Question

Using Le Châtelier's principle, explain how the addition of aqueous ammonia dissolves silver chloride. If HNO₃ is added after the AgCl has dissolved in the NH₃solution, it causes AgCl to re-precipitate. Explain by selecting all true statements.

1.) AgCl is an insoluble solid.

2.) Ag⁺reacts with NH₃ to form Ag(NH₃)₂⁺, which "adds" Ag⁺ to the AgCl equilibrium, causing more AgCl to dissolve.

3.) Ag⁺reacts with NH₃ to form Ag(NH₃)₂⁺, which "removes" Ag⁺ from the AgCl equilibrium, causing more AgCl to dissolve.

4.) Adding HNO₃, a strong acid, destroys the complex ion and "removes" Ag⁺ from the AgCl equilibrium, causing AgCl(s) to re-form.

5.) Adding HNO₃, a strong acid, destroys the complex ion and "adds" Ag⁺ to the AgCl equilibrium, causing AgCl(s) to re-form.

6.) None of these.

Answer 1

AgCl is a insoluble salt. The saturated solution of AgCl in aqueous solution is represented by the following equilibrium:

AgCl (s) ⇌ Ag^+(aq) + Cl^- (aq).......(1)

Now if a solution of NH3 is added to the solution, then NH3 reacts with the Ag^+ ions to form the [Ag(NH3)2]^+ complex. Thus the concentration of Ag^+ will get decreased and the equilibrium will be disturbed . In order to re-establish the equilibrium, more of AgCl will get dissolve to produce more Ag^+ ions and thus the reaction will be shifted in the forward direction according to the Le- Chatelier's Principle.

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

Now, if HNO3 is added, it will distroy the complex of [Ag(NH3)2]^+ to give the Ag^+ ions in the solution.

Now, as the concentration of the Ag^+ is increased, the equilibrium reaction (1) will get disturbed. In order to re-establish the equilibrium, the Ag^+ will react with the Cl^- and the reaction will proceed in backward according to the Le-Chatelier's Principle and more AgCl will be re-formed.

Hence, the correct statements are:

• AgCl is an insoluble solid.
• Ag^+ reacts with NH3 to form [Ag(NH3)2]^+ , which removes Ag^+ from the AgCl equilibrium, causing more AgCl to dissolve.
• Adding HNO3, a strong acid, destroys the complex ion and adds Ag^+ to the AgCl equilibrium, causing more AgCl(s) to re-form.

​​​​​​Hence, 1,3,5 are the correct statements.