Question

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?

Answer 1

S^{2-} =  10^{-19}}{15} = 6.67 * 10^{-20}  M

M^{2+} = {5 * 0.04}{15} = 0.0133  M

Ksp and Q Check

Compound	Ksp	Q = [M²⁺][S²⁻]	Ppt?
FeS	\( 4.9 \times 10^{-19} \)	\( 8.9 \times 10^{-22} \)	No
MnS	\( 2.5 \times 10^{-10} \)	\( 8.9 \times 10^{-22} \)	No
ZnS	\( 2 \times 10^{-25} \)	\( 8.9 \times 10^{-22} \)	Yes
CdS	\( 8 \times 10^{-27} \)	\( 8.9 \times 10^{-22} \)	Yes

Precipitation in ZnCl₂ and CdCl₂.