DP Chemistry (last assessment 2024)
Question 19M.2.hl.TZ2.5a(ii)
| Date | May 2019 | Marks available | [Maximum mark: 1] | Reference code | 19M.2.hl.TZ2.5a(ii) |
| Level | hl | Paper | 2 | Time zone | TZ2 |
| Command term | State | Question number | a(ii) | Adapted from | N/A |
a(ii).
[Maximum mark: 1]
19M.2.hl.TZ2.5a(ii)
Carbonated water is produced when carbon dioxide is dissolved in water under pressure. The following equilibria are established.
Equilibrium (1) CO2 (g) 
CO2 (aq)
Equilibrium (2) CO2 (aq) + H2O (l) 
H+ (aq) + HCO3− (aq)
Carbon dioxide acts as a weak acid.
(a(ii))
The hydrogencarbonate ion, produced in Equilibrium (2), can also act as an acid.
State the formula of its conjugate base.
[1]
Markscheme
CO32- [✔]
Examiners report
More than half the candidates were able to deduce that carbonate was the conjugate base but a significant proportion of those that did, wrote the carbonate ion with an incorrect charge.
