Cobalt thiocyanate test can be used to confirm the presence of water in ammonia complexes. This test is based on the fact that water molecules coordinated to the metal ion in an ammonia complex can be replaced by thiocyanate ions, resulting in the formation of a red-coloured complex.

Procedure:

1. To a solution of the ammonia complex, add a few drops of concentrated sulfuric acid.

2. Warm the solution gently until it becomes clear.

3. Add a few drops of a saturated solution of cobalt thiocyanate.

4. A red colouration indicates the presence of water in the ammonia complex.

Explanation:

In the presence of water, the cobalt thiocyanate complex forms a red-coloured species, [Co(NH3)5(SCN)]2+, due to the replacement of a water molecule by a thiocyanate ion. The formation of this complex can be represented as follows:

[Co(NH3)5(H2O)]3+ + 2SCN- → [Co(NH3)5(SCN)]2+ + H2O

The red colour of the complex is due to the absorption of light in the visible region by the thiocyanate ligand.