Substances and mixtures

In physical chemistry, A chemical substance is a kind of matter with a definite composition and set of properties.  So it could be a chemical compound or an amount of molecules.

A mixture is two or more chemical substances which have distinct properties that can be separated, usually through physical means due to the different properties that each substance has. 


Set up for a mixture of oil and water. image: wikimedia

A container filled with sand and iron dust can be separated by a magnet for example. 

For example air is a mixture of various gases. Metal alloys are also mixtures.

There are  various kinds of mixtures that often depend on the phases of the two substances. 

A colloid is a substance microscopically dispersed throughout another substance 

An emulsion is a mixture of two or more liquids that are normally immiscible (nonmixable or unblendable). Emulsions are part of a more general class of two-phase systems of matter called colloids.

Mixtures of oil and water are also examples of substances that can be separated.