Mixtures
Solutions
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
Suspensions
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
Colloids
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.
The 19th Century Irish scientist John Tyndall was born on August 2, 1820 in Leighlinbridge, Ireland. He
studied the Tyndall Effect in 1869.
The Tyndall Effect is the effect of light scattering in many directions in colloidal dispersion, while
showing no light in a true solution. This effect is used to determine whether a mixture is a true solution or a
colloid. "To be classified colloidal, a material must have one or more of its dimensions (length, width, or
thickness) in the approximate range of 1-1000 nm."
Because a colloidal solution or substance (like fog) is made up of scattered particles (like dust and water in
air), light cannot travel straight through. Rather, it collides with these micro-particles and scatters causing
the effect of a visible light beam. This effect was observed and described by John Tyndall as the Tyndall
Effect.
The Tyndall effect is an easy way of determining whether a mixture is colloidal or not. When light is shined
through a true solution, the light passes cleanly through the solution, however when light is passed through a
colloidal solution, the substance in the dispersed phases scatters the light in all directions, making it readily
seen.
For example, light being shined through water and milk. The light is not reflected when passing through the
water because it is not a colloid. It is however reflected in all directions when it passes through the milk,
which is colloidal. A second example is shining a flashlight into fog or smog; the beam of light can be easily
seen because the fog is a colloid.