JEE Advanced · 2007 · 08 Apr 2007 · Paper 2 · Practical and Analytical Chemistry

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A solution of a metal ion when treated with KI gives a red precipitate which dissolves in excess KI to give a colourless solution. Moreover, the solution of metal ion on treatment with a solution of cobalt(II) thiocyanate gives rise to a deep blue crystalline precipitate. The metal ion is

(A) $Pb^{2 +}$
(B) $Hg^{2 +}$ ✓ Correct
(C) $Cu^{2 +}$
(D) $Co^{2 +}$

Answer: (B)

Solution

The metal ion is

Hg^{2 +}

. With KI, it forms red

HgI_{2}

precipitate:

Hg^{2 +} + 2 I^{-} \to HgI_{2}

(red). In excess KI, this dissolves to form the soluble complex:

HgI_{2} + 2 KI \to K_{2} [HgI_{4}]

(colourless). With cobalt(II) thiocyanate,

Hg^{2 +}

forms blue crystalline

Hg (SCN)_{2}

. These reactions are characteristic of mercuric ion.

JEE Advanced · 2007 · 08 Apr 2007 · Paper 2 · Single correct option

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JEE Advanced · 2007 · 08 Apr 2007 · Paper 2 · Practical and Analytical Chemistry

Solution

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