How much solvent should ideally be used for dissolving a crude mixture for recrystallization?

The ideal amount of solvent used for dissolving a crude mixture in recrystallization is the minimal amount needed to completely dissolve the solids. This approach is critical for effective recrystallization because using a minimal volume of solvent helps to maximize the yield of pure crystals while minimizing the amount of impurities that can remain in solution.

When you use a minimal amount of solvent, the system becomes supersaturated upon cooling, promoting the formation of crystals as the temperature drops. If excess solvent is used, it may lead to the dissolution of impurities that could have otherwise been filtered out along with the solution, ultimately reducing the purity and yield of the desired product.

Using the exact weight of the solid as solvent is impractical and doesn't account for the solubility characteristics under various conditions. Instead, it's best to determine the minimal volume needed based on the solute's solubility in the chosen solvent, which ensures efficient crystallization and the isolation of the compound of interest.