Question

What modification would you suggest to Hardy Schulz rule?

Answer 1

Hardy Schulz law states the greater will be the valency of the flocculation ion, the greater will be its coagulation power. The amount of electrolyte that is being added for coagulation for a definite quantity of colloidal solution is dependent on the valency of the coagulating ion. The principal forces involved in this process are the electrostatic forces of attraction.

Complete answer:
We see that the property taken into accountability is the charge which is carried by the ion and not the size of the ion.

We know that smaller will be the size of the ion, greater will be its polarizing power. So, the law should be modified on the basis of polarizing power of the flocculating ion causing precipitation.

Hence the modified law will be as:
Greater the polarizing power of the flocculation ion, the greater will be its power to cause precipitation.
Therefore, both the size and the charge of the ion will determine the polarizing power of a colloidal solution.

Additional information: The minimum concentration of an electrolyte of the solution which is required to cause the flocculation or coagulation is known as the flocculation value. The maximum flocculating value for an electrolyte will be the one where the electrolyte will be having minimum coagulating power. Hence $NaCl$ has the lowest charge, hence it will have the lowest coagulating power and the maximum flocculating value.

Note: Flocculating ions are the ones which carry a charge that is opposite to the charge carried by the carried by the particles of the colloidal solution. Also flocculating ions are the ions which are capable of causing coagulation in the electrolyte. The flocculating ions are also known as the coagulating ions.