Final answer:
A good recystallization solvent should dissolve the compound at high temperatures but not at room temperature, allowing for the compound to precipitate upon cooling, facilitating fractional crystallization.
Step-by-step explanation:
A good recystallization solvent is one that will dissolve the compound to be purified at elevated temperatures but ensures that impurities remain soluble or that impurities and the compound have significantly different solubility profiles at various temperatures. The solvent should not readily dissolve the compound and impurity at room temperature; instead, it should do so only when heated (elevated temperatures), which allows for recrystallization upon cooling. Water can often be a good solvent for this purpose as many ionic and polar compounds have higher solubility in hot water and precipitate out as the solution cools, allowing for fractional crystallization. However, the ideal solvent choice is dependent upon the differing solubility of the compound and impurities across temperatures.