The reagent(s) that can selectively precipitate $\mathrm{S}^{2-}$ from a mixture of $\mathrm{S}^{2-}$ and $\mathrm{SO}_{4}^{2-}$ in aqueous solution is(are)

(C) $\mathrm{Pb}(\mathrm{OOCCH}_{3})_{2}$

(D) $\mathrm{Na}_{2}[\mathrm{Fe}(\mathrm{CN})_{5}\mathrm{NO}]$

JEE Advanced · 2016 · 22 May 2016 · Paper 1 · Practical and Analytical Chemistry

The reagent(s) that can selectively precipitate

S^{2 -}

from a mixture of

S^{2 -}

and

SO_{4}^{2 -}

in aqueous solution is(are)

(A) $CuCl_{2}$ ✓ Correct
(B) $BaCl_{2}$
(C) $Pb (OOCCH_{3})_{2}$
(D) $Na_{2} [Fe (CN)_{5} NO]$

Answer: (A)

Solution

C u^{2 +}

gives extremely insoluble

CuS

while

CuS O_{4}

is soluble, so

CuC l_{2}

precipitates only

S^{2 -}

BaC l_{2}

precipitates

S O_{4}^{2 -}

(as

BaS O_{4}

), not sulfide; lead acetate precipitates both

PbS

and

PbS O_{4}

(so it is not selective); sodium nitroprusside only gives a colour test, not a precipitate. Hence only A is selective.

JEE Advanced · 2016 · 22 May 2016 · Paper 1 · One or more correct options

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