Propene can be produced by cracking hydrocarbons from crude oil. Describe how propene can be used to make a polymer, and explain why propene is described as unsaturated.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Propene is an alkene, containing a carbon–carbon double bond.
In addition polymerisation, many propene molecules join together. The double bond in each propene opens, breaking the C=C bond, so the carbon atoms form new single bonds with adjacent monomers.
The resulting long‑chain polymer is poly(propene), a repeating unit of –CH₂–CH(CH₃)–.
Propene is described as unsaturated because it contains a C=C double bond and therefore does not have the maximum number of hydrogen atoms a saturated hydrocarbon of the same formula would possess.
In addition polymerisation, many propene molecules join together. The double bond in each propene opens, breaking the C=C bond, so the carbon atoms form new single bonds with adjacent monomers.
The resulting long‑chain polymer is poly(propene), a repeating unit of –CH₂–CH(CH₃)–.
Propene is described as unsaturated because it contains a C=C double bond and therefore does not have the maximum number of hydrogen atoms a saturated hydrocarbon of the same formula would possess.
Examiner tips
- Use the term ‘alkene’ and ‘double bond’ when describing propene.
- Explain that the double bond opens during addition polymerisation.
- Mention the product as poly(propene) with repeating units.
- Show the mechanism of bond breaking and new single bonds forming.
Common mistakes
- Calling propene a saturated compound.
- Forgetting to state that the double bond opens during polymerisation.
- Describing the polymer as a random mixture instead of a long‑chain repeating unit.
Mark scheme (5 marks)
- Propene is an alkene / contains a carbon–carbon double bond
- Unsaturated means the molecule contains a carbon–carbon double bond / does not contain the maximum number of hydrogen atoms
- Many propene monomers join together to form the polymer / addition polymerisation occurs
- The double bond in propene opens / breaks to allow monomers to join together
- The polymer formed is poly(propene) / a long-chain molecule with repeating units
Key terms in this question
Related
- All AQA A-Level Chemistry (7405) revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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