When ammonia is added to a solution of ferric chloride (FeCl₃), a chemical reaction occurs, resulting in the formation of a reddish-brown precipitate. Here's a breakdown of what happens:

The Reaction:

* Ferric ions (Fe³⁺) react with ammonia (NH₃) to form a complex ion called hexaammineiron(III) ion [Fe(NH₃)₆]³⁺:

Fe³⁺ (aq) + 6NH₃ (aq) → [Fe(NH₃)₆]³⁺ (aq)

* The [Fe(NH₃)₆]³⁺ ion is then hydrolyzed in water, resulting in the release of H⁺ ions and formation of a hydroxide precipitate (Fe(OH)₃):

[Fe(NH₃)₆]³⁺ (aq) + 3H₂O (l) → Fe(OH)₃ (s) + 6NH₄⁺ (aq)

The Result:

* The reddish-brown precipitate observed is ferric hydroxide (Fe(OH)₃).

* The solution also contains ammonium ions (NH₄⁺).

Additional Notes:

* The amount of ammonia added determines the outcome.

* If ammonia is added in excess, the precipitate may dissolve to form a colorless solution containing the [Fe(NH₃)₆]³⁺ complex ion.

* The reaction is an example of a complexation reaction, where a metal ion forms a complex with ligands (in this case, ammonia molecules).

* The formation of the precipitate is a reversible reaction. Adding acid can redissolve the precipitate by shifting the equilibrium towards the formation of [Fe(NH₃)₆]³⁺.

This reaction is a common laboratory test for the presence of ferric ions.