7.73 The concentration of sulphide ion in 0.1M HCl solution saturated with hydrogen sulphide is 1.0 × 10–19 M. If 10 mL of this is added to 5 mL of 0.04 M solution of the following: FeSO4, MnCl2, ZnCl2 and CdCl2. in which of these solutions precipitation will take place?

For precipitation to take place, it is required that the calculated ionic product exceeds theKsp value.Before mixing: [S2-]=1.0×10-19 M [M2+]=0.04 MValume=10 mL         Volume = 5 mLAfter mixing: [S2-]=?Volume=(10+5)=15 mL  [M2+]=?Volume=15 mL[S2-]=1.0×10-19×1015=6.67×10-20 M[M2+]=0.04×515=1.33×10-2MIonic product=[M2+][S2-]=(1.33×10-2)(6.67×10-20)=8.87×10-22This ionic product exceeds the Ksp of Zns and CdS. Therefore, precipitation will occur in CdCl2 and ZnCl2 solutions.