No abstract

Frequency-dependent electrical conductivities of solutions of aqueous sodium chloride have been measured from T = 298 K to T = 623 K at p = 20 MPa, over a very wide range of ionic strength (2·10 −5 to 0.17 mol·kg −1 ) using a unique highprecision flow-through alternating current (AC) electrical conductance instrument. Experimental values for the equivalent conductivity, Λ, were used to calculate molar conductivities at infinite dilution, Λ°, using the Fuoss−Hsia−Fernandez−Prini (FHFP) and Turq−Blum−Bernard−Kunz (TBBK) ionic conductivity models. The resulting values for the limiting conductivity Λ°and the ion association constant of NaCl, from this work and critically evaluated literature data above 277 K, were represented to within the combined experimental uncertainties, as functions of viscosity and solvent density, respectively. New values and new correlations are reported for the limiting equivalent conductivities of the sodium ion, λ°(Na + ), and the chloride ion, λ°(Cl − ) from 277 K and 100 kPa to 1073 K and 500 MPa.

Frequency-dependent molar electrical conductivities for aqueous solutions of potassium borate, and sodium borate have been measured from ambient to near-critical temperatures and pressures to an accuracy of ±3 percent, using a unique high-precision flow-through AC conductance instrument. The concentration dependence of these conductivities was analyzed with the Turq-Blum-Bernard-Kunz ("TBBK") theoretical model to yield (i) limiting conductivities of the borate ion, λ(0)[B(OH)4(-)], and (ii) ion-pair formation constants, KA, for the species NaB(OH) and KB(OH) from T = 298 K to T = 623 K at a constant pressure p ∼ 20 MPa. The ion-pair formation constants for both borate salts were found to be consistent with previous literature studies at temperatures below 473 K. No significant difference in KA was observed between the species NaB(OH) and KB(OH). As temperature was increased from 473 up to 623 K, the degree of association increased significantly, and was found to be considerably higher than for any other 1-1 electrolyte previously studied. For instance, at 623 K, the association constant log KA[NaB(OH)] = 2.75 ± 0.21 was an order of magnitude higher than log KA[NaCl(0)] = 1.53 ± 0.03, and approximately equal to that of a 2 : 1 electrolyte, log KA[SrCF3SO3(+)] = 2.58 ± 0.06. Deviations in the limiting conductivities from Stokes Law show that the borate ion's unusual "structure making" effect, observed by other workers at sub-ambient conditions, persists up to temperatures above 500 K. The temperature dependence of the Walden product ratio is very different from that observed for other monovalent anions for which experimental data are available over this wide range of temperatures.

Frequency-dependent electrical conductivities of solutions of aqueous sodium trifluoromethanesulfonate ("triflate") and strontium triflate have been measured from T = 298 K to T = 623 K at p = 20 MPa, over a very wide range of ionic strength [(2•10 −5 to 0.35) mol•kg −1 ], using a unique high-precision flowthrough AC electrical conductance instrument. Experimental values for the equivalent conductivity, Λ, of each electrolyte were used to calculate their equivalent conductivities at infinite dilution, Λ°, with the Turq−Blum−Bernard−Kunz (TBBK) ionic conductivity model. Values were derived for the limiting equivalent conductivity of the triflate ion, λ°(CF 3 SO 3 − ), and the strontium ion, λ°(Sr 2+ ). The TBBK fits to the concentration-dependent equivalent conductivity data for both NaCF 3 SO 3 and Sr(CF 3 SO 3 ) 2 required statistically significant ionic association constants for the species NaCF 3 SO 3 0 at temperatures T > 448 K, SrCF 3 SO 3 + at T > 448 K, and for Sr(CF 3 SO 3 ) 2 0 at T > 548 K. The stepwise association constants, K A , for the charged species SrCF 3 SO 3 + , were found to be greater or equal to than the ones for the neutral species Sr(CF 3 SO 3 ) 2 0 . The experimental value of K A for Sr(CF 3 SO 3 ) 2 0 was found to be similar to that for NaCF 3 SO 3 0 at 548 K but increased more steeply with temperature. At temperatures above 548 K, association constants derived from the concentration-dependent equivalent conductivities were increasingly sensitive to the assumptions used to calculate solution densities. Procedures for minimizing these effects are reported. The temperature dependence of the experimental association constants and limiting equivalent conductivities from (298 to 623) K could be represented accurately as functions of solvent density and viscosity, respectively.