CHE 317 "Fractional Distillation" 

Interpretation of Results and the Report

Follow the same format that was used in writing the report for the exercise on simple distillation of a single liquid.

Of particular importance in the interpretation of your observations is a comparison of the simple distillation of the mixture with the distillation of the same mixture through a fractionating column.  A tabulation of temperature-volume data for each distillation serves as the basis for the construction of two graphs, one for the simple and one for the fractional distillation.

Some comment on the efficacy of the distillation using the column should be offered.  For example, the data you obtained may have indicated that the fractions collected were mixtures, although of different composition than the original.  Thus an ideal separation may not have been achieved because of deficiencies in the apparatus (or your technique?).  Some recommendations about improvement of the fractionation assembly and conduct of the distillation are then in order.  The primary purpose of the experiment was not a determination of the boiling points of the components, so do not dwell on the aspect of it.

Remember, too, that it is not necessary to go into great detail in either the preliminary discussion or the Experimental section about the simple distillation procedure used in this experiment.  It is sufficient to state that the mixture was subjected to a simple distillation and to give the results of that operation.  A full account of the fractional distillation, including details of the apparatus used, should be given since it is being reported by you for the first time.

1. As before:  Title (specific), Your Name, Date, CHE 317

2.  In your own words, explain how fractional distillation works to separate volatile liquids.

3.  In one or two sentences, summarize what you did in this experiment.

4.  Make a table of the data you collected.

5.  Attach a graph (neat and professional using the computer) of the still head temp. vs. volume collected for the simple distillation.  On the same graph, plot the data for the fractional distillation in a different color.

6.  Describe the results you obtained from the simple and fractional distillation.  See if you can put into words the data that you collected and the resultant graph.

7.  What conclusions can you make from the results of your experiment?  Compare the two methods for efficacy.  If you have an opinion, back it up with data.  See previous page.

8.  Answer the following questions:

a.  What is Raoult’s Law?

b.  What is Dalton’s Law?

c.  Describe how Raoult’s and Dalton’s Laws relate to fractional distillation as a separation technique.

d.  What’s the difference between a packed column and an unpacked column a fractional distillation?

e.  What is a theoretical plate?

f.  On page 747 of your lab text is a temperature composition diagram for mixtures of two compounds, A & B.
(1) From the graph, what are the boiling points of pure A & pure B?

(2) For a mixture that contains 50 mole% A and 50 mole% B, what is the boiling point?  What is the composition of the first distillate and if this distillate were to be condensed, what at temperature would it boil?  What is the composition of the vapor at this temperature?

(3) For a boiling mixture at 60^oC, what is the composition of the vapor and the composition of the liquid?

g.  At what point do you change receivers during a fractional distillation if you are trying to separate the components?

h.  What observations during a simple distillation would cause you to redo the distillation using a fractionating column?

Attach notebook carbon copies. 

© Dr. Noel Sturm 2009