AQA A-Level Chemistry Paper 3, June 2022: Question 28

1 mark · Easy difficulty · Multiple Choice

Identify which polymer is not hydrolysed when heated with aqueous alkali.

Practise this question

Question

Multiple choice question 28 asking: 'Which polymer is not hydrolysed when heated with aqueous alkali?' The options listed are A Kevlar, B Nylon 6,6, C Poly(propene), and D Terylene. Worth 1 mark.
Question text

28 Which polymer is not hydrolysed when heated with aqueous alkali?

[1 mark]

A Kevlar

B Nylon 6,6

C Poly(propene)

D Terylene

Mark scheme

Show the mark scheme Mark scheme table row for question 28 showing the correct answer is C (AO3), awarded 1 mark, identifying Poly(propene).

28 C (AO3) 1 Poly(propene)

How to answer it

AQA A-Level Chemistry • Polymers

Reactivity and Hydrolysis of Addition vs Condensation Polymers

What this question tests

This question tests your ability to classify polymers by their linkage types and predict their chemical stability toward nucleophilic attack (hydrolysis):

  • Distinguishing between addition polymers and condensation polymers (polyesters and polyamides).
  • Understanding why polar linkages (ester -COO- and amide -CONH- ) are susceptible to alkaline hydrolysis by nucleophiles (OH⁻).
  • Recognising the inertness of non-polar carbon–carbon ( C–C ) single-bond backbones in addition polymers.

Question 28: Resistance to Alkaline Hydrolysis

1 Mark (AO3)

✅ Correct Answer

C: Poly(propene)

Poly(propene) is an addition polymer formed from propene monomers. Its polymer backbone consists entirely of non-polar C–C single bonds, which cannot be attacked by nucleophiles like aqueous hydroxide ions (OH⁻).

💡 Key Knowledge: Polymer Classes

  • Kevlar (Option A): A polyamide. Contains polar peptide/amide links ( -CONH- ). Hydrolysed by hot aqueous alkali into benzene-1,4-diamine and benzene-1,4-dicarboxylate salts.
  • Nylon 6,6 (Option B): An aliphatic polyamide. Contains amide links ( -CONH- ). Hydrolysed by hot aqueous alkali into hexane-1,6-diamine and hexanedioate salts.
  • Poly(propene) (Option C): An addition polymer. Contains only non-polar C–C and C–H bonds. Non-biodegradable and inert to acids and alkalis.
  • Terylene / PET (Option D): A polyester. Contains polar ester links ( -COO- ). Hydrolysed by hot aqueous alkali into ethane-1,2-diol and benzene-1,4-dicarboxylate salts.

🧠 Exam Technique: "Odd One Out" Strategy

Multiple-choice polymer reactivity questions almost always pit condensation polymers against addition polymers:

  • Highlight negative qualifiers such as not or except in the question stem.
  • Identify the polymer class of each option:
    • Kevlar = Condensation (Polyamide)
    • Nylon 6,6 = Condensation (Polyamide)
    • Poly(propene) = Addition (Alkene derivative)
    • Terylene = Condensation (Polyester)
  • Condensation polymers are biodegradable/hydrolysable because the carbonyl carbon has a partial positive charge ( Cδ+=Oδ- ) that attracts nucleophiles. Addition polymers lack this and are completely unreactive to hydrolysis.

❌ Common Errors & Misconceptions

  • Misjudging mechanical strength for chemical inertness: Many students select Kevlar because they know it is bulletproof and extremely strong. Mechanical strength (from planar alignment and tight hydrogen bonding) is NOT the same as chemical resistance—Kevlar will readily hydrolyse under prolonged reflux with concentrated acids or bases.
  • Missing the word "not": Glancing too quickly and choosing Terylene or Nylon because they recall learning their hydrolysis reactions in class.

Topics

Organic Chemistry · 3.3.4 Alkenes · 3.3.12 Polymers

Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.