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AS · Practice questions · Addition polymerisation

Open the double bond.

Six original Cambridge-style questions on addition polymerisation.

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

Two carbons in the backbone, everything else hangs off.

01
Recall
[3 marks]

Write the repeat unit of the addition polymer formed from (a) ethene, (b) chloroethene, (c) tetrafluoroethene.

  • (a) [–CH2–CH2–]n. ✓
  • (b) [–CH2–CHCl–]n. ✓
  • (c) [–CF2–CF2–]n. In each, the C=C has become C–C and a bond extends through each bracket. ✓
02
Analysis
[2 marks]

A section of an addition polymer is –CH2–CH(CN)–CH2–CH(CN)–CH2–CH(CN)–. Give the structural formula of the monomer and draw the repeat unit.

  • The repeating 2-carbon unit is CH2–CH(CN), so the monomer is CH2=CHCN (propenenitrile). ✓
  • Repeat unit: [–CH2–CH(CN)–]n. ✓
03
Calculation
[2 marks]

A sample of poly(chloroethene) has an average Mr of 1.25 × 105. Calculate the average number of monomer units per chain, and explain why the repeat unit has the same Mr as the monomer. (Ar: C 12.0, H 1.0, Cl 35.5)

  • Mr(C2H3Cl) = 24.0 + 3.0 + 35.5 = 62.5, so n = 1.25 × 105 ÷ 62.5 = 2.00 × 103. ✓
  • Addition polymerisation forms no by-product: only the π bond rearranges, so the repeat unit contains exactly the atoms of one monomer. ✓
04
Explain
[2 marks]

Explain why poly(ethene) is chemically unreactive and why this makes it non-biodegradable.

  • Poly(ethene) is saturated: it has only strong, non-polar C–C and C–H σ bonds and no C=C or polar groups to attack. ✓
  • Microorganisms and enzymes cannot break these bonds, so the polymer is not broken down and persists in landfill. ✓
05
Calculation
[3 marks]

1.00 kg of PVC waste is burned completely. Write an equation per repeat unit and calculate the mass and the volume at room conditions of hydrogen chloride produced. (Mr C2H3Cl 62.5, HCl 36.5; molar gas volume 24.0 dm3 mol−1)

  • C2H3Cl + 2.5O2 → 2CO2 + H2O + HCl. ✓
  • n(repeat units) = 1000 ÷ 62.5 = 16.0 mol, so n(HCl) = 16.0 mol and mass = 16.0 × 36.5 = 584 g. ✓
  • Volume = 16.0 × 24.0 = 384 dm3. ✓
06
Explain
[3 marks]

Discuss the problems of disposing of poly(alkene) waste by landfill, by incineration and by recycling.

  • Landfill: poly(alkenes) are non-biodegradable, so they persist for centuries and use up land. ✓
  • Incineration: releases CO2 (global warming) and toxic CO if combustion is incomplete; PVC also releases toxic, acidic HCl that must be removed from the waste gases. ✓
  • Recycling: plastics must be collected and sorted by type, which is costly, and the polymer degrades with each cycle. ✓

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.