3. Calculation of theoretical crystallization yield

Once the solubility of the product in a chosen solvent is known, it is possible to calculate the maximum yield of pure crystals that can be obtained by cooling or evaporating the solution. This is, of course, a maximum yield, as the calculation is based on the assumption that the solution returns to equilibrium (in a saturated state) when the deposited crystals are in suspension. The yield refers to the quantity of pure crystals obtained in the solution, but we know that in practice, the yield can be slightly higher than that calculated, as the mass of crystals always retains a small quantity of mother liquor, even after filtration. As a result, after drying, a thin film of material may surround each crystal, a layer that is less pure than the crystal core. This phenomenon all the more justifies the washing operation (paragraph