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O Level Combined Science Chemistry Materials Quiz
Free O Level Combined Sci Chemistry Materials quiz, HY3 Exam version, with questions, answers, and O Level-style practice for Singapore students.
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O-Level Combined Science Quiz - Chemistry Materials: Answer Key
Total Marks: 40
Topic: Chemistry Materials
Section A (1 mark each)
1. C
Metals have metallic bonding with delocalised electrons allowing layers to slide, making them malleable and ductile. A and B are false; D describes ionic/covalent brittle solids.
2. B
Poly(ethene) is made by addition polymerisation where ethene double bonds open and join without losing atoms.
3. C
Cellulose is a natural polymer from plants. Others are synthetic.
4. B
–CH₂–CH₂– is the repeating unit of poly(ethene), an addition polymer of ethene CH₂=CH₂.
5. B
Alloys are mixtures of metals or metal + non-metal (e.g., steel). They are usually harder and conduct electricity.
Section B (2 marks each unless stated)
6. [2]
Property: high melting point (or hard, brittle, conduct when molten).
Explanation: Strong electrostatic forces between oppositely charged ions in a lattice require much energy to overcome.
(Mark: 1 for property, 1 for bonding reason)
7. [2]
Diagram must show: regular rows of circles labelled "positive metal ions" and several dots labelled "delocalised electrons" between them.
Mark: 1 for lattice of positive ions, 1 for delocalised electrons labelled.
8. [1]
Chloroethene (CH₂=CHCl).
9. [2]
Diamond has a giant covalent network where each carbon atom is covalently bonded to four others tetrahedrally. Breaking many strong covalent bonds needs high energy → high mp.
(1 for network description, 1 for bond strength energy link)
10. [2]
Type: addition polymer (e.g., poly(ethene)). Reason: melts and sweet smell are typical of thermosoftening addition plastics.
(1 type, 1 reason)
Section C
11. [4]
(a) [2] Y (metal) has delocalised electrons free to move and carry charge; X (ionic) has ions fixed in lattice, no mobile charge in solid.
(b) [2] Z is simple molecular; weak intermolecular forces need little energy to overcome, so low mp.
12. [3]
Propene CH₂=CHCH₃ double bond breaks; monomers join end-to-end; repeating unit –CH₂–CH(CH₃)–.
Marks: 1 double bond opens, 1 chain forms, 1 correct repeating unit shown.
13. [3]
Uses: bags, pipes, insulation (any 2). Issue: non-biodegradable, persists in landfill/ocean, harms wildlife.
(2 for uses, 1 for issue)
14. [3]
(a) [1] 0.050 mol ethene → 0.050 mol repeating units (1:1).
(b) [2] mass = 0.050 mol × 28 g/mol = 1.4 g.
Working: n × M_r = 0.05 × 28 = 1.4 g.
15. [3]
Graphite: layers of hex rings, delocalised electrons between layers. Diamond: 3D network. Difference: graphite conducts electricity, diamond does not.
(2 structure compare, 1 property diff)
16. [2]
Stainless steel (iron + Cr/Ni) is hard, corrosion-resistant. Suitable as cutlery because it stays sharp and does not rust.
(1 property, 1 suitability)
17. [2]
Type: condensation polymer / thermosetting (e.g., melamine). Reason: cross-linked network prevents melting, chars on heating.
(1 type, 1 reason)
18. [2]
(a) [1] Limewater turns milky/cloudy.
(b) [1] Copper(II) carbonate / calcium carbonate (any decomposing carbonate).
19. [3]
Heat with alkali: nylon (condensation) may release amine/ammonia; poly(ethene) no reaction. Or hydrolysis test: nylon breaks down, PE does not.
(1 test, 2 expected diff)
20. [3]
(a) [1] Shape-memory alloy (e.g., Nitinol).
(b) [2] Application: dental braces / glasses frame. Property: returns to set shape on heating.
(1 app, 1 property link)
Common mistakes flagged:
- Confusing addition vs condensation polymers.
- Forgetting delocalised electrons in metals.
- Using "ions move" for solid ionic conductivity (they don't).
- Omitting units in calculation Q14.