When H_2S gas is passed through a solution co | vedclass

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(A) In qualitative analysis,$H_2S$ is a weak acid that dissociates as: $H_2S \rightleftharpoons 2H^+ + S^{2-}$.When $HCl$ is present,it provides a hig

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Presence of $HCl$ decreases the sulphide ion concentration.

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(A) In qualitative analysis,$H_2S$ is a weak acid that dissociates as: $H_2S \rightleftharpoons 2H^+ + S^{2-}$.When $HCl$ is present,it provides a high concentration of $H^+$ ions due to the common ion effect.This suppresses the dissociation of $H_2S$,significantly decreasing the concentration of $S^{2-}$ ions.Group $II$ cations have very low solubility products $(K_{sp})$,so they precipitate even at low $S^{2-}$ concentrations.Group $IV$ cations have higher $K_{sp}$ values and require a higher concentration of $S^{2-}$ to precipitate,which is not achieved in the presence of $HCl$.

When $H_2S$ gas is passed through a solution containing $HCl$,it precipitates the cations of the second group of qualitative analysis but not those belonging to the fourth group. This is because:

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