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:
 

1. Presence of HCl decreases the sulphide ion concentration
2. Sulphides of group IV cations are unstable in HCl
3. Solubility product of group II sulphides is more than that of group IV sulphides
4. Presence of HCl increases the sulphides ion concentration
Subtopic:  Common Ion Effect |
AIPMT - 2005
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