DistillationDistillation

Macroscale TechniqueMacroscale Technique

DefinitionsDefinitionsDistillationDistillation: Separation of compounds based on differences in Separation of compounds based on differences in their boiling pointtheir boiling pointEvaporation: 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.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 ofliquid equals to the external pressure applied to the surface of the the liquid (usually atmospheric pressure)liquid (usually atmospheric pressure)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 thits liquid state. Vapor pressure depends on the substance and the e temperature.temperature.

RaoultRaoult’’s Laws 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 solutionPP11

°° is the vapor pressure of compound 1is the vapor pressure of compound 1PP22

°° is the vapor pressure of compound 2is the vapor pressure of compound 2xx11 is the mole fraction of compound 1is the mole fraction of compound 1xx2 2 is the mole fraction of compound 2is the mole fraction of compound 2

⇒⇒The vapor contains a larger percent of the more volatile (i.e., The vapor contains a larger percent of the more volatile (i.e., lower lower boiling pointboiling point) compound) compound

Toluene b.p.

Cyclohexane b.p.

Vaporization

Simple DistillationSimple Distillation

A (liquid) + B (liquid)A (liquid) + B (liquid)

A (liquid)A (liquid) B (vapor)B (vapor)

B (liquid)B (liquid)A (liquid)A (liquid)

b.p. > 40 ºC apart

Heating (above b.p. of B)

Cooling (below b.p. of B)

One vaporization step = Simple One vaporization step = Simple ditillationditillation

Simple vs Fractional DistillationSimple vs Fractional DistillationSimpleSimple FractionalFractional

Fractional distillation = series of subsequent simple distillatFractional distillation = series of subsequent simple distillationsions

Condensation

Revaporization

Simple vs Fractional DistillationSimple vs Fractional Distillation

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

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ExperimentsExperimentsBegin building apparatus from round bottom flask (high enough soBegin building apparatus from round bottom flask (high enough so you 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 rubberbandband 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 setHave your TA check your set--up before starting anything.up before starting anything.Distill at a slow but steady rate: Distill at a slow but steady rate: 1 drop/21 drop/2--3 seconds3 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 DistillationSimple vs Fractional Distillation