Question 22M.2.hl.TZ2.7d
| Date | May 2022 | Marks available | [Maximum mark: 3] | Reference code | 22M.2.hl.TZ2.7d |
| Level | hl | Paper | 2 | Time zone | TZ2 |
| Command term | Explain | Question number | d | Adapted from | N/A |
The overall equation for the production of hydrogen cyanide, HCN, is shown below.
CH4 (g) + NH3 (g) +O2 (g) → HCN (g) + 3H2O (g)
Explain why transition metal cyanide complexes are coloured.
[3]
Any three from:
partially filled d-orbitals ✔
«CN- causes» d-orbitals «to» split ✔
light is absorbed as electrons transit to a higher energy level «in d–d transitions»
OR
light is absorbed as electrons are promoted ✔
energy gap corresponds to light in the visible region of the spectrum ✔
Do not accept “colour observed is the complementary colour” for M4.
This question appears frequently in exams but with slightly different approaches. In general candidates ignore the specific question and give the same answers, failing in this case to describe why complexes are coloured rather than what colour is seen. These answers appear to reveal that many candidates don't really understand this phenomenon, but learn the answer by heart and make mistakes when repeating it, for example, stating that the ‘d-orbitals of the ligands were split’- an obvious misconception. The average mark was 1.6/3, with a MS providing 4 ideas that would merit a mark
