DistillationDistillation

Macroscale TechniqueMacroscale Technique

DefinitionsDefinitions DistillationDistillation: Separation of compounds based on differences in Separation of compounds based on differences in

their boiling pointtheir boiling point Evaporation: Evaporation: process in which molecules in a liquid state gain process in which molecules in a liquid state gain

sufficient energy to enter the gaseous state.sufficient energy to enter the gaseous state. Vapor Pressure: Vapor Pressure: pressure exerted by a vapor in equilibrium with pressure exerted by a vapor in equilibrium with

its liquid state. Vapor pressure depends on the substance and its liquid state. Vapor pressure depends on the substance and the temperature.the temperature.

Boiling Point:Boiling Point: temperature at which the vapor pressure of a temperature at which the vapor pressure of a liquid equals to the external pressure applied to the surface of the liquid equals to the external pressure applied to the surface of the liquid (usually atmospheric pressure)liquid (usually atmospheric pressure)

Raoult’s LawRaoult’s Law PPTT = x = x11PP11

°° + x + x22PP22°°

(For a mixture of compounds 1 and 2)(For a mixture of compounds 1 and 2)

PPT T is the total vapor pressure of the solutionis the total vapor pressure of the solution

PP11°° is the vapor pressure of compound 1 is the vapor pressure of compound 1

PP22° ° is the vapor pressure of compound 2is the vapor pressure of compound 2

xx11 is the mole fraction of compound 1 is the mole fraction of compound 1 xx2 2 is the mole fraction of compound 2is the mole fraction of compound 2

The vapor contains a larger percent of the more volatile compoundThe vapor contains a larger percent of the more volatile compound

Simple vs Fractional Simple vs Fractional DistillationDistillationSimpleSimple FractionalFractional

Fractional distillation = series of subsequent simple distillationsFractional distillation = series of subsequent simple distillations

Simple vs Fractional Simple vs Fractional DistillationDistillation

Simple distillation if boiling points more than 40 Simple distillation if boiling points more than 40 °C apart°C apart Fractional Fractional distillation if boiling points less than 40 distillation if boiling points less than 40 °C apart°C apart Fractional distillation much more efficient but more costly (slower process)Fractional distillation much more efficient but more costly (slower process)

Distillation SetupsDistillation Setups

SimpleSimple FractionalFractional

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Use labjack to supportUse labjack to support

Plug to controller (not to wall)Plug to controller (not to wall)

rubber bandrubber band

Reuse mixture for fractional distillation

ExperimentsExperiments Begin building apparatus from round bottom flask (high enough so you Begin building apparatus from round bottom flask (high enough so you

can add or remove the heating device). can add or remove the heating device). Grease joints and use a rubberGrease joints and use a rubber bandband to secure vacuum adapter to condenser. to secure vacuum adapter to condenser.

Support heating device with a labjack. Support heating device with a labjack. Plug heating device to controllerPlug heating device to controller (not to the wall outlet).(not to the wall outlet).

Use a mixture of Use a mixture of Water and EthanolWater and Ethanol ( (25 mL of each25 mL of each). ). Reuse the same Reuse the same mixture for fractional distillationmixture for fractional distillation..

Add 2 boiling chips before the mixture is heated.Add 2 boiling chips before the mixture is heated. Have your TA check your set-up before starting anything.Have your TA check your set-up before starting anything. Distill at a slow but steady rate: Distill at a slow but steady rate: 1 drop/2-3 seconds1 drop/2-3 seconds.. Record temperature every Record temperature every 2 mL2 mL of distillate. of distillate. Use Use glass beadsglass beads to pack the fractionating column. to pack the fractionating column. Construct graph Construct graph Temperature vs VolumeTemperature vs Volume for each type of distillation for each type of distillation in in

your lab notebookyour lab notebook.. At the end of the experiment, At the end of the experiment, discard distillation mixture in the sinkdiscard distillation mixture in the sink..

Simple vs Fractional Simple vs Fractional DistillationDistillation