Lesson 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)
I can describe acid and base ester hydrolysis.Syllabus
Syllabus 9476, 11.8(h). Describe acid and base ester hydrolysis.
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 its hydrolysis, remember that the C=O stays with the acid part, and the group after the oxygen becomes the alcohol or phenol. Phenyl benzoate gives benzoic acid and phenol with acid. In excess strong alkali, it gives benzoate and phenoxide ions, because phenol also loses its proton. Adding acid afterwards gives back the neutral compounds.
Check your understanding
An ester gives propanoic acid and methanol on acidic hydrolysis. What was the ester?
Show the answer
Methyl propanoate, CH3CH2COOCH3
The alcohol part gives the first word (methyl), and the acid part gives the second (propanoate). The methyl group is attached to the single-bonded oxygen.