Question

Choose the correct answer from the alternatives given.
When alkaline earth metals dissolve in ammonia, they form coloured solutions like alkali metals. Which of the following observations regarding the reaction are correct?
1. Dilute solutions are bright blue in colour due to solvated electrons.
2. These solutions decompose to form amides and hydrogen.
3. From this solution the ammoniates ${\left[ {{\text{M}}{{\left( {{\text{N}}{{\text{H}}_{\text{3}}}} \right)}_{\text{6}}}} \right]^{{\text{2 + }}}}$ can be recovered by evaporation.
A. Only (i) and (ii)
B. Only (i) and (ii) and (iii)
C. Only (ii) and (iii)
D. Only (i)

Answer 1

The alkaline earth metals dissolve in liquid ammonia $\left( {{\text{N}}{{\text{H}}_3}} \right)$ and produce ammoniated cations and ammoniated electrons. The ammoniated electrons absorb energy in the visible region.

Complete step by step answer:
The elements in the group 2 of the periodic table are known as alkaline earth metals. Alkaline earth metals are beryllium $\left( {{\text{Be}}} \right)$, magnesium $\left( {{\text{Mg}}} \right)$, calcium $\left( {{\text{Ca}}} \right)$, strontium $\left( {{\text{Sr}}} \right)$, barium $\left( {{\text{Ba}}} \right)$ and radium $\left( {{\text{Ra}}} \right)$.
The alkaline earth metals dissolve in liquid ammonia $\left( {{\text{N}}{{\text{H}}_3}} \right)$ and produce ammoniated cations and ammoniated electrons. The reaction is as follows:
${\text{M}} + \left( {x + y} \right){\text{N}}{{\text{H}}_3} \to {\left[ {{\text{M}}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_x}} \right]^ + } + {\left[ {{\text{e}}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_y}} \right]^ - }$
The ammoniated cations are ${\left[ {{\text{M}}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_x}} \right]^ + }$ and the ammoniated electrons are ${\left[ {{\text{e}}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_y}} \right]^ - }$.
The solutions formed after the reaction are dark blue in colour. When these solutions are diluted, the solution becomes bright blue. The ammoniated electrons absorb energy in the visible region of light. Thus, the bright blue colour is due to the ammoniated electrons.
These blue coloured solutions on standing liberate hydrogen and result in formation of amide. Thus, the coloured solutions decompose to form amides and hydrogen.
If these solutions are evaporated, the ammonites ${\left[ {{\text{M}}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_x}} \right]^ + }$ can be recovered.
Thus, all the three alternatives (i), (ii) and (iii) are correct

So, the correct answer is Option B .

Additional Information:
The deep blue coloured contain solvated electrons ${\left[ {{\text{e}}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_y}} \right]^ - }$. The solvated electrons are unpaired electrons. Thus, the coloured solutions become paramagnetic in nature. On standing, the solution liberates hydrogen gas. Thus, the electrons leave the solution and the solution turns bronze in colour. Also, as the solution loses electrons, the solution becomes diamagnetic in nature.

Note:
Ammoniated electrons absorb energy and move to a higher energy level. The ammoniated electrons thus give deep blue coloured solutions. These solutions conduct electricity.