How are plastics made from alkenes, and why are they hard to dispose of?
Addition polymerisation of alkenes, drawing the repeat unit, the uses of common polymers, and the problems of polymer waste and disposal.
A focused answer to WJEC GCSE Chemistry topic 2.5 on polymers, covering how alkene monomers join by addition polymerisation, how to draw the repeat unit, the uses of common plastics, and the environmental problems of polymer waste and its disposal.
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What this topic is asking
WJEC wants you to explain how alkenes form polymers by addition, draw a repeat unit, and discuss the problems of plastic waste. This is part of topic 2.5 Crude oil, fuels and organic chemistry in Unit 2 of WJEC GCSE Chemistry (3430).
Addition polymerisation
Drawing the repeat unit
Uses of common polymers
Problems of polymer waste
Try this
Q1. Name the type of reaction that joins alkene monomers into a polymer. [1 mark]
- Cue. Addition polymerisation.
Q2. State one reason plastic waste is a problem. [1 mark]
- Cue. Most plastics are non-biodegradable, so they build up in landfill and the oceans.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC 20203 marksExplain how ethene molecules join together to make poly(ethene), naming the type of reaction.Show worked answer β
A topic 2.5 Explain question. The reaction is addition polymerisation (1 mark). Many small ethene molecules (the monomers), each with a C=C double bond, join together when the double bonds open up (1 mark). They link into one very long molecule, the polymer poly(ethene), with no other product formed (1 mark). Markers reward naming addition polymerisation, the opening of the double bonds, and the joining of many monomers into one long chain. A common error is to say a small molecule like water is also produced (that is condensation, not addition).
WJEC 20234 marksDiscuss the problems caused by disposing of plastics and two ways these problems can be reduced.Show worked answer β
A topic 2.5 discussion question. Most plastics are non-biodegradable, so they are not broken down by microbes and build up in landfill and oceans, harming wildlife (1 mark); burning them can release toxic gases and carbon dioxide (1 mark). Ways to reduce the problem (any two): recycling plastics so they are reused rather than dumped (1 mark); reducing use and reusing items, or developing biodegradable plastics (1 mark). Markers reward the disposal problems and two valid solutions. A common error is to give only the problems without the solutions.
Related dot points
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A focused answer to WJEC GCSE Chemistry topic 2.5 on crude oil, covering crude oil as a finite mixture of hydrocarbons, how fractional distillation separates it by boiling point, and how the properties of the fractions change down the column.
- Alkanes and alkenes as homologous series, the test for unsaturation, combustion of hydrocarbons, and cracking to make smaller alkanes and alkenes.
A focused answer to WJEC GCSE Chemistry topic 2.5 on alkanes and alkenes, covering their general formulae, the bromine water test for alkenes, complete and incomplete combustion, and how cracking converts large hydrocarbons into smaller alkanes and useful alkenes.
- Alcohols as a homologous series, the functional group, and the production of ethanol by fermentation and by hydration of ethene.
A focused answer to WJEC GCSE Chemistry topic 2.5 on alcohols, covering the alcohol homologous series and the -OH functional group, the uses of ethanol, and how ethanol is produced by fermentation of sugars and by the hydration of ethene.
Sources & how we know this
- WJEC GCSE Chemistry specification (3430) from 2016 β WJEC (2016)