Group IV cations forms sulphide precipitate with H2S which is the group IV reagent.
Confirmation of Zn2+:
Zinc sulphide dissolves in hydrochloric acid to form zinc chloride.
(a). When potassium ferrocyanide K4[Fe(CN)6] solution is added to the solution after neutralisation by NH4OH solution, a white or a bluish white precipitate
of zinc ferrocyanide appears.
2ZnCl2+K4[Fe(CN)6]→Zn2[Fe(CN)6]Zinc ferrocyanide+4KCl
(b). On addition of sodium hydroxide solution to zinc chloride, it gives a white precipitate of zinc hydroxide, which is soluble in excess of NaOH solution on heating.
This confirms the presence of Zn2+ ions.
ZnCl2+2NaOH→Zn(OH)2+2NaCl
Zn(OH)2+2NaOH→Na2ZnO2Sodium zincate+2H2O