Question

A metal X on heating with nitrogen gas gives Y. Y on treatment with ${{\text{H}}_2}{\text{O}}$ gives a colourless gas which when passed through ${\text{CuS}}{{\text{O}}_4}$ solution gives blue colour. Y is:
(A) ${\text{Mg(N}}{{\text{O}}_3}{)_2}$
(B) ${\text{M}}{{\text{g}}_{\text{3}}}{{\text{N}}_{\text{2}}}$
(C) ${\text{N}}{{\text{H}}_3}$
(D) ${\text{MgO}}$

Answer 1

Hint: Transition elements tend to form complexes which have different colours. In reaction with copper sulphate, a complex is formed.

Complete step by step answer:
We can divide the question into three parts as follows-
> A metal X on heating with Nitrogen gas gives Y. i.e.
\[{\text{X }}{\text{ + }}{{\text{N}}_2} \to {\text{ }}{{\text{X}}_3}{{\text{N}}_2}{\text{ (Y)}}\]
Y on treatment with water gives a colourless gas i.e.
\[{{\text{X}}_3}{{\text{N}}_2}{\text{(Y)}}{\text{ + }}{{\text{H}}_2}{\text{O }} \to {\text{ X(OH}}{)_2}{\text{ + Colorless gas}}\]
This colourless gas when passed through a solution of copper sulphate gives a blue colour i.e.
\[{\text{Colorless gas }}\xrightarrow{{{\text{CuS}}{{\text{O}}_{\text{4}}}}}{\text{ Blue color}}\]
Out of the four options given, 3 are compounds of Magnesium. So, let us assume that metal X is Magnesium.
Magnesium on reaction with nitrogen gas gives Magnesium nitride and the balanced chemical reaction for it is –
\[{\text{M}}{{\text{g}}_{}}{\text{ }}{\text{ + }}{{\text{N}}_{\text{2}}}{\text{ }} \to {\text{ M}}{{\text{g}}_3}{{\text{N}}_2}\]
Magnesium nitride when treated with water gives magnesium hydroxide and ammonia gas and the balanced chemical reaction is –
\[{\text{M}}{{\text{g}}_3}{{\text{N}}_2}{\text{ + }}{{\text{H}}_2}{\text{O }} \to {\text{3Mg(OH}}{{\text{)}}_2}{\text{ + N}}{{\text{H}}_3}\]
Ammonia is a colourless gas which when passed through the solution of copper sulphate, forms a deep blue coloured complex. The balanced chemical reaction is –
\[{\text{N}}{{\text{H}}_3}{\text{ + }}{\text{CuS}}{{\text{O}}_4}{\text{ }} \to {\text{[Cu(N}}{{\text{H}}_3}{)_4}]{\text{S}}{{\text{O}}_4}.{{\text{H}}_2}{\text{O}}\]
Hence, Y is magnesium nitride (${\text{M}}{{\text{g}}_3}{{\text{N}}_2}$) i.e. option B is correct.

Additional information:
Magnesium is the most chemically active element found in the second position in the periodic table. It is the eighth most abundant element and forms about 2% of earth’s crust. It is not only found in seawater but also in underground brines and salty layers.

Note: ${\text{Mg(N}}{{\text{O}}_3}{)_2}$ and ${\text{MgO}}$ are also compounds of Mg given in the options but the reactions they show with nitrogen gas are different. Only ${\text{M}}{{\text{g}}_3}{{\text{N}}_2}$ gives the correct products as mentioned in the question.