Simple and Fractional Distillation

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

Distillation is a method used to separate a mixture of liquids based on their different boiling points.

Simple Distillation

Simple distillation is a separation technique used to separate a solvent from a solution. It is typically used to separate liquids with a large difference in boiling points.

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

Illustration of a distillation apparatus setup. A distilling flask containing a liquid is heated by a burner. Vapours rise from the flask, passing through a thermometer, and then enter a condenser. Cold water flows into the condenser and warm water exits it. The vapours are cooled and condensed inside the condenser, then collected as distillate in a receiving flask.

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

Distillation of Saltwater

1. Using a Bunsen burner, heat the saltwater mixture in the round-bottomed flask.

2. Use a thermometer to monitor the temperature, aiming to reach the boiling point of the substance you want to collect.

3. Heat the solution 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). This 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 into a liquid.

6. The liquid water then flows through the tube and collects in the beaker, also known as the 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, these are the two main processes taking place:

  • Evaporation – occurs in the round-bottomed flask where the liquid water is heated to form water vapour.
  • Condensation – occurs in the condenser where the water vapour cools down and turns back into liquid form.

Distillation can be costly as it requires significant energy to heat the solution.

Fractional Distillation

Fractional distillation is a technique for separating a liquid from a mixture of two or more liquids. It can be used to separate liquids with similar boiling points.

Below is the apparatus for the fractional distillation process:

Illustration of a fractional distillation setup. The system includes a distilling flask containing a green liquid being heated by a burner, producing vapour. The vapour passes through a fractionating column and then a distillation adapter, which is monitored by a thermometer. The vapor then travels to a blue condenser where cold water enters and warm water exits. The vapour condenses inside the condenser and is collected as pink distillate in a receiving flask.

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

Fractional distillation is effective because it exploits the different boiling points of each liquid in the mixture. 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 test the purity of a liquid, you can compare its boiling point to that of the pure substance and heat it to that temperature. If the whole substance evaporates at that temperature then the substance is pure.

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