By separating these two phases and allowing the solvents to evaporate, we can cleanly separate I 2 and KMnO 4 . This technique can also be used to extract solutes from a solid. Coffee, for example, is decaffeinated by extraction. But many people who have grown to like the flavor of coffee want to reduce the amount of caffeine they consume and therefore turn to decaffeinated coffee. Caffeine can be extracted with hot water, but this also tends to extract the oils that give coffee its flavor.
Distillation is the technique used most frequently to purify liquids.
At its simplest, it involves heating the liquid, as shown in the figure below, until it boils. The vapor that escapes is passed through a water-cooled condenser, where it condenses to form a liquid, which collects in a clean flask. Describe the difference between the composition of the liquid in the distillation flask and the vapor given off when this liquid starts to boil. Click here to check your answer to Practice Problem 10 We can develop a general rule for distillations by constructing a phase diagram that describes the mixtures under all possible combinations of temperature and percent composition, as shown in the figure below. A phase diagram for a mixture of pentane and octane that shows the effect of changes in the composition of the mixture on the boiling point of the solution.