EXPERIMENT 2 : FRACTIONAL DISTILLATION

Objective
:This process separates mixture into two or more products that consist of different boiling points
through the vaporization of a liquid mixture component and the recycling of gas into
liquid flow in the column. We use fractional distillation rather than simple distillation because it is
used to separate components of complex mixtures with small boiling point differences.

Theory
Distillation is a method that uses the differences in boiling points of solutions. The boiling point is
the temperature at which the vapor pressure of the liquid is equal to the external pressure
applied to the surface of the liquid. Fractional distillation is used for a precise distillation process.
As the mixture is heated, the vapor rises and enters the fractionating column. As the vapor
cools, it condenses on the packing material of the column. The heat of rising vapor causes this
liquid to vaporize again, moving it along the column and eventually yielding a higher purity
sample of the more volatile component of the mixture.
We use fractional distillation widely in the refining oil industry . Distillation has some concepts
that are very important including boiling points of liquids, Raoult’s Law, Dalton’s Law and
azeotropes. Boiling point occurs when the vapor pressure exceeds the atmospheric
pressure which causes the solvent to vapor. According to Raoult’s Law, the vapor pressure of a
solvent above a solution is equal to the vapor pressure of the pure solvent at the same
temperature regarding mole fraction. Dalton's Law of partial pressures states that the total
pressure of a mixture of gases is equal to the sum of the partial pressures of the component
gases. Lastly, an azeotrope is a mixture of liquids that has a specific boiling point and the vapor
composition is exactly the same as the liquid.
Aparatus
⦁ round bottom flask
⦁ condenser
⦁ fractionated column instead of simple column
⦁ water aspirator
⦁ water bath and bunsen burner
⦁ thermometer
⦁ measuring cylinder
Chemical used
⦁ food colouring
⦁ distilled water
⦁ boiling chips
⦁ ethyl alcohol
⦁ ethanol- water
⦁ copper sulphate
 Procedure
❖ 50ml of water was poured into the distilling flask
❖ The same amount of ethanol (i.e 50ml) was also added to the same flask
❖ We introduced boiling chips before starting the fractional distillation.
❖ We recorded the temperature (with thermometer) while first ethanol was dropped
❖ Then,we collected the distillate substance directly into a measuring cylinder and
recorded the temperature every 5ml.
❖ Our thermometer reads at 50oC ,when the first ethanol was dropped.
❖ And the second ethanol was dropped at a temperature of 76oC .
❖ The temperature remained the same (i.e 76oC),all the way until we reached 15 ml
volume in the measuring cylinder.
❖ When the ethanol reached 20 ml, Our temperature started to drop to 70oC.
❖ At 30ml of ethanol the temperature drops to 51oC.

❖ After that we removed the flask from the water bath and placed it on the direct heat
source called bunsen burner.
❖ Till this step we only got pure ethanol because the water boiling point cannot reach the
capacity of a water bath. That's why we changed into a direct heat source which can boil
the water.
❖ The first water droplet was recorded at the temperature at 75oC.
❖ When the measuring cylinder reached 5 ml ,the thermometer read 90oC.
❖ The temperature remains the same (90oC) until the water has passed 15 ml,after it has
passed the temperature starts to drop due to energy deficiencies to climb the crystal
column.

The data calculated in tabular form

Volume of ethanol(ml) Temperature (oC)

0 25

First droplet 50

Second droplet 76

5 76

10 76

15 76

20 70

25 65

30 51
 Observation
We observed the first droplet of water came at 50oC and the temperature stabled to 76oC until it
reached 20ml. after passed 20ml the temperature started to drop and at 30 ml it reached
51oC.till this point we only observe pure ethanol; since the water bath cannot boil the water and
evaporates it.Therefore to reach the boiling point of the water we use direct heat source and we
observed the first water droplet at 75oC and after 5ml it reached to 90oc.the temperature of
water also remained the same till it reaches some point(i.e 15ml).Then it started to drop like
ethanol.

Summary
Fractional distillation is a separation technique used to separate two or more liquids
that have boiling points closer than 20oC.There is a difference in temperature between the liquid
in the round-bottomed flask and the vapor on top of the fractionating column (know which has a
higher temperature, the vapor on top of the fractionating column or the liquid in the flask).
Data was collected and it showed that fractional distillation was more efficient in purifying
ethanol than simple fractional distillation.The data collected in the experiment showed that
fractional distillation was more effective because the vapor was able to condense so many
times in the fractional column. In addition, the experiment also showed that pure ethanol
could not be distilled from a mixture that had less than 95.6% of ethanol

Quiz questions
1.calculate the mole fraction of each compound in a mixture of 95g ethanol and 5g water.
n(ethanol)=(m/M) of ethanol
=0.48
n(water)=(m/M) of water
=0.277
n(total)=n(ethanol)+n(water)=0.757

● X(ethanol) =n(ethanol)/n(total)
= 0.48/0.757 = 0.635
● X(water) =n(water)/n(total)
=0.277/0.757 = 0.365
2. What is the use of fractioning column and how is it made?
A fractionating column or fractional column is an essential item used in the distillation of liquid
mixtures to separate the mixture into its component parts, or fractions, based on the differences in
volatilities. Fractionating columns are used in small scale laboratory distillations as well as large
scale industrial distillations.it is made from plastic bead or glass bead.

3.what is an azetrope?
azeotrope is a mixture of liquids that has a specific boiling point and the vapor composition is
exactly the same as the liquid.
 Substance boiling point(oC)
Water ………………………………100
Ethanol………………………………78
Benzene……………………………..80

They are azetrope because they have different boiling points.

This means one is volatile and non-volatile so we can simply separate them by simple
distillation and this indicates they have a distinct difference there is distinction of purity.

Since one of liquid are volatile as temperature increase the vapor pressure increase,it means
the bp of the mixture is less than 160oC

5.why does the temperature fall down towards the end of fractional distillation?
Because we can see that the high boiling point substance that was above was condensing so
condensation creates a drop in temperature.