Carboxylic Acids — Structure, Properties and Reactions — AQA GCSE Chemistry (Separate)
Carboxylic acids are a homologous series with the –COOH functional group. They are weak acids.
The carboxylic acid series
Carboxylic acids contain the carboxyl functional group, –COOH. The first four are:
- methanoic acid (HCOOH)
- ethanoic acid (CH₃COOH) — the acid in vinegar
- propanoic acid
- butanoic acid
Properties and reactions
Carboxylic acids:
- Dissolve in water to form acidic solutions.
- React with carbonates to produce a salt, water and carbon dioxide (they fizz).
- React with alcohols (with an acid catalyst) to form esters, which have sweet/fruity smells.
Weak acids
Carboxylic acids are weak acids — they are only partially ionised in water. This means that, at the same concentration, they have a higher pH (are less acidic) than a strong acid like hydrochloric acid, and react more slowly with metals and carbonates.
Exam tips
- The functional group is –COOH; learn the first four acids (ethanoic = vinegar).
- They form acidic solutions and react with carbonates (→ salt + water + CO₂).
- They are weak acids (partially ionised) — higher pH than strong acids of the same concentration.
- With alcohols they form esters (fruity smells).