DP Chemistry (last assessment 2024)
Question 22M.2.hl.TZ1.2b(ii)
| Date | May 2022 | Marks available | [Maximum mark: 2] | Reference code | 22M.2.hl.TZ1.2b(ii) |
| Level | hl | Paper | 2 | Time zone | TZ1 |
| Command term | Calculate | Question number | b(ii) | Adapted from | N/A |
b(ii).
[Maximum mark: 2]
22M.2.hl.TZ1.2b(ii)
Magnesium is a reactive metal often found in alloys.
Magnesium is sometimes used as a sacrificial anode to protect steel from corrosion.
(b(ii))
Calculate the free energy change, ΔG⦵, in kJ, of the cell reaction. Use sections 1 and 2 of the data booklet.
[2]
Markscheme
«ΔGº = -nFEº»
n = 2
OR
ΔGº = «-»2×96500×1.92 / «-»370,560 «J» ✔
-371 «kJ» ✔
For n = 1, award [1] for –185 «kJ».
Award [1 max] for (+)371 «kJ»
Examiners report
Satisfactory performance; two major challenges in applying the equation ΔG° = −nFE° from the data booklet included:
Using n = 1, not 2, the number of electrons transferred in the redox reaction.
ΔG° unit from the equation is in J; some did not convert J to kJ as asked for.
