Pure and impure substances

 

Pure substances

Pure substances are made from only one type of particle, either an element or a compound.

For example, salt is a pure substance made only of one compound, sodium chloride.

 

Impure substances

A substance that has more than one type of particle, either elements or compounds, is impure, meaning it is a mixture.

A label for a bottle of water will often show a list of small amounts of other substances. These are called impurities.

For example, it is hard to make pure water. This mineral water has small amounts of impurities such as sodium and nitrate.

 

 

Mineral water is a mixture of water and other substances.

 

 

Melting points and boiling points of pure substances

A pure substance has a specific (fixed) temperature at which it changes from solid to liquid or from liquid to gas. This temperature does not change for a pure substance. For example, the temperature at which pure water freezes is 0 °C and the temperature at which it boils is 100 °C.

 

Summary:

 

• Most of the things we use are mixtures, which have more than one type of particle in them. Only a few things are pure elements or pure compounds, which have only one type of particle in them.
• In chemistry, a pure substance is something that is made of only one kind of particle. It does not have any other particles mixed with it. If a substance has impurities, it means it has other particles mixed with it.
• Impurities change the temperature at which a substance changes from solid to liquid or from liquid to gas.