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  1. 1. Distillation Macroscale Technique
  2. 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. 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. 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. 5. Simple vs Fractional Distillation Simple Fractional Condensation Revaporization Fractional distillation = series of subsequent simple distillations
  6. 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. 7. Distillation Setups Simple Fractional rubber band * * Use labjack to support Reuse mixture for fractional distillation Plug to controller (not to wall)
  8. 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.
  9. 9. Simple vs Fractional Distillation