OxfordAQA International GCSE Chemistry: Synthetic and naturally occurring polymers (9202) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

This set covers section 3.10.2 Synthetic and naturally occurring polymers, statements a to f, from the OxfordAQA International GCSE Chemistry (9202) specification, Version 6.2, for exams May/June 2018 onwards. No part of this qualification is tiered, so all eleven questions are for you. There is no required practical in 3.10.2; some questions draw on cracking and the bromine water test (3.10.1.3) and on relative formula mass. Questions 6, 10 and 11 are longer problems.

Learn the content first with the polymers study guide and the polymers revision notes. Other topics are on the OxfordAQA chemistry hub; print the course checklist to tick statements off. A free diagnostic shows which topics need work first.

Where needed, use these relative atomic masses: H = 1, C = 12, F = 19.

Questions

1. Ethene and propene can both be used to make polymers.

(a) State what is meant by a monomer. [1] (b) Name the homologous series that ethene and propene belong to. [1]

2. The monomer but-1-ene has the structure CH₂=CH–CH₂CH₃.

Draw the structure of the polymer formed from but-1-ene, showing one repeating section. [2]

3. A section of a polymer chain is shown:

–CH₂–CHF–CH₂–CHF–CH₂–CHF–

(a) Give the structure of the monomer. [1] (b) A technician wants to check that a sample of this polymer contains no unreacted monomer. Describe a chemical test she could use, and give the result if no monomer is present and if monomer is present. [3] (c) One chain of this polymer has a relative formula mass of 23 000. How many monomer units does this chain contain? Show your working. [2]

4. A drinks bottle is made from a thermosoftening polymer. When it is held in very hot water, it goes soft and loses its shape.

Explain why, in terms of the structure of the polymer and intermolecular forces. [3]

5. The casing of an electric socket warms up when the socket is in use. A manufacturer chooses a thermosetting polymer for the casing.

Explain why a thermosetting polymer is more suitable than a thermosoftening polymer for this use. [3]

6. A student is given two samples of poly(ethene), A and B. Each has a volume of 50.0 cm³.

Sample	Mass in g	Behaviour when bent
A	46.0	Bends easily
B	48.0	Stiff, hard to bend

(a) Calculate the density of each sample in g/cm³. [2] (b) Identify which sample is HD poly(ethene). [1] (c) Both samples were made from ethene. Explain why they have different properties. [3] (d) Suggest which sample is better for a squeezable sauce bottle. Give a reason. [1]

7. (a) A chain of poly(propene) has a relative formula mass of 63 000. Calculate the number of propene units in the chain. [2] (b) A plant converts 7.5 tonnes of ethene completely into poly(ethene). State the mass of poly(ethene) formed and explain your answer. [2]

8. Many polymers are not biodegradable.

(a) State what is meant by biodegradable. [1] (b) Explain one problem caused when non-biodegradable polymers are sent to landfill sites. [2] (c) Give one problem caused when non-biodegradable polymers are dropped as litter. [1]

9. New polymers are being developed for many uses.

(a) Small beads of a hydrogel are mixed into the soil around young plants. Suggest a property of the hydrogel that makes it useful here. [1] (b) The polymer chains in this hydrogel are joined by cross-links. Suggest why the beads swell in water but do not dissolve. [2] (c) Researchers are developing a shape memory polymer stitch that tightens once warmed by the body. Suggest one property the polymer needs and one test the team should carry out before it is used in patients. [2]

10. A town council plans to replace ordinary poly(ethene) shopping bags with bags made from poly(ethene) and cornstarch.

Evaluate this plan. [6]

11. Nonane, C₉H₂₀, can be cracked to form hexane and propene.

(a) Complete the equation: C₉H₂₀ → C₆H₁₄ + ______ [1] (b) Describe how bromine water could show which product is unsaturated. [2] (c) Write an equation, using structures, for the polymerisation of propene. [3] (d) A chain of the polymer has a relative formula mass of 50 400. Calculate the number of propene units in the chain. [2] (e) Poly(propene) is a thermosoftening polymer. Explain why waste poly(propene) can be melted and remoulded into new objects. [2]

Answers

1. (a) A small molecule that joins with many others to form a polymer [1] (b) Alkenes [1] Examiner insight: In (a) “a small unit” alone is vague; say it is a molecule and that many join to make a polymer.

2. Two carbons joined by a single bond, one carrying two H atoms and the other carrying one H and a CH₂CH₃ side group [1]; bonds extending through brackets on each side, with n after the closing bracket [1]:

      H   CH₂CH₃
      |   |
   —( C — C )—
      |   |
      H   H   n

Examiner insight: The CH₂CH₃ group must hang off the chain; drawing all four carbons in a line suggests the side group was part of the double bond and is unlikely to be credited.

3. (a) CH₂=CHF [1] (b) Shake the sample with bromine water [1]. No monomer: the bromine water stays orange [1]. Monomer present: it turns from orange to colourless [1]. (c) Mr of CH₂=CHF = (2 × 12) + (3 × 1) + 19 = 46 [1]; 23 000 ÷ 46 = 500 units [1] Examiner insight: Bromine water is already a clear (see-through) liquid, so write “colourless” for the result; “clear” does not describe a colour change.

