The concentration of sulphide ion in 0.1M HCl solution saturated with hydrogen sulphide is 1.0×10−19M. 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?
Given KspforFeS=6.3×10−18.MnS=2.5×10−13.ZnS=1.6×10−24.CdS=8.0×10−27
For precipitation to take place, it is required that the calculated ionic product exceeds the Ksp value.
Before mixing:
[S2−]=1.0×10−19M and [M2+]=0.04M
volume = 10 mL volume = 5mL
After mixing:
[S2−]=?[M2+]=?volume=(10+5)=15mLVolume=15mL
[S2−]=1.0×10−19×1015=6.67×10−20M[M2+]=0.04×515=1.33×10−2M
Ionic product =[M2+][S2−]=(1.33×10−2)(6.67×10−20)=8.87×10−22
This ionic product exceeds the Ksp of Zns and CdS. Therefore, precipitation will occur in CdCl2 and ZnCl2 solutions.