Sulphide precipitates. Several sulphide precipitates formed by adding different salt solutions to a solution of sodium sulphide (Na2S) in test tubes. The precipitates are, left to right: cadmium sulphide (CdS, bright yellow-orange), zinc sulphide (ZnS, white), silver sulphide (Ag2S, black), lead sulphide (PbS, black), nickel sulphide (NiS, black-brown), copper sulphide (CuS, dark indigo). The respective reactions are: Na2S + CdSO4 -> CdS + Na2SO4, Na2S + ZnSO4 -> ZnS + Na2SO4, Na2S + AgNO3 -> Ag2S + NaNO3, Na2S + Pb (NO3)2 -> PbS + NaNO3, Na2S + NiSO4 -> NiS + Na2SO4, Na2S + CuSO4 -> CuS + Na2SO4. These are all examples of a double replacement reaction. |