Question 22M.2.hl.TZ2.b(i)
| Date | May 2022 | Marks available | [Maximum mark: 2] | Reference code | 22M.2.hl.TZ2.b(i) |
| Level | hl | Paper | 2 | Time zone | TZ2 |
| Command term | Deduce | Question number | b(i) | Adapted from | N/A |
Standard electrode potential values, E⦵, can be used to predict spontaneity.
Molten zinc chloride undergoes electrolysis in an electrolytic cell at 450 °C.
Deduce the half-equations for the reaction at each electrode.
[2]
Cathode (negative electrode):
Zn2+ + 2e− → Zn (l) ✔
Anode (positive electrode):
2Cl− → Cl2 (g) + 2e−
OR
Cl− → ½ Cl2 (g) + e− ✔
3(bi)/(bii) Answers to both these questions revealed that many candidates struggle to conceptualize the equations that describe electrolysis. The question asked for products of the easiest case of electrolysis, a molten salt. However, many candidates proposed oxidation or reduction equations at both electrodes, or Zn and Cl2 (with no charge) as the initial species rather than the product; the average mark was 1.2/2 as only 55% answered correctly.