Question

Question 4 (1 point) Question 4 Unsaved For a solution containing at least one of the Group II cations involved in this experiment, when the solution is acidified to pH 0.5 and H2S is added, a precipitate results. KOH is added to the precipitate. The supernatant liquid is separated from the precipitate and tested with HCl/H2S. A colorless solution results, with no precipitate. The remaining original precipitate was treated with dilute HCl. The supernatant liquid was tested with NH3 and H2S. A yellow precipitate results. The precipitate that was treated with HCl was then dissolved in HNO3 and the resulting supernatant liquid was treated with NH3. A blue supernatant liquid results, with no precipitate. Which cation(s) may be present in the original solution tested? (Select all of the possible cations.) Question 4 options: Bismuth Cadmium Copper Tin

Answer 1

1) Hg2+, Pb2+, Bi3+, Cu2+, Cd2+, As3+, As5+,
Sb3+, Sb5+, Sn2+, Sn4+.

HgS, PbS and CuS are black,

2) As₂S₃, As₂S₅, Sb₂S₃, Sb₂S₅, SnS, SnS2, PbS would dissolve in KOH, but would precipitate in the presence of HCl/H2S, so these ions are NOT present there, that leaves you with
Hg²⁺, Bi³⁺, Cu²⁺, Cd²⁺ in the precipitate

3) most likely Cd²⁺, which is soluble in HCl and can be precipitated forming a yellow precipitate. All other ions are not soluble under these conditions, and may still be present in the precipitate.

4) HNO₃ will dissolve all but HgS, so since there's no precipitate left I assume it's not present in the initial solution. Adding NH₃ will form a blue complex with copper(II). Bi³⁺ would form a white precipitate and would not dissolve in excess ammonia

So you likely have Cu²⁺, Cd²⁺