When you have completed the simple distillation, you will proceed to the
fractional distillation of the same mixture. Wait until the round bottom flask has cooled,
then pour the distillate contained in the graduated cylinders into it. Add two new boiling
chips and assemble the apparatus for fractional distillation (see Figure 13.17 on p. 160).
Refer to the sample set-up in the yellow hood. The fractional distillation must be carried
out slowly. Turn on the thermowell to heat the mixture to boiling. Once boiling starts,
turn down the power. You should see a ring of condensate which gradually rises up the
length of the fractionating column, such that the column eventually acquires a uniform
temperature gradient. Increase the heat slightly if the ring of condensate stops rising.
The vapor-condensate mixture should reach the top of the column only after several
minutes. Once condensation of the vapors occurs, it should continue steadily at a rate not
greater than one drop per second. Increase the heat slightly if the flow rate decreases
significantly. Again, collect the distillate in the graduated cylinders, but do not place
them in ice. Record the temperature and volume of the distillate at 5 mL intervals until
the temperature starts to rise. When you see the temperature increase, record the
temperature and volume of distillate at intervals of 0.5 or 1 mL until the temperature no longer continues to increase. At this point, record the temperature and volume of the
distillate at 5 mL intervals until about 35 mL of total distillate has been collected.
Do notdistill to dryness.