Q73 / 160 · JIPMER 2012 · Chemistry

Ammonia is a Lewis base and it forms complexes with many cations. Which one of the following cations does not form a complex with ammonia?

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

Solution

Ammonia is a Lewis base. It forms complexes with transition elements like $\mathrm{Ag}^{+}, \mathrm{Cu}^{2+}$ and $\mathrm{Cd}^{2+}$ while it does not form complex with $\mathrm{Pb}^{2+}$ because Pb is not a transition element. $\mathrm{AgCl}+2 \mathrm{NH}_4 \mathrm{OH} \longrightarrow\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)_2\right] \mathrm{Cl}+2 \mathrm{H}_2 \mathrm{O}$ $\begin{aligned} & \mathrm{CuSO}_4+4 \mathrm{NH}_4 \mathrm{OH} \longrightarrow {\left[\mathrm{Cu}\left(\mathrm{NH}_3\right)_4\right] \mathrm{SO}_4 } +4 \mathrm{H}_2 \mathrm{O}\end{aligned}$ $\begin{aligned} & \mathrm{CdSO}_4+4 \mathrm{NH}_4 \mathrm{OH} \longrightarrow\left[\mathrm{Cd}\left(\mathrm{NH}_3\right)_4\right] \mathrm{SO}_4 +4 \mathrm{H}_2 \mathrm{O} \end{aligned}$

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