Synthetic Polymers
6 marks · NormalA company makes 1200 kg of polyester each day by condensation polymerisation, starting from a diol and a dicarboxylic acid. Poly(ethene), an addition polymer, is also made in the same factory.
During polyester formation, a small molecule is eliminated in the reaction. Name this small molecule.
Calculate the total mass of this eliminated small molecule if 1200 kg of polyester is produced and the elimination forms 19% of the total mass of products. Give your answer to the nearest kg.
Addition polymers do not eliminate any small molecule in their formation. Suggest how this difference affects the disposal of polyesters compared to addition polymers.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Water
(b) 282 kg
(c) Polyesters, as condensation polymers, may biodegrade more easily because the links between their units can be broken down (e.g., by hydrolysis); addition polymers are more resistant to decomposition.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Names water as the eliminated molecule.
M1 (b) · 1 mark · Recognises that the eliminated small molecule is 19% of total (polyester + water) mass.
M2 (b) · 1 mark · Correctly sets up and rearranges the equation: 1200 = 81% × total mass. (follow-through)
A1 (b) · 1 mark · Calculates (to nearest kg) the mass of water as 282 kg. (follow-through)
B2 (c) · 1 mark · Correctly notes that condensation polymers can be broken down (biodegrade/hydrolyse), unlike addition polymers.
B3 (c) · 1 mark · Offers a correct link to disposal or environmental impact.
Worked solution
a) The small molecule eliminated is water.
b) Let total mass of products = x. Polyester is 81% of the total, so: 1200 = 0.81 × x. Thus, x = 1200 / 0.81 = 1481.48 kg.
Water produced = x − 1200 = 1481.48 − 1200 = 281.48 kg ≈ 282 kg (to the nearest kg).
c) Polyesters, as condensation polymers, can sometimes be broken down (hydrolysed or biodegrade) because of the ester linkages. Addition polymers are inert and do not biodegrade, so they persist in the environment. This makes disposal of polyesters easier in some cases.