Purpose:
In this lab our job was to determine the physical quantities of both 1-butanol and ethanol by
using fractional distillation. We
used an equimolar mixture of
these closely boiling subtances.
We assessed the efficiency of the
separation by measuring the
composition of four fractions
collected. Even though our
temperature stayed a constant
73°C, we still got good
separations of both substances.
The apparatus we used was a
vigreux column, and this helped
slowly separate both mixtures to
their pure forms.
us
Procedure/Methods:
After weighing out the 5ml of both 1- butanol and ethanol, we filled the lowermost chamber of
the Hickman still with 2.5 mL of ether and 2.5 mL of butanol as well as boil stones. Once we
assembled the the glassware for the vigreux column, we placed a thermometer to record the
temperature range of each fraction taken. We then packed the air condenser with steel wool to
increase the surface area within the packed column. The wool shown at the bottom around the
boiling flask increased the heat contained. The fractions contained condensed liquid from the
vapors that were collected in the Hickman still. These fractions are what we used to obtain a gas
chromatograph.
Results:
Fractional Distillation
Figure 1: This was the graph for the first fraction ran via gas chromatography. Ethanol is the only
peak shown which means that the first fraction was 100% pure.
Figure 2: This is the graph for the second fraction. Here we see that we do not have a pure
substance because there are two peaks located. The first peak is ethanol in which the mixture
contained 98.84% of this substance. The second peak is 1-butanol in which the mixture
contained 1.16%.
Figure 3: This is
the third fraction
in which has a
single peak of 1butanol. This is
another pure
substance.
Figure 4: This was our fourth and final fraction taken by gas chromatography and was again pure
1-butanol.
Simple Distillation
Figure 5: First fraction taken from using simple distillation. The two peaks shown tell us the
amounts of 1-butanol and ethanol separated.
Figure 6: Section fraction taken, this one showing more ethanol than butanol separated.
Figure 7: This is the third fraction taken, again showing the different amounts of 1-butanol and
ethanol separated.
Figure 8: This was the last fraction taken, showing us that almost all of the 1-butanol has been
separated from the ethanol.
Simple distillation shows a gradual change of percentages, unlike our fractional distillation.
These graphs help show us the difference between fractional and simple distillation. Simple
distillation had no pure substance of either ethanol or 1-butanol. On our graphs, you can see three
of them are pure and one of them has a mixture of both components. The disadvantage of simple
distillation is that you do not get the purest substances you can get. If you want good fractions,
you need gradual heating, a long cylinder to slowly capture the pure fractions.
The reason we used fractional distillation was because the two components we used we close in
boiling temperatures. To use simple distillation, the boiling points have to be greater than a 25°C
difference. In fractional distillation, the gas will condense on the surface area of the packing
material in the fractionating column, and will be reheated by the rising hot gas, to be vaporized
again until it becomes ‘pure’. Contrariwise, simple distillation is often used to separate the liquid
substance from the solid substance.
Summary:
In this lab, we got efficient separations of both 1-butanol and ethanol. We compared our data to
our constructors data, who did not use fractional distillation. He used simple distillation, whose
fractions are as follows, 90:10 ethanol to butanol, 70:30 ethanol to butanol, 30:70 ethanol to
butanol, and 2:98 ethanol to butanol. This shows us the differences between fractional and
simple distillation, and teaches us that simple distillation is mainly used when separating solids
from liquids, because we did not get completely pure separations like we did with fractional
distillation. This seems to indicate that a long path with a packed column gives a better
separation.