6. Distillation: Simple & Fractional Distillation

1. Simple Distillation

• Purpose: Separates a liquid from a solution (e.g., getting pure water from seawater).

• Equipment:

  • Flask: Contains the mixture and is sealed with a bung.

  • Thermometer: Measures the internal temperature.

  • Condenser: A pipe surrounded by a "water jacket" with cold flowing water.

  • Beaker: Collects the condensed pure liquid.

• Process:

  • The solution is heated until the liquid evaporates into a gas (vapor).

  • The vapor rises and is forced into the condenser.

  • Inside the condenser, the cold water jacket cools the vapor, causing it to condense back into a liquid.

  • The pure liquid drips into the beaker, leaving the solid (like salt) behind in the flask.

2. Fractional Distillation

• Purpose: Separates a mixture of different liquids, especially when they have similar boiling points (e.g., methanol, ethanol, and propanol).

• Equipment Addition:

  • Fractionating Column: Placed between the flask and the condenser. It is filled with glass rods (high surface area) and is cooler at the top than at the bottom.

• Process:

  • The mixture is heated to the boiling point of the liquid with the lowest boiling point.

  • That liquid evaporates, rises through the column, and enters the condenser to be collected.

  • If other liquids with higher boiling points also start to evaporate, they hit the cool glass rods in the column, condense back into liquid, and fall back into the flask.

  • Once the first liquid is collected, the temperature is raised to the boiling point of the next liquid, and the process is repeated.

3. Key Comparisons

• Simple Distillation: Best for separating substances with very different boiling points (like a solid and a liquid).

• Fractional Distillation: Necessary for separating substances with similar boiling points (like several different liquids).