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Simple Distillation

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  1. Preparation of the Laboratory

    Here, we show the laboratory preparation for 10 students working in pairs, with some excess. Please adjust quantities as needed.

    • Before you begin, put on a lab coat, splash-proof safety glasses, and nitrile gloves.
    • Set out the following glassware and equipment that the students will need to build the distillation apparatus (we suggest that students work in pairs):
       2    Lab stands
       1    Stir plate
       1    Heating mantle
       1    Temperature controller
       1    Round-bottom flask
       1    Cork lab ring
       1    Distilling head
       1    Condenser
       1    Connecting tube
       1    10-mL graduated cylinder
       2    1-mL volumetric pipettes
       1    Pipette bulb or controller
       1    Thermometer adapter
       1    Small beaker of sand
       1    Thermometer
       1    Stir bar
       4    Joint clips
       2    Pieces of rubber tubing
       1    Tube of vacuum grease
       2    Stand clamps
    • Set up an example distillation apparatus for the students to refer to. First, place two stands next to each other in the hood and set a stir plate on the base of one of the stands.
    • Place a heating mantle on the stir plate and plug the mantle into a temperature controller. Clamp the round-bottom flask to the stand over the heating mantle.
    • Next, carefully insert the thermometer into the adapter by gently pushing and twisting it through the top. Insert the adapter into the distilling head and adjust the thermometer until the bulb is below the bend. Then, insert the distilling head into the round-bottom flask.
    • Now, clamp the condenser to the second stand, with it oriented diagonally toward the side joint of the distilling head.
    • Connect a piece of rubber tubing to the tap water faucet in the hood and to the inlet port of the condenser, which is the port further from the distilling head.
    • Attach the other tubing to the outlet port, which is the port closer to the distilling head, and place the free end in the drain.
    • Connect the condenser to the distilling head, and then attach the connecting tube to the other end of the condenser.
    • Finally, place a 10-mL graduated cylinder below the connecting tube and secure each joint with a plastic clip.
    • Prepare the two solvents the students will use in the experiment. Each group will need 2 mL of toluene and 2 mL of cyclohexane, so ensure that you have enough for all groups.
    • Pour an appropriate amount of each solvent into a labeled glass bottle, so that the students can measure their solvents without handling any large stock bottles.
    • Set these solvents in the instructor hood for students to access during the experiment.

What is the vapor pressure of a liquid?

The vapor pressure of a pure component is the pressure exerted by the vapor on the liquid in a closed system.

At what point does a liquid boil?

A liquid boils when the vapor pressure of the liquid is equal to the atmospheric pressure.

In a mixture of miscible liquids, at which temperature does the solution boil?

A miscible solution boils at a temperature between the boiling points of the pure components. The vapor pressure of the mixture is equal to the sum of the product of the partial vapor pressures and mole fractions of the components.

How does the composition of the distillate change over time during a distillation of a mixture of liquids?

Initially, the vapor — and by extension, the distillate — is rich with the more volatile component. As that component boils off, the less volatile component enters the vapor phase. At the end of the distillation, the vapor phase is rich with the molecules of the less volatile component.

How is a vapor-liquid equilibrium diagram used to determine the composition of the liquid and vapor in a distillation?

The vapor-liquid diagram is a plot relating the temperature of the vapor and liquid to the mole fraction of each component. At a given temperature, the composition of the liquid and vapor phases can be determined.

  • Lab stand (+2 for reference setup)
  • Stir plate (+1 for reference setup)
  • Heating mantle (+1 for reference setup)
  • Temperature controller (+1 for reference setup)
  • Round-bottom flask (+1 for reference setup)
  • Cork lab ring
  • Distilling head (+1 for reference setup)
  • Glass condenser (+1 for reference setup)
  • Connecting tube (+1 for reference setup)
  • 10-mL glass graduated cylinder (+1 for reference setup)
  • 1-mL volumetric pipette
  • Pipette bulb or controller
  • Thermometer adapter (+1 for reference setup)
  • 50-mL glass beaker with sand
  • Thermometer (+1 for reference setup)
  • Stir bar
  • Plastic joint clips (+4 for reference setup)
  • Rubber tubing (+2 for reference setup)
  • Vacuum grease
    5 tube
  • Medium 3-prong clamp (+2 for reference setup)
  • Cyclohexane
    30 mL
  • Toluene
    30 mL
  • 250-mL glass vial with solvent-resistant cap
  • Glass funnel


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