Simple and Fractional Distillation

When countries have a lot of rain, there is a large supply of safe drinking water. However, in countries where there isn’t much rain, the citizens need to get their drinking water from sea water. We can separate drinkable water from sea water using distillation.

Simple distillation is a separation technique which is used to separate a solvent from a solution.

The diagram below shows the apparatus used to carry out distillation.

This method can be used to separate water from a saltwater solution.

Distillation of Saltwater

1. Heat the saltwater mixture (in the round-bottomed flask) using a Bunsen burner.

2. Monitor the temperature of the mixture using a thermometer, so we can reach the boiling point of the substance we want to collect.

3. The solution will be heated until the liquid water becomes water vapour.

4. Water vapour rises up and out of the tube, then passes through the condenser, where it cools down – The condenser has a small thin tube in the middle (where the evaporated substance passes through) – the tube is surrounded by glassware, which constantly has cold water passing in and out (to keep the condenser cool).

5. When the water vapour passes through the cold condenser, it will condense, turning back to a liquid.

6. The Liquid water then finishes travelling through the tube into the beaker (receiving flask).

7. The condensed water is the distillate, which is now safe to drink and salt crystals will remain in the round bottomed flask.

In the distillation process, two main processes are taking place:

  • Evaporation that takes place in the round bottomed flask – This is where the water vapour was heated, forming water vapour
  • Condensation that takes place in the condenser – This is where the water vapour cooled and became a liquid

Distillation is expensive because it requires a lot of energy to heat the solution.

Fractional Distillation

Fractional distillation is a technique for separating a liquid from a mixture of two or more liquids. Below is the apparatus for the fractional distillation process:

An example of this is how we can use fractional distillation to separate ethanol from a mixture of ethanol and water.

Fractional distillation works because each liquid in the mixture has a different boiling point. The mixture is heated to the boiling point of the substance you want to collect, given that this liquid has the lowest boiling point. When heated, it will evaporate before the other liquids.

To check the purity of a liquid, you can check the boiling point of the substance then heat it to that temperature. If the whole substance evaporates at that temperature then the substance is pure.