Organic Chemistry Lab 315
Fall, 2014
DUE DATES
• Today
– At beginning of lab – Gas Chromatography
Report
– At end of lab -- copy of laboratory
notebook pages for today's experiment
– Spectroscopy Problem II #3
• Next Week
– Distillation of a Mixture Report (see my
web page for special instructions)
– Spectroscopy Problem II #4
In Lab Today
• Your vial of caffeine will be returned.
Please discard the contents in the
Waste Jar, rinse the vial, and return
the vial to the Instructor’s bench.
• Distillation (separation) of a mixture of
ethyl acetate and butyl acetate by
Simple Distillation and Fractional
Distillation.
In Lab Today
• Simple and Fractional Distillation.
– The mole percent composition of the ethyl
acetate/butyl acetate mixture is unknown.
– You will compare the efficiency of Simple
vs. Fractional Distillation in separating
these two components.
• “Efficiency” is determined by how well the
mixture is separated into its components
• The closeness of your calculated mole %
composition for the two procedures to the
actual composition will be the measure of
efficiency.
Distillation of a Mixture
Vol. distillate (ml)
• Simple Distillation of a
pure compound.
Distillation of a pure compound
12
10
8
– Most of the compound distills
around the boiling point.
6
4
2
0
40
60
70
80
Temperature (deg. C)
90
100
10
8
6
4
2
0
40
60
80
Temperature (deg. C)
Graphs of Volume of distillate
vs. Temperature
• Simple Distillation of a
mixture where boiling
points are very different
or a Fractional Distillation.
Distillation of a Mixture
12
Vol. distillate (ml)
50
100
120
– The two compounds are
efficiently separated. Each
component distills around its
boiling point.
Distillation of a Mixture
Temperature vs. time
behavior of a single
component during distillation
Temperature vs. time
behavior of two components
with similar boiling points
Temperature vs. time behavior of
two components with very
different boiling points
Distillation of a Mixture
• Simple Distillation
– Relatively pure substances can be
separated from a mixture if the boiling
points of the components differ by >100oC
or if impurity <10%.
• EtOAc (b.pt. = 77oC)
• Fractional Distillation
BuOAc (b.pt. = 125oC)
– Separates components by distilling them
through a longer path with more
vaporization-condensation cycles (just like
re-distilling over and over again).
Experimental Procedure
• Set up distillation
apparatus
– Simple or fractional
(which you do will be decided
later)
• Put mixture of
EtOAc/BuOAc in
distilling flask with
boiling stones
• Be sure to position
thermometer correctly
• Conduct distillation
slowly but steadily
Experimental Procedure
• Collect fractions in test
tubes.
– The liquid that distills over
a 5-deg. interval is
collected in one test tube.
– It may be a large or small
volume of liquid. It doesn’t
matter.
– If you accidently mess up
an interval, write down the
actual temperature
interval and then proceed
with a new 5-deg. interval.
Experimental Procedure
• Measure the volume
of each fraction.
• Save fractions until
you are finished.
• Place three fractions
in vials, properly
labeled.
– Beginning, middle, end
• The saved fractions
will be analyzed by
Gas Chromatography
next week.
Experimental Procedure
• You are going to graph Volume of Fraction
vs. Temperature
– For a single pure component, all the volume
would be collected near the boiling point, as in
your purification of the unknown for IR
spectroscopy.
– Expect to collect the most volume at the
temperature(s) nearest the boiling point of
each component.
– See the graphs on a previous slide.
Notes
•
Measure volume of unknown mixture with graduated cylinder, ±1.0 ml.
•
Wrap fractionating column and head with Al foil.
•
Collect all fractions in test tubes, over ICE!.
•
I need to check your set-up before you begin the distillation – have
everything ready except turning on the hot plate.
•
Control distillation rate (~ 1 drop/sec) by moving the distillation
apparatus up or down (only if necessary). Too fast a drip rate will
decrease the amount of separation.
•
WASTE Distillation waste in marked jar in hood.
Notes
•
In the fractional distillation, you may have to increase the heat to
reach the boiling point of BuOAc.
•
Each fraction is collected over a 5-degree temperature interval.
•
Save all fractions until the experiment is over.
•
Place 3 fractions from each distillation in individual vials, properly
labeled. (Beginning, middle, end from each distillation)
•
Remember: boiling points may not exactly match the literature. They
should be close.
•
You will analyze the fractions next week using Gas Chromatography.
Notes
•
Working in Groups –
– One Pair = 2 students who conduct a distillation together, either simple or
fractional. One Group = Two pairs (1 pair = simple; 1 pair = fractional) will
pool data to analyze.
– No member of the Group may leave the lab until the distillations are
completed and all the data are recorded in everyone’s notebooks (record all
group members’ names near the top of your notebook copy)
– Something always goes wrong, or differently, among the pairs. Be sure that
everyone in the group understands everything that happened unexpectedly –
whatever – and PUT IT IN YOUR NOTEBOOK BEFORE LEAVING THE LAB.
It will be Your fault if you do not understand the data, whether or not you
did that particular distillation.
•
See my lab web page for special instructions on writing the Report.
•
Make a photocopy of your report before turning it in next week. You
will need to refer to it for following week’s experiment: Gas
Chromatography of Distillate Fractions
Lab Clean-up
• Khoa Tang