Question

When sodium is dissolved in liquid ammonia, a solution of deep blue colour is obtained. The colour of the solution due to:
(A) Ammoniated electron
(B) Sodium ion
(C) Sodium amide
(D) Ammoniated sodium ion

Answer 1

Hint: This phenomenon is exhibited by all of the alkali metals. In other words, we can say that the blue colour is due to the solvated electron which is released by the sodium metal. Sodium ion is solvated in the solution.

Complete answer:
When sodium metal is allowed to dissolve in ammonia, it reacts with the solvent in a different manner.
- We know that sodium is an alkali metal and it will donate its valence electron in order to complete its octet. Here, it donates electrons to ammonia molecules and becomes cation. The reaction is shown as below.
     \[Na+(x+y)N{{H}_{3}}\to {{[Na{{(N{{H}_{3}})}_{x}}]}^{+}}+{{[e{{(NH)}_{y}}]}^{-}}\]
- Thus, here we can see that sodium metal loses its electron and forms a cation in which it is coordinated to ammonia molecules also. The electron released from the sodium metal also gets solvated and gets surrounded by a number of ammonia molecules. This electron is called a solvated electron. This complex can absorb in the visible region of light and gives light blue colour when present in lower concentrations.
- This phenomenon is exhibited by all of the alkali metals including Li, Na, K, Cs and Rb.
- When concentration of these solvated ions in the solution of sodium in liquid ammonia is higher, the colour of the solution changes to copper colour.
Thus, we can conclude that the colour of the solution is due to the ammoniated electron.

Therefore, the correct answer is (A).

Note:
Remember that ammonium ions are not generated in the solution as sodium gets dissolved. This solution of sodium metal in liquid ammonia can conduct electricity as it has ions. This solution is used in Birch reduction.