O-LevelChemistryOrganic Chemistry5070/22 · Oct/Nov 2015 · Q910 Marks

When rubber is heated in the absence of air, a small amount of isoprene is formed. The structure of isoprene is shown. H H H C=C—C=C H H H

(a)Isoprene is an unsaturated hydrocarbon. Describe a test for an unsaturated hydrocarbon.[2]
(b)Isoprene is a liquid at 25 °C. Describe the arrangement and motion of the particles in isoprene at 25 °C.[2]
(c)Isoprene reacts with sulfur dioxide to form methylsulfolene. C5H8 + SO2 → C5H8SO2 isoprene methylsulfolene Calculate the maximum mass of methylsulfolene that can be formed from 100 g of isoprene.[3]
(d)(i)What feature of the isoprene molecule is responsible for it forming an addition polymer?[1]
(d)(ii)Perspex is also an addition polymer. The diagram shows part of the polymer chain of Perspex. CO2CH3 CO2CH3 CO2CH3 —CH2—C—CH2—C—CH2—C— CH3 CH3 CH3 Deduce the formula of the monomer used to make Perspex.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2015). The mark or mark type is shown in brackets.

[2] (a) bromine water/aqueous bromine/bromine (1) decolourises/goes colourless (1)
[2] (b) arrangement: not ordered/disordered/no fixed arrangement/no fixed position/ random/irregular (shape) (1) motion: slide over each other/move over each other (1)
[3] (c) correct molar masses of isoprene and methylsulfolene: 68 AND 132 or 68 + 64 (1) 100/68 or 1.47 mol isoprene (1) (x 132) = 194.1 g methylsulfolene (1)
[1] (d) (i) double bond/C=C (bond) (1)
[2] (d) (ii) CO2CH3 | CH2 = C | CH3 1 mark for CH2=C correct; 1 mark for rest of molecule correct

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