Question

Answer the following questions:
The hardy-Schulze rule explains why the coagulating power of phosphate is higher than chloride?

Answer 1

Hint: Higher the valence of the flocculating ions added, the greater is its power to cause precipitation.

Complete answer:
Hardy-Schulze rule: Higher the valence of the coagulating ions added, the greater is its power to cause precipitation.
Charge and solvation of the colloidal particles are responsible for the stability of lyophilic sol. If these two factors are removed then lyophilic sol gets coagulated and this is one by adding an electrolyte and adding a suitable solvent like alcohols, acetone etc.
Coagulating power: The minimum concentration of an electrolyte in millimoles per litre required to cause precipitation of a solution. Coagulating power depends upon charge on flocculating ions.
Coagulating power for negatively charged solution: for example $A{l^3} > B{a^{2 + }} > N{a^ + }$and coagulation power for positively charged solution:${\left[ {Fe{{\left( {CN} \right)}_6}} \right]^{4 - }} > P{O_4}^{3 - } > S{O_4}^{2 - } > C{l^ - }$
In phosphate ion has \[\left( {-{\text{ }}3} \right)\] charge and chloride ion has\[( - 1)\]charge so that greater the charge on flocculating ion, smaller is the amount of electrolyte required for precipitation and thus higher is the coagulating power. That is why phosphate is of higher coagulating power than that of chloride.

Note:The coagulation of colloids is due to neutralization of charge due to which the particles come nearer to each other to form aggregates and settle down under the force of gravity. The process of setting of colloidal particles is called coagulation of the sol. The coagulation of lyophobic sols can be carried out in the following ways: By electrophoresis, by mixing two oppositely charged sol, by boiling, by addition of electrolytes.