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S6 Chemistry: Polymers and Plastics (Paper 4: Error Clinic)
S6 Chemistry: Polymers and Plastics (Paper 4: Error Clinic)
Ten items retraining three common slips: monomer against repeat unit, water masses and mass percentages.
Direct answers Answers in order: no, C2H4, a condensation polymer (a polyamide), 56.8 per cent, 1 000, dilute acid or alkali hydrolyses the ester links, 18 g, 192, polyesters such as polylactic acid degrade, 62.5.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: S6 Chemistry: Polymers and Plastics |
| Level | S6 |
02 Questions (10 items)
- FoundationError replay: poly(ethene) is made from ethene. Is any small molecule released during the polymerisation?
- FoundationError replay: a student writes C2H5 for the repeat unit of poly(ethene). What is correct?
- FoundationError replay: a student calls nylon an addition polymer. What is correct?
- IntermediateError replay: a student answers 35.5 per cent for the mass percentage of chlorine in PVC. What is correct?
- IntermediateError replay: a student divides 28 000 by 28 and answers 999 for the degree of polymerisation. What is correct?
- IntermediateError replay: a student says a polyester cannot be hydrolysed. What is correct?
- ChallengeError replay: 1.0 mol of a diamine and 1.0 mol of a diacid condense fully and a student answers 36 g of water. What is correct?
- ChallengeError replay: a student obtains 228 for the PET repeat unit. What is correct?
- ChallengeError replay: a student claims every plastic is non-biodegradable. What is correct?
- Error redoError replay: a student uses 28, the mass of ethene, for the PVC repeat unit. What is the correct repeat unit mass?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | No | Addition opens the double bond into single bonds and every atom stays inside the polymer. |
| 2 | C2H4 | The repeat unit keeps all the atoms of the monomer, and ethene is C2H4, so the repeat unit matches. |
| 3 | A condensation polymer, a polyamide | Nylon forms from a diamine and a diacid with loss of water, so it carries amide links and is a condensation polymer. |
| 4 | 56.8 per cent | 35.5 is only the relative atomic mass of chlorine; divide it by the 62.5 repeat unit to get a percentage. |
| 5 | 1 000 | 28 000 divides exactly by 28 to give 1 000, and there is no reason to take one away. |
| 6 | Dilute acid or alkali hydrolyses the ester links | An ester link is a functional group that acid or alkali can break, so a polyester degrades where poly(ethene) does not. |
| 7 | 18 g | One to one monomers give one water per repeat unit, so 1.0 mol of water weighs 18 g. |
| 8 | 192 | Adding 62 and 166 gives the monomers; subtract the 36 from two waters to obtain the repeat unit. |
| 9 | Polyesters such as polylactic acid do degrade | Polylactic acid is a polyester with hydrolysable ester links, so it breaks down under composting conditions. |
| 10 | 62.5 | C2H3Cl is 24 plus 3 plus 35.5, giving 62.5, because chlorine makes the repeat unit heavier. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
Write three numbers at the top of your notes: repeat units 28, 62.5 and 192.Tutor Registration →
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