DP Chemistry (last assessment 2024)

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Question 19M.3.sl.TZ2.1c(i)

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.3.sl.TZ2.1c(i)
Level sl Paper 3 Time zone TZ2
Command term Explain Question number c(i) Adapted from N/A
c(i).
[Maximum mark: 2]
19M.3.sl.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

This question was an equilibrium question. Many students received 1 mark for either concentration of lead decreased, or lead chloride was produced and quite a few recognized that the explanation was the reaction shifted to the reactant or left side for the second mark.

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