A solution containing a mixture of metal cations was treated as follows 1. Dilut

Question

A solution containing a mixture of metal cations was treated as follows 1. Dilute HCI was added and a precipitate formed. The precipitate was filtered off 2. H2S was bubbled through the acidic solution. Again, a precipitate formed and was filtered off 3. The pH was raised to about 9 and H2S was again bubbled through the solution. No precipitate formed 4. 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? Cation Group Description form insoluble chlorides Present in the original solution? Bi3+ Cd2+ Cu2+ Ha?+ |form acid-insoluble Bi3", Cd, Cu, Pb2, Sb3, Sn2 Sn Al3+, Co2, Cr3+, Fe2 sulfides form base-insoluble 3t Ni2+ ,2+ ,2+ | sulfides or hydroxides Ba2+, Ca2, Mg2+, Sr2 formnsoluble carbonates Li, Nat, K, NH4 completely soluble None of these ions were present. unknown All of these ions were present. At least one of these ions was present.

Explanation / Answer

1. As on treating with dil HCl a ppt was formed hence first cation group may be present. As they form in soluble chlorides.

2.when H2S was bubbled in the acidic solution ppt was observed hence 2nd group cation may be present.as they form insoluble sulphide in acidic solution.

3. When pH was made basic and then H2S was bubbled then no ppt was observed hence group 3rd cation were not present as they form ppt in basic solution when H2S bubbled.

4.when NaCO3 was added then ppt was observed hence group 4th cation may be present. As they form insoluble carbonate.

. ) 5th group cation may be present as they form completely salts. Hence they do not form ppt but they may be present.

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