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In the qualitative analysis of cations, in which groups are the cations precipitated as sulphides?

1. Group II and III
2. Group II and IV
3. Group II and V
4. Group VI and III

Correct answer: Group II and IV

Solution

In the standard scheme of qualitative cation analysis: Group II (Cu2+, Pb2+, Bi3+, Cd2+, As3+, Sb3+, Sn2+) are precipitated as insoluble sulphides by passing H2S in dilute HCl. Group III (Fe3+, Al3+, Cr3+) are precipitated as hydroxides by NH4OH. Group IV (Co2+, Ni2+, Mn2+, Zn2+) are precipitated as sulphides in ammoniacal solution (NH4OH + NH4Cl + H2S). So sulphide precipitation occurs in Group II and Group IV.

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