AQA A-Level Chemistry Paper 3, 2024: Question 31

Core idea (AO1)

• Recognising which polymers do and do not contain hydrolysable functional groups.
• Linking polymer structure (bond type in the backbone) to susceptibility to hydrolysis.

Exam skill

• Multiple choice elimination: identify which options contain amide/ester links vs simple C–C chains.
• Fast recall: addition polymers are generally hardest to hydrolyse.

✅ Correct answer (what scores the mark)

A — polyalkene

Mark breakdown: 1 mark (AO1) for selecting A.

💡 Key knowledge (why A is correct)

• Hydrolysis is cleavage by water of polar functional groups such as esters (–COO–) and amides (–CONH–).
• Polyalkenes are addition polymers with a backbone of C–C and C–H bonds only (non-polar, no hydrolysable linkage).
• Therefore, polyalkenes are most resistant (most difficult to hydrolyse).

🧠 Exam technique (fast elimination)

1. Scan options for condensation polymers (they contain ester/amide links).
2. Eliminate:
   • Polyester → contains ester links → hydrolyses (acid/alkali).
   • Polyamide → contains amide links → hydrolyses (often slower than esters, but still hydrolysable).
   • Protein → polypeptide = polyamide (peptide links) → hydrolysable.
3. Only polyalkene lacks a hydrolysable functional group → choose A.

❌ Common errors (why students lose marks)

• Choosing polyamide/protein because “amides are quite stable” — stability ≠ impossible to hydrolyse. They still have a hydrolysable amide (peptide) bond.
• Forgetting proteins are polyamides (polypeptides), so they can be hydrolysed to amino acids.
• Assuming “hardest to hydrolyse” means “strongest polymer” rather than “contains a bond that hydrolysis can attack”.