Question

After addition of HCl to the mixture, why did a precipitate form?

Consider the following equilibria:

Ag+(aq)+Cl−(aq)⇌AgCl(s)

Ag+(aq)+2NH3(aq)⇌ [Ag(NH3)2]+

NH3(aq)+H+(Aq)⇌NH+4(aq)

Increasing the NH3 concentration shifts the second equilibrium to the right. This decreases the Ag+ concentration, shifting the first equilibrium to the right. AgCl dissolves. Adding H+ removes NH3 from the second equilibrium via the third equilibrium, shifting the second equilibrium to the right. This increases the Ag+ concentration. The first equilibrium shifts to the right; AgCl precipitates.

Increasing the NH3 concentration shifts the second equilibrium to the right. This decreases the Ag+ concentration, shifting the first equilibrium to the left. AgCl dissolves. Adding H+ removes NH3 from the second equilibrium via the third equilibrium, shifting the second equilibrium to the left. This increases the Ag+ concentration. The first equilibrium shifts to the right; AgCl precipitates.

Increasing the NH3 concentration shifts the second equilibrium to the left. This decreases the Ag+ concentration, shifting the first equilibrium to the right. AgCl dissolves. Adding H+ removes NH3 from the second equilibrium via the third equilibrium, shifting the second equilibrium to the right. This increases the Ag+ concentration. The first equilibrium shifts to the left; AgCl precipitates.

Increasing the NH3 concentration shifts the second equilibrium to the left. This decreases the Ag+ concentration, shifting the first equilibrium to the left. AgCl dissolves. Adding H+ removes NH3 from the second equilibrium via the third equilibrium, shifting the second equilibrium to the left. This increases the Ag+ concentration. The first equilibrium shifts to the left; AgCl precipitates.

Answer 1

Increasing the NH₃ concentration shifts the second equilibrium to the right. This decreases the Ag⁺ concentration, shifting the first equilibrium to the left. AgCl dissolves. Adding H⁺ removes NH₃ from the second equilibrium via the third equilibrium, shifting the second equilibrium to the left. This increases the Ag⁺ concentration. The first equilibrium shifts to the right; AgCl precipitates.

Explanation: When NH₃ concentration is increased formation of Ag(NH₃) ₂⁺ increases and Ag⁺ concentration decrases. When HCl is added, H⁺ removes NH_{​​​​​​3} from Ag(NH₃) ₂⁺ forming NH₄⁺. Hence Ag⁺ concentration increases which combines with Cl^- from HCl forming AgCl precipitate.