Distillation Techniques for Separating Liquid Mixtures

Introduction

• Two main types of distillation used to separate mixtures containing liquids:
  • Simple Distillation
  • Fractional Distillation

Simple Distillation

• Used for separating a liquid from a solution (e.g., pure water from seawater).
• Equipment Required:
  • Flask: Contains the liquid mixture.
  • Bung: Seals the flask to prevent gas escape.
  • Thermometer: Measures temperature inside the flask.
  • Condenser:
    • Main pipe surrounded by a water jacket.
    • Cold water flows from bottom to top.
  • Beaker: Captures the pure liquid.
  • Heating Device: E.g., Bunsen burner to heat the flask.

Process

1. Heat the mixture.
2. Desired liquid evaporates.
3. Pressure forces vapor into the condenser.
4. Vapor cools and condenses into liquid form.
5. Collect liquid in the beaker.
6. Example: Heating seawater to get pure distilled water, leaving salt in the flask.

Limitations of Simple Distillation

• Ineffective for mixtures with liquids having similar boiling points (e.g., methanol, ethanol, propanol).

Fractional Distillation

• Suitable for separating mixtures of liquids with similar boiling points.

Equipment Differences

• Fractionating Column:
  • Contains glass rods: Provide high surface area.
  • Tall column: Cooler at the top than the bottom.

Process

1. Heat mixture to specific temperatures for each liquid based on boiling points.
2. Separating Methanol, Ethanol, and Propanol:
   • Methanol: Evaporates at ~65°C, goes through the fractionating column, condenses in the condenser, collected as pure methanol.
   • Ethanol: Raise temperature to ~78°C, repeat process to collect pure ethanol.
   • Propanol: Left in the flask, can assume purity or boil off as needed.

Conclusion

• Simple and fractional distillation are effective techniques for separating liquids based on boiling points.
• Fractional distillation is necessary when dealing with liquids with similar boiling points.

Note

• In real applications, substances are colorless; colors are for illustrative purposes.