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