Fractional Distillation

Introduction

• Fractional distillation is used to separate a mixture of liquids.
• Requires liquids to have different boiling points.

Apparatus

• Similar to simple distillation with a key addition: the fractionating column.
• Components:
  • Flask with liquid mixture
  • Fractionating column with glass beads
  • Thermometer at the top of the column
  • Condenser with circulating cold tap water

Process

1. Heating the Mixture

   • Mixture of liquids gently heated.
   • Liquid with lower boiling point evaporates more easily.

2. Fractionating Column

   • Vapors enter the column, condense, and drip back.
   • Repeated evaporation and condensation enriches the lower boiling point component in the column.
   • Red arrows indicate lower boiling point vapor moving up the column.

3. Temperature Monitoring

   • As vapors rise, thermometer shows an increase in temperature.
   • Indicates mixture of vapors; more of lower boiling point component.
   • Vapors condense into a liquid, still a mixture.

4. Fraction Collection

   • Temperature stabilizes at the lower boiling point (e.g., 80°C).
   • Mainly lower boiling point chemical collected in a beaker.
   • This is the first proper fraction.

5. Second Fraction

   • Temperature rises again, indicating a vapor mix.
   • Stabilizes at the higher boiling point (e.g., 100°C).
   • Second chemical collected relatively pure.

Important Considerations

• Similar Boiling Points: Harder to separate, may require multiple distillations.
• Scale: Apparatus not suitable for large volumes (e.g., crude oil refining).

Additional Resources

• More questions and exercises available in the revision workbook linked in the lecture.