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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?
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The correct answer is:
$\mathrm{Pb}^{2+}$
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.
$\mathrm{AgCl}+2 \mathrm{NH}_4 \mathrm{OH} \longrightarrow\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)_2\right] \mathrm{Cl}+2 \mathrm{H}_2 \mathrm{O}$
$\begin{aligned} & \mathrm{CuSO}_4+4 \mathrm{NH}_4 \mathrm{OH} \longrightarrow {\left[\mathrm{Cu}\left(\mathrm{NH}_3\right)_4\right] \mathrm{SO}_4 } +4 \mathrm{H}_2 \mathrm{O}\end{aligned}$
$\begin{aligned} & \mathrm{CdSO}_4+4 \mathrm{NH}_4 \mathrm{OH} \longrightarrow\left[\mathrm{Cd}\left(\mathrm{NH}_3\right)_4\right] \mathrm{SO}_4 +4 \mathrm{H}_2 \mathrm{O} \end{aligned}$
$\mathrm{AgCl}+2 \mathrm{NH}_4 \mathrm{OH} \longrightarrow\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)_2\right] \mathrm{Cl}+2 \mathrm{H}_2 \mathrm{O}$
$\begin{aligned} & \mathrm{CuSO}_4+4 \mathrm{NH}_4 \mathrm{OH} \longrightarrow {\left[\mathrm{Cu}\left(\mathrm{NH}_3\right)_4\right] \mathrm{SO}_4 } +4 \mathrm{H}_2 \mathrm{O}\end{aligned}$
$\begin{aligned} & \mathrm{CdSO}_4+4 \mathrm{NH}_4 \mathrm{OH} \longrightarrow\left[\mathrm{Cd}\left(\mathrm{NH}_3\right)_4\right] \mathrm{SO}_4 +4 \mathrm{H}_2 \mathrm{O} \end{aligned}$
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