Question 22N.2.sl.TZ0.4a.ii
| Date | November 2022 | Marks available | [Maximum mark: 2] | Reference code | 22N.2.sl.TZ0.4a.ii |
| Level | sl | Paper | 2 | Time zone | TZ0 |
| Command term | Explain | Question number | a.ii | Adapted from | N/A |
An organic compound, A, reacts with ethanoic acid to produce B using concentrated sulfuric acid as a catalyst.
Explain, with reference to Le Châtelier’s principle, the effect of using dilute rather than concentrated sulfuric acid as the catalyst on the yield of the reaction.
[2]
dilute adds «excess» water
OR
water is a product ✔
shift left AND decreases yield ✔
This was the most challenging question on the paper according to the difficulty index. Many candidates stated that catalysts do not affect the position of an equilibrium and hence the yield is not changed. Some candidates stated that the rate of reaction would be slower and the yield per unit time would be lower. Only a few candidates recognized that the dilute sulfuric acid catalyst would introduce more water, and since water is a product it would shift the equilibrium to the left and lower the yield of the ester. 23% of the candidates did not answer the question. Some teachers commented in their feedback that it was not fair to expect the students to know about the dehydrating property of H2SO4, but this was not intended. The students were expected to deduce the effect.
