Dispersed Phase and Dispersion Medium - Definition, Examples and FAQs

Dispersed Phase And Dispersion Medium

The substance present in the form of fine particles in a colloid or heterogeneous mixture is called the dispersed phase. And the dispersion medium is the continuous phase in which these particles are distributed. Think of the dispersed phase as the solute and the dispersion medium as the solvent in a solution. The dispersed phase is particles, and the dispersed medium is called the continuous phase. Both combined and formed the colloids.

We have classified colloids on the basis of the dispersed phase and the dispersion medium, such as:

Colloids

Between the two extremes of suspensions and solutions, we come across a large group of systems called colloidal dispersions or simply colloids. A colloid is a heterogeneous system in which one substance is dispersed (dispersed phase) as very fine particles in another substance called the dispersion medium.

The essential difference between a solution and a colloid is that of particle size. While in a solution, the constituent particles are ions or small molecules, in a colloid, the dispersed phase may consist of particles of a single macromolecule (such as a protein or synthetic polymer) or an aggregate of many atoms, ions, or molecules. Colloidal particles are larger than simple molecules but small enough to remain suspended. Their range of diameters is between 1 and 1000 nm(10^–9 to 10^–6 m). Colloidal particles have an enormous surface area per unit mass as a result of their small size.

On the basis of the types of particles in the dispersed phase, colloids can be classified into the following types:

1. Multimolecular colloids
2. Macromolecular colloids
3. Associated colloids

Multimolecular Colloids

Multimolecular colloids are colloidal systems in which individual atoms or small molecules of a substance aggregate to form particles of colloidal size (1–1000 nm). These aggregates act as the dispersed phase, while the surrounding liquid or gas acts as the dispersion medium. The particles are held together by Van der Waals forces or weak chemical bonds.

Macromolecular Colloids

Macromolecular colloids are colloidal systems in which are composed of molecules with very large molecular weight, highly stable due to their large size and strong interaction with the medium. In macromolecular colloids, the dispersed phase consists of large molecules (macromolecules) whose sizes are in the colloidal range (1–1000 nm).

Associated Colloids

Associated colloids are substances that behave as normal electrolytes at low concentrations but form colloidal-sized aggregates (micelles) at higher concentrations. These aggregates are known as micelles. Such colloids show properties of both true solutions and colloids.

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Some Solved Examples

Question.1 Which of the following statements is true about a colloidal system?
a) Only one phase is present
b) Both dispersed phase and dispersion medium are present
c) No continuous phase exists
d) Colloids are always solids

Solution:

Both dispersed phase and dispersion medium are present
A colloid always consists of two components—the dispersed phase (particles) and the dispersion medium (continuous phase).

Hence, the correct option is (b)

Question.2 In milk, the dispersed phase and dispersion medium are respectively:
a) Water and fat
b) Fat and water
c) Protein and water
d) Water and protein

Solution:

Milk is an emulsion where fat globules are the dispersed phase and water is the dispersion medium.

Hence, the correct option is (b) Fat and water

Question.3 Which of the following pairs is correctly matched for smoke?
a) Dispersed phase – Air, Dispersion medium – Carbon particles
b) Dispersed phase – Carbon particles, Dispersion medium – Air
c) Dispersed phase – Water, Dispersion medium – Air
d) Dispersed phase – Air, Dispersion medium – Water

Solution:

Smoke is a solid in gas colloid, where carbon particles are dispersed in air.

Hence, the correct option is (b) Dispersed phase – Carbon particles, Dispersion medium – Air

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