Classifying Colloids

Colloids can be classified based on the phase of the dispersed substance and the phase it is dispersed in. The primary types of colloids are sol, emulsion, foam, and aerosol.

1. A sol is a colloidal suspension where solid particles are dispersed in a liquid.
2. An emulsion involves the dispersion of one liquid within another.
3. Foam is generated when numerous gas particles are trapped within a liquid or solid.
4. An aerosol consists of small liquid or solid particles dispersed within a gas.

When water serves as the dispersion medium, we often refer to the resulting colloidal system as a hydrocolloid. The dispersed phase particles may exist in different phases depending on the quantity of water present. For instance, when you mix Jello powder with water, you create a hydrocolloid. Hydrocolloids are commonly used in the production of medical dressings.

Examples of Colloidal Solutions

Colloidal solutions are quite common in our everyday life. Some examples include whipped cream, mayonnaise, milk, butter, and gelatin. These consist of two components: colloidal particles and the dispersing medium. In a fruit juice, for instance, the fruits serve as the colloidal particles and the water they are mixed in is the dispersing medium.

Here are some more examples of colloidal solutions:

Properties of Colloidal Solutions

Colloidal solutions exhibit several unique properties, which include:

(1) Physical properties:

• Heterogeneous nature: Colloidal solutions are heterogeneous mixtures comprising two phases - the dispersion phase and the dispersion medium.
• Stability: Colloidal solutions are quite stable. The particles are always in motion and do not settle at the bottom of a container.
• Filterability: Colloidal particles can easily pass through ordinary filter papers.

(2) Colligative properties:

• The observed values of colligative properties like relative decrease in vapour pressure, boiling point elevation, freezing point depression, and osmotic pressure are smaller than expected due to the formation of associated molecules.
• The number of particles in a given solution is comparatively small.

(3) Mechanical properties:

• Diffusion: The sol particles diffuse from higher to lower concentration regions. However, their size causes them to diffuse at a slower rate.
• Sedimentation: Colloidal particles settle down very slowly under the influence of gravity. This phenomenon is used to determine the molecular mass of macromolecules.