Question 22M.2.hl.TZ2.7c
| Date | May 2022 | Marks available | [Maximum mark: 1] | Reference code | 22M.2.hl.TZ2.7c |
| Level | hl | Paper | 2 | Time zone | TZ2 |
| Command term | Suggest | Question number | c | 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)
Suggest why hydrogen chloride, HCl, has a lower boiling point than hydrogen cyanide, HCN.
[1]
HCN has stronger dipole–dipole attraction ✔
Do not accept reference to H-bonds.
This proved to be the most challenging question (10%). It was a good question, where candidates had to explain a huge difference in boiling point of two covalent compounds, requiring solid understanding of change of state where breaking bonds cannot be involved). Yet most considered the triple bonds in HCN as the cause, suggesting covalent bonds break when substance boil, which is very worrying. Others considered H-bonds which at least is an intermolecular force, but shows they are not too familiar with the conditions necessary for H-bonding.
