Polymers: Practice Questions

These are original questions written for Marlbridge, in the style and at the standard of the examination. They are not reproduced past-paper questions — examination boards hold copyright in their own papers. Use these alongside the official past papers available free from your board.

Related: Polymers revision notes

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Section A

1. Define the terms monomer, polymer and repeat unit. [3]

2. Name the polymer made from each monomer: ethene, propene, chloroethene. [3]

Section B

3. Poly(ethene) is made from ethene.

(a) Describe what happens to the double bond during polymerisation. [2] (b) Draw or describe the repeat unit, explaining the two features that must be shown. [3] (c) Beyond the specification — not examinable, background only (“atom economy” is not a defined term in 0620/5070). Explain why no reactant mass is wasted in addition polymerisation.

4. Explain why most addition polymers are non-biodegradable, and give two environmental consequences. [4]

5. Compare three methods of disposing of waste plastic, giving one advantage and one disadvantage of each. [6]

6. Explain the difference between addition and condensation polymerisation, and give one example of a condensation polymer with the linkage it contains. [4]

7. A sample of poly(chloroethene) (PVC) has the repeat unit –[CH₂–CHCl]–.

(a) Deduce the structure of the monomer used to make this polymer, explaining your method. [3] (b) State the type of polymerisation used, and explain how you can tell from the repeat unit alone. [2]

8. Proteins and nylon both contain the same type of linkage.

(a) Name the linkage common to both, and name the natural monomers that join to form it in proteins. [2] (b) Explain, with reference to hydrolysis, what this linkage breaks down into in each case. [2] (c) Beyond the specification — not examinable, background only. Starch and cellulose are natural polymers of glucose. Name the linkage joining glucose units, and state the product of hydrolysing starch.

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Answers

1. Monomer — a small molecule that joins to others to form a polymer [1]. Polymer — a very long molecule made of many repeating units joined together [1]. Repeat unit — the smallest section of the chain that repeats along its length [1].

2. Poly(ethene) [1]; poly(propene) [1]; poly(chloroethene) or PVC [1].

3. (a) The C=C double bond breaks, becoming a single bond [1], leaving each carbon free to bond to the next monomer [1]. (b) –[CH₂–CH₂]– with n outside the bracket [1]; the bonds must extend through the brackets to show the chain continues [1] and there must be no double bond [1]. (c) (Background only — not examinable.) All of the atoms in the monomer end up in the polymer; there is no other product, so none of the reactant mass is wasted.

4. The chain has a backbone of strong, non-polar C–C bonds [1] that cannot be attacked by water or by the enzymes microorganisms produce [1]. Consequences: waste accumulates in landfill for hundreds of years, taking up space [1]; plastics enter rivers and oceans where animals ingest or become entangled in them [1].

5. Landfill — cheap and simple [1]; but uses up land and the plastic remains for centuries, and toxic additives may leach out [1]. Incineration — reduces volume greatly and the heat can generate electricity [1]; but produces carbon dioxide and, from PVC, toxic gases such as hydrogen chloride and dioxins [1]. Recycling — conserves crude oil as a finite raw material and reduces landfill [1]; but plastics must be sorted by type, which is labour-intensive and costly, and the recycled material is often of lower quality [1].

6. In addition polymerisation, unsaturated monomers join with no other product [1]. In condensation polymerisation, each monomer has two functional groups and a small molecule such as water is eliminated at each link [1]. Example: nylon, which contains amide linkages [1] [1]. (Or a polyester containing ester linkages.)

7. (a) Working backwards: put the double bond back between the two carbons and remove the extending bonds [1], giving CH₂=CHCl [1], chloroethene [1]. (b) Addition polymerisation [1]; the repeat unit shows only a two-carbon unit joined by single C–C bonds with no other linking group — no ester or amide link and no small molecule needed to explain how the units joined, which is the signature of addition rather than condensation [1].

8. (a) The amide (peptide) linkage, –CONH– [1]; amino acids [1]. (b) Hydrolysis breaks the amide linkage back into its original monomers in both cases [1]: in nylon this regenerates the diamine and diacid used to make it, and in protein it regenerates the amino acids that made up the chain [1]. (c) (Background only — not examinable.) The glycosidic linkage; hydrolysing starch produces glucose.

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Where marks are usually lost

• Leaving the double bond in the repeat unit.
• Forgetting the bonds must pass through the brackets.
• Giving an advantage of recycling without acknowledging the sorting problem.
• Saying condensation polymers waste no reactant mass — unlike addition polymerisation, a small molecule (e.g. water) is also produced.
• Trying to “work backwards” from a repeat unit by simply deleting the brackets and n, without putting the double bond back in — the double bond has to be reinserted between the two carbons that were joined by single bonds in the polymer.
• Describing proteins as synthetic polymers, or forgetting that the same amide linkage found in nylon also holds proteins together — this is exactly why the two are compared so often.

Both new questions above rely on running the logic of the Polymers revision notes in reverse — deducing a monomer from a given repeat unit, or a linkage’s breakdown products from hydrolysis — rather than only building a polymer forwards from its monomer, which is the direction most textbook questions default to.