Mixture

In chemistry, a mixture is a material made up of two or more different substances which are physically combined. Normally in nature, it is very unlikely that the matter is in the form of a pure substance, in fact, most of the time it comes in the form of a mixture. The components of a mixture can be solid, liquid, or gaseous.

Mixtures can be either homogeneous or heterogeneous. A mixture is called homogeneous if it consists of a single-phase and its components are no longer distinguishable from direct observation. A homogeneous mixture is called a solution. An example of homogeneous mixtures is represented by alloys. Homogeneous mixtures can be separated only through state transitions that involve the components in a different way. For example, the salt dissolved in the water constitutes a homogeneous mixture and can be separated by heating the mixture: in this way the water evaporates, while the salt precipitates as a solid (this process takes place in the salt pans).

A mixture is heterogeneous if it consists of two or more phases and its components are easily distinguishable. A suspension is an example of a heterogeneous mixture. Heterogeneous mixtures can be separated more easily than homogeneous mixtures, also through mechanical methods. When two or more substances are combined to form a mixture, they do not change their intimate chemical structure, as happens instead in chemical reactions.

Classification of mixtures

Homogeneous mixtures: occur in a single phase (particle diameter < 1 nm)

Heterogeneous mixtures: they occur in several phases (particle diameter > 1 nm)

• dispersions (particle diameter > 1 µm)
• foams (dispersed phase: gas; continuous phase: liquid)
• emulsions (dispersed phase: liquid; continuous phase: liquid)
• suspensions (dispersed phase: solid; continuous phase: liquid)
• mists (dispersed phase: liquid; continuous phase: gas)
• fumes (dispersed phase: solid; continuous phase: gas)
• colloids (particle diameter < 1 µm)
• colloidal emulsion (dispersed phase: liquid; continuous phase: liquid)
• liquid aerosol (dispersed phase: liquid; continuous phase: gas)
• solid aerosol (dispersed phase: solid; continuous phase: gas)
• colloidal foam (dispersed phase: gas; continuous phase: liquid)
• sol (dispersed phase: solid; continuous phase: liquid)
• solid foam (dispersed phase: gas; continuous phase: solid)
• gel (dispersed phase: liquid; continuous phase: solid)
• colloidal solid suspension (dispersed phase: solid; continuous phase: solid)