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Describe about condensation methods of preparation of colloids. (OR) Describechemical 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 + 4HI to 3H_2O _ 3I_(2"(sol)")` (ii) Reduction method:- Gold sol is prepared by reduction of auric chloride using formaldehyde. `2AuCl_3 + 3HCHO + 3H_2O to 2Au_("(sol)") + 6HCl + 3HCOOH` iii) Hydrolysis:- FERRIC chloride is hydrolysed to get ferric hydroxide colloid `FeCl_3 + 3H_2O 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_2O_3 + 3H_2S to As_2 S_3 + 3H_2O` (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_2O_3^(2-) +2H^(+) to S_("(sol)") + H_2O + SO_2` |
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