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Date May 2017 Marks available 1 Reference code 17M.2.sl.TZ1.5
Level SL Paper 2 Time zone TZ1
Command term Draw Question number 5 Adapted from N/A

Question

This question is about carbon and chlorine compounds.

Ethane, C2H6, reacts with chlorine in sunlight. State the type of this reaction and the name of the mechanism by which it occurs.

[1]
a.

Formulate equations for the two propagation steps and one termination step in the formation of chloroethane from ethane.

[3]
b.

One possible product, X, of the reaction of ethane with chlorine has the following composition by mass:

carbon: 24.27%, hydrogen: 4.08%, chlorine: 71.65%

Determine the empirical formula of the product.

[2]
c.i.

The mass and 1H\(\,\)NMR spectra of product X are shown below. Deduce, giving your reasons, its structural formula and hence the name of the compound.

[3]
c.ii.

Chloroethene, C2H3Cl, can undergo polymerization. Draw a section of the polymer with three repeating units.

[1]
d.

Markscheme

substitution AND «free-»radical
OR
substitution AND chain

 

Award [1] for “«free-»radical substitution” or “SR” written anywhere in the answer.

[1 mark]

a.

Two propagation steps:
C2H6 + •Cl → C2H5• + HCl

C2H5• + Cl2 → C2H5Cl + •Cl

One termination step:
C2H5• + C2H5• → C4H10
OR
C2H5• + •Cl → C2H5Cl
OR
•Cl + •Cl → Cl2

 

Accept radical without • if consistent throughout.

Allow ECF from incorrect radicals produced in propagation step for M3.

[3 marks]

b.

\({\text{C}} = \frac{{24.27}}{{12.01}}\) = 2.021 AND \({\text{H}} = \frac{{4.08}}{{1.01}}\) = 4.04 AND \({\text{Cl}} = \frac{{71.65}}{{35.45}} = 2.021\)

«hence» CH2Cl

 

Accept \(\frac{{24.27}}{{12.01}}\) : \(\frac{{4.08}}{{1.01}}\) : \(\frac{{71.65}}{{35.45}}.\)

Do not accept C2H4Cl2

Award [2] for correct final answer.

[2 marks]

c.i.

molecular ion peak(s) «about» m/z 100 AND «so» C2H4Cl2 «isotopes of Cl»

two signals «in 1H\(\,\)NMR spectrum» AND «so» CH3CHCl2
OR
«signals in» 3:1 ratio «in 1H\(\,\)NMR spectrum» AND «so» CH3CHCl2
OR
one doublet and one quartet «in 1H\(\,\)NMR spectrum» AND «so» CH3CHCl2

1,1-dichloroethane

 

Accept “peaks” for “signals”.

Allow ECF for a correct name for M3 if an incorrect chlorohydrocarbon is identified

[3 marks]

c.ii.

 

Continuation bonds must be shown.

Ignore square brackets and “n”.

Accept    M17/4/CHEMI/SP2/ENG/TZ1/05.d/M .

Accept other versions of the polymer, such as head to head and head to tail.

Accept condensed structure provided all C to C bonds are shown (as single).

[1 mark]

d.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.i.
[N/A]
c.ii.
[N/A]
d.

Syllabus sections

Core » Topic 10: Organic chemistry » 10.1 Fundamentals of organic chemistry
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