Question

Only about 0.16mg of AgBr(s) will dissolve in 1.0L of water (this volume of solid is smaller than the head of a pin). In a solution of ammonia that contains 0.10 mol ammonia per liter of water, there are about 555 water molecules for every molecule of ammonia. However, more than 400 times as much AgBr (68mg) will dissolve in this solution as in plain water. Explain how such a tiny change in the composition of the solution can have such a large effect on the solubility of AgBr.

Answer 1

Solution :-

AgBr is the sparingly soluble salt that means its solubility in the pure water is very low. But when the ammonia is added to the water then it increases the solubility of the AgBr by about 400 times because the ammonia forms the soluble complex with the Ag^+ ion and therefore it increases the solubility of the AgBr. Because the addition of the ammonia causes the right side shift in the equilibrium of the dissociation of the AgBr

The reaction equation is as follows

AgBr(s) ---- > Ag^+(aq) + Br^-(aq)   

Ag^+(aq) + 2NH3(aq) ---- > Ag(NH3)2^+(aq)

Overall equation is

AgBr(s) + 2NH3(aq) ---- > Ag(NH3)2(aq) + Br^-(aq)

Therefore when the ammonia is added in the water then solubility of the AgBr increases because the formation of the soluble complex with ammonia.