A very dilute acidic solution of Cd^{2+} and | vedclass

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(B) In qualitative analysis,$Cd^{2+}$ belongs to group $II$ and $Ni^{2+}$ belongs to group $IV$. Group $II$ cations are precipitated as sulfides in th

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Solubility product $(K_{sp})$ of $CdS$ is less than that of $NiS$.

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(B) In qualitative analysis,$Cd^{2+}$ belongs to group $II$ and $Ni^{2+}$ belongs to group $IV$. Group $II$ cations are precipitated as sulfides in the presence of dilute $HCl$ because their solubility product $(K_{sp})$ is very low. Group $IV$ cations require a higher concentration of sulfide ions $(S^{2-})$ for precipitation,which is achieved in a basic medium. Since the solution is acidic,the concentration of $S^{2-}$ is very low due to the common ion effect of $H^+$. Thus,only $CdS$ (which has a much lower $K_{sp}$ than $NiS$) precipitates,while $NiS$ remains in the solution.

$A$ very dilute acidic solution of $Cd^{2+}$ and $Ni^{2+}$ gives only yellow precipitate of $CdS$ on passing $H_2S$ gas. This is due to:

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