep the answer concise – no extra words; use correct UK spelling (e.g. carbonate, ethanoic).

Common mistakes

  • Writing the reaction as CH₃COOH + Na₂CO₃ → CH₃COONa + CO₂ (omitting NaOH); forgetting to list the first four acids; using the wrong functional group name (e.g. carboxylate instead of –COOH).

Mark scheme (5 marks)

  1. Carboxylic acids contain the functional group –COOH
  2. The first four members are methanoic acid, ethanoic acid, propanoic acid and butanoic acid
  3. Carboxylic acids dissolve in water to produce acidic solutions
  4. Ethanoic acid reacts with sodium carbonate to produce a salt (sodium ethanoate)
  5. Carbon dioxide gas is also produced / effervescence is observed

Key terms in this question

carboxylic acids · homologous series · ethanoic acid · sodium carbonate

Related

More Carboxylic acids and derivatives (A-Level only) questions

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