Isentropic compressibilities of electrolytes in acetonitrile at 25 °C

Abstract

The sound velocities of some 1:1 electrolytes in acetonitrile were measured by the "sing around" method. Apparent molal isentropic compressibilities [Formula: see text] of the electrolytes were derived from these data and from previously determined densities. Infinite dilution partial molal compressibilities [Formula: see text] were obtained by extrapolation from the plot [Formula: see text] against the square-root of the molality. Approximate ionic values are obtained on the assumption that [Formula: see text] In general, [Formula: see text] of inorganic ions are much more negative in acetonitrile than in water and, except for Li+, show little dependence on ionic size. On the other hand, [Formula: see text] of tetraalkylammonium bromides become increasingly positive as the size of the cations increases. This is again in contrast with [Formula: see text] of these electrolytes in water which remain negative. These large positive values arise from the free space between the ions and the solvent molecules, which is large in acetonitrile solutions.