Volume and compressibility changes in mixed-salt solutions at 25 °C

Abstract

The excess molar volumes of mixing (Δ_mV^ex) and compression of mixing [Δ_m(βV)^ex] have been calculated from the measured density and sound-velocity data for aqueous binary and ternary solutions involving NaBr–KBr, Bu₄NBr–KBr and Bu₄NBr–Et₄NBr as solutes at 25 °C (in the concentration range 0.05–1.0 mol kg^–1 and at constant ionic strength of I≈ 0.2, 0.5 and 1.0 in ternary solutions. The Δ_mV^ex and Δ_m(βV)^ex values exhibit parabolic behaviour as a function of y[the fraction of ionic strength due to an electrolyte (AX) in a mixture of two electrolytes (AX + BX)]. On application of Friedman equation the Δ_mV^ex values show the presence of large cation–cation interactions in the solutions involving n-tetrabutylammonium bromide. The excess compression values of solutions and their variation with ionic strength indicate the effect of ion–ion interactions on the co-sphere water in a subtle way.