2. Definitions
Distillation: Separation of compounds based on differences in
Distillation
their boiling point
Evaporation: process in which molecules in a liquid state gain
sufficient energy to enter the gaseous state.
Boiling Point: temperature at which the vapor pressure of a
liquid equals to the external pressure applied to the surface of the
liquid (usually atmospheric pressure)
Vapor Pressure: pressure exerted by a vapor in equilibrium with
its liquid state. Vapor pressure depends on the substance and the
temperature.
3. Raoult’s Law
PT = x1P1° + x2P2°
Toluene b.p.
(For a mixture of compounds 1 and 2)
PT is the total vapor pressure of the solution
P1° is the vapor pressure of compound 1
P2° is the vapor pressure of compound 2
x1 is the mole fraction of compound 1
x2 is the mole fraction of compound 2 Vaporization
Cyclohexane b.p.
⇒The vapor contains a larger percent of the more volatile (i.e., lower
boiling point) compound
4. Simple Distillation
b.p. > 40 ºC apart
A (liquid) + B (liquid)
Heating (above b.p. of B)
A (liquid) B (vapor)
Cooling (below b.p. of B)
A (liquid) B (liquid)
One vaporization step = Simple ditillation
5. Simple vs Fractional Distillation
Simple Fractional
Condensation
Revaporization
Fractional distillation = series of subsequent simple distillations
6. Simple vs Fractional Distillation
Simple distillation if boiling points more than 40 °C apart
Fractional distillation if boiling points less than 40 °C apart
Fractional distillation much more efficient but more costly (slower process)
7. Distillation Setups
Simple Fractional
rubber band
*
*
Use labjack to support
Reuse mixture for fractional distillation
Plug to controller (not to wall)
8. Experiments
Begin building apparatus from round bottom flask (high enough so you
can add or remove the heating device). Grease joints and use a rubber
band to secure vacuum adapter to condenser.
Support heating device with a labjack. Plug heating device to controller
(not to the wall outlet).
Use a mixture of Water and Ethanol (25 mL of each). Reuse the same
mixture for fractional distillation.
Add 2 boiling chips before the mixture is heated.
Have your TA check your set-up before starting anything.
Distill at a slow but steady rate: 1 drop/2-3 seconds.
Record temperature every 2 mL of distillate.
Use glass beads to pack the fractionating column.
Construct graph Temperature vs Volume for each type of distillation in
your lab notebook.
At the end of the experiment, discard distillation mixture in the sink.
