Class 12 Chemistry Surface Chemistry Classification of colloids

Classification of colloids

Colloids are classified in 2 different ways

Based on the physical state of the dispersed phase and dispersed medium:

S.No

Dispersed Phase

Dispersed Medium

Name of Colloid

Examples

1.

Solid

Solid

Solid sol

Gem stones

2.

Solid

Liquid

Sol

Muddy water, Paint, cell fluids

3.

Solid

Gas

Aerosol

Smoke,dust

4.

Liquid

Solid

Gel

Cheese, butter, jelly

5.

Liquid

Liquid

Emulsion

Milk, Hair cream

6.

Liquid

Gas

Aerosol

Fog, mist, cloud

7.

Gas

Solid

Solid Foam

Pumice Stone

8.

Gas

Liquid

Foam

Froth, soap lather

 

Based on nature of Interaction Between Dispersed Phase and Dispersed Medium

Lyophilic Colloids(liquid loving)-

  • Some substances which can from colloids directly on mixing them with a suitable liquid(dispersion medium). These colloids are called lyophilic colloids. Examples of these substances are gum, geltine, starch, rubber.
  • They are also called Reversible sols as in these sols(colloids) when the dispersion phase is separated from the dispersion medium (by say evaporation) , the sol can be formed again by just mixing the dispersion phase and medium again.
  • They are also very stable and cannot be coagulated

 

Lyophobic colloids(liquid hating)

  • Some substances cannot form colloid just by directly mixing them with a liquid. Their colloidal sols are prepared by special methods and are called lyophobic colloids. Examples of these substances are metals, metal sulphides.
  • They are also called Irreversible colloids as on precipitation, they don’t give back the colloid on simply mixing the dispersed phase and the dispersed medium.
  • They are unstable and coagulate easily by heating shaking or adding electrolytes. Stabilising agents are used to preserve them

 

Based on the Types of Particles of the Dispersed Phase-

  • Multimolecular Colloids: Many particles(atoms or small molecules) of the dispersed phase aggregate together to form species having the size of a colloidal particle( 1-1000nm). These colloids are called multimolecular colloids. Example-gold sol, Sulphur sol

 

  • Macromolecular colloids: Substances with large molecules (macromolecules) in suitable solvents form solutions but these macromolecules might be in the colloidal range. These solutions are called macromolecular colloids and resemble true solutions in many ways. Example- Starch, Cellulose, Proteins are natural macromolecules.       Nylon, polythene, polystyrene are man-made macromolecules

 

  • Associated Colloids: Some substances at high concentrations act as colloids due to the formation of aggregates. But at low concentrations they behave like normal strong electrolytes. These aggregates formed are called micelles. Such colloids are called associated colloids.

Kraft Temperature- The formation of micelles takes place only above a particular temperature called Kraft’s temperature

Critical Micelle Concentration(CMC) – The concentration above which micelle formation takes place

Example- Soaps, synthetic detergents

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