Question

PJ’s unknown solid 1) dissolves in hot ethanol, 2) is essentially insoluble in hexane, and 3) is insoluble in cold water, but sparingly soluble in warm water. Outline the recrystallization procedure you would suggest she use here.

Answer 1

Answer:

1. The solid is dissolved in the hot solvent (ethanol or water);

2. If the impurities are not dissolved, they are separated by filtration;

3. The solution is then cold, and the crystals of the solid are formed;

4. The solution is filtrated and the pure solid is obtained.

Explanation:

The recrystallization is a process to separate impurities from a solid. The solid with the impurities is dissolved in a hot solvent, and, is insoluble in the cold one. But the impurities must be soluble in the cold solvent, or insoluble in the hot one.

If the impurities are soluble in the cold solvent, then, the crystals of the analyte will be removed, and if they are insoluble in the hot solvent, then its crystal is removed first.

So let's assume that the solid is insoluble in hot ethanol, and soluble in hot water. Because its insoluble in hexane, the recrystallization is not possible with it. So the procedure would be:

1. The solid is dissolved in the hot solvent (ethanol or water);

2. If the impurities are not dissolved, they are separated by filtration;

3. The solution is then cold, and the crystals of the solid are formed;

4. The solution is filtrated and the pure solid is obtained.