plz explain 'hardy - schulze rule" ...

Hi Kinshuk,

 

The minimum amount of an electrolyte that must be added to 1litre of colloidal solution so as to bring about the complete coagulation is called the coagulation or flocculation value of that electrolyte.

Hardy –Schulze rule states that greater is the valency of the oppositely charged ion of the electrolyte being added, the faster is the coagulation. It means that the coagulating power of an electrolyte is directly proportional to the fourth power of the valency of the effective ion i.e. ion having charge opposite to that of the colloidal particles.

 

For e.g. for a negatively charged sol As₂S₃, the coagulating powers of the cations are in the order:

Al³⁺>Ba²⁺>Na⁺

 

Other example for positively charged colloid is Fe (OH)₃. The coagulating powers of the anions follow the order as:

PO₄^3->SO₄^2->Cl^-