Question

extration of caffeine.

a.Magnesium sulfate is the drying agent used in this experiment. Why is it necessary to use a drying agent before removing the organic solvent on the rotary evaporator?

b. Adding sodium chloride can often help cause emulsions to breakdown and separate in to distinct layers. Use the principles of solubility to explain why this works.

Answer 1

a. It is easy to remove solvent from the organic compound when the compound is is dried under vacuum, the solvent can be easily vaporized due to is low boiling point and low vapour pressure. When water is present it becomes difficult to remove even under low pressure because of its high boiling point and low vapour pressure.

When anhydrous magnesium sulfate is added before removal of solvent it adsorbs water which is present in trace amount to form decahydrate which is crystalline solid and can be removed by filtration.

b. On addition of sodium chloride the density of aqueous layer increases and hence the separation of less denser organic layer and the more denser aqueous layer becomes easy.