2025 O Level Chem P1 Q38 — Organic Chemistry / Polymers Solution
Question
How many molecules of water are needed to depolymerise this polymer?
Correct answer: C
Video Solution
Explanation
Answer: C. The polymer shown is a polyester. Look closely at the repeat unit: per single repeat, there are four ester linkages (–CO–O–) along the backbone.
Depolymerisation by hydrolysis breaks each ester linkage back into its original diol and diacid components. Each ester linkage requires one water molecule to break: ester + H₂O → carboxylic acid + alcohol.
So per repeat unit: 4 ester linkages × 1 water molecule = 4 H₂O. For n repeat units: 4n water molecules.
Answer C (4n).
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