Butanoic acid is a carboxylic acid. A student adds an excess of sodium carbonate powder to a sample of butanoic acid solution. Describe what the student would observe, name the type of reaction occurring, and state the name of one gas produced.

Pearson Edexcel International GCSE Chemistry (4CH1) — 4.6 Carboxylic acids · Describe · 4 marks · View as Markdown

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

Butanoic acid has the molecular formula C₃H₇COOH and is the fourth member of the carboxylic acids homologous series. Like all carboxylic acids, it displays typical acidic properties.

Model answer (4 marks)

Effervescence (fizzing) is observed as bubbles.
The sodium carbonate powder dissolves into the solution.
The reaction is a neutralisation (acid–base) reaction.
The gas produced is carbon dioxide (CO₂).

Examiner tips

  • Use the word "effervescence" or "fizzing" for bubbles. Mention that the solid dissolves. State the reaction type as "neutralisation" or "acid–base". Name the gas as "carbon dioxide (CO₂)".

Common mistakes

  • Writing "bubbles" instead of "effervescence" or "fizzing". Forgetting to note that the solid dissolves. Calling the reaction a "combination" or "decomposition" instead of neutralisation. Naming the gas as "CO" or "O₂" instead of CO₂.

Mark scheme (4 marks)

  1. Effervescence / bubbles are observed (accept: fizzing)
  2. The sodium carbonate (solid) dissolves / disappears (accept: the powder dissolves into the solution)
  3. The type of reaction is a neutralisation reaction (accept: acid–base reaction)
  4. The gas produced is carbon dioxide (accept: CO₂)

Key terms in this question

carboxylic acid

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