AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Students should be able to recognise carboxylic acids from their names or…
Full specification wording
Carboxylic acids: Students should be able to recognise carboxylic acids from their names or from given formulae.
Recognising a carboxylic acid means spotting the clues in either its name or its formula.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 4 of 4
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Recognising a carboxylic acid means spotting the clues in either its name or its formula. In a name, the ending '-anoic acid' signals the –COOH group, and the stem meth-, eth-, prop- or but- gives the number of carbon atoms. In a formula, look for the –COOH unit, which may be written as COOH, CO₂H or drawn with the carbon double-bonded to oxygen and single-bonded to –OH. For example, CH₃CH₂COOH is propanoic acid because it contains –COOH and has three carbon atoms in total. This skill supports later work on reactions with carbonates, water and alcohols, and on explaining weak acidity, because identifying the functional group tells you which reactions to expect.
What earns the marks
- Recognise the '-anoic acid' ending in a name as showing a carboxylic acid.
- Use the stem of the name to count the carbon atoms in the chain.
- Identify the –COOH unit in displayed, structural or molecular formulae.
- Count the –COOH carbon when working out the name from a formula.
- Distinguish carboxylic acids from alcohols and esters by the presence of the complete –COOH group.
- Link recognition of the group to the reactions and weak acidity expected of the compound.
Common mistakes and how to put them right
Mistaking an alcohol for a carboxylic acid because both contain –OH.
Put it right by checking whether the –OH is part of a –COOH group.
Ignoring the –COOH carbon when counting chain length.
Put it right by including it so the name matches the total number of carbon atoms.
Reading a formula such as CH₃COOH as an ester.
Put it right by identifying the –COOH unit, which is absent from esters.
Exam tips
- Scan a formula for the –COOH unit first, then count carbons to choose the correct stem.
- Check names for the '-anoic acid' ending before deciding a compound is a carboxylic acid.
- Practise mixed examples of alcohols, carboxylic acids and esters so you can justify your identification by the functional group present.
Try the lesson
The start of the Carboxylic acids: Students should be able to recognise carboxylic acids from their names or from given formulae. lesson, made from checked teaching notes for this specification point.
Have a go first
Which of the following formulae represents a carboxylic acid?
Listen
Recognising a carboxylic acid means spotting the clues in either its name or its formula. In a name, the ending '-anoic acid' signals the –COOH group, and the stem meth-, eth-, prop- or but- gives the number of carbon atoms. In a formula, look for the –COOH unit, which may be written as COOH, CO₂H or drawn with the carbon double-bonded to oxygen and single-bonded to –OH. For example, CH₃CH₂COOH is propanoic acid because it contains –COOH and has three carbon atoms in total. This skill supports later work on reactions with carbonates, water and alcohols, and on explaining weak acidity, because identifying the functional group tells you which reactions to expect. A strong answer earns marks for these points. Recognise the '-anoic acid' ending in a name as showing a carboxylic acid. Use the stem of the name to count the carbon atoms in the chain. Identify the –COOH unit in displayed, structural or molecular formulae. Count the –COOH carbon when working out the name from a formula. A common slip: Mistaking an alcohol for a carboxylic acid because both contain –OH. Instead, checking whether the –OH is part of a –COOH group. Exam tip: Scan a formula for the –COOH unit first, then count carbons to choose the correct stem.
Key words
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-anoic acid
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Stem
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–COOH unit
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Functional group
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See every definition
- -anoic acid
- The ending in a name that signals the –COOH group and shows a carboxylic acid.
- Stem
- The part of a name, meth-, eth-, prop- or but-, that gives the number of carbon atoms.
- –COOH unit
- The group looked for in a formula, which may be written as COOH, CO₂H or drawn with the carbon double-bonded to oxygen and single-bonded to –OH.
- Functional group
- The group present that tells you which reactions to expect, such as the complete –COOH group that distinguishes carboxylic acids from alcohols and esters.
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