Chem 334
Expt. #3
Simple and Fractional Distillation; Analysis of Distillation Fractions
by GC
Figure 1 Figure 2
What factors affect the boiling point of a compound?
Experiment #3 compounds
EA = ethyl acetate CH3CO2CH2CH3
EP = ethyl propionate CH3CH2CO2CH2CH3
b.p. = 77oC
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
4
8
12
70 etc.
Record your data:
Temp. & # drops
Also collect data for
Fractional Distillation
Simple Distillation Set-up
Add boiling chip
collect the 1st two drops here, in a receiving vial.
Label!
Thermometer position
Figure 1
*
Continue recording your data
Fractional Distillation Set-up
Micro-column
& steel sponge
Be careful not to cut your hand with the steel sponge when packing the column.
Figure 2
*
Do not “stuff” the column too tightly
Simple & Fractional Distillation Plot Both Curves on one Graph
0 4 8 12 16 20 24 28 …………………..etc. Volume of distillate (# drops)
98 oC
oC
oC
oC
Plot both S1 and F1 curves on the same graphTemperature
Part C. Analysis of Distillation Fractions by GC
HP 5890 Gas Chromatograph
GC Detector
Open Tubular Capillary Column
Carrier Gas
Injector
SampleFlow Diagram for a Capillary GC
vent
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!
Retention time
Injection point
Each peak (in a good separation) represents one compound.
Each peak (in a good separation) represents one compound.
The area under each peak corresponds to moles of the compound
EA
EP
Gas chromatogram of a 50:50 (v:v) EA/EP mixture
In diethyl ether
Remember:
Diethyl ether ≠ Petroleum ether !!!
Next time:
• Gas chromatography (conclusion)
• Steam distillation: Isolation of eugenol from cloves