Question

How does ammonia react with the solution of Cu?

Answer 1

Hint: To solve this question we should note that ammonia is a Lewis base and when it forms a deep blue colour compound when it reacts with copper because of the presence of lone pair of electrons on ammonia.

Complete step by step solution:
Ammonia $N{H}_3$ acts as a Lewis base because it has the tendency to donate electron pairs. The electron pair in ammonia is present on the nitrogen atom. This is because the valency of nitrogen is five but there are only three hydrogens which are attached to nitrogen in ammonia and the remaining two electrons are the lone pair. Ammonia can form complex compounds due to the presence of lone pairs on nitrogen atoms.
The copper can be any form of the solution. We will take copper as $C{u}^{2+}$ in the form of copper chloride. When the ammonia reacts with copper chloride it forms a light blue precipitate. The product formed is copper hydroxide and ammonium chloride.
The reaction involved is shown below:
$$CuC{l}_2+2N{H}_3+3H_{2}O\to Cu{(OH)}_2+2N{H_4}^{+}Cl$$
When the copper hydroxide reacts with excess ammonia, the copper ion again forms a deep blue colour ammonia complex. The reaction involved is shown below:
$$Cu{(OH)}_2+4N{H}_3\to {[Cu{(N{H}_3)}_4]}^{2+}+2O{H}^{-}$$
$${[Cu{(N{H}_3)}_4]}^{2+}$$ is the deep blue coloured complex which is formed as a product in the above reaction and hydroxyl ion is also produced.

Note: While working with ammonia we should remember that ammonia has the ability to form coordinate bonds with the electron-deficient molecules. Ammonia can also form a coordinate bond with transition metal cation and it leads to the formation of complex compounds.