Q. H₂S gas when passed through a solution of cations containing HCl precipitates the cations of second group of qualitative analysis but not those belonging to the fourth group. It is because :
A) presence of HCl decreases the sulphide ion concentration
B) presence of HCl increases the sulphide ion concentration
C) solubility product of group II sulphides is more than that of group IV sulphides
D) sulphides of group IV cations are unstable in HCl
Explanation
[Solution from source] HCl suppresses ionisation of H₂S by the common-ion (H⁺) effect, lowering [S²⁻]. This low [S²⁻] still exceeds the very small Ksp of group II sulphides but not the larger Ksp of group IV sulphides. Group II sulphides have smaller, not larger, Ksp. Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.