DP Chemistry (last assessment 2024)

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Question 17N.3.hl.TZ0.9

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Date November 2017 Marks available [Maximum mark: 4] Reference code 17N.3.hl.TZ0.9
Level hl Paper 3 Time zone TZ0
Command term Determine, State Question number 9 Adapted from N/A
9.
[Maximum mark: 4]
17N.3.hl.TZ0.9

Heavy metal ions are an important environmental concern.

(a)

State the name of one method, other than precipitation, of removing heavy metal ions from solution in water.

[1]

Markscheme

adsorption

OR

chelation

OR

ion exchange

Accept other valid methods such as “phytoremediation” OR “Fenton reaction” OR “electrolysis”.

(b)

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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