Question

Consider the reaction shown in Equation 1 at equilibrium. Would the concentration of [Cu(NH₃)₄]₂⁺ increase if the equilibrium were disturbed by adding hydrochloric acid?

[Cu(H₂O)₄]₂⁺(aq) + 4NH₃(aq) → [Cu(NH₃)₄]₂⁺(aq) + 4H₂O(l)
A.
Yes, because the equilibrium in Equation 1 would shift to the left
B.
No, because the equilibrium in Equation 1 would shift to the left
C.
Yes, because the equilibrium in Equation 1 would shift to the right
D.
No, because the equilibrium in Equation 1 would shift to the right

Answer 1

Adding hydrochloric acid to the equilibrium mixture will increase H+ concentration which reacts with ammonia (NH3), a component of [Cu(NH3)4]2+ complex formation. This disturbance will shift the equilibrium to the left, leading to a decrease in [Cu(NH3)4]2+ concentration.

Step-by-step explanation:

When hydrochloric acid (HCl) is added to an equilibrium system, the concentration of hydrogen ions (H+) increases. The reaction that we are considering involves the complex ion [Cu(NH3)4]2+, which forms in the presence of copper ions and ammonia. According to Le Chatelier's Principle, the equilibrium will shift to counteract the increase in H+ concentration.

Since the equilibrium constant for the formation of [Cu(NH3)4]2+ is large, the system initially lies far to the right, favoring the formation of the complex ion. If more H+ ions are added to the system, they will react with the NH3, a base, reducing its availability to form [Cu(NH3)4]2+. Therefore, the equilibrium will shift to the left, decreasing the concentration of the complex ion [Cu(NH3)4]2+, not increasing it, as the formation of the complex is disturbed by the consumption of NH3.