Question

Account for your observations. Consider the following equilibria:
Ag^+(aq)+Cl^-(aq)<->AgCl(s)
Ag^+(aq)+2NH3(aq)<->[Ag(NH3)2]^+(aq)
NH3(aq)+H^+(aq)<->NH4^+(aq)
Observations:
   adding NaCl: went from clear to a white solution
adding NH3: went from white solution to. clear solution
adding HNO3: solution warmed up

Answer 1

Let us start with the first equilibria. This is a precipitation reaction as the silver (I) ion react with chloride ion to form silver chloride which is poorly soluble in water, hence precipitates out which appears as white solution.

Ag⁺ (aq) + Cl^- (aq)   AgCl (s)

Second equilibria: Here the reaction is between silver chloride and aqueous ammonia. As the ammonia is added to the white solution, the silver ions which present in very low concentration react immediately with ammonia to form the complex [Ag(NH₃)₂]⁺ ion which is soluble in water. This reaction stops the first equilibria to give forward. Hence, the available silver ions continuous to react with ammonia until all silver ions react with ammonia and get a clear solution.

Ag⁺ (aq) + 2 NH₃ (aq)   [Ag(NH₃)₂]⁺ (aq)

The third equilibria belongs to the reaction of excess ammonia with HNO₃ to give ammonium ion which is an exothermic reaction.

NH₃ (aq) + H⁺ (aq) NH₄⁺ (aq)