Question

When an alkali metal dissolves in liquid ammonia the solution can acquire different colours. Explain the reasons for this type of colour change.

Answer 1

A solvated electron is a free electron in (solvated in) a solution, and is the smallest possible anion. Solvated electrons occur widely, although it is difficult to observe them directly since their lifetimes are so short.[1]The deep color of solutions of alkali metals in ammonia arises from the presence of solvated electrons: blue when dilute and copper-colored when more concentrated (> 3 molar).[2] Classically, discussions of solvated electrons focus on their solutions in ammonia, which are stable for days, but solvated electrons also occur in water and other solvents -- in fact, in any solvent that mediates outer-sphere electron transfer. The real hydration energy of the solvated electron can be estimated by using the hydration energy of proton in water combined with kinetic data from pulse radiolysis experiments. The solvated electron forms an acid-base pair with atomic hydrogen.

The solvated electron is responsible for a great deal of radiation chemistry.

Alkali metals dissolve in liquid ammonia giving deep blue solutions which are conducting in nature. The blue colour of the solution is due to ammoniated electrons which absorb energy in the visible region of light. Alkali metals also dissolve in hexamethylphosphoramide, forming blue solutions.

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Answer 2

When an alkali metal dissolve in liquid ammonia, the solution can acquire different colors,I mean dilute solutions of alkali metals in liquid ammonia exhibit dark blue color this is because of ammoniated electrons absorb energy in the visible region of light.

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