fractional distillation boiling point of mixtures separation of mixtures by distillation

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  • 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

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