Biodegradable polyesters

2 marks · Normal

State the two types of functional groups present in lactic acid that allow it to form a biodegradable polyester.

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Carboxylic acid and alcohol (hydroxyl) groups.

Also accept: –COOH group and –OH group; Carboxyl group and hydroxyl group; A carboxylic acid group and an alcohol group

Common mistakes: Only giving one functional group; Confusing with amine group

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Marking points

B1 · 1 mark · Correctly identifies the carboxylic acid group (–COOH).

B2 · 1 mark · Correctly identifies the alcohol group (–OH).

Worked solution

Lactic acid contains a carboxylic acid group (–COOH) and an alcohol (hydroxyl) group (–OH). Both groups are needed for the polymerisation reaction to produce a polyester.