Question

In the process of recrystallization, after dissolving the product in hot methanol, why do we have to add water to the boiling solution until a slight cloudiness develops?

Answer 1

Sometimes we are not able to crystallize the compounds with single solvent so we use mixture of solvents for recrystallization.

So we must have chosen methanol as one solvent as the solubility of the compound is better in it as compared to water. So the compound is dissolved in hot methanol. When water is added to it the solubility of solute decreases in the mixture so it causes insolubility of solute.

so when the cloudiness appears we can recrysattalize the compound.

Here we have to choose two solvents which are miscible in each other.