A solution containing a mixture of metal cations was treated as follows. Dilute

Question

A solution containing a mixture of metal cations was treated as follows. Dilute HCI was added and a precipitate formed. The precipitate was filtered off. H_2 S was bubbled through the acidic solution. Again, a precipitate formed and was filtered off. The pH was raised to about 9 and H_2 S was again bubbled through the solution. No precipitate formed. Finally, sodium carbonate was added. A precipitate formed and was filtered off. What can be said about the presence of each of these groups of cations in the original solution?

Explanation / Answer

The given salt is dissolved in distilled water. The solution obtained is known as original solution.

1) To a little of the original solution dil. HCI is added and precipitate formed-This indicates the presence of group1 (Ag+, Pb2+ Hg2+) At least one of these ion was present.

The precipitate was filtered off.

2) To above filtrate H2S gas is passed through the acidic solution and again precipitate formed-This indicates the presence of group2 (Cu2+, Pb2+ Hg2+, Bi3+ Sn2+ ,Sn4+ Sb3+) At least one of these ion was present

The precipitate was filtered off.

3) The PH was raised about 9 and H2S was again bubbled through the solution. No precipitate formed. This indicates the absence of group3 (Fe2+, Fe3+, Al3+, Co2+ Ni2+ and Cr3+)

None of these ions were present

4) Finally, sodium carbonate was added .A precipitate formed-This indicates the presence of group4 (Ba2+, Ca2+, Mg2+andSr2))

At least one of these ions was present.

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