PROPERTIES OF SOLS

PROPERTIES OF SOLS :

OPTICAL PROPERTIES OF SOLS:    

Sols exhibit Tyndall effect:

When a strong beam of light is passed through a sol and viewed at right angles, the path of light shows up as a hazy beam or cone. This is due to the fact that sol particles absorb light energy and then emit it in all directions in space. This ‘scattering of light’, as it is called, illuminates the path of the beam in the colloidal dispersion.

     The phenomenon of the scattering of light by the sol particles is called Tyndall effect.

The illuminated beam or cone formed by the scattering of light by the sol particles is often

referred as Tyndall beam or Tyndall cone.

            Tyndall effect (Illustration).

Tyndall effect in nature.

KINETIC PROPERTIES OF SOLS:

Brownian Movement: 

     The continuous rapid zig-zag movement executed by a colloidal particle in the dispersion

medium is called Brownian movement or motion.

An illustration of Brownian movement

This motion is independent of the nature of the colloidal particles. It is more rapid when the size of the particles is small and the solution is less viscous.

ELECTRICAL PROPERTIES OF SOLS:

The sol particles carry an electric charge:

The most important property of colloidal

  

dispersions is that all the suspended particles posses either a positive or a negative charge. The mutual forces of repulsion between similarly charged particles prevent them from aggregating and settling under the action of gravity. This gives stability to the sol. The sol particles acquire positive or negative charge by preferential adsorption of positive or negative ions from the dispersion medium. For example, a ferric hydroxide sol particles are positively charged because these adsorb Fe3+ ions from ferric chloride (FeCl3) used in the preparation of the sol. Since the sol as a whole is neutral, the charge on the particle is counterbalanced by oppositely charged ions termed counterions (in this case Cl–) furnished by the electrolyte in medium.