Question
Chemistry Question on Equilibrium
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:
presence of HCl decreases the sulphide ion concentration
presence of HCl increases the sulphide ion concentration
solubility product of group II sulphides is more than that of group IV sulphides
sulphides of group IV cations are unstable in HCl
presence of HCl decreases the sulphide ion concentration
Solution
H2S is passed when HCl is present in the qualitative analysis of the second group of cations. The ionisation of H2S declines and fewer sulphide ions are produced as a result of the common ion effect. Due to the lower value of their solubility product (Ksp), these sulphide ions are adequate for the precipitation of second group cations in the form of their sulphides. Because they need beyond their ionic product to their solubility products and greater sulphide ion concentrations owing to their higher (Ksp), which is not achieved here due to common ion effect, fourth group cations are not precipitated in this situation.
Therefore, the correct option is (A): presence of HCl decreases the sulphide ion concentration