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, Li 2 SO4, K 2 SO4 and mixtures H 2 SO4-Na 2 SO4-H 2 O 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 10-5-10-3 mol kg-1 at temperatures 298-673 K and pressures up to 28 MPa. 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 573-663 K the adjustable parameters are the proton limiting equivalent conductance and the HCl dissociation constant. At the measured state point of lowest water density (228.8 kg m-3 ; 673 K) the additional account of ion triplets gives good fit to the data.

Electrical conductivity of HCl-bearing aqueous fluids to 700 ºC and 1 GPa

“…A regression fit yielded 1 = 2550.14 ± 99.57, 2 = −505.10 ± 117.76, 3 = −429,437 ± 22,442 (R 2 = 0.97). Figure 5 compares measured and predicted values, including also some data from Ho et al (2001) and Balashov et al (2017) measured at relatively low pressures up to about 30 MPa. Note that in contrast to the regression equation used by Sinmyo and Keppler (2017) for the limiting molar conductivity of NaCl, Eq.…”

“…They were fitted to a model Λ 0 = 1 + 2 + 3 ∕T with 1 = 2,550.14 ± 99.57, 2 = −505.10 ± 117.76, 3 = −429,437 ± 22,442; R 2 = 0.97. For comparison, data from Ho et al (2001;blue circles) and Balashov et al (2017;green circles) are also shown for fluid densities >0.5 g/ cm 3 . For lower fluid densities, the uncertainties in the measured values become very large Fig.…”

“…However, the quantitative interpretation of these measurements for a long time was hampered by the lack of electrical conductivity data for fluids at the relevant pressures and temperatures. Traditionally, such data were measured with externally heated autoclaves, which limited pressures to a maximum of 400 MPa (e.g., Franck 1956;Frantz and Marshall 1984;Ho et al 2001;Balashov et al 2017). Moreover, most of the measurements were carried out in physical chemistry with solutions of very low concentrations to constrain dissociation constants and ionic mobilities.…”

Critical Review of Transport and Equilibrium Properties of Potassium Chloride in High Temperature Water

“…The Arrhenius energy term, [E η − E λ ] = c + d ln ρ w , was taken from the expression for the standard molar internal energy of reaction from the "density" model, 7,67,68 which describes the solvent compressibility effects on chemical equilibria at elevated temperatures and pressures. The equation is similar to Balashov's model 6 for NaCl discussed below but does not include the second structural term expressed by "α 10 ln ρ w + α 1 κ κ + α 2 ρ ρ w ." Balashov and Wood Sodium Chloride Based Correlation.…”

“…Balashov and Wood Sodium Chloride Based Correlation. 6 The most recent approach has been reported by Balashov et al 6 and involved calculation of the product of Λ°N aCl η w via a logarithmic relationship of this product to temperature, solvent density, compressibility values, and six parameters obtained by regression.…”