Question

Consider the following two solvents

Solubility

Solvent A 52g of product in 100mL at 100 celcius; 29g of product in 100mL at 25 celcius

Solvent B 8.1g of product in 100mL at 100 celcius; 0.91g of product in 100mL at 25 celcius

(a) Which solvent is a good crystallization solvent for the product? Explain your reasoning.

(b) If a student started out with 2.5021g of crude product, what will be the % yield after one crystallization step by using the minimum amount of solvent A that is required for the crystallization step?

(c) If a student started out with 2.5021g of crude product, what will be the % yield after one crystallization step by using the minimum amount of solvent B that is required for the crystallization step?

Answer 1

The solute must be relatively insoluble in the solvent at room temperature but much more soluble in the solvent at higher temperature. At the same time, impurities that are present must either be soluble in the solvent at room temperature or insoluble in the solvent at a high temperature.

Solvent A 52g of product in 100mL at 100 celcius; 29g of product in 100mL at 25 celcius

Solvent B 8.1g of product in 100mL at 100 celcius; 0.91g of product in 100mL at 25 celcius

a.

52g of product in 100mL at 100 Celsius, this is good system for crystallization.

Reason- If you see condition for crystallization, compound should be insoluble in solvent at room temp but should soluble at higher temp and should use minimum amount of solvent. This system is perfectly following rules.

b and c – It is not possible to calculate % yield from given data. If student start with 2.5 g crude, how can one guess the exact crystallization amount of produc?. It’s not possible.