Let's take a look at some common methods to separate mixtures:

Evaporation - This process uses heat to separate solids from liquids. The easiest example is salt (solid) mixed with water (liquid). If you want to separate the solid, you can evaporate the water. The salt cannot evaporate so it is left behind.

Distillation - This process uses boiling to separate mixtures, it is similar to evaporation. Think about the example of saltwater again. If you boil the water, the water will evaporate leaving the salt behind, but what if you want the water instead of the salt? To do this you have to collect the steam. When the steam cools down it will turn back into water, and there you have it!

Post Image

This process of collecting the solvent from a solution is called distillation. If you want to separate two liquids from each other it is called fractional distillation. It is similar to normal distillation but both liquids will evaporate. The difference is that they will evaporate at different temperatures.

Filtration - This process is used to separate substances that have different particle sizes. An example is sand and water. If you pour this mixture through a sieve or filter, the water particles which are smaller than the sand particles will slip through the holes. The sand which is bigger will not. You can also use filtration to separate dirt from water to obtain cleaner water. The water that runs through the sieve is called the filtrate and the sand that is removed is called the residue.

Post Image

Paper chromatography - This is often used by food scientists to know what colourings are in food. Mixtures are dissolved in liquid or gas to make a solution. The solution is then put on a solid, like paper, and then dipped into a liquid like water or ethanol. The substances within the mixture will start to separate and form coloured bands called chromatograms.


Fun facts

  • Decanting gold is a method of separating gold found in rivers by swirling the mixture in a pan. The gold particles settle to the bottom of the pan because they are heavier and the lighter particles stay suspended in the water.
  • A centrifuge is used in medicine to separate blood. It spins so fast, up to 30,000 times a minute! The heavier particles sink to the bottom and the lighter particles sit at the top. 
  • Paint is a mixture of colour pigment and a solvent like water or oil. Evaporation is used to separate the mixture. When the solvent dries and evaporates, the colour pigment is left.

Post Image

  • Winnowing is a separation process used to separate husks from grains. By throwing the mixture in the air, the wind blows away the lighter parts leaving the heavier grains behind.
  • Magnetism is great for separating mixtures of solids where one is magnetic.