Making a polyester
2 marks · EasyA polyester is made by reacting 3 molecules of propane-1,3-diol (CH2OHCH2CH2OH) with 3 molecules of ethane dioic acid (HOOC–COOH). Calculate the total number of water molecules produced in this reaction.
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6 (±0)
Also accept: six
Common mistakes: 3; 5; 2
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Marking points
M1 · 1 mark · Correctly relates number of reactions to the number of water molecules produced (2n).
A1 · 1 mark · Correct answer of 6 water molecules.
Worked solution
Each time a diol reacts with a dicarboxylic acid, a water molecule is formed at each end (2 per pair). For 3 of each monomer, number of water molecules = 2 × 3 = 6.