Chemistry Activity
Fractional Distillation Purpose To separate a mixture of two miscible liquids (liquids that mix in all proportions) with different boiling points. Your mixture will consist of water and 2-propanol (isopropyl or rubbing alcohol). | | Menu Purpose
Background
Safety
Procedure
Data Analsysis
Implications and Applications
Concluding Questions |
Background
Distillation is a physical process used to separate mixtures that contain at least one liquid. Distillation works because each substance in the mixture has its own unique boiling point. So, as a mixture is heated, the temperature of the mixture rises until it reaches the temperature of the lowest boiling substance in the mixture. The lowest boiling substance boils away, of course. Meanwhile, the other components of the mixture remain in their original phase—either solid or liquid—until the lowest boiling component has all boiled off. Only then does the temperature of the remaining mixture rise and other components are boiled off.
If the original mixture contains a solid and a liquid, the liquid will boil off as the mixture is heated. As the liquid boils, it turns into a gas. If we can remove that gas from the original container and then cool it, the gas will condense into its original form—a liquid. The solid from the original mixture would then be in one container and the original liquid in another container. The separation would be complete.
This is the simplest kind of distillation. In fact, it is nature's method for purifying water. You may have studied the water cycle in an earth science class. As the heat from the sun warms the waters of the earth, the liquid water turns into water vapor, leaving behind any dissolved impurities. The water vapor is then cooled by the atmosphere—that is, it is condensed—and returns to the earth as a liquid, otherwise known as rain.
If the original is a mixture of liquids, each boils off at its boiling point and is cooled in turn to form a