Explain any 2 methods for the preparation of colloids.

Explanation

Method-1 : Bredig's arc Method : This process consists of dispersion and condensation colloids of Gold, Platium, Silver arc prepared by this method. In this method an electric are is struck between the electrodes of the metal immersed in the dispersion medium. The heat produced vapourises the metal which then condensed to colloidal size.
Method-2 : Colloids can be prepared by chemical reactions like double decomposition, oxidation , reduction and hydrolysis .
Double decomposition: `As_(2)O_(3) + 3H_(2)S to AS_(2)S_(3) ("sol")+ 3H_(2)O`
Oxidation : `SO_(2) + 2H_(2)S to 3S("sol") + 2H_(2)O`
Reduction : `2AuCl_(3) + 3HCHO + 3H_(2)O to 2 Au ("sol") + 3HCOOH + 6HCl`
Hydrolysis : `FeCl_(3)+ 3H_(2)O to Fe(OH)_(2) ("sol") + 3HCl`