The capacity of an ion to coagulate a colloidal solution depends onA. the magnitude of charge onlyB. its size onlyC. both the size of ion and the magnitude of charge in itD. both sign and magnitude of charge.

The capacity of an ion to coagulate a colloidal solution depends onA.

1.	The capacity of an ion to coagulate a colloidal solution depends onA. the magnitude of charge onlyB. its size onlyC. both the size of ion and the magnitude of charge in itD. both sign and magnitude of charge.
Answer» Correct Answer - D Different electolytes have different coagulation values.The coagulation behaviour of various elecrolytes was studied in detail by Hardy and Schulze. They found that `(1)` the ions carrying charge opposite to that of sol particles are effective in causing the coagulation of the sol. `(2)` coagulating power of an electrolyte is directly proportional to the fourth power of the valency of the ions causing coagulation. Thus,for the coagulation of sols carrying negative charge (like `As_(2)S_(3)` Sol), `Fe^(3+)` ions are more effective than `Ba^(2+)` or `Na^(+)` ions .Similarly, for the coagulation of sols carrying positive charge (such as `Fe(OH)_(3)` sol), `PO_(4)^(3-)` ions are more efficient than `SO_(4)^(2-)` or `Cl^(-)` ions. The two observations given above are collectively called Hardy-Schulze rule. These observations show that utmost care should be taken to keep sols away from environment containing even small amount of elecrolytes.