What is the difference between a pure substance and a mixture?

A pure substance contains only one kind of molecule, and a mixture is a combination of two or more pure substances. Distilled water, aluminum foil and table sugar are each made from only one type of particle. However, salt water is a mixture because it contains salt as well as water.

Both pure substances and mixtures can exist as solids, liquids or gases. Most ordinary things are mixtures with at least two types of molecules. For example, air is a mixture of pure substances, including nitrogen, oxygen and carbon dioxide. Apple juice is another common mixture that includes particles of water, sugar, flavoring and vitamins.