If hydrochloric acid is added to the equilibrium of [Cu(NH3)4]2+, what happens to the concentration of that complex?

If hydrochloric acid is added to the equilibrium of [Cu(NH3)4]2+, what happens to the concentration of that complex?

• A. The concentration increases
• B. The concentration decreases
• C. No change occurs
• D. The solution becomes more acidic

Answer: (B)

When hydrochloric acid is added to the equilibrium system involving the complex ion [Cu(NH3)4]2+, the concentration of the complex decreases due to the following reasons: Hydrochloric acid dissociates in water to produce hydrogen ions (H+) and chloride ions (Cl-). The addition of H+ ions increases the acidity of the solution. Ammonia (NH3), which is a weak base, is sensitive to changes in pH. In acidic conditions, ammonia may react with protons (H+) to form ammonium ions (NH4+). This reaction reduces the availability of ammonia for complex formation with copper ions. As the concentration of ammonia decreases due to its conversion to ammonium ion, the equilibrium shifts according to Le Chatelier's principle. Since the formation of the complex [Cu(NH3)4]2+ relies on a sufficient concentration of ammonia, decreasing the availability of NH3 will lead to a reduction in the concentration of the copper complex. Therefore, the overall effect of adding hydrochloric acid to the equilibrium is a decrease in the concentration of [Cu(NH3)4]2+ as the equilibrium shifts to counteract the change by favoring the reactants over the products.

When hydrochloric acid is added to the equilibrium system involving the complex ion [Cu(NH3)4]2+, the concentration of the complex decreases due to the following reasons:

Hydrochloric acid dissociates in water to produce hydrogen ions (H+) and chloride ions (Cl-). The addition of H+ ions increases the acidity of the solution. Ammonia (NH3), which is a weak base, is sensitive to changes in pH. In acidic conditions, ammonia may react with protons (H+) to form ammonium ions (NH4+). This reaction reduces the availability of ammonia for complex formation with copper ions.

As the concentration of ammonia decreases due to its conversion to ammonium ion, the equilibrium shifts according to Le Chatelier's principle. Since the formation of the complex [Cu(NH3)4]2+ relies on a sufficient concentration of ammonia, decreasing the availability of NH3 will lead to a reduction in the concentration of the copper complex.

Therefore, the overall effect of adding hydrochloric acid to the equilibrium is a decrease in the concentration of [Cu(NH3)4]2+ as the equilibrium shifts to counteract the change by favoring the reactants over the products.