Ethanol can be converted into ethanoic acid by microbial oxidation. Ethanoic acid belongs to the homologous series of carboxylic acids. Explain why ethanoic acid is classified as a member of the carboxylic acid homologous series, and describe how the properties of ethanoic acid are similar to those of propanoic acid.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Ethanol undergoes microbial oxidation to produce ethanoic acid. Ethanoic acid and propanoic acid are both members of the carboxylic acid homologous series.
Model answer (4 marks)
Ethanoic acid contains the –COOH functional group, which is the defining feature of carboxylic acids.
All members of a homologous series share the same functional group and therefore have similar chemical properties.
Because of the –COOH group, both ethanoic acid and propanoic acid behave as acids – they react with metals, carbonates and alkalis to give salts and water.
The only structural difference between the two acids is the addition of one –CH₂– unit; they have the same general formula and therefore show very similar properties, differing mainly in chain length.
All members of a homologous series share the same functional group and therefore have similar chemical properties.
Because of the –COOH group, both ethanoic acid and propanoic acid behave as acids – they react with metals, carbonates and alkalis to give salts and water.
The only structural difference between the two acids is the addition of one –CH₂– unit; they have the same general formula and therefore show very similar properties, differing mainly in chain length.
Examiner tips
- Use the term ‘functional group –COOH’ first. Show that the series shares this group. Mention the typical acidic reactions. Explain the –CH₂– difference to justify similarity.
Common mistakes
- Forgetting to state the –COOH group. Confusing the homologous series with the alkane series. Over‑emphasising the difference rather than the similarity.
Mark scheme (4 marks)
- Ethanoic acid contains the functional group –COOH
- All members of a homologous series share the same functional group and have similar chemical properties
- Both ethanoic acid and propanoic acid show typical acidic properties, such as reacting with metals / carbonates / alkalis
- Ethanoic acid and propanoic acid differ only by a –CH₂– unit / differ in chain length but have the same general formula
Key terms in this question
homologous series · carboxylic acids · microbial oxidation
Related
- All Pearson Edexcel International GCSE Chemistry (4CH1) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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