Chem 334
Figure 1
Figure 2
Expt. #3
Simple and Fractional Distillation;
Analysis of Distillation Fractions
by GC
What factors affect the boiling
point of a compound?
Experiment #3 compounds
EA = ethyl acetate
CH3CO2CH2CH3
b.p. = 77oC
EP = ethyl propionate CH3CH2CO2CH2CH3
b.p. = 99oC
Where would you expect the
boiling point of a mixture of
ethyl acetate and ethyl
propionate?
See Techniques 2 and 3
Where would you expect the boiling point of a
mixture of ethyl acetate and ethyl propionate?
Boiling Point - Composition for a
Liquid-Liquid Mixture
Raoult’s Law
“mixture of two liquids will have a b.p. that is
between the b.ps. of the pure liquids”
PX = PoXNX
where PX is the partial pressure of X
PoX is vapor pressure of pure X
NX is the mole fraction of X in mixture
(Exception: Azeotropes)
Assume a mixture of
x moles of EA and y moles of EP
What would be the mole ratio?
What would be the mole fraction of
EA in the mixture?
Boiling Point - Composition
for EA - EP mixture
Total vapor pressure of mixture “Ptotal” is the
sum of the partial pressures due to EA and
EP.
Ptotal = PEA + PEP
If “Ptotal” is equal to the external pressure,
boiling occurs.
Your experiment:
We will do two distillations:
A simple distillation
and a
fractional distillation.
Work in teams of two:
One student sets up the simple distillation and
the other student sets up the fractional distillation
glassware.
Table for Simple (Fractional)
Distillation
Temp oC # drops
1
Record your data:
Temp. & # drops
4
8
12
Also collect data
for
70 etc.
Fractional
Distillation
Simple Distillation Set-up
Thermometer
position
collect the 1st two
drops here, in a
receiving vial.
Label!
*
Figure 1
Add boiling chip
Continue recording your data
Fractional Distillation Set-up
Do not “stuff” the
column too tightly
Micro-column
& steel sponge
Be careful not to cut
your hand with the
steel sponge when
packing the column.
*
Figure 2
Simple & Fractional Distillation
Plot Both Curves on one Graph
Temperature
98 oC
Plot both S1 and F1 curves on the same graph
oC
oC
oC
0
4
8 12 16 20 24 28 …………………..etc.
Volume of distillate (# drops)
Part C. Analysis of Distillation
Fractions by GC
HP 5890 Gas Chromatograph
Flow Diagram for a
Capillary GC
Sample
Injector
Carrier Gas
vent
GC
Detector
Open Tubular
Capillary Column
Gas Chromatography
A separation method for volatile compounds
A chromatography method:
Stationary phase and moving phase
Separation is based on
1) physical & chemical properties of each
compound
2) different interaction with the stationary phase
A true microscale method!
Each peak (in a
good separation)
represents one
compound.
Retention time
Injection point
Each peak (in a
good separation)
represents one
compound.
The area under each
peak corresponds to
moles of the
compound
Gas chromatogram of a 50:50 (v:v) EA/EP mixture
In diethyl ether
EA
EP
Remember:
Diethyl ether ≠
Petroleum ether !!!
Next time:
• Gas chromatography (conclusion)
• Steam distillation: Isolation of eugenol
from cloves