Q48 / 180 · AIIMS 2010 · Chemistry

A complex $\mathrm{PtCl}_4 .5 \mathrm{NH}_3$ shows a molar conductance of $402 \mathrm{ohm}^{-1} \mathrm{~cm}^2 \mathrm{~mol}^{-1}$ in water and precipitates three moles of $\mathrm{AgCl}$ with $\mathrm{AgNO}_3$ solution. The formula of the complex is

  • A
    $\left[\mathrm{Pt}\left(\mathrm{NH}_3\right)_6\right] \mathrm{Cl}_4$
  • B
    $\left[\mathrm{Pt}\left(\mathrm{NH}_3\right)_4 \mathrm{Cl}_2\right] \mathrm{Cl}_2$
  • Correct answer
    C
    $\left[\mathrm{Pt}\left(\mathrm{NH}_3\right)_5 \mathrm{Cl}\right] \mathrm{Cl}_3$
  • D
    $\left[\mathrm{Pt}\left(\mathrm{NH}_3\right)_3 \mathrm{Cl}_3\right] \mathrm{Cl}$

Solution

The complex $\mathrm{PtCl}_4 .5 \mathrm{NH}_3$ is designated as $\left[\mathrm{Pt}\left(\mathrm{NH}_3\right)_5 \mathrm{Cl}\right] \mathrm{Cl}_3$ which ionizes to $\left[\mathrm{Pt}\left(\mathrm{NH}_3\right)_5 \mathrm{Cl}\right]^{3+}$ $+3 \mathrm{Cl}^{-}$ions. Thus total ions produced are four but three moles of $\mathrm{AgCl}$ are produced from $3 \mathrm{Cl}^{-}$ions with $\mathrm{AgNO}_3$.

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

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