Purification of colloidal solution can be done by the following methods.
(i) Dialysis
(ii) Electrodialysis
(iii) Ultrafilteration.

The main impurities present in a colloidal solutions are electrolytes.

The colloidal solutions due to their different methods of preparation may contain impurities. If they are not removed, they may destablise and precipitate the colloidal solution.

When the substance for colloidal particle is present as small sized particle, molecule or ion they are brought to the colloidal dimension by condensation methods.

Sound waves of frequency more than 20kHz (audible limit) could cause transformation of course suspension to colloidal dimensions.

Colloidal are prepared by the following methods.
(i) Dispersion methods: In this method larger particles are broken to colloidal dimension.
(ii) Condensation method: In this method smaller atom or molecules are converted into larger colloidal sized particles.

In a colloidal, the substance present in larger I amount is called dispersion medium and the substance present in less amount is called dispersed phase.

Limitations:
(i) The intermediate compound theory fails to explain the action of catalytic poison and activators (promoters).
(ii) This theory is unable to explain the mechanism of heterogeneous catalysed reactions.

Intermediate compound formation theory:
(i) the specificity of a catalyst and
(ii) the increase in the rate of the reaction with increase in the concentration of a catalyst

(i) This equation is purely empirical and valid over a limited pressure range.
(ii) The values of constants k and n also found vary with temperature.
(iiii) No theoretical explanations were given.

A plot between the amount of adsorbate adsorbed and pressure or concentration of adsorbate at constant temperature is called adsorption isotherms.

When amount of adsorption is plotted vers temperature at constant pressure it is called adsorption isobar.

(i) In adsorption, if the concentration of a substance in the interface is high, then it is called positive adsorption.
(ii) In adsorption, if the concentration of a substance in the interface is less, then it is called negative adsorption.

The surface of separation of the two phases where the concentration of adsorbed molecule is high is known as interface.

A minimum of 6.6 ml of AB is required to coagulated the sol.
The number of moles of AB in the sol is
= \(\cfrac { 6.6\times 0.1 }{ 20 } \) 
= 0.033 moles
This means that minimum of 0.033 moles or 33 millimoles are required to coagulate 1litre of sol.
∴ Flocculating value of AB for sol = 33.