Question

When a metal of group 1 was dissolved in liquid ammonia, the following observations were obtained
(a) Blue solution was obtained initially.
On concentrating the solution, blue colour changed to bronze colour.How do you account for the blue colour of the solution? Given the name of the product formed on keeping the solution for some time.

Answer 1

(a) The reaction that takes place when alkali metal is dissolved in liquid ammonia is `M +(x+y)NH_(3) rarr [M(NH_(3))_(x)]^(+)+ [(NH_(3))_(y)]^(-e)`
The blue colour of the solution is due to the presence of ammoniated electron which absorb energy in the visible region of light and thus, impart blue colour to the solution.
(b) In concentrated solution, the blye colour changes to bronze colour due to the formation of metal ion clusters. The blue solution on keeping for some time liberate hydrogen slowly with the formation of amide.
`underset("Ammoniacal")(M^(+)+e^(-))+NH_(3)rarr underset("Amide")(MNH_(2))+(1)/(2)H_(2)`