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Describe about condensation methods of preparation of colloids. |
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Answer» Solution :When the substance for colloidal particle is present as small sized particle, molecule or ION, they are brought to the colloidal dimension by condensation methods. i. Oxidation method:- When hydroiodic acid is treated with iodic acid `I_(2)` sol is OBTAINED. `HIO_(3)+5HI to 3H_(2)O +3I_(2"(sol)")` ii. Reduction method:- GOLD sol is prepared by reduction of auric chloride using formaldehyde. `2AuCl_(3)+3HCHO+3H_(2)O to 2Au_((sol))+6HCl+3HCOOH` iii. Hydrolysis:- Ferric chloride is hydrolysed to get ferric hydroxide colloid `FeCl_(3)+3H_(2)O to Fe(OH)_(3)(sol)+3HCl` iv. Double decomposition:- When hydrogen sulphide gas is passed through a solution of ARSENIC OXIDE, a yellow coloured arsenic sulphide is obtained as a colloidal solution. `As_(2)O_(3)+3H_(2)S to As_(2)S_(3)+3H_(2)O` v. Decomposition:- When few drops of an acid is added to a dilute solution of sodium thiosulphate, sulphur colloid is produced by the decomposition of sodium thio sulphate. `S_(2)O_(3)^(2-)+2H^(+) to S_((sol))+H_(2)O+SO_(2)` |
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