What mistakes do students make with Biodegradability and disposal of polymers (A-level only)?

Saying the polyalkene chain is too strong rather than saying it is non-polar. Putting the δ⁺ charge on the oxygen and the δ⁻ charge on the carbon. Describing the attack in a polyester as happening at a C-C bond in the chain.

AQA · A-Level · Chemistry

Course version: 7405 · Version from Sept 2016

Students should be able to: explain why polyesters and polyamides can be…

Full specification wording

Biodegradability and disposal of polymers (A-level only): Students should be able to: explain why polyesters and polyamides can be hydrolysed but polyalkenes cannot.

The difference is in the backbone, not in how the polymer was made.

Checked against the AQA 7405 specification (opens in a new tab) on 20 September 2026.

Point 4 of 4

Study notes

From the checked teaching notes for this specification point.

The idea

What earns the marks

Identifying the ester or amide link as the polar part of the backbone.
The carbonyl carbon being δ⁺ because oxygen or nitrogen is more electronegative than carbon.
A nucleophile attacking that carbon and breaking the chain.
The polyalkene backbone being non-polar, with no δ⁺ carbon for a nucleophile to attack.

Common mistakes and how to put them right

Saying the polyalkene chain is too strong rather than saying it is non-polar.
Putting the δ⁺ charge on the oxygen and the δ⁻ charge on the carbon.
Describing the attack in a polyester as happening at a C-C bond in the chain.
Answering only that polyalkenes are addition polymers, with no reference to bonding.

Exam tips

This is a compare-and-contrast answer: make the same point twice, once for each polymer, rather than describing one and stopping.
Write δ⁺ on the carbon in your diagram; a labelled structure often earns the mark faster than a sentence.

Try the lesson

The start of the Biodegradability and disposal of polymers (A-level only): Students should be able to: explain why polyesters and polyamides can be hydrolysed but polyalkenes cannot. lesson, made from checked teaching notes for this specification point.

Have a go first

Which type of bond in a polyester is broken when the polymer is hydrolysed?

Tip: press 1 to 4 to choose

Listen

The difference is in the backbone, not in how the polymer was made. A polyester or polyamide chain has a carbonyl carbon at every link, bonded to an oxygen or a nitrogen. Those atoms are more electronegative than carbon, so they draw electron density away and leave that carbon with a δ⁺ charge. A nucleophile, water or a hydroxide ion, is attracted to it, bonds to it and the chain is cut. A polyalkene chain has no such site: every bond in the backbone is C-C or C-H, the electronegativities are almost equal, so the bonds are non-polar and no carbon is electron deficient. With nothing to attract a nucleophile, hydrolysis never starts, whatever the conditions. A strong answer earns marks for these points. identifying the ester or amide link as the polar part of the backbone. the carbonyl carbon being δ⁺ because oxygen or nitrogen is more electronegative than carbon. a nucleophile attacking that carbon and breaking the chain. the polyalkene backbone being non-polar, with no δ⁺ carbon for a nucleophile to attack. Exam tip: This is a compare-and-contrast answer: make the same point twice, once for each polymer, rather than describing one and stopping.

See it

A top-down flowchart with two branches. The left branch starts at a node labelled 'Polyester or polyamide chain', which leads to 'Carbonyl carbon at every link, bonded to O or N', then to 'O or N more electronegative than carbon', then to 'Carbonyl carbon has δ⁺ charge', then to 'Nucleophile (water or hydroxide) attracted and bonds to it', and ends at 'Chain is cut: hydrolysis'. The right branch starts at 'Polyalkene chain', which leads to 'Backbone bonds are C-C or C-H', then to 'Electronegativities almost equal, bonds non-polar', then to 'No electron-deficient carbon', and ends at 'No nucleophile attracted, hydrolysis never starts'. — It contrasts why a polyester or polyamide chain is hydrolysed, through a δ⁺ carbonyl carbon attacked by a nucleophile, with a polyalkene chain, which is non-polar and has no such site.

Label the diagram

Some boxes have lost their names. Pick the right name for each number.

The diagram again, with 3 boxes numbered instead of named. A top-down flowchart with two branches. The left branch starts at a node labelled 'Polyester or polyamide chain', which leads to 'Carbonyl carbon at every link, bonded to O or N', then to 'O or N more electronegative than carbon', then to 'Carbonyl carbon has δ⁺ charge', then to 'Nucleophile (water or hydroxide) attracted and bonds to it', and ends at 'Chain is cut: hydrolysis'. The right branch starts at 'Polyalkene chain', which leads to 'Backbone bonds are C-C or C-H', then to 'Electronegativities almost equal, bonds non-polar', then to 'No electron-deficient carbon', and ends at 'No nucleophile attracted, hydrolysis never starts'.

1Box 1
2Box 2
3Box 3

0 of 3 labelled

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