Distillation of Organic Liquids

The boiling point of a liquid depends on that liquid’s vapor pressure, which is the pressure exerted by vaporized molecules as they hit the sides of a closed container.

Therefore, during the course of the distillation, the liquid with the lower boiling point will be selectively removed from the original binary mixture.

Distillation Set-Up

Procedure

Part I:

1. Place 25 mL of hexane in a flask and add a magnetic stir bar

2. Start water circulating through the condenser

3. Heat flask until the hexane boils

4. Record temperatures as liquid drips as you collect 1, 3, 5, 7, 9 and 11 mL of distillate

5. After collection, lower the lab jack with the hot plate to allow apparatus to cool

Part II

1. Place 25 mL of hexane and 25 mL of toluene to a round bottom flask and add a magnetic stir bar

2. Start water circulating and heat flask and collect fractions 2, 5 and 7 in prelabeled vials

3. After collecting fraction 2, wrap the condenser with red tape in foil above the liquid level in the flask all the way up to the thermometer bulb.

4. Adjust the heat so it distills slowly and steadily

5. Record the temperature after every 5 mL distilled

6. After collection, lower the lab jack with the hot plate to allow your apparatus to cool.

Distillation of Organic Liquids

Results

Conclusion

Comparing the two compounds, toluene possessed a higher boiling point than hexane, and because the percent composition of toluene increased, the boiling point of the distillate increased.

According to our results as both fraction number and temperature increased during the distillation process, the percent composition of toluene increased.

While the percent of toluene increased, the percent composition of hexane decreased.

In summary, this experiment was conducted to demonstrate the basic process of distillation. Gas chromatography was used to determine the composition of the distillate; the results of the experiment correlate with what is already known about the basic principles of distillation.

(Amount of distillate collected at recorded temperatures)

(5 mL increments of distillate at recorded temperatures)

(How much original mixture remained as temperature increased)

Other Supplies

2 Blue Clips

Hot Plate

Graduated Cylinder

Lab Jack

Receiving Flask Attachment

Distillation Flask

Thermometer Piece

Attach the Thermometer Piece and the Condenser together via the side arm of the Thermometer Piece, and use one of the blue clips to lock the two into place. Make sure the outlets for water are facing upwards.

Next put the Receiving Flask Attachment to the other end of the Condenser, and add the final blue clip to lock these two in place as well. Make sure the Receiving Flask Attachment is facing down.

Background Information

Using the Lab Jack, place a receiving flask under the Receiving Flask Attachment so that any liquid leaving will be collected by the flask.

Condenser

For a Simple Distillation ignore the Binary Mixture Attachment and connect the Thermometer Piece directly to the Distillation Tube. For separation of a binary mixture, put the Binary Mixture Attachment to the Thermometer Piece and then to the Distillation Flask as shown to the right. This should complete the apparatus setup.

Binary Mixture Attachment

The purpose of distillation is to separate and purify organic liquids using variances in boiling point.

The boiling point is defined as the temperature at which the pressure of the surroundings is equal to vapor pressure of the liquid.

1st Distillate: Mostly Liquid With Lowest Boiling Point

In distillation, frequently two miscible liquids with different boiling points are combined to form a binary mixture.

2nd Distillate: Mostly Liquid With Higher Boiling Point

Because the two liquids have different boiling points, when the mixture is heated to an increasingly high temperature during the distillation process, the liquid with the lower boiling point will evaporate first and therefore distill first.

Vapor pressure and boiling point is the key

When distilling out all our nasty debris

Combined liquids are hard to use

So exploit the boiling point to diffuse

Different boiling points separate the mixture

1, 2, 3 there goes the liquid in our fixture

First the lower, then the higher

Two different liquids as we desire

Lower temp gets more liquid

Higher temp gets barely sifted

In this way the two are seen

to be taken from the unclean