The PVT properties of concentrated aqueous electrolytes. IV. Changes in the compressibilities of mixing the major sea salts at 25°C

The speed of sound of mixtures of the six possible combinations of the major sea salt ions (Na⁺, Mg²⁺, Cl^-, and SO₄^2-) have been determined at I=3.0 and at 25°C. The results have been used to determine the changes in the adiabatic compressibility of mixing ΔK_m the major sea salts. The values of ΔK_m have been fit to the equation ΔK_m=y₂y₃I²[k₀+k₁(1-2y₃)] where y_i is the ionic strength fraction of solute i, k₀ and k₁ are parameters related to the interactions of like-charged ions. The Young cross-square rule is obeyed to within ±0.04×10^-6 cm³-kg^-1-bar^-1. A linear correlation was found between the compressibility k₀ and volume v₀ interaction parameters (10⁴k₀=-0.24+3.999 v₀, s=0.15) in agreement with out earlier findings. Estimates of the sound speeds for the cross square mixtures (NaCl+MgSO₄ and MgCl₂+Na₂SO₄) were made using the equations of Reilly and Wood. The estimated sound speeds were found to agree on the average with the measured values to ±0.36 m-sec^-1.