A solution containing a mixture of metal cations was treated with dilute HCI and

Question

A solution containing a mixture of metal cations was treated with dilute HCI and no precipitate formed. Next, H_2S was bubbled through the acidic solution. A precipitate formed and was filtered off. Then, the pH was raised to about 8 and H2S was again bubbled through the solution. A precipitate again formed and was filtered off. Finally, the solution was treated with a sodium carbonate solution, which resulted in no precipitation. Which metal ions were definitely present, which were definitely absent, and which may or may not have been present in the original mixture?

Explanation / Answer

No precipitation with dilute HCl conforms the absence of Group-1 cations like Ag+, Pb2+, Hg22+ . Hence these cations are definitely absent.

Formation of acidic insoluble sulfide(under acidic condition) precipitation conforms the presence of Group - 2 cations like  Cd2+, Sb3+, Sn2+, Hg2+. and Pb2+ .

Formation of basic insoluble sulfide(under basic condition) precipitation conforms the presence of group-4 cations like Mn2+, Co2+, and Ni2+.

No precipitation with carbonate conforms the absence of Group-5 cation like Ca2+, and Mg2+.

K+ may or may not be present.

Hence

Cations definitely present: Cd2+, Sb3+, Sn2+, Hg2+, Pb2+, Mn2+, Co2+, and Ni2+.

Cations definitely absent: Ag+, Pb2+, Hg22+, Ca2+, and Mg2+.

Cation possibly present: K+

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