Question

Why do alkali metals give a blue solution of an alkali metal in liquid ammonia?

Answer 1

Hint: when alkali metals dissolve in ammonia, ammoniated electrons are produced. Energy from the visible region is absorbed. Energy from the red region is absorbed to excite these electrons and light corresponding to the blue region is transmitted.

Complete step by step solution:
-Alkali metals belong from group 1 of the periodic table. Alkali metals are s block elements.
- In alkali metals, the last electron enters in s orbital, so they are s block elements.
-Alkali metals are sodium, potassium which with liquid ammonia produce blue coloured solutions.
-Alkali metals dissolve in liquid ammonia to produce ammoniated electrons.
-When visible light falls, these ammoniated electrons absorb energy from the red region of the visible region.
-This absorbed energy is used to excite electrons to higher energy levels.
-Blue coloured light is transmitted which results in imparting a blue coloured solution.
-The colour of the solution is determined by the colour of the transmitted light.
-Blue coloured solutions are conductive in nature. These solutions exhibit paramagnetism.
-Blue coloured solutions produce amide slowly on standing by liberating hydrogen.
\[M+(x+y)N{{H}_{3}}\xrightarrow{{}}{{[M{{(N{{H}_{3}})}_{x}}]}^{+}}+{{[e{{(N{{H}_{3}})}_{y}}]}^{-}}\]
Alkali metals with ammonia produce solutions with different concentrations. Different concentrations exhibit different colours.
-Concentrated blue coloured solutions, change colour to bronze and are diamagnetic in nature.
So, alkali metals give a blue solution of an alkali metal in liquid ammonia due to formation of ammoniated electrons.

Note: Alkali metals dissolve in liquid ammonia to produce ammoniated electrons. These ammoniated electrons absorb energy from the red region of the visible region. -Blue coloured light is transmitted which results in imparting a blue coloured solution. The colour of the solution is determined by the colour of the transmitted light.