DP Chemistry (last assessment 2024)
Question 20N.3.sl.TZ0.b
| Date | November 2020 | Marks available | [Maximum mark: 1] | Reference code | 20N.3.sl.TZ0.b |
| Level | sl | Paper | 3 | Time zone | TZ0 |
| Command term | Suggest | Question number | b | Adapted from | N/A |
b.
[Maximum mark: 1]
20N.3.sl.TZ0.b
Aspirin is formed by reacting salicylic acid with ethanoic anhydride. The structure of aspirin is given in section 37 of the data booklet.
Aspirin crystals are rinsed with water after recrystallization to remove impurities.
Suggest why cold water is used.
[1]
Markscheme
to avoid dissolving the crystals/aspirin ✔
Accept “to avoid loss of product” OR “aspirin is less soluble in cold water”.
Examiners report
While there were many good answers it was worrying to correct as many where the student clearly didn't establish a connection between solubility and purification. Many incorrect responses indicated the cold water was to "stay below the melting point of the aspirin" rather than relate it to the solubility of the final product.
