Electrical conductances of aqueous solutions of inorganic nitrates at 25–505°C and 100–490 bar

Abstract

A simple Pt electrode was used to determine the electrical conductances of 0.00393, 0.00992 and 0.0379 m NaNO 3 and 0.00911 m LiNO 3, 0.00910 m CsNO 3 and 0.00946 m Ca(NO 3) 2 solutions. Temperatures ranged from 25 to 505°C at pressures ranging from 100 to 490 bar. The electrode was calibrated against the conductance of 0.010 m hydrothermal NaCl solutions. Preliminary limiting equivalent conductances and dissociation constants were obtained for hydrothermal NaNO 3 solutions. The alkali nitrate series behaved similarly to the alkali chloride series: the electrical conductance decreases with decreasing cation radius. This seemingly paradoxical result is due to the stronger electric field and hence the greater tendency for ion pairing and larger solvation spheres associated with smaller cations. Nearly complete ion association is observed at low-density supercritical conditions. Maximum conductances were obtained at about 300°C and densities increasing from about 500 kg m −3 to 725 kg m −3 with increasing concentration. Limiting conductances and p K a values for NaNO 3 solutions were similar to those for NaCl solutions, with NaNO 3 being the weaker electrolyte. Ca(NO 3) 2 conductances follow similar trends to K 2SO 4. The data suggests that nearly complete dissociation occurs below 200°C, but that appreciable association to form monovalent cations occurs at higher temperatures.