Q3 / 66 · JEE Advanced 2007 (Paper 2) · Chemistry

A solution of a metal ion when treated with $\mathrm{KI}$ gives a red precipitate which dissolved 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 precipitqte. The metal ion is

  • A
    $\mathrm{Pb}^{2+}$
  • Correct answer
    B
    $\mathrm{Hg}^{2+}$
  • C
    $\mathrm{Cu}^{2+}$
  • D
    $\mathrm{Co}^2$

Solution

$$ \begin{aligned} & \mathrm{Hg}^{2+}+2 \mathrm{I}^{-} \longrightarrow \mathrm{HgI}_2, \mathrm{HgI}_2+\mathrm{H}^{-} \\ & \text {(Excess) }\left.\longrightarrow \mathrm{HgI}_4\right]^{2-} \\ & \text { Soluble }^{2-} \\ & \mathrm{Hg}^{2+}+\mathrm{Co}(\mathrm{SCN})_2 \longrightarrow \mathrm{Hg}(\mathrm{SCN})_2 \end{aligned} $$ Blue crystalline ppt.

Hence, the correct answer is option: 'B'.

Relevant Questions