Electrical conductances of aqueous electrolytes at high temperatures: Limiting mobilities of several ions including the proton and HCl dissociation constant

Abstract

The empirical equation of R.H. Wood for limiting equivalent NaCl conductance and a set of equations for a proton and other ions in the aqueous solutions HCl, LiCl, NaCl, KCl, Li2SO4, K2SO4 and mixtures H2SO4–Na2SO4–H2O are revisited and compared with equations of other authors. The Wood equation is unique in an accurate description of the region close to the critical point of water. In this region the decrease in limiting ion mobilities correlate with the increase in water compressibility. In a remarkable way this effect corresponds to the decisive drop in the limiting proton mobility making it similar to the other univalent ions mobilities. Probably, in this water region the critical decrease in the number of hydrogen bonds per water molecule takes place and finally impeding the jump mechanism of proton mobility. The new high temperature data on electrical conductance of aqueous HCl are represented for molalities 10−5–10−3molkg−1 at temperatures 298–673K and pressures up to 28MPa. The HCl conductivities have been fitted to the Turq, Blum, Bernard and Kunz equation using Wood mixing rule and mean spherical approximation activity coefficients. At 573–663K the adjustable parameters are the proton limiting equivalent conductance and the HCl dissociation constant. At the measured state point of lowest water density (228.8kgm−3; 673K) the additional account of ion triplets gives good fit to the data.