AQA · A-Level · Chemistry
Course version: 7405 · Version from Sept 2016
Alkenes produced by this method can be used to produce addition polymers…
Full specification wording
Elimination: Alkenes produced by this method can be used to produce addition polymers without using monomers derived from crude oil.
Ethene is normally cracked from crude oil fractions, but there is another route.
Checked against the AQA 7405 specification (opens in a new tab) on .
- Point 3 of 5
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Ethene is normally cracked from crude oil fractions, but there is another route. Sugar from a crop is fermented to ethanol, the ethanol is dehydrated over an acid catalyst to ethene, and that ethene is polymerised to poly(ethene). The carbon in the polymer then comes from carbon dioxide fixed by a plant in the last growing season rather than from a finite fossil resource, so the process conserves crude oil and is renewable in principle. The polymer itself is chemically identical to poly(ethene) from oil, so it is no more biodegradable. The route also has real costs: land, fertiliser and water for the crop, and a large energy input to distil and dehydrate the ethanol.
What earns the marks
- The route, sugar to ethanol by fermentation, ethanol to ethene by dehydration, ethene to poly(ethene) by addition polymerisation.
- Saying the monomer comes from a renewable plant source rather than crude oil.
- A sustainability advantage, such as conserving a finite resource.
- A limitation, such as land use or the energy needed for distillation and dehydration.
Common mistakes and how to put them right
Claiming the polymer made this way is biodegradable, when it is the same compound as poly(ethene) from oil.
Calling the whole process carbon neutral with no qualification.
Confusing ethanol with ethene in the equations for the two stages.
Saying crude oil is not used at all, ignoring the fuel used to run the process.
Exam tips
- Set the route out as three labelled arrows with reagents and conditions above each.
- Separate the source of the carbon from the properties of the polymer; only the source changes.
- Where the command word is discuss, give one advantage and one disadvantage.
Try the lesson
The start of the Elimination: Alkenes produced by this method can be used to produce addition polymers without using monomers derived from crude oil. lesson, made from checked teaching notes for this specification point.
Have a go first
Ethanol can be dehydrated to ethene, which is then used to make poly(ethene). Which starting material for making ethene does this route avoid relying on?
Listen
Ethene is normally cracked from crude oil fractions, but there is another route. Sugar from a crop is fermented to ethanol, the ethanol is dehydrated over an acid catalyst to ethene, and that ethene is polymerised to poly(ethene). The carbon in the polymer then comes from carbon dioxide fixed by a plant in the last growing season rather than from a finite fossil resource, so the process conserves crude oil and is renewable in principle. The polymer itself is chemically identical to poly(ethene) from oil, so it is no more biodegradable. The route also has real costs: land, fertiliser and water for the crop, and a large energy input to distil and dehydrate the ethanol. A strong answer earns marks for these points. the route, sugar to ethanol by fermentation, ethanol to ethene by dehydration, ethene to poly(ethene) by addition polymerisation. saying the monomer comes from a renewable plant source rather than crude oil. a sustainability advantage, such as conserving a finite resource. a limitation, such as land use or the energy needed for distillation and dehydration. Exam tip: Set the route out as three labelled arrows with reagents and conditions above each.
See it
Key words
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renewable monomer
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fermentation then dehydration
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conserving crude oil
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same polymer, same properties
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See every definition
- renewable monomer
- The monomer comes from a renewable plant source rather than crude oil.
- fermentation then dehydration
- Sugar from a crop is fermented to ethanol, then the ethanol is dehydrated over an acid catalyst to ethene.
- conserving crude oil
- The carbon in the polymer comes from carbon dioxide fixed by a plant rather than from a finite fossil resource.
- same polymer, same properties
- The polymer is chemically identical to poly(ethene) from oil, so it is no more biodegradable.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
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