Abstract
MANY procedures for titrimetric nitrate determinations are based on reduction by ferrous salts. Ferrous iron reduces nitrates boiled in acid medium to nitrous oxide. In alkaline medium the reduction proceeds at a concentration of 28 per cent sodium hydroxide, and the product is ammonia. Cotte and Kahane1 have found that silver sulphate catalyses the reduction at a suitably lower concentration of hydroxide. The ammonia formed was distilled into acid, the excess of which was measured. Our method is based on the same reduction; but the reduced nitrate is measured in another manner. The reduction is effected in a boiling 3 per cent sodium hydroxide solution, containing ammoniacal silver sulphate, by the action of ferrous hydroxide precipitated from a measured sample of ferrous ammonium sulphate. When the reaction is completed, the mixture is acidified with sulphuric acid and the excess of the ferrous iron is titrated with potassium permanganate. A blank titration must also be carried out. The reduction—without regard to the catalysis—proceeds by the following reactions: As can be seen from the equations, 8 moles of Fe(OH)2 are necessary for the reduction of 1 mole of nitrate. 1 ml. of 0.1 N potassium permanganate is equivalent to 0.7751 mgm. of NO3.
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Cotte, J., and Kahane, E., Bull. Soc. Chim., 542 (1946).
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SZABÓ, Z., BARTHA, L. Titrimetric Determination of Nitrates with an Equivalent Ratio of I : 8. Nature 166, 309 (1950). https://doi.org/10.1038/166309a0
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DOI: https://doi.org/10.1038/166309a0
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