Iodometric microdetermination of boric acid and borax separately or in a mixture.
Boric acid is determined by first treating it with mannitol and then with solid potassium iodate and potassium iodide. The iodine liberated is titrated with thiosulphate. Borax is determined by reacting it with a known and excessive volume of hydrochloric acid and determining the surplus acid by iodometry. From the amount of acid consumed, the quantity of borax is calculated. Mixtures of borax and boric acid are analysed by combination of the two methods. Borax is determined first, then the mannitol procedure is applied to a second sample and the total boric acid (original plus that produced in the borax-HCl reaction) is determined iodometrically. The boric acid content of the sample is obtained by difference. The procedures can be used for determining 0.01-0.1 mmole of these substances with an average deviation of 0.1-0.4%. The end-points obtained are sharper than those for potentiometric acid-base titrations. Furthermore, the procedures are applicable at much lower concentrations.
Saxena
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Department of Chemistry, University of Jabalpur, Jabalpur (M.P. 482001, India.
Verma
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