Ncert Exercises & Solutions

Question 10.10:

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

When an alkali metal is dissolved in liquid ammonia, it results in the formation of a deep blue coloured solution.

M + (x + y) {NH}_{3} \to M^{+} {({NH}_{3})}_{x} + e^{- 1} {({NH}_{3})}_{y}

The ammoniated electrons absorb energy corresponding to red region of visible light. Therefore, the transmitted light is blue in colour.
At a higher concentration (3 M), clusters of metal ions are formed. This causes the solution to attain a copper–bronze colour and a characteristic metallic lustre.

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