Practice Problem 2

The iodide ion reacts with iodine in aqueous solution to form the I₃^-, or triiodide, ion.

I^-(aq) + I₂(aq) I₃^-(aq)

What would happen if CCl₄ was added to an aqueous solution that contained a mixture of KI, I₂, and KI₃?

Answer

KI and KI₃ are both salts. One contains the K⁺ and I^- ions; the other contains the K⁺ and I₃^- ions. These salts are more soluble in polar solvents, such as water, than in nonpolar solvents, such as CCl₄. KI and KI₃ would therefore remain in the aqueous solution. I₂ is a nonpolar molecule, which is more soluble in a nonpolar solvent, such as carbon tetrachloride. The I₂ would therefore leave the aqueous layer and enter the CCl₄ layer, where it would exhibit the characteristic violet color of solutions of molecular iodine.