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Date November 2021 Marks available 1 Reference code 21N.2.sl.TZ0.4
Level SL Paper 2 Time zone TZ0
Command term Identify Question number 4 Adapted from N/A

Question

1-chloropentane reacts with aqueous sodium hydroxide.

The reaction was repeated at a lower temperature.

Identify the type of reaction.

[1]
a(i).

Outline the role of the hydroxide ion in this reaction.

[1]
a(ii).

Suggest, with a reason, why 1-iodopentane reacts faster than 1-chloropentane under the same conditions. Use section 11 of the data booklet for consistency.

[2]
a(iii).

Sketch labelled Maxwell–Boltzmann energy distribution curves at the original temperature (T1) and the new lower temperature (T2).

[2]
b(i).

Explain the effect of lowering the temperature on the rate of the reaction.

[2]
b(ii).

Markscheme

«nucleophilic» substitution/SN2 ✔


Do not accept if “electrophilic” or “free radical” substitution is stated.

a(i).

«acts as a» nucleophile/Lewis base
OR
donates/provides lone pair «of electrons»
OR
attacks the «partially» positive carbon ✔

a(ii).

bond enthalpy C–I lower than C–Cl
OR
C–I bond weaker than C–Cl ✔


«weaker bond» broken more easily/with less energy
OR
lower Ea «for weaker bonds» ✔


Accept the bond enthalpy values for C–I and C–Cl for M1.

a(iii).

peak at T1 to right of AND lower than T2

lines begin at origin AND T1 must finish above T2

b(i).

«rate is» lower AND «average» kinetic energy of molecules is lower
OR
«rate is» lower AND less frequent collisions
OR
«rate is» lower AND fewer collisions per unit time ✔

«rate is» lower AND fewer/smaller fraction of molecules/collisions have the E ≥ Ea


Lower «rate» needs to be mentioned once only.

Do not accept “fewer collisions” without reference to time/frequency/probability for M1.

b(ii).

Examiners report

[N/A]
a(i).
[N/A]
a(ii).
[N/A]
a(iii).
[N/A]
b(i).
[N/A]
b(ii).

Syllabus sections

Core » Topic 10: Organic chemistry » 10.2 Functional group chemistry
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