Solids, liquids and gases
Melting and boiling points of pure substances and mixtures
- The temperature at which a solid changes into a liquid as it is heated. is the temperature at which a solid changes into a liquid.
- The temperature at which a substance rapidly changes from a liquid to a gas. is the temperature at which a liquid changes into a gas.
Pure substances have specific melting and boiling points. Mixtures melt and boil over a range of temperatures.
The graphs below show the cooling curves for a pure sample of a A substance formed when two or more elements are chemically combined. called salol (C13H10O3) and an impure sample.
In a sample of pure salol, the temperature stays the same as it changes state.
In a sample of impure salol (salol mixed with other substances), the temperature falls gradually as it freezes.
We can use these differences between melting and boiling points to distinguish between pure substances and mixtures.