Question

What is observed when adding ammonia to Cu2+ solution, and why does this happen?

Answer 1

A blue solution will form.

Explanation:

The reaction between copper(II) ions and aqueous ammonia will create a beautiful blue color of aqueous copper(II) ions.

An example would be to combine copper(II) sulfate and ammonia solution. The equation for this reaction is:

`CuSO_4(aq)+2NH_4OH(aq)->(NH_4)_2SO_4(aq)+Cu(OH)_2(s)darr`

The blue color comes from the copper(II) complex ions, such as `Cu(H_2O)_4(OH)_2`.

When an excess of ammonia is added, you get a dark-blue color. This happens when ammonia becomes a ligand and surrounds the copper ion. The equation then becomes:

`Cu(H_2O)_4(OH)_2(aq)+4NH_4OH(aq)->[Cu(NH_3)_4(H_2O)_2]^(2+)(aq)+2H_2O(l)+2OH^(-)(aq)`