AN ISOPIESTIC STUDY OF AQUEOUS-SOLUTIONS OF THE ALKALI-METAL HYDROGENSULFATES AT ELEVATED-TEMPERATURES

Isopiestic molalities of LiHSO4(aq), KHSO4(aq), and CsHSO4(aq) have be en measured over the temperature range 383.46 K to 498.19 K with NaCl( aq) serving as the reference electrolyte for the calculation of excess thermodynamic quantities. Molalities of the reference electrolyte ran ged from about 0.5 mol . kg(-1) to greater than 6 mol . kg(-1). The io n-interaction model of Fitter gave an excellent description of the exp erimental results when the solutions were treated as mixed-electrolyte systems resulting from partial ionization of HSO4-(aq). A simple poly nomial model for the temperature dependence of the ion-interaction par ameters is sufficient to reproduce the experimental results. When calc ulated as stoichiometric activity coefficients for 1-2 charge types, t he resulting quantities are quite small, especially when compared with activity coefficients based on the assumption of a 1-1 charge type. T he activity coefficients are consistent with limited dissociation of t he hydrogensulfate anion which decreases with increasing temperature. (C) 1996 Academic Press Limited