CONDUCTANCE OF DILUTE LICL, NACL, NABR, AND CSBR SOLUTIONS IN SUPERCRITICAL WATER USING A FLOW CONDUCTANCE CELL

Conductivities of LiCl(aq), NaCl(aq), NaBr(aq), and CsBr(aq) solutions have been measured in the range of concentrations from 0.013 to 4 x 1 0(-8) mol.dm(-3) using a flow conductance cell at temperatures between 603 K and 674 K and pressures between 15 MPa and 28 MPa (water densit ies from 650 to 200 kg.m(-3)). Limiting equivalent conductances and io nization equilibrium constants calculated from the concentration depen dence of the equivalent conductance are reported. Previous measurement s of equilibrium constants in the low-density supercritical region, al though of lesser accuracy, agree well with the present results. Even a t the critical density and 2.5 K above the critical temperature there is no evidence for the critical effects which make the Debye-Huckel li miting law invalid at the critical isotherm-isobar. No critical scalin g of ho is observed. Walden's rule is not obeyed and the Stokes radius increases by 70% near the critical region as the density goes from 70 0 to 200 kg.m(-3), suggesting an increase in the number of water molec ules carried along with the ion. The differences in mobility between d ifferent ions are rather small when compared to the differences in cry stallographic ionic radii. The association constants are in the order CsBr < NaBr < NaCl approximate to LiCl.