Question

Ammonia gas is passed through copper (II) chloride salt solution​

Answer 1

First, a pale blue precipitate of cupric hydroxide is formed which is found to be soluble when excess of ammonia gas is passed through the solution, and dissolves to form a deep blue or inky blue colouration.

The complex unstable ion that is formed in this case is [Cu(NH3)4] +2

The deep blue or inky blue colouration consists of [Cu(NH3)4]Cl2 in dissolved form.

The reactions taking place are:

NH3 + H2O-------> NH4OH

CuCl2 + NH4OH--------> Cu(OH)2 + NH4Cl

Cu(OH)2 + 2NH4OH + 2NH4Cl---------> [Cu(NH3)4]Cl2(inky blue) + 4H2O