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

ID: 1033084 • Letter: A

Question

A solution containing a mixture of metal cations was treated with dilute HCI and no precipitate formed. Next, H2S 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 forned 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? Definitely present Definitely absent Possibly present ??

Explanation / Answer

Qualitative analysis of cations

Group I : cation precipitate out in dil HCl

Group II : cations precipitate out in dil HCl + H2S

Group III and group IV : precipitate out with basic + H2S medium

So,

Definitely absent

Hg2^2+

Ag+

Pb2+

Ba2+

Mg2+

--

Definitely present

Cd2+

Sn4+

Hg2+

Sb3+

Zn2+

--

Possibly present

Fe2+

Al3+

K+

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