DP Chemistry (last assessment 2024)
Question 19M.3.hl.TZ2.1c(i)
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.hl.TZ2.1c(i) |
| Level | hl | Paper | 3 | Time zone | TZ2 |
| Command term | Explain | Question number | c(i) | Adapted from | N/A |
c(i).
[Maximum mark: 2]
19M.3.hl.TZ2.1c(i)
This question is about a mug made of a lead alloy.
The rate of lead dissolving in common beverages with various pH values was analysed.
(c(i))
Lead(II) chloride, PbCl2, has very low solubility in water.
PbCl2 (s) Pb2+ (aq) + 2Cl− (aq)
Explain why the presence of chloride ions in beverages affects lead concentrations.
[2]
Markscheme
equilibrium shifts to the left/towards reactants [✔]
lead «compounds/ions» precipitate
OR
concentration of lead «ions»/[Pb2+] decreases [✔]
Note: Award [2] for “equilibrium shifts to the left/towards reactants due to common ion effect”.
Accept “lead ions/[Pb2+] removed from solution” for M2.
Examiners report
Several candidates missed that this question was based on the equilibrium and it will shift to the left in presence of chloride ions.
