Alkenes are unsaturated hydrocarbons that can undergo addition polymerisation. Explain how monomers of ethene form poly(ethene) and describe one property of poly(ethene) that makes it suitable for use as a plastic packaging material.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Poly(ethene) is one of the most widely produced plastics in the world. It is made from ethene, a small molecule obtained from cracking fractions of crude oil.
Model answer (5 marks)
Ethene has a C=C double bond.
During addition polymerisation the double bond opens, allowing the monomers to link.
Many ethene molecules join to give a long polymer chain.
Only the polymer is produced – no other product.
Poly(ethene) is flexible and lightweight, making it suitable for packaging.
During addition polymerisation the double bond opens, allowing the monomers to link.
Many ethene molecules join to give a long polymer chain.
Only the polymer is produced – no other product.
Poly(ethene) is flexible and lightweight, making it suitable for packaging.
Examiner tips
- Use the word ‘addition polymerisation’ and mention the opening of the C=C bond.
- Show that the reaction gives only the polymer, no by‑products.
- State a specific property such as flexibility or lightweight that is relevant to packaging.
Common mistakes
- Failing to mention the opening of the double bond.
- Claiming that other products are formed.
- Giving a property that is not relevant to packaging.
Mark scheme (5 marks)
- Ethene molecules contain a C=C double bond
- The double bond opens/breaks during addition polymerisation
- Many ethene monomers join together to form a long polymer chain
- No other product/by-product is formed (addition polymerisation produces only the polymer)
- A named property of poly(ethene) that makes it suitable for packaging, e.g. it is flexible / lightweight / does not react with food / waterproof / can be moulded into different shapes
Key terms in this question
addition polymerisation · monomer · polymer · unsaturated
Related
- All Edexcel A-Level Chemistry (9CH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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