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Question 17N.3.hl.TZ0.b

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Date November 2017 Marks available [Maximum mark: 3] Reference code 17N.3.hl.TZ0.b
Level hl Paper 3 Time zone TZ0
Command term Determine Question number b Adapted from N/A
b.
[Maximum mark: 3]
17N.3.hl.TZ0.b

Heavy metal ions are an important environmental concern.

The solubility product, Ksp , of cadmium sulfide, CdS, is 8.0 × 10–27. Determine the concentration of cadmium ions in 1.0 dm3 of a saturated solution of cadmium sulfide to which 0.10 mol of solid sodium sulfide has been added, stating any assumption you make.

[3]

Markscheme

Calculation:

Ksp = [Cd2+] x [S2–] ✔

[Cd2+] = 8.0 x 10–26 «mol dm–3» ✔

Assumption:

volume of solution remains 1.0 dm3

OR

concentration of sulfide ions in original solution is negligible

OR

hydrolysis of sulfide ions is negligible

Award [2] for correct numerical answer of [Cd2+] for M1 and M2.

Accept “0.10 + x ∼ 0.10 «mol dm–3»”.

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