Isopiestic studies of aqueous solutions at elevated temperatures VI. LiCl and CsCl

Abstract

Isopiestic measurements have been made for LiCl(aq) and CsCl(aq) over the temperature range 382.96 to 473.61 K. NaCl(aq) served as the reference electrolyte for the calculation of osmotic coefficients and the molalities ranged from about 0.6 to 6 mol kg −1, for NaCl(aq). An ion-interaction model gave an excellent fit to the experimental osmotic coefficients with a standard error of fit ranging from 0.0004 to 0.0016 in the osmotic coefficient. Parameters obtained from the fit were used to calculate the activity coefficients. The osmotic and activity coefficients both decreased with increasing temperature over this temperature range. LiCl(aq) is somewhat unusual among the alkali-metal chlorides in that the osmotic (and activity) coefficient is much more dependent on molality at the higher molalities and there is no maximum between 273.15 and 373.15 K in the osmotic coefficient as a function of temperature. For both LiCl(aq) and CsCl(aq) there is an excellent correlation between the isopiestic results and the vapor pressures of Lindsay and Liu. Existing electrochemical results between 283.15 and 343.15 K are consistent with our calculated activity coefficients for CsCl(aq).