1. Figure Figure 2
Chem 334
Expt. #3
Simple and Fractional Distillation; Analysis of Distillation Fractions by GC
CHEM 334 Expt 3 Lecture

2. What factors affect the boiling point of a compound?
22 C (degrees) difference, need about 12 theoretical plates to separate these two liquids.
CHEM 334 Expt 3 Lecture

3. Experiment #3 compounds
EA = ethyl acetate CH3CO2CH2CH3
EP = ethyl propionate CH3CH2CO2CH2CH3
b.p. = 77oC
b.p. = 99oC
22 C (degrees) difference, need about 12 theoretical plates to separate these two liquids.
CHEM 334 Expt 3 Lecture

4. Where would you expect the boiling point of a mixture of ethyl acetate and ethyl propionate?
22 C (degrees) difference, need about 12 theoretical plates to separate these two liquids.
CHEM 334 Expt 3 Lecture

5. See Techniques 2 and 3
Where would you expect the boiling point of a mixture of ethyl acetate and ethyl propionate?

6. 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)

7. x moles of EA and y moles of EP What would be the mole ratio?
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?
22 C (degrees) difference, need about 12 theoretical plates to separate these two liquids.
CHEM 334 Expt 3 Lecture

8. 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.

9. CHEM 334 Expt 3 Lecture

10. 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.
22 C (degrees) difference, need about 12 theoretical plates to separate these two liquids.
CHEM 334 Expt 3 Lecture

11. Table for Simple (Fractional) Distillation
Temp oC
# drops
Record your data:
Temp. & # drops 1 4 8 12
70 etc.
Also collect data for
Fractional Distillation

12. Simple Distillation Set-up
Thermometer position
collect the 1st two drops here, in a receiving vial.
Label! *
Add boiling chip
Figure 1

13. Continue recording your data

14. Fractional Distillation Set-up
Micro-column
& steel sponge
Do not “stuff” the column too tightly
Be careful not to cut your hand with the steel sponge when packing the column. *
Figure 2

15. Simple & Fractional Distillation Plot Both Curves on one Graph
Temperature
Plot both S1 and F1 curves on the same graph
98 oC oC
…………………..etc Volume of distillate (# drops)

16. Part C. Analysis of Distillation Fractions by GC
HP 5890 Gas Chromatograph

17. Flow Diagram for a Capillary GC
Sample
Injector
Carrier Gas
GC Detector
vent
Open Tubular Capillary Column

18. Gas Chromatography A separation method for volatile compounds
A chromatography method: Stationary phase and moving phase
Separation is based on
physical & chemical properties of each compound
different interaction with the stationary phase
A true microscale method!

19. Each peak (in a good separation) represents one compound.
Retention time
Injection point

20. Each peak (in a good separation) represents one compound.
The area under each peak corresponds to moles of the compound

21. Gas chromatogram of a 50:50 (v:v) EA/EP mixture
In diethyl ether EA EP
Remember:
Diethyl ether ≠ Petroleum ether !!!

22. Next time: Gas chromatography (conclusion)
Steam distillation: Isolation of eugenol from cloves