Surface Chemistry

Classification of Colloids

Colloids occur widely in nature as well as are manufactured synthetically. Since these have a wide industrial application, it is important to have a proper system for the classification of colloids. Colloids consist of a dispersed phase and a dispersion medium. They are classified on the basis of different properties of the dispersed phase and the medium. Let us learn about them here.

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Classification of Colloids

Based on the Nature of Interaction Between Dispersed Phase and Dispersion Medium

  • Hydrophilic colloids: These are water-loving colloids. The colloid particles are attracted to the water. They are also known as reversible sols. Examples include Agar, gelatin, pectin, etc
  • Hydrophobic colloids: These are the opposite in nature to hydrophilic colloids. The colloid particles are repelled by water. They are also called irreversible sols. Examples include Gold sols, clay particles, etc

Learn more about Stabilization and Application of Colloids here.

Based on Type of Particles of Dispersed Phase

Depending upon how different substances forming colloidal solution acquire the size of particles in this range, colloidal solutions may be classified into the following three categories.

  • Multimolecular Colloids: The solution that is formed as a result of the aggregation of a large number of atoms or small molecules (having diameters of less than 1nm) of the dispersed media. The dispersed particles are held together by Van der Val forces
    Example: Gold sol, Sulphur sol.
  • Macromolecular Colloids: Molecules have very high molecular masses that result in the formation of large molecules that are termed as macromolecules. When such substances are dispersed in a suitable dispersion medium, the resulting colloidal solutions are known as macromolecular colloids. Thus, macromolecular colloids consist of high molecular mass. Generally, lyophilic colloids are macromolecular in nature.
    Examples include the colloidal dispersion of naturally occurring macromolecules such as starch, proteins, gelatin, cellulose, nucleic acids, etc. as well as synthetic polymers such as polyethylene, polypropylene, synthetic rubber, etc. also form macromolecular colloids when dispersed in suitable solvents.
  • Associated Colloids (Micelles): Certain colloids behave as strong electrolytes at lower concentrations but exhibit colloidal properties at higher concentrations. At a particular concentration, the molecules of dispersed phase align in such a way as to form micellar structures. This particular concentration is known as critical micellar concentration. The colloids that form micelles are known as associated colloids.

Learn about Emulsion and Adsorption here.

Depending Upon the State of Dispersed and Dispersion Medium

Depending upon the state of dispersed particles and the dispersion medium, the following system of Classification of colloids can be employed.

1] When the Dispersion Medium is Liquid

  • Foams – When the dispersed medium is gas. Examples include whipped cream, shaving cream, etc
  • Emulsions – When the dispersed phase is liquid. Examples include milk, mayonnaise, etc
  • Sol – When the dispersed phase is solid. Examples include blood, pigmented ink, etc

2] When the Dispersion Medium is Gaseous

  • Liquid Aerosol – When the dispersed phase is liquid. Examples include fog, mist, hair sprays, etc.
  • Solid Aerosol –  When the dispersed phase is solid. Examples include smoke, ice cloud, etc.

3] When the Dispersion Medium is Solid

Classification of colloids

Cranberry Glass

  • Solid Foam – When the dispersed medium is gas. Examples include styrofoam, pumice, etc
  • Gel – When the dispersed medium is liquid. Examples include agar, gelatin, etc
  • Solid Sol – When the dispersed medium is solid. Examples include cranberry glass

Properties of Colloidal Solutions

Solved Questions For You

Que: Which of these systems of colloids are not known to exist?

  1. Liquid in Liquid
  2. Solid in Solid
  3. Liquid in Solid
  4. Gas in Gas

Ans: The correct option is “D”. Gas in Gas. No such type of colloid has been reported to exist.

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