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GCSE Chemistry · key term
An acid that is only partially ionised in aqueous solution.
Used by AQA, Edexcel and OCR
Specification 4.4.2.6, 4.7.2.4 · Paper 1, Paper 2
Revise: Strong and Weak AcidsA weak acid is only partially ionised in aqueous solution. Only some of its acid particles form ions; many remain as un-ionised acid particles.
An acid that ionises only partially in water, leaving many acid molecules un-ionised.
Specification 3.8, 9.30C · Paper 1, Paper 2
An acid that only partially dissociates into ions in aqueous solution.
Revise: Weak vs Strong AcidsA weak acid only partially dissociates in aqueous solution.
An acid that only partially ionises when dissolved in water.
Specification C3.3g · Paper 1 (Foundation), Paper 3 (Higher)
An acid for which only a proportion of its particles ionise in aqueous solution.
Revise: Acid Strength and ConcentrationA solution can therefore contain a concentrated strong acid, a dilute strong acid, a concentrated weak acid or a dilute weak acid. This distinction matters because everyday language sometimes uses “strong” to mean concentrated, but that is not what strong acid means in chemistry.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
An acid that ionises only partly in water.
Revise: Weak/Strong vs Dilute/ConcentratedA weak acid ionises only partly: some particles form ions, while others remain as acid molecules. Hydrochloric acid is a strong acid; ethanoic acid is a weak acid.
Only compare the pH values of strong and weak acids directly when their concentrations are the same.
Do not describe a weak acid as one that does not ionise: it is partially ionised.
Do not confuse acid strength with concentration. A weak acid only partially ionises; a concentrated solution contains a large amount of acid per unit volume.
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