Question

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

FeSCN2+(aq) ⇄ Fe3+(aq) + SCN–minus(aq)

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

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

(1 point)
Responses

adding an ion that causes SCN–minus to precipitate
adding an ion that causes SCN – minus to precipitate

adding KSCN, which dissociates into K+ and SCN–minus
adding KSCN, which dissociates into K + and SCN – minus

adding FeCl3, which dissociates into Fe3+ and Cl–minus
adding FeCl 3 , which dissociates into Fe 3+ and Cl – minus

adding an ion that causes Fe3+ to precipitate
adding an ion that causes Fe 3+ to precipitate
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Answer 1

Answer: adding an ion that causes SCN– to precipitate.

Reason: removing SCN– (a product) shifts the equilibrium right (Le Chatelier), producing more Fe3+ (pale yellow) and consuming the red FeSCN2+ complex, so the solution becomes more yellow. Adding KSCN or Fe3+ would shift left (more red), and precipitating Fe3+ would remove yellow from solution, so it would not make the solution turn pale yellow.