Question

Use the equation showing the dissociation of iron thiocyanate in water to answer the question.

FeSCN2+(aq) ⇄ Fe3+(aq) + SCN–(aq)

In solution, FeSCN2+ ions are red, Fe3+ ions are pale yellow, and SCN– ions are colorless.

When a solution at equilibrium is orange, which change would cause the solution to become pale yellow?

(1 point)

adding an ion that causes Fe3+ to precipitate

adding FeCl3, which dissociates into Fe3+ and Cl–

adding KSCN, which dissociates into K+ and SCN–

adding an ion that causes SCN– to precipitate

Answer 1

adding an ion that causes SCN– to precipitate

Removing SCN– (a product) shifts the equilibrium right (FeSCN2+ → Fe3+ + SCN–), so more FeSCN2+ dissociates, increasing pale-yellow Fe3+ and decreasing the red FeSCN2+, making the solution paler yellow.