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A solution initially is 0.10 M in both Cd2+ and Tl+ and is kept saturated with hydrogen sulfide gas Equilibrium Chemistry Question

Question

A solution initially is 0.10 M in both Cd2+ and Tl+ and is kept saturated with hydrogen sulfide gas ([H2S] = 0.1 M). In what pH range will one of the metal ions be precipitated quantitatively (> 99.9%) while the other remains completely in solution?
Ksp of CdS = 1.0 ´ 10–27 Ksp of Tl2S = 6.0 ´ 10–22
Ka of H2S = 8.9 ´ 10–8 Ka of HS– = 1.0 ´ 10–19

A.

Between 0.5 and 6.8

B.

Between 2.0 and 3.9

✓ Correct
C.

Between 4.0 and 6.8

D.

There is no pH at which this is possible.

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