3.2Chemistry In Society
Plastics — SQA National 5 Chemistry — SQA National 5 Chemistry Revision Notes & Topical Questions
5 min read 2 parts Lesson 2 of 5
Section 1 of 2Addition polymerisation
1Polymers
2Addition polymerisation3 points
- Monomers must contain a carbon-carbon double bond (C=C) (alkenes).
- During polymerisation, the double bond opens up to form single bonds linking adjacent monomer units.
- Example: Poly(ethene) from ethene: n(CH2=CH2) → -[CH2-CH2]n-
3Naming polymers3 points
- Ethene → Poly(ethene)
- Propene → Poly(propene)
- Phenylethene (styrene) → Poly(phenylethene) / Polystyrene
4Deducing monomer from repeating unit
Section 2 of 2Types of plastics and environmental impact
| Type | Structure | Thermal Behavior | Common Uses |
|---|---|---|---|
| Thermoplastic (thermosoftening) | Linear polymer chains held by weak intermolecular forces; no cross-links | Melts and softens when heated; can be reshaped repeatedly | Polythene bags, drink bottles (PET), food tubs |
| Thermosetting | Polymer chains permanently interconnected by strong covalent cross-links | Does not melt on heating; chars and decomposes at high temperature | Electrical plug sockets, saucepan handles, epoxy resins |
- Disposal issuesMost synthetic plastics are non-biodegradable and persist in landfills or oceans for centuries.
- Incineration can produce toxic gases like hydrogen chloride or carbon monoxide.
- Biodegradable plastics made from plant starches offer eco-friendly alternatives.
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🌳 Student Search Tree & Frequently Asked Exam Questions: plastics
Step-by-step problem-solving guide, mark scheme criteria, and experimental error analysis curated by Dr. Khaled Dabour (DABOURHUB).
1. Identify all given values and convert non-standard units, 2. State the primary formula or physiological/chemical principle, 3. Calculate to 3 significant figures and clearly state units.
Avoid confusing independent vs dependent variables in practical questions. In calculation questions, double-check percentage change formula: (change / original) × 100.
Where can I find plastics past paper questions by topic with the mark scheme?
On DABOURHUB every plastics question is grouped by syllabus point and shown with the mark-scheme wording, so you can see exactly which sentence earns the mark instead of scrolling through whole year papers.
What is the most common plastics exam question and why do students lose marks on it?
The repeated pattern on IGCSE papers is a short stem that asks you to apply plastics and then justify it with a command word (explain, suggest, compare). Marks are lost by stating the fact without linking it back to the wording of the question, so each plastics item here is written as a full-mark answer.
Is there an alternative to Save My Exams or Physics and Maths Tutor for plastics?
Yes: the plastics notes, topical questions and MCQ quizzes on this site follow the same syllabus headings as the official specification, and they open straight from the search result with no download step.
How do I revise plastics in two weeks before the exam?
Three passes: read the plastics notes once, then do the topical questions and mark them against the mark scheme, then redo only the ones you missed. The quiz on the page gives instant feedback so the third pass takes minutes rather than an evening.