Identify Pure Substances From Their Melting and Boiling Points

In chemistry, substances can either be pure or impure

Pure substances have specific melting and boiling points, which means they will always melt or boil at exactly the same temperature. For example, pure water has a melting point of 0°C and its boiling point is 100°C. 

The opposite of a pure substance is an impure substance. An impure substance can also be referred to as a mixture.

Impure substances or mixtures melt and boil over a range of temperatures, so may have a melting point of 34-39^oC for example, depending on the exact composition of the mixture. 

So we can use these differences in melting and boiling point to identify if a substance is a pure substance or an impure substance. We just need to compare the melting point of the substance with published reference data of what the melting point should be if it is a pure substance.

Think you can work out whether a substance is pure or impure just from its melting or boiling point?

Let's try some questions.