What Is a Colloid? Definition and Examples

What Is a Colloid - Definition and Examples
A colloid is a mixture consisting of microscopic particles suspended in another medium. Examples include milk, smoke, gelatin, ink, and hand lotion.

In chemistry, a colloid is a mixture of tiny particles that are dispersed in another medium. The particles are microscopic in size, ranging from 1 nanometer (nm) to 1 micrometer (μm) in diameter. In contrast, particles in a solution are smaller than this size, while particles in a suspension are larger. As in a solution, the particles in a colloid do not separate upon standing. The particles in a colloid are called the dispersed phase, which is spread throughout the dispersion medium.

Types and Examples of Colloids

Colloids are classified as foams, aerosols, emulsions, gels, or sols, depending on the nature of the dispersed phase and dispersion medium. Familiar examples of colloids include mayonnaise, milk, fog, smoke, and gelatin.

  • A gel is a colloid of solid particles in a liquid medium.
  • A sol consists of liquid particles in a solid medium.
  • An emulsion is a colloid formed by two or more liquids.
  • A foam forms by gas particles trapped within a liquid or solid.
  • An aerosol is a colloid consisting of liquid or solid particles dispersed in a gas.
  • There are no known gas-gas colloids, although it is possible helium or xenon may be insoluble in certain situations.
Dispersion MediumGas Dispersed PhaseLiquid Dispersed PhaseSolid Dispersed Phase
Gasnone knownliquid aerosol
(mist, fog, hair spray, steam)
solid aerosol
(smoke, ice cloud)
(shaving cream, whipped cream)
(milk, mayonnaise, hand lotion)
(ink, paint, precipitates)
Solidsolid foam
(aerogel, pumice, styrofoam, marshmallow)
(gelatin, agar, jelly, butter)
solid sol
(cranberry glass, uranium glass, colored gems)

The Tyndall Effect

The Tyndall effect is the scattering of light by the particles in a colloid or fine suspension. A good example is the way a glass of skim milk (a colloid) shows a flashlight beam, while a glass of salt water (a solution) does not. It is a quick and easy test that distinguishes a colloid or suspension from a solution.

Not all colloids display the Tyndall effect. Sometimes the dispersion medium is opaque or too dark. For example, you don’t see the Tyndall effect in whipped cream. However, it is evident in gelatin, opal, mist, smoke, milk, and aerogel.

Difference Between a Colloid and a Suspension

The particles in a suspension are larger than in a colloid. So, the particles in a suspension typically settle out of their medium, while those in a colloid remain mixed and appear homogeneous (under a microscope, they are heterogeneous). A good example of a suspension is a mixture of flour and water. The flour particles are suspended after freshly mixing the ingredients, but gravity pulls them to the bottom of the container pretty quickly.

Difference Between a Colloid and a Solution

The particle size in a solution is smaller than in a colloid,. Also, the solute and solvent constitute one phase of matter in a solution. For example, a solution of table salt in water or sugar in water consists solely of the liquid phase. The salt breaks into component ions, while the sugar dissolves into individual molecules. In either case, the particles are in aqueous solution. In contrast, the particles in a sol are not necessarily the same phase as the medium. For example, milk contains solid protein particles dispersed in the liquid.

homogeneousvisually homogeneous, microscopically heterogeneousheterogeneous
particle size 0.01-1 nm
atoms, ions, molecules
particle size 1-1000 nm
molecules or aggregates
particle size >1000 nm
large particles or aggregates
do no separate on standingdo not separate on standingparticles settle out
cannot be separated by filtrationcannot be separated by filtrationcan be separated by filtration
does not scatter lightTyndall effect or opaqueTyndall effect or opaque

How to Prepare a Colloid

There are two methods of preparing colloids:

  1. Mechanical action, such as shaking, spraying, or milling, disperses particles or droplets into the medium.
  2. Small molecules aggregate into colloidal particles, via condensation, precipitation, or redox reactions.


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  • Hiltner, P.A.; Krieger, I.M. (1969). “Diffraction of light by ordered suspensions”. J. Phys. Chem. 73 (7): 2306. doi:10.1021/j100727a049
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  • Stepto, Robert F. T. (2009). “Dispersity in polymer science (IUPAC Recommendations 2009)”. Pure and Applied Chemistry. 81 (2): 351–353. doi:10.1351/PAC-REC-08-05-02