Question

Classify colloids where the dispersion medium is water. State their characteristics and write an example of each of these classes.

Answer 1

We know that when a substance which is microscopically dispersed in another substance is referred to as colloids. It has a dispersed phase and a dispersion medium. We have seen several examples of colloids having dispersion mediums as water.

Complete step by step answer:
Colloids can be classified into several types based on different properties. Some properties include types of particles of dispersed phase, original states of their constituent parts, nature of interaction between dispersed phase and dispersion medium, etc.
Based on the nature of interaction between dispersion medium and dispersed phase, colloids are classified into lyophilic and lyophobic colloids. The term “lyo” means liquid or solvent and the term “philic” means loving or attracting. The term “phobic” means hating or repelling. Here, water is taken as liquid. Thus the classification will be hydrophilic and hydrophobic, i.e. water loving and water hating. The dispersion medium is water.
In hydrophobic colloids, the colloidal particles have a very high attraction towards water molecules. These colloids, generally, have a sticky consistency. Some examples are starch, gum etc. These types of colloids are generally stable because the dispersed phase particles are surrounded by positive, negative charges and a layer of water. These are generally reversible because the dispersion medium can be remixed with dispersed phase even if it gets separated.
In hydrophobic colloids, the particles are repelled to the water molecules. These particles have a very low concentration. It does not have a sticky consistency. It is comparatively less stable because it is surrounded by only charges. In addition to electrolytes, or heating or shaking can precipitate these colloids.
Some examples are gold in water, ${{Fe}}{\left( {{{OH}}} \right)_3}$, ${{A}}{{{s}}_2}{{{S}}_3}$ etc.

Note: Hydrophilic colloids can be prepared by simply mixing the dispersed phase in dispersion medium. For example, dissolving acacia in water. Hydrophobic colloids, generally, have an irreversible nature. It cannot be prepared by simple mixing.