4 Examples of Suspensions

This is a close-up look at a suspension of mercury droplets in oil.
This is a close-up look at a suspension of mercury droplets in oil. DR JEREMY BURGESS, Getty Images

In chemistry, a suspension is a mixture in which the solute particles—whether liquid or solid—do not dissolve. Most of the suspensions you encounter in everyday life consist of solid particles in liquids, but suspensions can also form from two liquids or even from a solid or liquid in a gas. One key way to identify a suspension is that the components typically separate over time. Mixing or shaking needs to occur to form a suspension. Given time, suspensions usually separate on their own.

Mercury Shaken in Oil

Mercury is a metallic element that is liquid at standard temperature and pressure. Because of its liquid properties, the element can be mixed with oil to produce a suspension. The mercury particles will disperse throughout the oil when the solution is shaken, but the particles will never dissolve. If left to sit, the two liquids will eventually separate.

Oil Shaken in Water

Water molecules, because of their polarity, are highly attracted to each other. They exhibit a "stickiness" that can be seen by slowly moving two water droplets toward each other. Oil molecules, on the other hand, are non-polar, or hydrophobic, which prevents them from joining together with water molecules. Oil shaken in water will produce a suspension as the oil particles are momentarily scattered. Left undisturbed, however, the two elements will separate from each other.

Dust in Air

Dust in the air is an example of a solid-gas suspension. Dust—tiny particles that include pollen, hair, dead skin cells, and other materials—is lifted by wind and ventilation systems and scattered throughout the air, producing a suspension. Because the particles of dust are solid, however, they will eventually return to earth and form a fine layer of sediment on the solid surfaces below.

Soot in Air

Soot—which takes the form of black smoke—is made up of carbon particles released through the combustion of coal and other carbon-rich energy sources. When it is first released, soot forms a solid-gas suspension in the air. This can be seen in fireplaces, power plants, and vehicles. Like dust in the air, soot eventually settles, blackening chimneys and other surfaces.