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MolSynapse / Question bank / Qualitative Analysis: Cations / Group V and VI cations (Ba, Sr, Ca, Mg) and NH4+

JEE Advanced levelOne or more correct optionsDifficulty 3 of 3qc154

Zinc(II) and manganese(II) are not precipitated by $H X_{2} S$ in group II (in 0.3 M $HCl$ ) but appear in group IV. Which statements are correct?

AIn 0.3 M $HCl$ , $[S X^{2 -}]$ is so low that the ionic product of $ZnS$ stays below its $K_{s p}$ .
B $K_{s p}$ values of $CuS$ and $CdS$ are much smaller than those of $ZnS$ and $MnS$ .
C $ZnS$ would precipitate if $H X_{2} S$ were passed through a neutral solution of $Zn X^{2 +}$ (no added acid).
D $Zn X^{2 +}$ is held in solution in dilute $HCl$ as a very stable chloro complex.

Answer: A, B, C

The common ion

H X^{+}

suppresses

H X_{2} S 2 H X^{+} + S X^{2 -}

, so only sulphides with very small

K_{s p}

(

CuS

,

CdS

, etc.) precipitate in group II. In neutral or ammoniacal solution

[S X^{2 -}]

is high and white

ZnS

precipitates. Zinc does not form a stable chloro complex in dilute HCl, so D is false.

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