Question 23M.2.HL.TZ2.3a
| Date | May 2023 | Marks available | [Maximum mark: 6] | Reference code | 23M.2.HL.TZ2.3a |
| Level | HL | Paper | 2 | Time zone | TZ2 |
| Command term | Annotate, Deduce, Describe, Explain | Question number | a | Adapted from | N/A |
An electrolytic cell was set up using inert electrodes and a dilute aqueous solution of magnesium chloride, MgCl2 (aq).
Annotate the diagram to show the movement of particles that conduct electricity in this cell.
[2]
electron flow from anode to battery OR from battery to cathode ✓
Mg2+/H+ ions to − electrode
AND
Cl−/OH− ions to + electrode ✓
Do not award M1 if electrons are shown in electrolyte.
Deduce the half-equation for the reaction at each electrode. Use section 24 of the data booklet.
Positive electrode: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Negative electrode: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
[2]
Positive electrode:
H2O(l) → ½ O2(g) + 2H+(aq) + 2e−
OR
2OH−(aq) → ½O2(g) + H2O(l) + 2e−✓
Negative electrode:
2H2O(l) + 2e− → H2(g) + 2OH−(aq)
OR
2H+(aq) + 2e− → H2(g) ✓
Accept 2Cl−(aq) → Cl2(g) + 2e− for M1.
Award [1 max] for correct equations at wrong electrodes.
Graphite rods are sometimes used as inert electrodes. Describe the structure of graphite and explain why graphite conducts electricity.
[2]
layers «of carbon atoms in a giant structure» ✓
delocalized electrons «flow along layers» ✓
Accept suitable diagram for M1.
Accept two-dimensional network for M1.
Accept electrons are mobile/flow for M2.
