Mechanism of Sol Protection
(i) The actual mechanism of sol protection is very complex. However it may be due to the adsorption of the protective colloid on the lyophobic sol particles, followed by its solvation. Thus it stabilises the sol viasolvation effects.
(ii) Solvation effects contribute much towards the stability of lyophilic systems. For example, gelatin has a sufficiently strong affinity for water. It is only because of the solvation effects that even the addition of electrolytes in small amounts does not cause any flocculation of hydrophilic sols. However at higher concentration, precipitation occurs. This phenomenon is called salting out.
(iii) The salting out efficiency of an electrolyte depends upon the tendency of its constituents ions to get hydrated i.e, the tendency to squeeze out water initially fied up with the colloidal particle.
(iv) The cations and the anions can be arranged in the decreasing order of the salting out power, such an arrangement is called lyotropic series.
Ammonium sulphate, due to its very high solubility in water, is oftenly used for precipitating proteins from aqueous solutions.
(v) The precipitation of lyophilic colloids can also be affected by the addition of organic solvents of non-electrolytes. For example, the addition of acetone or alcohol to aqueous gelatin solution causes precipitation of gelatin. Addition of petroleum ether to a solution of rubber in benzene causes the precipitation of rubber.