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Jan Balej

Solubility in the System (NH4)2S2O8—NH3—H2O and Mean Activity Coefficients of Saturated Solutions of (NH4)2S2O8

The solubility data of ammonium peroxodisulfate in aqueous ammonia solutions at 15.5 °C have been evaluated using the relative activity coefficient expansion. Using the known value of the mean activity coefficient of saturated solution of ammonium peroxodisulfate in pure water, values of the mean activity coefficients of this salt in the saturated solutions of the given system have been calculated.

Open access

Jan Balej

Abstract

Probable values of the degree of ion-pairing (ion-association) of aqueous solutions of alkali metal and ammonium peroxodisulfates have been calculated for various estimated values of association constants, in dependence a) on the concentration of the binary solution, b) on the concentration of the other electrolyte in the polycomponent solution with the common ion, able or not able to form ion pair, and c) on the value of the activity quotient Q a. It followed that in the presence of another component with a common cation and neglecting the influence of activity coefficients, the ion-association degree of peroxodisulfate α > 0.5 in solutions with total molality m t > 0.1 mol kg-1; as mostly Q a < 1.0, the ion-association degree is even higher so that in such cases the alkali metal and ammonium peroxodisulfates can prevailingly behave as uni-univalent electrolytes. In agreement with these results, evaluation of the solubility of sodium, potassium and ammonium peroxodisulfates in some ternary and quaternary systems has been performed under the simplified assumption of a complete ion-association to MS2O8 1- ions. It has been shown that the mean deviations between the calculated and observed solubilities of the crystallizing components are almost equally low as under the assumption of a total dissociation of the corresponding substances. The results indicated that the prevailing ion-association of more concentrated solutions of peroxodisufates could be taken as an acceptable approach for the quantitative evaluation of physico-chemical behaviour of systems containing peroxodisulfates.

Open access

Jan Balej

Abstract

Solubility data of the conversion system 2NH4 + - 2Na+ - S2O8 2- - SO4 2- - H2O at 20 °C and 30 °C for the partial pseudoternary systems Na2S2O8-(NH4)2SO4-H2O, (NH4)2S2O8-Na2SO4-H2O, Na2S2O8-NaNH4SO4-H2O and (NH4)2S2O8-NaNH4SO4-H2O have been correlated using the relative activity coefficient expansion of the crystallizing component. The obtained correlation equations have been used for the calculation of mean activity coefficients of ammonium and sodium peroxodisulfates in their saturated solutions of the mentioned pseudoternary systems.