Butanedioic acid is a dicarboxylic acid found in unripe fruit. It reacts with sodium carbonate solution. Describe what you would observe during this reaction and explain why butanedioic acid behaves in this way. Include in your answer the name of the gas produced and how you would confirm its identity.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Butanedioic acid is a dicarboxylic acid. Like all carboxylic acids, it reacts with sodium carbonate solution.
Model answer (5 marks)
Effervescence is observed as bubbles of gas form.
The solid sodium carbonate dissolves and the solution fizzes.
The gas released is carbon dioxide.
Butanedioic acid behaves this way because it is an acid that donates H⁺ ions; carboxylic acids react with carbonates to give a salt, water and CO₂.
To confirm the gas, bubble it through limewater – a positive test is that the limewater turns milky or cloudy.
The solid sodium carbonate dissolves and the solution fizzes.
The gas released is carbon dioxide.
Butanedioic acid behaves this way because it is an acid that donates H⁺ ions; carboxylic acids react with carbonates to give a salt, water and CO₂.
To confirm the gas, bubble it through limewater – a positive test is that the limewater turns milky or cloudy.
Examiner tips
- Use the word "effervescence" or "fizzing" to show you know the visual cue. Mention that CO₂ is produced and explain the acid–carbonate reaction. State the confirmatory test (limewater) and the expected result (milky cloud).
Common mistakes
- Writing that the gas is water or oxygen instead of CO₂. Failing to explain that the acid donates H⁺ ions. Omitting the limewater test or the milky cloud result.
Mark scheme (5 marks)
- Effervescence / bubbles / fizzing is observed
- The solid sodium carbonate dissolves / the solution fizzes and the solid disappears (or if solution stated, fizzing in solution is acceptable)
- Carbon dioxide is the gas produced
- Butanedioic acid reacts with sodium carbonate because it is an acid / it donates H⁺ ions / carboxylic acids react with carbonates to form a salt, water and carbon dioxide
- To confirm the identity of the gas, bubble it through limewater — a positive result is that the limewater turns milky / cloudy
Key terms in this question
Related
- All WJEC A-Level Chemistry (Wales) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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