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Colloidal suspensions are basically formed in two ways. One of them is by drops or particles that are dispersed in a certain medium by the effect of a spray, by grinding, by injection at high speed or by agitation. The other is by dissolved substances that precipitate or condense into small particles within the solute due to pH changes, REDOX reactions, or temperature or pressure changes.
At first sight it seems difficult to differentiate a colloidal suspension from a solution or from a suspension of particles , since in the definition they only differ by the size of the particles dispersed in a certain medium. However, let’s see two simple ways to identify a colloidal suspension. In a suspension the particles settle over time, while in a colloidal suspension the colloids are always dispersed in the medium. On the other hand, if a light beam is made to shine on a colloidal suspension, the Tyndall effect will be observed, causing the light beam to be scattered by the colloids. An example is car headlights scattered by fog.
Examples of colloidal suspensions or mixtures
Aerosols are colloidal suspensions, some examples being fog, a dispersed insecticide, clouds, and smoke. Fluid foams, such as heavy whipping cream or shaving foam, and solid foams, such as marshmallows and Styrofoam, are examples of colloidal suspensions. So are emulsions, such as milk, mayonnaise, and lotions; gels, such as gelatin, butter and jelly; liquid suspensions, such as ink, gum, and detergent; and solid suspensions, such as pearls, gems, some colored glass, and some alloys.
To better understand the concept, let’s differentiate some examples according to the type of colloid and the medium in which it is dispersed.
- A solid in a gas: smoke.
- A liquid in a gas: the fog.
- A solid in another solid: glass.
- A gas in a liquid: shaving foam.
- A gas in a solid: the pumice stone.
- A solid in a liquid: butter.
Fountain
Valenzuela, C. General Chemistry: Introduction to theoretical chemistry. Editions of the University of Salamanca, Spain. nineteen ninety five.
