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Account for the fact that the charge of the colloidal particles is due to the selective adsorption of the ions. Give one example. |
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Answer» Solution :The colloidal solutions GENERALLY contain traces of electrolytes. The charge on the colloidal particles is due to the preferentially adsorption of positive or negative ions from the electrolyte. If the colloidal particles adsorb positive ions, they get positive charge. Similarly, if the colloidal particles have preference to adsorb negative charge, they acquire negative charge. In general, the particles constituting the dispersed phase adsorb only those ions preferentially which are common with their own lattice ions. LET us consider an example The `FE(OH)_3 `sol prepared by the hydrolysis of `FeCl_3` . has positive charge because it preferentially adsorbs` Fe^(3+)`ions on its surface from the solution. `FeCl_3 iff Fe^(3+) + 3Cl^(-)` `Fe(OH)_3 + Fe^(3+) iff Fe(OH)_3. Fe^(3+)` (sol) This colloidal sol may also be REPRESENTED as ` [Fe(OH)_3] Fe^(3+) : 3Cl^(-)` where `[Fe(OH)_3] ` implies precipitate of FERRIC hydroxide on which `Fe^(3+)`are adsorbed. The ions on the right of dotted line represent ions present in excess in dispersion medium. |
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