Ethanol can be oxidised to form ethanoic acid. Compare the properties and uses of ethanol and ethanoic acid, and explain why ethanol is classified as an alcohol rather than a carboxylic acid.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Ethanol has the formula C₂H₅OH. Ethanoic acid has the formula CH₃COOH.
Model answer (5 marks)
Ethanol contains a hydroxyl group (–OH) and is neutral, so it does not react with carbonates and has a pH close to 7. Ethanoic acid contains a carboxyl group (–COOH); it is acidic, reacts with carbonates to give CO₂, and has a lower pH. Ethanoic acid is used mainly to make esters (e.g. ethyl acetate) and as a food preservative, whereas ethanol is used as a fuel, solvent and in alcoholic beverages. Ethanol is classified as an alcohol because its functional group is –OH, not –COOH, and the functional group determines the homologous series.
Examiner tips
- Use the functional‑group comparison first, then list one key property and one use for each compound, and finish with the classification reason.
- Show the acidic vs neutral behaviour and the carbonate test to earn the chemistry points.
Common mistakes
- Confusing the acidity of ethanol with that of ethanoic acid; writing ethanol as acidic.
- Failing to mention the carbonate reaction or the ester‑making property of ethanoic acid.
Mark scheme (5 marks)
- Ethanol contains the functional group –OH (hydroxyl group)
- Ethanoic acid contains the functional group –COOH (carboxyl group)
- Ethanoic acid is acidic / reacts with carbonates / has a lower pH than ethanol OR ethanol is neutral / does not react with carbonates
- Ethanoic acid can be used to make esters (by reacting with an alcohol) / ethanol can be used as a fuel or solvent
- Ethanol is an alcohol because its functional group is –OH (not –COOH) / the functional group determines which homologous series a compound belongs to
Key terms in this question
Related
- All AQA A-Level Chemistry (7405) revision notes →
- How to answer a "Compare" question →
- Decode the mark scheme abbreviations →
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