GCSE Chemistry revision

Carboxylic acids

Reactions of alkenes and alcohols (chemistry only)

AQA 4.7.2.4 Includes HT-only content

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Carboxylic acids are a homologous series of organic compounds containing the functional group –COOH.
Their names all end in '-anoic acid', and the key members to know are methanoic, ethanoic, propanoic, and butanoic acid.
When writing their molecular formulae, the –COOH group should always be written together at the end (e.g.
CH₃COOH for ethanoic acid).

1. What Are Carboxylic Acids? AQA

Carboxylic acids are a homologous series of organic compounds containing the functional group –COOH.
Their names all end in '-anoic acid', and the key members to know are methanoic, ethanoic, propanoic, and butanoic acid.
When writing their molecular formulae, the –COOH group should always be written together at the end (e.g.
CH₃COOH for ethanoic acid).

Carboxylic acids are weak acids, meaning they do not fully ionise in solution.
Because ionisation is incomplete, it is represented using an equilibrium arrow (⇋) rather than a one-way arrow (→).
When a carboxylic acid ionises, it releases a hydrogen ion (H⁺) and forms a negative ion whose name ends in '-anoate' (e.g. propanoic acid forms the propanoate ion).

2. Carboxylic Acids as Weak Acids AQA

Carboxylic acids are weak acids, meaning they do not fully ionise in solution.
Because ionisation is incomplete, it is represented using an equilibrium arrow (⇋) rather than a one-way arrow (→).
When a carboxylic acid ionises, it releases a hydrogen ion (H⁺) and forms a negative ion whose name ends in '-anoate' (e.g. propanoic acid forms the propanoate ion).

Like all acids, carboxylic acids react with metal carbonates to produce a salt, water, and carbon dioxide.
For example, ethanoic acid reacting with potassium carbonate produces potassium ethanoate (the salt), water, and carbon dioxide.
The salt formed always takes its name from the carboxylic acid used, ending in '-anoate' (e.g. ethanoic acid → ethanoate salt).

3. Reactions of Carboxylic Acids AQA

Like all acids, carboxylic acids react with metal carbonates to produce a salt, water, and carbon dioxide.
For example, ethanoic acid reacting with potassium carbonate produces potassium ethanoate (the salt), water, and carbon dioxide.
The salt formed always takes its name from the carboxylic acid used, ending in '-anoate' (e.g. ethanoic acid → ethanoate salt).

Carboxylic acids are produced by oxidising alcohols using an oxidising agent.
The oxidising agent effectively adds an oxygen atom, converting the alcohol into the corresponding carboxylic acid.
For example, oxidising butanol (4 carbons) produces butanoic acid, as the carbon chain length remains the same throughout the reaction.

4. Making Carboxylic Acids by Oxidation AQA

Carboxylic acids are produced by oxidising alcohols using an oxidising agent.
The oxidising agent effectively adds an oxygen atom, converting the alcohol into the corresponding carboxylic acid.
For example, oxidising butanol (4 carbons) produces butanoic acid, as the carbon chain length remains the same throughout the reaction.