Partial molar isentropic compressibilities and volumes of selected electrolytes and nonelectrolytes in dimethylsulfoxide

Precision densities and sound velocities for solutions of selected univalent electrolytes and nonelectrolytes in DMSO have been measured at 25°C, and apparent molar isentropic compressibilities and volumes evaluated. The data were extrapolated to infinite dilution to obtain standard state partial molar quantities, K_s,2^°, and V₂^°. Values of V₂^° and K_s,2^° for alkali metal halides in DMSO are very similar to those in water. The results confirm conclusions derived from data in water and other nonaqueous solvents that K_s,2^° and V₂^° for alkali metal halides are strongly dependent on solvent compressibility. K_s,2^° becomes more negative and V₂^° decreases as solvent compressibility increases. Attempts to determine ionic K_s,2^° values suggest that a significant dissymmetry exists between ₄P⁺ and ₄B^– in DMSO, whereas in water and MeOH, these large ions appear to behave similarly. Ionic V₂^° values support this conclusion. Steric hindrance in the DMSO molecule is believed to be responsible for this dissymmetry.