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.
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.
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).
Explain how the catalyst increases the rate of the reaction.
Solid copper(II) chloride absorbs moisture from the atmosphere to form a hydrate of formula CuCl2•H2O.
A student heated a sample of hydrated copper(II) chloride, in order to determine the value of . 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 .
State how current is conducted through the wires and through the electrolyte.
Wires:
Electrolyte:
Write the half-equation for the formation of gas bubbles at electrode 1.
Markscheme
[Ar] 3d10
OR
1s2 2s2 2p6 3s2 3p6 3d10 ✔
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.
Ea (cat) to the left of Ea ✔
peak lower AND Ea (cat) smaller ✔
«catalyst provides an» alternative pathway ✔
«with» lower Ea
OR
higher proportion of/more particles with «kinetic» E ≥ Ea(cat) «than Ea» ✔
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 = «=» 0.0246 «mol»
OR
moles of CuCl2 =«= » 0.0126 «mol» ✔
«water : copper(II) chloride = 1.95 : 1»
« =» 2 ✔
NOTE: Accept « =» 1.95.
NOTE: Award [3] for correct final answer.
Wires:
«delocalized» electrons «flow» ✔
Electrolyte:
«mobile» ions «flow» ✔
2Cl− → Cl2 (g) + 2e−
OR
Cl− → Cl2 (g) + e− ✔
NOTE: Accept e for e−.