Question

The confirmation test for Ag^+ is to add HNO3 to the [Ag(NH3)2] ^+ and see if a precipitate of AgCl forms. Where does the Cl ^ - come from? Why does adding HNO3 make AgCl precipitate? Write an appropriate balanced reaction

Answer 1

Nitric acid decomposes the diamine complex and releases the silver ion to the solution.

2HNO3 + Ag(NH3)2^+ --> 2NH4+ + Ag+ + 2NO3^-

Generally, diamine complex is prepared by dissolving the silver chloride in ammonia solution.
2NH3 + AgCl ---> Ag(NH3)2Cl
Hence, the chloride ion comes from the AgCl.

Therefore, when acid is added to the solution containing diamine complex, the complex will dissociates into Ag+ and NH3.
Then. the Ag+ ions then react with Cl- to form AgCl precipitate.

Therefore, the balanced reaction is :
2HNO3(aq) + Ag(NH3)2 Cl --> AgCl(s) + 2NH4NO3