Purification of Liquids
Simple and Fractional Distillation

In this laboratory we will experience the technique of distillation. Distillation is useful for the purification of liquid mixtures when the boiling points of the components of the mixture are distinct and low enough to allow distillation without degradation. If the lower boiling component of a mixture is not valuable (i.e. it can be discarded afterwards) and the higher boiling component has a boiling point different by at least 20°C, then simple distillation may be used to purify the higher boiling component. If the liquids have very similar boiling points or if the low boiling material is of value, then fractional distillation is employed. Other techniques are also available but are outside the scope of this laboratory exercise.

Simple distillation

Obtain 40 mL of a liquid mixture. Note that the liquid mixture will contain two chemicals from the following list. Be sure to prepare by finding all relavant data for those materials.
acetone
1-butanol
2-butanol
isobutanol (2-methyl-1-propanol)
tert-butyl alcohol (2-methyl-2-propanol)
ethyl acetate

Working with a partner, set up a simple distillation of the mixture. Once the first drop of distillate is collected note the temperature and continue to do so with each 0.5 mL collected. Also record the time for each of these data entries. You should set the temperature to distill at a rate between 10-20 drops per minute. Faster than that will give very poor results. After collecting a total of 30 mL distillate, allow the apparatus to cool and proceed as directed by your laboratory instructor. Based on the data that you obtained, can you hypothesize the identity of the two liquids in the mixture? Comment in your lab notebook.

Fractional distillation

Set up to perform a fractional distillation of the mixture. Begin with 40 mL of liquid. Again measure the vapor temperature at the first drop of distillate and each 0.5 mL thereafter. Again, record the time for each data entry. During the distillation collect three fractions. The first fraction will be from the first drop until the temperature begins to transition (as described in the prelab lecture). The second (small) fraction will be from the time of the transition until the temperature begins to level off. The third fraction will be of the higher boiling material after the temperature stabilizes. Save each fraction in a clean, dry, labelled vial. After collecting about 5 mL of the third fraction, allow the apparatus to cool and transfer the remaining distillate to the bottle from which is was obtained. (NOTE! This is a VERY unusual step. We will NEVER AGAIN put chemicals which have been used back into their stock bottle. Why is it acceptable to do this today?)

Use the computer to graph the temperature (on the y-axis) vs. the mL collected (x-axis) for both the simple and fractional distillation (on the same graph). Mark the graph to show the location at which each of the fractions was collected.

Literature Sources:

Safety and Risk Phrases

ChemExper for bp/safety/risk
Fisher Scientific, bp/MSDS
Aldrich Chemical Company, bp/MSDS
Acros Chemicals, bp/MSDS
NIST Chemistry Webbook for bp

SIRI MSDS Index
MSDS, Oxford University
TOXNET Hazardous Substances Database