Why can a water-ethanol solution be used for recrystallization but not a water-hexane solution?
Water and ethanol are miscible; water and
hexane are not.
A water-ethanol solution can be used for recrystallization because ethanol is partially soluble in water. When a solid is dissolved in a water-ethanol solution and then cooled, it can form crystals as the solute is less soluble in the colder solvent mixture. This allows for the purification and separation of the desired compound.
On the other hand, a water-hexane solution is not suitable for recrystallization because hexane is nonpolar and immiscible with water. Hexane does not form a homogeneous solution with water and does not create an appropriate solvent environment for recrystallization.
Recrystallization is a process that relies on the solute's solubility behavior. When choosing a solvent for recrystallization, we want one that is a good solvent for the solute at high temperatures but a poor solvent at lower temperatures. This allows the solute to dissolve at an elevated temperature, effectively removing impurities, and then separate out as pure crystals upon cooling.