Fractional distillation is a process that separates a mixture of liquids based on their volatility, or tendency, to vaporize. In a mixture of two liquids, the temperature will remain constant as one distills and shoots up abruptly to a different temperature where the other liquid will distill. A distillation curve plots temperature versus the amount of distillate collected. A distillation curve will clearly show the boiling point of each liquid in the mixture and their respective volumes.
Assemble the setup for fractional distillation. This setup is identical to the one for simple distillation, except for the presence of a distilling column between the flask and the connecting adapter. Fractional distillation will determine the boiling points of the liquids in the mixture and the amount of each liquid present. Tighten all the materials in the setup to create a closed system and to produce accurate results.
Draw a chart for temperature and volume of distillate collected. Leave the temperature column empty. For the volume, write equal increments of liquid. If the mixture is 10 milliliters (ml), there should be 10 rows in the volume column starting at 1 and increasing by 1ml until 10. By preparing this chart before performing the experiment, you will have a better ability to record the results accurately.
Heat the mixture slowly and continuously. The distillation must occur at a constant rate to optimize percent recovery and obtain exact results. Place the Bunsen burner close to the mixture flask. This will reduce the effect of an air breeze on the flame and sustain the constant application of heat to the mixture.
Record the temperature of the mixture when distillation begins. The distillation starts as soon as the first drop of distillate is collected. This temperature is the boiling point of the first liquid in the mixture. For each ml, record the temperature. At some point during distillation, the temperature will rapidly shoot up and plateau at a higher number. This will be the boiling point of the second liquid.
Plot the collected data as a line graph of temperature versus volume. To visualize the results better, the temperature should be on the Y-axis and the volume of the distillate on the X-axis. The graph will have two plateaus; each plateau will indicate the boiling point of a particular liquid in the mixture.
Heat slowly. Heating too quickly will cause the mixture to distill too quickly and prevent you from accurately recording the temperature. Dry the materials thoroughly. Any condensation will compromise the results.
The glass materials can become very hot during distillation. Allow them to cool before disassembling.