AQA GCSE Chemistry Chemistry Paper 2 (Higher), November 2021: Question 4

9 marks · Standard Demand difficulty · Short Answer

Answer questions on the polymerisation of ethene, properties of thermosoftening polymers, structures of HDPE and LDPE, and condensation polymerisation to form polyesters.

Practise this question

Question

Question text

04 This question is about poly(ethene) and polyesters.

04.1 Poly(ethene) is produced from ethene.

Figure 3 shows part of the displayed structural formula equation for the reaction.

Complete Figure 3.

[2 marks]

Figure 3

04.2 Poly(ethene) is a thermosoftening polymer.

Suggest why poly(ethene) is easier to recycle than thermosetting polymers.

[2 marks]

04.3 Ethene produces different forms of poly(ethene).

How can different forms of poly(ethene) be produced from ethene?

[1 mark]

04.4 Two different forms of poly(ethene) are:

• high density poly(ethene) (HDPE)

• low density poly(ethene) (LDPE).

*12* Figure 4 represents part of the structures of HDPE and LDPE.

Figure 4

HDPE LDPE

Explain why HDPE has a higher density than LDPE.

[2 marks]

Figure 5 shows three monomers, A, B and C.

Monomer A can react with monomer B and with monomer C to produce polyesters.

Figure 5

04.5 Draw a circle on Figure 5 around an alcohol functional group.

[1 mark]

04.6 Complete Table 2 to show the formula of the small molecule produced when:

• monomer A reacts with monomer B

• monomer A reacts with monomer C.

[1 mark]

Table 2

Reacting monomers Formula of small molecule produced

A and B

A and C

Mark scheme

Show the mark scheme

Question 4

AO /

Question Answers Extra information Mark

Spec. Ref.

04.1 2 AO1

4.7.3.1

if equation incorrect

allow 1 mark for 5 single bonds

allow 1 mark for n

AO /

Spec. Ref.

04.2 allow converse statements

about thermosetting polymers

(poly(ethene)) melts allow thermosoftening 1 AO1

polymers melt

(so) can be reshaped (into new 1 AO3

products)

4.10.3.3

AO /

Spec. Ref.

04.3 use different (reaction) allow use different temperatures 1 AO1

conditions / pressures 4.10.3.3

AO /

Spec. Ref.

04.4 allow converse statements AO3

about LDPE 4.10.3.3

(in HDPE) polymer chains / allow (HDPE has) unbranched 1

molecules are closer together polymer chains / molecules

(so) more atoms per unit volume allow (so) more molecules per 1

unit volume

Question 4 continued

AO /

14 Question Answers Extra information Mark

Spec. Ref.

04.5 circle around HO– or –OH 1 AO2

on monomer A 4.7.2.3

4.7.3.2

AO /

Spec. Ref.

04.6 H2O must be in this order 1 AO3

and 4.7.3.2

HCl

Total 9

How to answer it

AQA GCSE Chemistry: Polymers & Polymerisation

What this question tests

This question assesses fundamental organic chemistry and materials knowledge: writing addition polymerisation equations, explaining why thermosoftening plastics can be recycled, recalling how reaction conditions alter polymer structure (HDPE vs LDPE), identifying functional groups (alcohols vs carboxylic acids), and deducing condensation polymer byproducts.

Question 04.1: Completing the Addition Polymerisation Equation

2 Marks • Assessment Objective: AO1

✅ What to Draw on Figure 3

Complete the repeating unit on the right-hand side:

Change the double bond to a single C–C bond between the two carbon atoms.
Draw extension bonds through each bracket on the sides (showing the chain continues).
Keep the 4 single C–H bonds (two on each carbon).
Add a lowercase letter n as a subscript at the bottom right outside the bracket.

❌ Common Errors to Avoid

Leaving the double bond intact inside the bracket (it must become a single bond!).
Forgetting extension bonds that break through the brackets.
Writing a capital N or putting n in front of the product instead of as a subscript outside the bracket.

Mark Allocation: 1 mark for 5 single bonds (1 central C–C bond + 4 C–H bonds with trailing extension bonds). 1 mark for the subscript n in the correct position.

Question 04.2: Recycling Thermosoftening Polymers

2 Marks • Assessment Objectives: AO1 & AO3

✅ Correct Answer (Two-Step Reason)

Poly(ethene) melts (or softens) when heated.
Therefore, it can be reshaped / remoulded into new products.

🧠 Exam Technique

Always state the physical effect of heating first, then the practical consequence for recycling:

Heating effect: "It melts..." → Outcome: "...so it can be reshaped."

Converse statements are fully accepted: Thermosetting polymers do not melt when heated (they char/burn), so they cannot be reshaped.

Mark Allocation: [1 mark] for states that it melts / softens upon heating. [1 mark] for states that it can be reshaped into new products.

Question 04.3: Producing Different Forms of Poly(ethene)

1 Mark • Assessment Objective: AO1

✅ Correct Answer

Use different reaction conditions.

Also allowed: specify different temperatures, different pressures, or using different catalysts.

💡 Key Knowledge

Both LDPE and HDPE are made from the same monomer (ethene). Their properties differ solely because they are made using different conditions (e.g. high pressure vs lower pressure with a catalyst).

Mark Allocation: [1 mark] for "different conditions" OR "different temperature / pressure / catalyst".

Question 04.4: Explaining HDPE vs LDPE Density

2 Marks • Assessment Objective: AO3

✅ Model Answer

In HDPE, the polymer chains are unbranched, meaning the chains are closer together (pack more tightly).
This means there is more mass / more molecules per unit volume.

❌ Common Errors

Stating HDPE is heavier without referencing volume. Density is mass per unit volume.
Confusing branching: LDPE has branched chains that cannot pack closely; HDPE has unbranched chains that pack neatly together.

Mark Allocation: [1 mark] for polymer chains/molecules are closer together / HDPE is unbranched. [1 mark] for more molecules / atoms / mass per unit volume.

Question 04.5: Identifying an Alcohol Functional Group

1 Mark • Assessment Objective: AO2

✅ What to Circle on Figure 5

Draw a circle around either the HO– or the –OH group on Monomer A.

🧠 Exam Trap: Look at the Whole Group

Do not circle the –OH group on Monomer B! On Monomer B, the –OH is bonded directly to a C=O (carbonyl carbon), making it a carboxylic acid group (–COOH), not an alcohol group.

Mark Allocation: [1 mark] for neatly circling strictly the HO– or –OH group on Monomer A only.

Question 04.6: Byproducts of Condensation Polymerisation

1 Mark • Assessment Objective: AO3

✅ Table 2 Completed

Reacting Monomers	Formula of small molecule
A and B	H₂O
A and C	HCl

💡 How to Work This Out

A + B: Diol loses –H and dicarboxylic acid loses –OH . Combined: H + OH = H₂O (water).
A + C: Diol loses –H and the acyl chloride monomer loses –Cl . Combined: H + Cl = HCl (hydrogen chloride).

Mark Allocation: [1 mark] for both H₂O and HCl written in the correct order. Formulae must have correct subscripts/capitalisation.

Topics

Chemistry · C7: Organic Chemistry · C10: Using Resources

Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 2 (Higher), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.