NCERT Class XI Chemistry Equilibrium Solutions

Question : 73

Total: 73

The concentration of sulphide ion in 0.1 M 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 Ksp for
FeS = 6.3 × 10–18
MnS = 2.5 × 10–13
ZnS = 1.6 × 10–24
CdS = 8.0 × 10–27

Solution:

Precipitation will take place in the solution for which ionic product is greater than solubility product. As 10 mL of solution containing S2– ion is mixed with 5 mL of metal salt solution, after mixing
[S2–] = 1.0 × 10–19 ×

= 6.67 × 10−20
[Fe2+] = [Mn2+] = [Zn2+] = [Cd+] =

× 0.04 = 1.33 × 10−2M
Hence the ionic product [M2+][S2–] = 1.33 × 10–2 × 6.67 × 10–20 = 8.87 × 10–22
Therefore in ZnS (Ksp = 1.6 × 10–24) and CdS (Ksp = 8.0 × 10–27), ionic product exceeds solubility product. Hence, precipitation will take place.

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