Ethanoic acid is a carboxylic acid found in vinegar. Describe what is observed when ethanoic acid is added to sodium carbonate solution, and explain why this reaction occurs.

Edexcel GCSE Chemistry (1CH0) — 10.3 Alcohols and carboxylic acids (Chem only) · Describe and Explain · 4 marks · View as Markdown

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

Vinegar contains ethanoic acid, which has the functional group –COOH. Sodium carbonate solution is an aqueous solution of Na₂CO₃.

Model answer (4 marks)

Bubbles of gas are seen.
The gas is CO₂.
Ethanoic acid donates a proton to the carbonate ion, forming CO₂, water and sodium acetate.
Thus the reaction is an acid–carbonate reaction producing a salt and water.

Examiner tips

Use the word ‘bubbles’ or ‘effervescence’ for the observation. State that CO₂ is the gas. Show the acid donates a proton to carbonate. Mention the salt (sodium acetate) and water to show the reaction type.

Common mistakes

Saying the gas is O₂ instead of CO₂. Forgetting to mention the salt or water. Describing the reaction as a neutralisation without noting the proton transfer.

Mark scheme (4 marks)

Bubbles / effervescence are produced
Carbon dioxide gas is produced / released
Ethanoic acid reacts with / donates a proton to sodium carbonate because it is an acid (or: carboxylic acids react with carbonates)
A salt (sodium ethanoate) and water are also produced, showing this is an acid–carbonate reaction

Key terms in this question

carboxylic acid · carbonate

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