AQA · A-Level · Chemistry
Course version: 7405 · Version from Sept 2016
Common uses of esters (eg in solvents, plasticisers, perfumes and food…
Full specification wording
Carboxylic acids and esters (A-level only): Common uses of esters (eg in solvents, plasticisers, perfumes and food flavourings).
Esters are volatile and have strong, pleasant smells, which is why they are used in perfumes and food flavourings; short-chain esters are what a pear drop or a banana sweet is imitating.
Checked against the AQA 7405 specification (opens in a new tab) on .
- Point 3 of 8
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Esters are volatile and have strong, pleasant smells, which is why they are used in perfumes and food flavourings; short-chain esters are what a pear drop or a banana sweet is imitating. Volatility comes from the bonding: the C=O makes the molecule polar, so there are permanent dipole-dipole forces, but there is no O-H left, so ester molecules cannot hydrogen bond to one another and the forces holding them together are relatively weak. That same polarity with low boiling point makes esters good solvents for glues, inks and nail varnish remover. As plasticisers they are mixed into a polymer such as PVC, where the ester molecules sit between the chains and hold them apart, weakening the forces between chains so the chains slide and the plastic becomes flexible.
What earns the marks
- Linking volatility and a sweet smell to use as a perfume or a food flavouring.
- Stating that ester molecules have no O-H so cannot hydrogen bond to each other.
- A plasticiser being described as sitting between the polymer chains.
- The intermolecular forces between the chains being weakened, so the polymer is more flexible.
Common mistakes and how to put them right
Claiming ester molecules hydrogen bond to each other because they contain oxygen.
Saying a plasticiser bonds covalently into the polymer chain.
Stating that a plasticiser makes the polymer stronger rather than more flexible.
Listing a use with no property attached, so there is nothing for the explanation mark.
Exam tips
- A 'suggest a use' mark usually needs the property as well as the use, so write both in one sentence.
- An ester in an NMR spectrum gives a peak near δ = 4.1 ppm for the hydrogens on the carbon attached to the single-bonded oxygen; use that shift to place the ester group.
Try the lesson
The start of the Carboxylic acids and esters (A-level only): Common uses of esters (eg in solvents, plasticisers, perfumes and food flavourings). lesson, made from checked teaching notes for this specification point.
Have a go first
Which of the following is a common industrial or commercial use of esters?
Listen
Esters are volatile and have strong, pleasant smells, which is why they are used in perfumes and food flavourings; short-chain esters are what a pear drop or a banana sweet is imitating. Volatility comes from the bonding: the C=O makes the molecule polar, so there are permanent dipole-dipole forces, but there is no O-H left, so ester molecules cannot hydrogen bond to one another and the forces holding them together are relatively weak. That same polarity with low boiling point makes esters good solvents for glues, inks and nail varnish remover. As plasticisers they are mixed into a polymer such as PVC, where the ester molecules sit between the chains and hold them apart, weakening the forces between chains so the chains slide and the plastic becomes flexible. A strong answer earns marks for these points. linking volatility and a sweet smell to use as a perfume or a food flavouring. stating that ester molecules have no O-H so cannot hydrogen bond to each other. a plasticiser being described as sitting between the polymer chains. the intermolecular forces between the chains being weakened, so the polymer is more flexible. Exam tip: A 'suggest a use' mark usually needs the property as well as the use, so write both in one sentence.
Key words
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volatility
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permanent dipole-dipole forces
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plasticisers
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See every definition
- volatility
- The tendency of ester molecules to enter the vapour phase readily, because they cannot hydrogen bond to one another and the forces holding them together are relatively weak.
- permanent dipole-dipole forces
- Forces arising because the C=O makes the molecule polar, and these are the forces present between ester molecules.
- plasticisers
- Substances mixed into a polymer such as PVC, where the ester molecules sit between the chains and hold them apart, weakening the forces between chains so the chains slide and the plastic becomes flexible.
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