Alkenes & polymers
Edexcel GCSE Chemistry revision on Alkenes & polymers. Aligned to the Pearson Edexcel GCSE Chemistry 1CH0 specification. This bank has 8 practice questions on this topic.
Sample questions (3 of 8)
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Question 1
The general formula for alkenes is...
- A) CnH2n+2
- B) CnH2n
- C) CnH2n-2
- D) CnHn
Show answer
Answer: CnH2n
Alkenes: ethene C2H4, propene C3H6, butene C4H8. Have a C=C double bond -> 'unsaturated'. Much more REACTIVE than alkanes (the double bond is reactive). Used as monomers to make polymers. Test for alkenes: bromine water (orange) -> decolourised (becomes colourless) when bromine reacts with the double bond.
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Question 2
The test that distinguishes an alkene from an alkane is...
- A) Lit splint - alkenes don't burn
- B) Bromine water
- C) Boiling point
- D) Density
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Answer: Bromine water
Bromine water test: orange bromine water added. Alkene: bromine ADDS across the double bond -> colourless dibromo compound. Alkane: no reaction, water stays orange. The C=C of the alkene is reactive. e.g. ethene + Br2 -> 1,2-dibromoethane (colourless).
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Question 3
Polymerisation involves...
- A) Splitting big molecules
- B) Many small monomers joining together to form long polymer chains
- C) Adding water
- D) Cooling rapidly
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Answer: Many small monomers joining together to form long polymer chains
ADDITION polymerisation: alkene monomers' double bonds break + reform as single bonds linking the monomers. Example: many ethene (C2H4) monomers -> poly(ethene) [-CH2-CH2-]n. No atoms lost (no by-product). The polymer is a long chain (thousands of repeat units). Polythene, PVC, polypropene, polystyrene all made this way.
Want to test yourself on the remaining cards for this topic?
5 more questions on Alkenes & polymers — plus mistakes tracking and spaced repetition across the whole Chemistry spec.