Bromatometry-converted first semster PDF

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Very simple notes of bromatometry analysis first semester...

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BROMATOMETRY Potassium bromate is a powerful oxidising agent in acid medium. Redox titration which employed potassium bromate as an oxidising agent is called bromatometry. Reducing agents first convert the bromate to bromide BrO3- + 6H+ + 6e-

Br- + 3 H2O

An acid solution is required because H + ions are involved in the conversion of bromate to bromide ions The rate of reaction is slow so inorder to accelerate the reaction titration is performed in heated and strongly acidic condition. Here the bromate ion is reduced to bromide ion during the titration. So as soon as excess bromate appears in the solution the bromide ion reacts with bromate ions BrO3- + 5Br- + 6H+

3Br2 + 3 H2O

Free bromine thus forms colours the solution a pale yellow. This colour is pale and so cannot be used for the detection of end point. So indicators such as methyl orange and methyl red are used. Bromatometry can be done by direct or indirect titration methods. In direct titration method the analyte is titrated with bromate solution in the presence of HCl. In indirect methods, excess bromine is added to the analyte solution and the excess of bromine is determined iodometrically by adding excess KI and liberated iodine is determined by titration using sodium thiosulphate

Preparation of 0.05 M bromine Dissolve 3 g of potassium bromate and 15 g of potassium bromide in sufficient water to produce 1000 ml. Standardisation of 0.05M bromine Pipette 25.0 ml of the solution into a 500 m1 iodine flask and dilute with 120 m1 of water. Add 5 ml of hydrochloric acid, insert the stopper in the flask and shake it gently. Add 5 ml of potassium iodide solution, again insert the stopper and to stand for 5 minutes in the dark. Titrate the liberated iodine with 0.1 M sodium thiosulphate using 3 ml of starch solution, added towards the end of the titration, as indicator. 1 ml of 0.1 M sodium thiosulphate is equivalent to 0.01598 g of Br2.

Store in dark amber-coloured, glass stoppererd bottles.

Applications 1. Various metals like aluminium, copper, iron, zinc, cadmium, cobalt, nickel etc can be determined by using oxime and bromatometry 2. Phenols can be determined by bromatometry 3. Hydroxylamine can be determined by bromatometry by indirect titration method REFERENCES IP 2010, Volume 1, page no: 631 Pharmaceutical Analysis-I by Dr.Uttam Singh Baghel ,page no: 82...