Simple Distillation

Simple Distillation

Experimental Organic Chemistry: A Miniscale and Microscale Approach. 4th Edition.

By Gilbert and Martin. Section: 4.4

Introduction:

Distillation is a technique used to purify various liquids. In a simple distillation, a liquid is boiled and the vapors work through the apparatus until they reach the condenser where they are cooled and reliquified. Liquids are separated based upon their differences in boiling point in which each pure substance is at least greater than 40-50 oC. A liquid has a specific boiling temperature at standard pressure conditions. If there are two liquids in a solution, the liquid with the lowest boiling point can be boiled out of the solution without removing a significant amount of the other liquid. By vaporizing the liquid and condensing it in another container, one can obtain a pure sample of the liquid. Any impurities and liquids with higher boiling points remain in the original container.

Another part of this lab is boiling point determination. If a thermometer is added to the distillation apparatus, the vapor of a boiling liquid will condense on the thermometer bulb. Since a substance condenses at the same temperature that it boils, the temperature at which the vapor condenses on the thermometer will be the boiling point. The boiling point is useful in the identification of liquids, much like the melting point is useful in identification of solids.

Experimental Procedure:

First of all, assemble glassware as shown on page 129 of the text. Note that the tip of the thermometer must be correctly positioned slightly below the center of the condenser to accurately reflect the temperature of the vapors and the water supply should be connected to the lower port in the condenser and the drainage tube connected to the upper. Secure all glassware with the blue security clamps. Power the transformer and heat the heating mantel to a gradual high temperature so that distillation continues at a steady rate of 2-4 drops per second. Record the temperature once the head temperature is constant and continue heating until only 2-3ml of impure cyclohexane is left. Finally, record the volume of cyclohexane that remains in the distillation flask.