You may have heard the phrase 24 karat gold. You may have also heard 18 karat gold. If you know a bit about jewellery, you will know that 18 karat gold is cheaper than 24 karat gold. That is because 24 karat gold is pure gold, whereas 18 karat gold is a mixture of gold and other materials.

In many situations, it is important to know if some material is pure or impure. In this module, we will look at the difference between pure substances and mixtures, and discuss the different kinds of mixtures.