Question

Choose the correct answer form the alternatives given.
When alkaline earth metals dissolve in ammonia, they form coloured solution like alkali metals . Which of the following observations regarding the reaction are correct?
(i) Dilute solution are bright blue in colour due to solvated electrons.
(ii) These solutions decompose to form amides and hydrogen.
(iii) From this solution the ammoniates $\left[M\right(N{H}_3{)}_6{]}^{2+}$ can be recovered by evaporation.

• A. Only (i) and (ii)
• B. Only (i) and (ii) and (iii)
• C. Only (ii) and (iii)
• D. Only (i)

Answer 1

Answer: (B)

Only (i) and (ii) and (iii)

• All alkali metal dissolve in liquid ammonia giving deep blue solutions which are conducting in nature. These solutions contain ammoniated cations and ammoniated electrons as shown below:
  

$M+(x+y)N{H}_3\to M+(N{H}_3{)}_x+e^{-}(N{H}_3{)}_y$

The blue colour of the solution is considered to be due to ammoniated electrons which absorb energy corresponding to red region of the visible light for the their excitation to higher energy levels. The transmitted light is blue which imparts blue colour to the solutions.

• From this solution the ammoniates $\left[M\right(N{H}_3{)}_6{]}^{2+}$ can be recovered by evaporation.
  
• These solutions decompose to form amides and hydrogen.