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Date November 2019 Marks available 2 Reference code 19N.2.sl.TZ0.5
Level SL Paper 2 Time zone TZ0
Command term State Question number 5 Adapted from N/A

Question

Copper forms two chlorides, copper(I) chloride and copper(II) chloride.

An electrolysis cell was assembled using graphite electrodes and connected as shown.

State the electron configuration of the Cu+ ion.

[1]
a(i).

Copper(II) chloride is used as a catalyst in the production of chlorine from hydrogen chloride.

4HCl (g) + O2 (g) → 2Cl2 (g) + 2H2O (g)

Calculate the standard enthalpy change, ΔHθ, in kJ, for this reaction, using section 12 of the data booklet.

[2]
a(ii).

The diagram shows the Maxwell–Boltzmann distribution and potential energy profile for the reaction without a catalyst.

Annotate both charts to show the activation energy for the catalysed reaction, using the label Ea (cat).

[2]
a(iii).

Explain how the catalyst increases the rate of the reaction.

[2]
a(iv).

Solid copper(II) chloride absorbs moisture from the atmosphere to form a hydrate of formula CuCl2xH2O.

A student heated a sample of hydrated copper(II) chloride, in order to determine the value of x. The following results were obtained:

Mass of crucible = 16.221 g
Initial mass of crucible and hydrated copper(II) chloride = 18.360 g
Final mass of crucible and anhydrous copper(II) chloride = 17.917 g

Determine the value of x.

[3]
b.

State how current is conducted through the wires and through the electrolyte.

Wires: 

Electrolyte:

[2]
c(i).

Write the half-equation for the formation of gas bubbles at electrode 1.

[1]
c(ii).

Markscheme

[Ar] 3d10
OR
1s2 2s2 2p6 3s2 3p6 3d10

a(i).

ΔHθ = ΣΔHθf (products) − ΣΔHθf (reactants) ✔
ΔHθ = 2(−241.8 «kJ mol−1») − 4(−92.3 «kJ mol−1») = −114.4 «kJ» ✔

 

NOTE: Award [2] for correct final answer.

a(ii).

Ea (cat) to the left of Ea ✔                        

 

peak lower AND Ea (cat) smaller ✔

a(iii).

«catalyst provides an» alternative pathway ✔

«with» lower Ea
OR
higher proportion of/more particles with «kinetic» EEa(cat) «than Ea» ✔

a(iv).

mass of H2O = «18.360 g – 17.917 g =» 0.443 «g» AND mass of CuCl2 = «17.917 g – 16.221 g =» 1.696 «g» ✔

moles of H2O = «0.443g18.02g mol1=» 0.0246 «mol»
OR
moles of CuCl2 =«1.696g134.45g mol1= » 0.0126 «mol» ✔

«water : copper(II) chloride = 1.95 : 1»
«x =» 2 ✔

NOTE: Accept «x =» 1.95.

NOTE: Award [3] for correct final answer.

b.

Wires:
«delocalized» electrons «flow» ✔

Electrolyte:
«mobile» ions «flow» ✔

c(i).

2Cl → Cl2 (g) + 2e
OR
Cl 1 2 Cl2 (g) + e

NOTE: Accept e for e.

c(ii).

Examiners report

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

Syllabus sections

Core » Topic 9: Redox processes » 9.2 Electrochemical cells
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