what is hardy schulze rule ?

Hardy Schulze Rule:

  • The coagulation capacity of different electrolytes is different. It depends upon the valency of the active ion are called flocculating ion, which is the ion carrying charge opposite to the charge on the colloidal particles.
  • “According to Hardy Schulze rule, greater the valency of the active ion or flocculating ion, greater will be its coagulating power”

Thus, Hardy Schulze law state:

(i) The ions carrying the charge opposite to that of sol particles are effective in causing coagulation of the sol.

(ii) Coagulating power of an electrolyte is directly proportional to the valency of the active ions (ions causing coagulation).


For example :

To coagulate negative sol of As2S3, the coagulation power of different cations has been found to decrease in the order as, Al3+ > Mg2+ > Na+

Similarly, to coagulate a positive sol such as Fe(OH)3, the coagulating power of different anions has been found to decrease in the order : [Fe(CN)6]4– > PO4 3– > SO4 2– > Cl

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schultz - hardy rule :

An increase in the charge of ions results in a large increase in their flocculating power.

here,........Flocculation,  is a process wherein colloids come out of suspension   in the form of floc or flakes by the addition of a clarifying agent. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually dissolved in a solution . In the flocculated system, there is no formation of a cake, since all the flocs are in the suspension.
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