JEE Advanced 2016 · Paper 1 · Chemistry Q28

ChemistryMultiple correct+4 / -2Question 28 of 54

The reagent(s) that can selectively precipitate $\ce{S^{2-}}$ from a mixture of $\ce{S^{2-}}$ and $\ce{SO4^{2-}}$ in aqueous solution is(are)

\ce{CuCl2}

\ce{BaCl2}

\ce{Pb(OOCCH3)2}

\ce{Na2[Fe(CN)5NO]}

Answer and worked solution

Official answer: A

(A) $\ce{CuCl2}$ gives black CuS with sulphide, while $\ce{CuSO4}$ stays in solution. It is selective. True.
(B) $\ce{BaCl2}$ precipitates sulphate ( $\ce{BaSO4}$ ), not sulphide. False.
(C) Lead acetate gives black PbS. PbSO₄ is also sparingly soluble, so its selectivity is debatable. That is why the key accepts both A and AC.
(D) Sodium nitroprusside gives a violet colour with $\ce{S^{2-}}$ , not a precipitate. False.

Answer: (A) (the key accepts A, or A and C)

JEE Advanced 2016 · Paper 1, Chemistry question 28