PVT properties of concentrated aqueous electrolytes: V. Densities and apparent molal volumes of the four major sea salts from dilute solution to saturation and from 0 to 100°C

Abstract

The densities of the major sea salts (NaCl, Na₂SO₄, MgCl₂, and MgSO₄) have been measured from 25 to 95°C and to saturation. These results have been combined with literature data and fitted to equations of the form

$$\Delta d = Am{\text{ }} + {\text{ }}Bm^{3/2} {\text{ }} + {\text{ }}Cm^2 {\text{ }} + {\text{ }}Dm^{5/2} $$

where Δd=d−d_o (d_o is the density of water) and A, B, and C, etc., are polynomial functions of temperature. The standard deviations of the fits were better than ±50×10⁻⁶ g-cm⁻³ for all the salts from 0 to 95°C and to saturation. The apparent molal volumes V_ϕ of the salts have been fitted to the equations of Pitzer. The infinite dilution values of V_ϕ were in good agreement with literature data, provided the results were not overfit. The large deviations of V_ϕ for MgSO₄ from additivity as a function of concentration were attributed to the formation of MgSO₄ ion pairs.