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The absorptiometric determination of sodium sulphide and the kinetics of its oxidation Hong, Charles Chuan-Chi

Abstract

A study of the Lauth's Violet absorptiometry method for the analysis of sodium sulphide was carried out. The order of adding the reactants in the development of the color, the use of three different methods of titration for standardizing the solutions used for determining the calibration factor, and the effects of varying the concentrations of the reagents were all investigated. In the formation of Lauth's Violet from sodium sulphide, addition of reactants in the order base electrolyte, sodium sulphide, and p-phenylenediamine was shown to be best. The arsenious oxide method of titration was selected for determining the concentration of sodium sulphide in standard solutions used for calibration. If the reagents: base electrolyte containing ferric chloride, and p-phenylenediamine, were used at the concentrations of 0.16% and 5% by weight, respectively, the calibration factor remained constant up to concentrations 16 grams per litre of sodium sulphide. The applicability of the Lambert-Beer law and the effect of sodium thiosulphate on the absorptiometry method also were studied in detail. The oxidation of sodium sulphide was studied under atmospheric pressure at various temperatures by use of two different apparatuses. From the measurements of the amounts of oxygen absorbed, the oxidation of sodium sulphide probably gives disulphide, thiosulphate, sulphite and sulphate. The stoichiometry corresponds to thiosulphate being the main product of this reaction. The rate of absorption of oxygen with simultaneous, oxidation of sodium sulphide was observed to decrease, with increasing temperature from 25° to 45°C Nevertheless, the maximum absorption rate was found at 55°C, and the absorption rate decreases again with temperature at least to 85°C. The reaction orders for the oxidation of sodium sulphide depend upon temperature, being second order at 25°C, order of 1.5 at 35° and 45°C., and first order from 55° to 85°C. The reaction order with respect to oxygen is first order, irrespective of temperature. The maximum rate of oxidation also occurs at 55°C.

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