Question

Sodium dissolved in ammonia has blue colour due to:
a.) Solvated sodium molecule
b.) Amide ion
c.) Solvated electron
d.) Lone pair of electrons on nitrogen in ammonia

Answer 1

Different concentrations of alkali metals when dissolved in liquid ammonia results in different colours. The colour in the dilute solution is due to the presence of electrons that absorb energy in the visible light.

Complete Solution :
- Ammonia allows basic chemistry reactions as it is a water like solvent.
- When sodium is added to liquid ammonia, sodium amide compound is obtained and the blue colour formed is associated with the ammoniated electrons, also known as solvated electrons. These electrons are stabilized by various ammonia molecules.
- Solvated electrons are the smallest anion and free electrons in the solution. They absorb energy in the visible light region, due to which dilute solutions are bright blue in colour.
-This reaction can be illustrated as follows:
$Na(s)+N{{H}_{3}}(l)\to 12{{H}_{2}}(g)$

So, the correct answer is “Option C”.

Additional Information:
Solvated electrons, when solvent is ammonia, have a short lifetime to such a degree as to almost become invisible. The sodium amide is a solid white compound.

Note: Alkali metals dissolve in liquid ammonia giving deep blue solutions, which conduct electricity. The dilute solutions are deep blue in colour due to presence of ammoniated electrons while the concentrated solutions have copper bronze colour as ammoniated metal ions are bound by free electrons in the solution.