PVT properties of concentrated aqueous electrolytes. II. Compressibilities and apparent molar compressibilities of aqueous NaCl, Na₂SO₄, MgCl₂, and MgSO₄ from dilute solution to saturation and from 0 to 50°C

The relative sound velocities (U-U°) of aqueous NaCl, Na₂SO₄, MgCl₂, and MgSO₄ solutions were measured from 0.05m to saturation and from 0 to 45°C. The sound speeds were combined with our earlier work and fitted to a function of molality and temperature to standard deviations within 0.3 m-sec^-1. The adiabatic compressibilities, β_s, were determined from the sound speeds and used to calculate adiabatic apparent molar compressibilities, K_φ{symbol},s, isothermal compressibilities, β, and apparent molar compressibilities, K_φ{symbol}, were determined from the adiabatic values using literature data for expansibilities and heat capacities. The values of K_φ{symbol} have been extrapolated to infinite dilution using an extended limiting law. The resulting K⁰ at various temperatures are in reasonable agreement with literature values. The results of this study have been combined with our earlier results to derive a secant bulk modulus equation of state for NaCl, Na₂SO₄, MgCl₂, and MgSO₄ solutions valid from 0 to 50°C and 0 to 1000 bar.