In which of the following cases would recrystallization be favored over extraction when purifying a mixture of two solid compounds? 1. When both compounds have the same functional group(s).
II. When the desired compound is poorly soluble in the solvent pair at low temperatures and greatly soluble in the solvent pair at high temperatures.
III. When there is a significant excess of the desired compound.
A. I and III.
B. II.
C. II and III.
D. I and II.
E. All of the above.
F. None of the above.

B. II.

Explanation:

The idea of recrystallization works when the solubility of the target substance decreases as the temperature of the solution decreases.

The method of recrystallization involves dissolving the solute in a suitable hot solvent and then allow the solution to cool gradually. The pure solute dissolves in the hot solvent and then separates out of the solution as it is cooled to room temperature.

Hence recrystallization is preferred over solvent extraction when the desired compound is poorly soluble in the solvent pair at low temperatures and greatly soluble in the solvent pair at high temperatures.