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why Fe(oh)3 easily coagulated by Na3Po4?
The coagulation capacity of electrolyte depends on the valence of the active ion or flocculating ion. This is expressed by Hardy-Schulz law which states : ‘ the greater the valence of the flocculating ion, the greater will be its coagulating power' . Thus the coagulation of the negatively charged As2S3sol, the coagulating power of positive ions decrease in the order :
                                           Al3+> Ba2+> Na+
Similarly, the coagulation of positive sol of Fe(OH)3 , the flocculating power of negative ions decreases in the order :
                  [Fe(CN)6]4?> PO43?> SO42?> Cl?.
However, the rule is only approximate. The minimum concentration (in millimoles per litre) of an electrolyte which is required to cause the flocculation of a sol is known as flocculation value of the electrolyte.


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