You are working with the following equilibrium system in which one chromium complex is blue and one chromium complex is purple. The system is at equilibrium and is currently blue.

Predict how the color will change if aqueous Ag+ ions are added. Ag+ reacts with NH3 to form a colorless silver-ammonia complex ion.

[Cr(H2O)6]3+ (aq) + 6 NH3 (aq) arrow
[Cr(NH3)6]3+ (aq) + 6 H2O (l)

Reactant side is blue and product side is purple

a. The solution will turn from blue to purple.
b. The solution will become a darker blue.
c.The solution will become a lighter blue.
d.The solution will not change colors.

The system is on the blue side. If we add Ag^+, it will form the Ag(NH3)^+ complex which will remove NH3 from the system and that will shift the equilibrium to the left. Of the answers listed, the most likely is d. Whether b is correct, or not, also, depends upon how blue the solution is at equilibrium. If the blue color is pronounced, however, the additional shift to the left will not be enough to notice a change in intensity of the blue color.

To predict the color change when aqueous Ag+ ions are added to the equilibrium system, we need to consider the reaction between Ag+ and NH3.

Ag+ reacts with NH3 to form a colorless silver-ammonia complex ion:

Ag+ (aq) + 2 NH3 (aq) -> [Ag(NH3)2]+ (aq)

In the equilibrium system, we have the chromate complex [Cr(H2O)6]3+ (aq) on the reactant side, which is blue, and the chromium-ammonia complex [Cr(NH3)6]3+ (aq) on the product side, which is purple.

When Ag+ ions are added, they react with NH3 to form the colorless [Ag(NH3)2]+ complex ion. Since the Ag+ ions are consumed, there will be a shift in the equilibrium towards the reactant side to replenish the NH3. This means more [Cr(H2O)6]3+ complex will be formed, leading to a higher concentration of the blue species.

Therefore, the solution will become a darker blue, as more [Cr(H2O)6]3+ complex is formed. The correct answer is option b - "The solution will become a darker blue."