Question

A solution on treatment with $N{{H}_{3}}$ turns blue; it contains:
a.) $C{{u}^{2+}}$
b.) $C{{a}^{2+}}$
c.) $C{{o}^{2+}}$
d.) $M{{n}^{2+}}$

Answer 1

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

Complete step by step answer:
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 hydrogen 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.
For example, 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 light blue precipitate. Product formed is copper hydroxide and ammonium chloride.
The reaction involved is shown below:
$CuC{{l}_{2}}+2N{{H}_{3}}+3{{H}_{2}}O\to Cu{{(OH)}_{2}}+2N{{H}_{4}}^{+}Cl$

When the copper hydroxide reacts with excess of ammonia, the copper ion again forms a deep blue color ammonia complex. The reaction involved is shown below:
$Cu{{(OH)}_{2}}+4N{{H}_{3}}\to {{[Cu{{(N{{H}_{3}})}_{4}}]}^{2+}}+2O{{H}^{-}}$

Hence the correct answer is option (A) i.e. A solution on treatment with $N{{H}_{3}}$ turn’s blue, it contains$C{{u}^{2+}}$
So, the correct answer is “Option A”.

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.