Question 19M.2.sl.TZ2.a(iii)
| Date | May 2019 | Marks available | [Maximum mark: 1] | Reference code | 19M.2.sl.TZ2.a(iii) |
| Level | sl | Paper | 2 | Time zone | TZ2 |
| Command term | State | Question number | a(iii) | Adapted from | N/A |
Carbonated water is produced when carbon dioxide is dissolved in water under pressure.
The following equilibria are established.
Carbon dioxide acts as a weak acid.
When a bottle of carbonated water is opened, these equilibria are disturbed.
State, giving a reason, how a decrease in pressure affects the position of Equilibrium (1).
[1]
shifts to left/reactants AND to increase amount/number of moles/molecules of gas/CO2 (g) [✔]
This was a relatively challenging question. Only about a quarter of the candidates explained how a decrease in pressure affected the equilibrium. Some candidates stated there was no shift in the equilibrium as the number of moles is the same on both sides of the equation, not acknowledging that only gaseous substances need to be considered when deciding the direction of shift in equilibrium due to a change in pressure. Some candidates wrote that the equilibrium shifts right because the gas escapes.
