When a metal of group 1 was dissolved in liquid ammonia, the following observations were obtained:
(i) Blue solution was obtained initially.
(ii) On concentrating the solution, blue colour changed to bronze colour.
How do you account for the blue colour of the solution? Give the name of the product formed on keeping the solution for some time.
Alkali metals dissolve in liquid ammonia to give a deep blue colour. These solutions are also conducting in nature. The blue colour is obtained because of ammoniated electron which absorbs energy in the visible region of light and thus imparts blue colour to the solution. The reaction is given as
M + (x+y)NH3 → [M(NH3)x]+ + [e(NH3)y]-
As the concentration of the metal increases, the colour of the solution become bronze in colour, which is due to the formation of metal ion clusters.
If the product formed is kept standing for some time, it slowly liberates hydrogen resulting in the formation of amide.
M+(am) + e- +NH3(l) → MNH2(am) +1/2H2(g)