Simple Distillation

Introduction
(Adapted from Mohrig, pp. 109-112.)

The boiling point of a pure organic liquid is a physical property of that liquid. It is defined as the temperature at which the vapor pressure of the liquid exactly equals the pressure exerted on it. Boiling points can be determined using the technique of simple distillation. Distillation is a technique that is used to purify a mixture of liquids or to obtain a boiling point of a pure liquid (in the case of this course). Essentially, the liquid is heated to boiling and the vapors condensed above the boiling liquid.

Apparatus
This is a 4.5 minute movie on how to set up a simple distillation apparatus. Please feel free to scroll through it to get to sections that interest you. A complete setup of this apparatus will be on the front bench of lab.

Procedure for Boiling Point Determination

Once you have set up your simple distillation apparatus according to the movie above, place the liquid to be distilled in the distilling flask. The flask should be no more than two-thirds full at the start of the distillation because the contents may foam and boil over. Remember to place one or two boiling stones in the flask to promote even boiling. Ensure that all joints are tight. Turn on the water for the condenser. Only a small stream of water is needed; too much water pressure will cause the tubing to pop off. Turn on the Variac and the distillation can begin. Adjust the Variac until the distillate drops at a regular rate of about one drop per second. Allow 10 drops of distillate to collect and then discard. Collect the remaining distillate. At the point at which the temperature has become the highest and most stable, record the temperature. This is your boiling point. Never boil the distilling flask to dryness because, in some cases, high-boiling explosive peroxides can become concentrated. Stop the distillation when a small amount of liquid is left in the distilling flask. Turn off the Variac and remove the heating mantle to allow the flask to cool more quickly.