AQA A-Level Chemistry Paper 3, 2024: Question 30

Acid Hydrolysis of an Aromatic Ester (Phenyl Benzenecarboxylate)

What this question tests AO2 • 1 mark

Recognising phenyl benzenecarboxylate as an ester (benzoate ester).
Knowing the products of acid hydrolysis of esters: carboxylic acid + alcohol/phenol.
Picking the correct product from formula options (here: benzoic acid, C₆H₅COOH).

Examiner focus: This is a recall + application multiple-choice item. You only get the mark if you select the correct product consistent with ester hydrolysis.

Part (a): Which compound is formed by the acid hydrolysis of phenyl benzenecarboxylate? 1 mark

✅ Correct answer (from mark scheme)

D — C₆H₅COOH (benzoic acid)

Mark breakdown: 1 mark (AO2) for selecting D / writing C₆H₅COOH .

💡 Key knowledge: ester hydrolysis

Acid hydrolysis of an ester produces a carboxylic acid and an alcohol (or phenol if the ester contains a phenyl group attached through oxygen).
General: RCOOR′ + H₂O ⇌ RCOOH + R′OH (acid-catalysed, reversible).
Here, the “benzenecarboxylate” part corresponds to benzoic acid: C₆H₅COOH .

🧠 Exam technique: decode the name fast

“...carboxylate” = the acid part of the ester. So “benzenecarboxylate” points to benzenecarboxylic acid (benzoic acid).
“phenyl” = the group attached to oxygen (so the other product would be phenol, C₆H₅OH), but notice phenol is not one of the options—so focus on the acid product.
In MCQs, if one option is a clear carboxylic acid matching the acyl part, it’s usually the target.

❌ Common errors (why students lose the mark)

Choosing C₆H₅CH₂OH (benzyl alcohol): confusing phenyl (C₆H₅–) with benzyl (C₆H₅CH₂–).
Choosing C₆H₅CHO (benzaldehyde) or C₆H₅COCH₃ (a ketone): these are oxidation/reduction products, not ester hydrolysis products.
Forgetting ester hydrolysis gives acid + alcohol/phenol (not aldehydes/ketones).

📐 Calculations?

None needed. This is a structure/functional group recognition question.

💡 Extra clarity: what hydrolysis would produce overall

Phenyl benzenecarboxylate is the ester: C₆H₅COO–C₆H₅

Acid hydrolysis:

C₆H₅COOC₆H₅ + H₂O ⇌ C₆H₅COOH + C₆H₅OH

Examiner insight: In this MCQ, only the acid product appears in the options, so selecting C₆H₅COOH secures the mark.

Quick self-check

🧠 10-second method for similar questions

Spot the ester linkage idea: name includes …oate / …carboxylate.
Identify the acyl (acid) part from the “...oate”/“...carboxylate”.
Hydrolysis gives the corresponding carboxylic acid (easy mark).

❌ Trap to avoid

Don’t invent products based on “benzene” words. Always map ester hydrolysis to: acid + alcohol/phenol .