Exam Practice

Topic 3.3.12: Polymers

Test your understanding of addition and condensation polymers, and compare their biodegradability and disposal.

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📋 Structured Questions

Question 1: Addition vs Condensation

6 marks

(a) Describe two differences in the formation of addition polymers compared to condensation polymers. [2]

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  • Addition polymerisation requires unsaturated monomers (alkenes with C=C double bonds), whereas condensation polymerisation requires monomers with two functional groups [1]
  • Addition polymerisation forms only the polymer (100% atom economy), whereas condensation polymerisation also eliminates a small molecule (such as H2O or HCl) [1]

(b) Explain why poly(ethene) is non-biodegradable, whereas polyesters like Terylene are biodegradable. Refer to chemical bonding in your answer. [4]

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  • Poly(ethene) has a non-polar carbon-carbon (C-C) backbone [1]
  • These C-C bonds are strong and inert, meaning they cannot be attacked by nucleophiles (such as water) [1]
  • Terylene contains polar ester linkages (-COO-) in its backbone [1]
  • The carbonyl carbon is electron-deficient (delta-positive) and can be attacked by nucleophiles (like water or hydroxide ions), allowing the polymer chain to undergo hydrolysis and break down [1]
Examiner tip: Always structure answers by comparing the polarity of the bonds in the backbones. Non-polar C-C bonds resist attack; polar C-O or C-N bonds can be hydrolysed.

Question 2: Polyamides

6 marks

(a) Write the IUPAC names or draw the structures of the two monomers used to form Nylon-6,6. [2]

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  • Monomer 1: 1,6-diaminohexane (or H2N-(CH2)6-NH2) [1]
  • Monomer 2: hexanedioic acid (or HOOC-(CH2)4-COOH) [1]

(b) Nylon-6,6 can be hydrolysed under acidic conditions. Write the structures of the organic products formed when a repeating unit of Nylon-6,6 is completely hydrolysed using hot aqueous hydrochloric acid. [2]

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  • Hexanedioic acid: HOOC-(CH2)4-COOH [1]
  • Protonated 1,6-diaminohexane salt: +H3N-(CH2)6-NH3+ (or Cl-+H3N-(CH2)6-NH3+Cl-) [1]
Examiner tip: Under acidic conditions, the amine groups released are protonated to form ammonium salts (+NH3+). The carboxylic acid remains unchanged. If alkaline hydrolysis was used, you would instead get carboxylate salt anions (-COO-) and free neutral amine groups.

(c) Kevlar is a polyamide used in bulletproof vests. Explain how its structure makes it so strong. [2]

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  • The planar benzene rings allow the polymer chains to align parallel and pack closely together [1]
  • This close packing maximizes the extensive hydrogen bonding that forms between N-H and C=O groups of adjacent chains [1]

Question 3: Disposal of Polymers

4 marks

(a) Evaluate the environmental impacts of disposing of polymers via incineration compared to landfill. [3]

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  • Landfill: Uses valuable land space and non-biodegradable polymers persist indefinitely, causing visual pollution and potential microplastic accumulation [1]
  • Incineration (Advantage): Significantly reduces the volume of waste and can generate heat or electricity [1]
  • Incineration (Disadvantage): Releases greenhouse gases (CO2) and can release highly toxic gases, such as acidic HCl from PVC, unless gas scrubbers are used [1]

(b) Explain why sorting polymers is a major challenge in the recycling process. [1]

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Waste contains a complex mixture of different polymer types (with different properties and melting points) which must be separated before melting/processing, which is expensive and labor-intensive [1]

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