fractional distillation boiling point of mixtures separation of mixtures by distillation

Fractional DistillationBoiling point of mixtures

Separation of mixtures by distillation.

Boiling Points - DistillationsEthylene glycol, HOCH2CH2OH, boils at 198oC and melts at -13o C.What happens to the melting point of water if you add antifreeze?Melting point goes down.

Add antifreezeWhat happens to the boiling point of water if you add antifreeze?The boiling point goes up.

MixturesSolidsUsually melt lowLiquidsUsually boil between the two components

Vapor pressure of water vs. temperatureSolution boils when the vapor pressure = applied pressure

Add Salt Melting PointIf you add salt, NaCl, to water what happens to the melting point?Impurities depress the melting point so it goes down.

Add Salt Boiling PointIf you add salt, NaCl, to water what happens to the boiling point?The boiling point goes up.

Raoults LawP = Po*NObserved PressurePure SubstanceMole Fraction

Two Volatile Liquids

Boiling Point Two Volatile LiquidsPa = Poa * NaPb = Pob * NbMixture boils whenPa + Pb = Papplied

Plot of boiling point vs. mole fractionMixture of acetone and benzene.

Boiling point of an acetone-benzene mixtureMole fraction benzene = 0.50What is the composition of the vapor?

Vapor CompositionVapor richer in the lower boiling component

Fractional Distillation

Temperature vs. Volume

Packed ColumnHETP = 1.5 cm

Vigreux ColumnHETP = 10 cm

Which column has the greater holdup?Packed because it has the larger surface area.

Separate Pentane and Octane.Which column would you use to separate a mixture of pentane, b.p. 36o and octane, b.p. 99o?Vigreux

Separate Methanol and WaterWhich column would you use to separate a mixture of methyl alcohol, b.p. 65o and water, b.p. 100o ?Packed

ExperimentSeparate mixture of methanol and water. Plot volume distilled vs. temperature.

Equipment

Methyl alcohol is toxic!CH3OH

Standard Taper Joints14/2020 mm14 mm

Grease joints to prevent sticking.

Thermowell

Use Variable TransformerPlug the thermowell into the variable transformer

Put boiling chips in bottom of flaskBoiling Chips

Equipment

Thermometer Adapter

Water in

Water out

Joint Hose Clamps

IDEAL MIXTURES:

Same interactions between like and unlike moleculesNONIDEAL MIXTURES:Strong attractions between like moleculesStrong attractions between unlike moleculesA.B.

Ethanol - Benzene

Minimum - boiling azeotrope

Azeotrope

Acetone - ChloroformMaximum-boiling azeotrope

Maximum Azeotrope

Simple Distillation

Sample Equipment

Distillation Equipment

Solvent Purification