Question 22M.2.hl.TZ2.b(ii)
| Date | May 2022 | Marks available | [Maximum mark: 2] | Reference code | 22M.2.hl.TZ2.b(ii) |
| Level | hl | Paper | 2 | Time zone | TZ2 |
| Command term | Deduce | Question number | b(ii) | Adapted from | N/A |
Standard electrode potential values, E⦵, can be used to predict spontaneity.
Deduce the overall cell reaction including state symbols. Use section 7 of the data booklet.
[2]
ZnCl2 (l) → Zn (l) + Cl2 (g)
balanced equation ✔
correct state symbols ✔
Accept ionic equation.
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.
The determination of the states proved to be even more difficult, with many stating the ions were aqueous in spite of the fact that the question is clearly about molten zinc chloride. Allowing ECF for the overall equation allowed marks for many candidates, but very few realised that both ionic species in ZnCl2 were actually liquid (being a molten salt). As a result, correct answers were below 45% and the average mark was 0.9/2.
