When copper sulfate (CuSO₄) is mixed with ammonia (NH₃), a series of interesting reactions occur, leading to the formation of different copper-ammonia complexes:

1. Formation of a Deep Blue Solution:

* Initially, upon adding ammonia to a solution of copper sulfate, a pale blue precipitate of copper hydroxide (Cu(OH)₂) forms:

CuSO₄(aq) + 2NH₃(aq) + 2H₂O(l) → Cu(OH)₂(s) + (NH₄)₂SO₄(aq)

* As more ammonia is added, the precipitate dissolves, forming a deep blue solution. This is due to the formation of the tetraamminecopper(II) complex ion ([Cu(NH₃)₄]²⁺):

Cu(OH)₂(s) + 4NH₃(aq) → [Cu(NH₃)₄]²⁺(aq) + 2OH^-(aq)

2. Formation of Other Complexes:

* The reaction with ammonia doesn't stop there. Depending on the concentration of ammonia, other copper-ammonia complexes can form, including:

* [Cu(NH₃)]²⁺

* [Cu(NH₃)₂]²⁺

* [Cu(NH₃)₃]²⁺

Key Observations:

* Color Change: The solution turns from pale blue (copper sulfate) to deep blue ([Cu(NH₃)₄]²⁺).

* Precipitate Formation and Dissolution: Initially, a pale blue precipitate forms, which then dissolves with the addition of more ammonia.

Important Note:

* The formation of these copper-ammonia complexes is an example of ligand exchange reactions, where ammonia molecules replace water molecules coordinated to the copper ion.

* The stability of these complexes depends on the concentration of ammonia and the pH of the solution.

This reaction is a classic example of the versatile chemistry of transition metals and their ability to form complexes with different ligands.