Mixture Chemistry

By Anne Marie Helmenstine, Ph.D

Colloids and solutions may be distinguished based on their appearance. These are chemical solutions; light passes through them cleanly.
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A solution is a homogeneous mixture of two or more components. The dissolving agent is the solvent. The substance which is dissolved is the solute. The components of a solution are atoms, ions, or molecules, which makes them 10-9 m or smaller in diameter.

Example: Sugar and Water


The particles in suspensions are larger than those found in solutions. Components of a suspension can be evenly distributed by a mechanical means, like by shaking the contents, but the components will settle out.

Example: Oil and Water


Particles intermediate in size between those found in solutions and suspensions can be mixed such that they remain evenly distributed without settling out. These particles range in size from 10-8 to 10-6 m in size and are termed colloidal particles or colloids. The mixture they form is called a colloidal dispersion. A colloidal dispersion consists of colloids in a dispersing medium.

Example: Milk

More Dispersions

Liquids, solids, and gases all may be mixed to form colloidal dispersions.

Aerosols: solid or liquid particles in a gas.

Examples: Smoke is a solid in a gas. Fog is a liquid in a gas.

Sols: solid particles in a liquid.

Example: Milk of Magnesia is a sol with solid magnesium hydroxide in water.

Emulsions: liquid particles in liquid.

Example: Mayonnaise is oil in water.

Gels: liquids in solid.

Examples: gelatin is protein in water. Quicksand is sand in water.

Telling Them Apart

You can tell suspensions from colloids and solutions because the components of suspensions will eventually separate. Colloids can be distinguished from solutions using the Tyndall effect. A beam of light passing through a true solution, such as air, is not visible. Light passing through a colloidal dispersion, such as smoky or foggy air, will be reflected by the larger particles and the light beam will be visible.