Question 22M.2.sl.TZ1.1c(ii)
| Date | May 2022 | Marks available | [Maximum mark: 1] | Reference code | 22M.2.sl.TZ1.1c(ii) |
| Level | sl | Paper | 2 | Time zone | TZ1 |
| Command term | Suggest | Question number | c(ii) | Adapted from | N/A |
When heated in air, magnesium ribbon reacts with oxygen to form magnesium oxide.
When magnesium is burnt in air, some of it reacts with nitrogen to form magnesium nitride according to the equation:
3 Mg (s) + N2 (g) → Mg3N2 (s)
Suggest an explanation, other than product being lost from the crucible or reacting with nitrogen, that could explain the yield found in (b)(iii).
[1]
incomplete reaction
OR
Mg was partially oxidised already
OR
impurity present that evaporated/did not react ✔
Accept “crucible weighed before fully cooled”.
Accept answers relating to a higher atomic mass impurity consuming less O/O2.
Accept “non-stoichiometric compounds formed”.
Do not accept "human error", "wrongly calibrated balance" or other non-chemical reasons.
If answer to (b)(iii) is >100%, accept appropriate reasons, such as product absorbed moisture before being weighed.
Quite a few students realised that incomplete reaction would lead to this, but only 30% of students gave a correct answer rather than a non-specific guess, such as "misread balance" or "impurities".
