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A2 · Practice questions · Degradable polymers

Give it a weak spot.

Six original Cambridge-style questions on degradable polymers.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Hydrolysis at the link, or UV at the C=O.

01
Explain
[3 marks]

Explain why poly(lactic acid) is biodegradable but poly(propene) is not.

  • Poly(lactic acid) is a polyester with ester links containing a polar C=O; the δ+ carbon is attacked by water (catalysed by acid, alkali or enzymes). ✓
  • Hydrolysis breaks the chain back to lactic acid. ✓
  • Poly(propene) has only non-polar C–C and C–H bonds, so there is no site for hydrolysis or enzyme attack. ✓
02
Recall
[2 marks]

Give the structures of the organic products when nylon-6,6 is heated with excess NaOH(aq).

  • Sodium hexanedioate, NaOOC(CH2)4COONa. ✓
  • Hexane-1,6-diamine, H2N(CH2)6NH2. ✓
03
Recall
[2 marks]

Give the structures of the organic products when PET is heated with dilute hydrochloric acid.

  • Benzene-1,4-dicarboxylic acid, HOOCC6H4COOH. ✓
  • Ethane-1,2-diol, HOCH2CH2OH. ✓
04
Explain
[2 marks]

Explain how a photodegradable polymer breaks down, and state one limitation.

  • Carbonyl (C=O) groups in the chain absorb ultraviolet radiation, and the energy breaks bonds near them, splitting the chain into small pieces. ✓
  • Limitation: it needs light, so buried or covered waste does not degrade (and fragments may persist as microplastics). ✓
05
Analysis
[3 marks]

Compare incineration and landfill as ways of disposing of poly(chloroethene), PVC.

  • Landfill: PVC is non-biodegradable, so it persists for centuries and uses up land. ✓
  • Incineration destroys it and can recover energy, but produces CO2 (greenhouse gas) and toxic HCl. ✓
  • HCl must be removed from flue gases (for example with a base); incomplete burning can form dioxins. ✓
06
Calculation
[2 marks]

1.92 g of PET (repeat unit Mr 192) is completely hydrolysed by acid. Calculate the mass of benzene-1,4-dicarboxylic acid (Mr 166) formed.

  • n(repeat units) = 1.92 ÷ 192 = 0.0100 mol, each giving one molecule of the acid. ✓
  • Mass = 0.0100 × 166 = 1.66 g. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.