Use the dissociation reaction to answer the question.

Question

FeSCN^2+ (aq) ⇆ Fe^3+ (aq) + SCN^- (aq)

In the reaction, FeSCN^2+ ions are red, Fe^3+ ions are pale yellow, and SCN^− ions are colorless. A solution at equilibrium is yellow-orange. The concentration of SCN^− ions is increased by a moderate amount. Which color will the solution most likely become?

A. yellow
B. intense orange
C. red
D. colorless

Answer 1

In the dissociation reaction given:

FeSCN^2+ (aq) ⇆ Fe^3+ (aq) + SCN^- (aq)

We can observe that the equilibrium consists of red FeSCN^2+ ions and pale yellow Fe^3+ ions, with SCN^- being colorless. When the concentration of SCN^- ions is increased, according to Le Chatelier's principle, the equilibrium will shift to counteract this change by favoring the formation of more FeSCN^2+ ions.

As more FeSCN^2+ ions are formed, the color will shift towards the color of the FeSCN^2+ complex, which is red. Hence, the solution will become more red.

So, the solution will most likely become:

C. red