Topic 26 of 34
Acid hydrolysis is reversible; alkaline hydrolysis traps the carboxylate
Use the medium to decide whether the acid or its salt is the product.
A-Level 9476 (2026-2027)
Acid hydrolysis is reversible; alkaline hydrolysis traps the carboxylate
Use the medium to decide whether the acid or its salt is the product.
| Conditions | Equation | Consequence |
|---|---|---|
| Aqueous acid and heat | CH3COOC2H5 + H2O ⇌ CH3COOH + C2H5OH. | Acid catalysis; an equilibrium mixture forms. |
| Aqueous alkali and heat | CH3COOC2H5 + OH- → CH3COO- + C2H5OH. | Carboxylate formation makes the overall hydrolysis effectively irreversible under these conditions. |
| Acidify after alkaline hydrolysis | CH3COO- + H+ → CH3COOH. | Required when the isolated target is the free carboxylic acid. |
To identify an ester from hydrolysis, the acid-side carbonyl stays with the carboxylic fragment and the group after oxygen becomes the alcohol or phenol. Phenyl benzoate gives benzoic acid and phenol in acidic hydrolysis. In excess strong alkali, its products are benzoate and phenoxide because the phenol product is also deprotonated; acidification recovers the neutral compounds.
Check your understandingAn ester gives propanoic acid and methanol on acidic hydrolysis. What was the ester?Think it through, then reveal the answer
Methyl propanoate, CH3CH2COOCH3. The methyl group is attached to oxygen; the three-carbon propanoyl fragment comes from the acid.