ELECTRICAL-CONDUCTIVITY MEASUREMENTS OF AQUEOUS SODIUM-CHLORIDE SOLUTIONS TO 600-DEGREES-C AND 300-MPA

Electrical conductance measurements of dilute (< 0.1 mol-kg(-1)) aqueo us NaCl solutions were made primarily to quantify the degree of ion as sociation which increases with increasing temperature and decreasing s olvent density. These measurements were carried our at temperatures fr om 100 to 600 degrees C and pressures up to 300 MPa with a modified ve rsion of the apparatus used previously in the high temperature study i n this laboratory. Particular emphasis was placed on conditions close to the critical temperature/pressure region of water, i.e., at 5 degre es intervals from 370 to 400 degrees C. The results verify previous fi ndings that the limiting equivalent conductance Lambda(0) of NaCl incr eases linearly with decreasing density from 0.75 to 0.3 g-cm(-1) and a lso with increasing temperature from 100 to 350 degrees C. Above 350 d egrees C, Lambda(0), is virtually temperature independent. The logarit hm of the molal association constant as calculated exclusively from th e data greater than or equal to 400 degrees C is represented as a func tion of temperature (Kelvin) and the logarithm of the density of water (g-cm-(-3)) as follows: log K-m = 0.997 - 650.07/T - (10.420 - 2600.5 /T)log rho(W) Note that this function also provides a good representat ion of the log K-m values obtained from 350 to 395 degrees C at densit ies greaser than ca. 0.6 g-cm(-3). More precise conductance data now a vailable in the literature suggest a systematic error of unknown origi n may exist in the data obtained at lower densities in this region. Th e relevant thermodynamics quantities derived from differentiation of t his equation with respect to temperature and pressure are listed in th e text.