When it comes to recrystallization, the choice of solvent is crucial for obtaining pure crystals. A water ethanol solution is often ideal because it offers a good balance between solubility and crystallization properties. Ethanol and water can form a homogenous solution, allowing many organic substances to dissolve when heated and then to crystallize out as the solution cools.
On the other hand, a water hexane solution is not suitable for recrystallization. Hexane is a non-polar solvent, while water is polar. These two solvents do not mix well and create a biphasic system, which means that most substances would either not dissolve in one of the solvents or would precipitate out of the solution immediately rather than providing a clear pathway for recrystallization. Therefore, the lack of solubility and the inability to form a homogeneous solution prevent water hexane from being an effective solvent for recrystallization.