Isentropic compressibilities of univalent electrolytes in methanol at 25�C

Abstract

A flow densimeter and an ultrasonic sound velocimeter have been used to measure densities and isentropic compressibilities of solutions of LiBr, NaCl, NaBr, Nal, KF, KCl, KBr, Kl, RbBr, Rbl, CsF, CsBr, Ph 4 PBr, and NaBPh 4 in anhydrous methanol at 25°C. the latter two electrolytes were also investigated in water at 25°C. Concentrations ranged from about 0.005 m to above 0.25m, solubility permitting. Apparent molar isentropic compressibilities, KS,ϕ, have been calculated and extrapolated to infinite dilution to obtain K S,ϕ o . The K S,ϕ o values in methanol are all negative, and significantly more negative than the corresponding data in water. Additional data from the literature for acetonitrile and ethanol solutions show that K S,ϕ o for the alkali metal halides become more negative in direct proportion to increasing solvent isentropic compressibility. Furthermore, the dependence of K S,ϕ o in ionic size also varies in proportion to solvent isentropic compressibility. An explanation of this behavior is presented.