Outline how the functional groups present in ethanoic acid and ethylamine allow each compound to be classified as belonging to a homologous series, and identify one chemical property that distinguishes them from each other.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Ethanoic acid contains a carboxyl (–COOH) functional group, so it is a carboxylic acid and belongs to the carboxylic‑acid homologous series.
Ethylamine contains an amino (–NH₂) functional group, so it is an amine and belongs to the amine homologous series.
The carboxyl group makes ethanoic acid acidic – it donates a proton (H⁺). The amino group makes ethylamine basic – it accepts a proton (H⁺).
Thus the two compounds differ in acidity/basicity: ethanoic acid is acidic, ethylamine is basic, and they can react to form the salt ethylammonium ethanoate.
Ethylamine contains an amino (–NH₂) functional group, so it is an amine and belongs to the amine homologous series.
The carboxyl group makes ethanoic acid acidic – it donates a proton (H⁺). The amino group makes ethylamine basic – it accepts a proton (H⁺).
Thus the two compounds differ in acidity/basicity: ethanoic acid is acidic, ethylamine is basic, and they can react to form the salt ethylammonium ethanoate.
Examiner tips
- Use the exact functional‑group names (carboxyl, amino). Mention the homologous series (carboxylic acid, amine). State the acid/base property clearly. Keep the answer short and to the point.
Common mistakes
- Calling ethanoic acid a ‘carboxylate’ instead of a carboxylic acid. Mixing up the acid/base behaviour (e.g. saying ethylamine is acidic). Adding unnecessary detail such as reaction mechanisms beyond the salt formation.
Mark scheme (4 marks)
- Ethanoic acid contains a carboxyl (–COOH) functional group, which classifies it as a carboxylic acid.
- Ethylamine contains an amino (–NH₂) functional group, which classifies it as an amine.
- Ethanoic acid is acidic / donates a proton (H⁺), whereas ethylamine is basic / accepts a proton (H⁺).
- Ethanoic acid reacts with ethylamine (or other bases/carbonates) but ethylamine does not react in the same way / they react together to form a salt (ethylammonium ethanoate).
Key terms in this question
functional group · homologous series
Related
- All IB DP Chemistry Standard Level (2023 syllabus) revision notes →
- How to answer a "Outline" question →
- Decode the mark scheme abbreviations →
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