4. The polymer is made of separate, tangled chains with no cross-links [1]. The chains are held to each other only by weak intermolecular forces [1]. Heat gives the chains enough energy to overcome these forces, so the chains slide past each other and the bottle softens [1]. Examiner insight: Saying the covalent bonds break is wrong chemistry and is likely to cost credit; the bonds within each chain stay intact.

5. A thermosetting polymer has cross-links between its chains [1]. The cross-links are strong covalent bonds, so the chains cannot slide past each other [1]. The casing therefore does not soften or melt when it warms up and keeps its shape [1]. Examiner insight: A bare “it is stronger” is unlikely to gain credit; the answer needs cross-links, the type of bond, and the effect on heating.

6. (a) Density = mass ÷ volume. A: 46.0 ÷ 50.0 = 0.920 g/cm³ [1]; B: 48.0 ÷ 50.0 = 0.960 g/cm³ [1] (b) B (higher density) [1] (c) They were made using different catalysts and reaction conditions [1]. This gives chains with different amounts of branching: B has few branches, A has many [1]. B’s straighter chains pack more closely, so its density is higher and the intermolecular forces between chains are stronger, making it stiffer [1]. (d) A, because it bends easily (it is flexible) [1]. Examiner insight: In (c) “they are different polymers” is wrong; both are poly(ethene), so the answer must point to the conditions of manufacture.

7. (a) Mr of propene, C₃H₆ = (3 × 12) + (6 × 1) = 42 [1]; 63 000 ÷ 42 = 1500 units [1] (b) 7.5 tonnes [1]. Poly(ethene) is the only product, so all the mass of ethene ends up in the polymer [1]. Examiner insight: In (b) the question asks you to explain, so a mass with no reason is incomplete; say that the polymer is the only product.

8. (a) It can be broken down by microbes [1]. (b) The polymers are not broken down, so they stay in the landfill for a very long time [1]. Landfill sites fill up and new sites need more land [1]. (c) Litter lasts for years and can harm animals that eat it or get trapped in it (or it spoils the appearance of an area) [1]. Examiner insight: “Breaks down naturally” in (a) is not enough; the definition needs microbes.

9. (a) It absorbs and holds a large amount of water, releasing it to the plants slowly [1]. (b) Water molecules move into the spaces between the chains, so the beads swell [1]. The cross-links are covalent bonds that hold the chains together, so the chains cannot separate and spread out into the water [1]. (c) Property: it must change shape at body temperature (or be safe and not toxic in the body) [1]. Test: check that the polymer tightens at body temperature, or test it for safety on cells or in trials before use in people [1]. Examiner insight: “Suggest” questions accept any sensible answer, but each must be linked to the stated use; a general property such as “strong” with no reason is weak.

10. For: microbes can break down the cornstarch, so the bags fall apart more easily [1], meaning less long-lasting litter and less waste building up in landfill [1]. Cornstarch comes from plants, a renewable resource, so less crude oil is used per bag [1]. Against: the poly(ethene) part is still not biodegradable, so small fragments remain in the environment [1]. Land is needed to grow the crop for cornstarch, which could otherwise grow food (or breakdown needs microbes, water and air, which may be limited in landfill) [1]. Conclusion: a justified judgement, for example that the plan reduces the problem but does not remove it, so it should be combined with reuse of bags [1]. Examiner insight: With the command word evaluate, give benefits and drawbacks of the plan and finish with a judgement that follows from them; listing only benefits is unlikely to reach full credit.

11. (a) C₃H₆ [1] (b) Add bromine water to each product and shake [1]. Propene turns it from orange to colourless; hexane leaves it orange [1]. (c) n in front of the propene monomer [1]; chain unit showing C–C (no double bond) with CH₃ as a side group [1]; bonds through the brackets and n after the closing bracket [1]:

     H   CH₃            H   CH₃
     |   |              |   |
 n   C = C     →     —( C — C )—
     |   |              |   |
     H   H              H   H   n

(d) Mr of C₃H₆ = 42 [1]; 50 400 ÷ 42 = 1200 units [1] (e) The chains are not joined by cross-links and are held together only by weak intermolecular forces [1]. On heating these forces are overcome so the polymer melts, and on cooling they re-form in the new shape [1]. Examiner insight: In (c) check the left-hand side as well as the polymer; leaving out the n before the monomer means the equation does not balance.

Where marks are usually lost

• Leaving a C=C in the drawn polymer, or drawing a chain with no bonds through the brackets.
• Forgetting n, or putting n only on one side of a polymerisation equation.
• Putting the side group into the main chain.
• Saying heating breaks the covalent bonds in a thermosoftening polymer.
• Calling cross-links weak forces.
• Writing “clear” instead of “colourless” for decolourised bromine water.
• Explaining HD and LD differences as “different monomers”.
• Defining biodegradable without microbes.
• Giving only advantages when the command word is evaluate.

Next steps

• Polymers revision notes
• Back to the polymers study guide
• Bonding, structure and properties practice
• Quantitative chemistry practice
• OxfordAQA chemistry topics hub
• Printable course checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

OxfordAQA International GCSE Chemistry (9202) specification, Version 6.2, for exams May/June 2018 onwards, published by OxfordAQA. Unit covered: 3.10.2 Synthetic and naturally occurring polymers, statements a to f, with links to 3.10.1.3.