Distillation Techniques

Simple Distillation

  • Used for separating a liquid from a solution (e.g., separating pure water from seawater).

  • Equipment:

    • Flask: Contains the solution; sealed with a bung.
    • Thermometer: Measures the temperature inside the flask.
    • Condenser: A pipe surrounded by a water jacket with cold water flowing through it (water enters at the bottom and exits at the top).
    • Beaker: Collects the pure liquid.
    • Heating device: Like a Bunsen burner, placed under the flask.

  • Process:

    1. Heat the mixture to evaporate the desired liquid.
    2. The vapor rises and is forced down the condenser.
    3. Cold water in the water jacket cools the vapor, causing it to condense into a liquid.
    4. The liquid runs down the pipe and collects in the beaker.
    5. Example: Heating seawater results in distilled water being collected, leaving salt in the flask.

Fractional Distillation

  • Used for separating mixtures of liquids with similar boiling points (e.g., methanol, ethanol, and propanol).

  • Equipment:

    • Similar to simple distillation but includes a fractionating column between the flask and the condenser.
    • Fractionating Column:
      • Filled with glass rods to provide a high surface area.
      • Cooler at the top than at the bottom.

  • Process:

    1. Heat the mixture.
    2. Vapors pass through the fractionating column before entering the condenser.
    3. Liquids with lower boiling points evaporate first.
    4. As vapors rise, those with higher boiling points condense on the glass rods (which are cooler) and fall back into the flask.
    5. The liquid with the lowest boiling point makes it to the top of the column, enters the condenser, and is collected.
    6. Raise the temperature gradually to evaporate and collect liquids with progressively higher boiling points.

  • Example:

    • Separating methanol (boiling point ~65°C), ethanol (boiling point ~78°C), and propanol.
      1. Heat to ~65°C: Methanol evaporates, rises through the column, condenses, and is collected.
        • Ethanol and propanol may evaporate slightly but will condense on the cooler glass rods and fall back.
      2. Increase temperature to ~78°C: Ethanol evaporates and is collected.
      3. Remaining liquid is assumed to be propanol; temperature can be raised again to ensure propanol is evaporated and collected.