The Reaction
* Formation of Amide: Alkali metals (like lithium, sodium, potassium, etc.) readily react with liquid ammonia to form metal amides and hydrogen gas. The general reaction looks like this:
2M + 2NH₃ → 2MNH₂ + H₂
where M represents the alkali metal.
* Example with Sodium:
2Na + 2NH₃ → 2NaNH₂ + H₂
This reaction generates sodium amide (NaNH₂) and hydrogen gas.
Solution Properties
* Color: The resulting solution is initially blue, but as the concentration of the alkali metal increases, it turns bronze. This color change is due to the formation of solvated electrons.
* Solvated Electrons: The alkali metal atoms donate their valence electrons to the ammonia molecules, forming solvated electrons. These electrons are free to move within the solution, giving it a metallic sheen and excellent conductivity.
* Highly Reactive: The presence of solvated electrons makes the ammonia solution highly reactive, capable of reducing many compounds.
Further Reactions
* Decomposition: The metal amides formed in the initial reaction can decompose further upon heating, generating the free metal and nitrogen gas:
2MNH₂ → 2M + N₂ + 3H₂
* Reaction with Oxygen: The solution is highly sensitive to oxygen and will react with it, forming metal oxides and other products.
Safety Precautions
* Highly Exothermic: The reaction between alkali metals and ammonia is highly exothermic and can release significant amounts of heat.
* Flammable: Hydrogen gas is produced, which is flammable.
* Reactive: The solution is highly reactive and can react violently with other substances.
Applications
* Strong Bases: Metal amides are strong bases used in various organic synthesis reactions.
* Reducing Agents: The solvated electrons in the solution make it a powerful reducing agent, useful in organic and inorganic chemistry.
In Summary:
The reaction between alkali metals and ammonia produces a unique solution containing solvated electrons, which are responsible for its color, conductivity, and reactivity. The reaction is highly exothermic and requires careful handling due to the generation of flammable hydrogen gas and the reactivity of the solution.
