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K326 / K328 / 2027
Organic Chemistry

Lesson 5 of 7

Carboxylic acids: recognise -COOH

A functional group gives a family its characteristic chemistry.

O-Level 5086 / 5088 (2026) / SEC G3 K326 / K328 (2027)

  • I can recognise carboxylic-acid series.Syllabus

    Syllabus K326 / K328, 11.3(e). Recognise carboxylic-acid series

  • I can explain ethanol oxidation.Syllabus

    Syllabus K326 / K328, 11.3(f). Explain ethanol oxidation

Carboxylic acids: recognise -COOH

A functional group gives a family its characteristic chemistry.

Carboxylic acids contain the -COOH group, also written -CO2H. This includes a C=O bond and an O-H bond on the same carbon. Ethanoic acid is CH3COOH; it can form when ethanol is oxidised by oxygen in air or by warm acidified potassium manganate(VII). The carbon skeleton is retained in this conversion.

Check your understanding

What distinguishes the functional group in ethanol from the one in ethanoic acid?

  1. Ethanol has a C=O group, while ethanoic acid has two -OH groups on one carbon.
  2. Ethanol has -OH on a chain; ethanoic acid has -COOH, a C=O and OH on one carbon.
  3. Ethanol has -OH and ethanoic acid has -OH too, so the two functional groups are the same.
Show the answer

Ethanol has -OH on a chain; ethanoic acid has -COOH, a C=O and OH on one carbon.

In ethanoic acid the -OH is part of the carboxyl group, which makes it acidic. Recognise the whole group, not just the letters OH.

Exam-style question

Describe a chemical test to distinguish ethanol from ethanoic acid. State what you would observe with each. [2]

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