The PVT properties of concentrated aqueous electrolytes IX. The volume properties of KCl and K₂SO₄ and their mixtures with NaCl and Na₂SO₄ as a function of temperature

Abstract

The densities of KCl and K₂SO₄ were measured from dilute solutions to saturation from 5 to 95°C. The data were combined with literature data to produce density and apparent molal volume, V_φ, equations from 0 to 100°C and to saturation. The standard deviations of the density equations were 30×10⁻⁶ g-cm⁻³ and 32×10⁻⁶ g-cm⁻³, respectively, for KCl and K₂SO₄. Pitzer equations were used to fit the V_φ data. The resulting infinite dilute partial molal volumes, V^o, were in reasonable agreement with literature data. The densities of the mixtures of the six combinations of the salts KCL, K₂SO₄ NaCl and Na₂SO₄ were measured at I=2.0 and t=5, 25, 55 and 95°C. The resulting volumes of mixing were fitted to equations of the form

$$\Delta V_m = y(1 - y)I^2 [\nu _0 + \nu _1 (1 - 2y)]$$

wherev ₀ andv ₁ are interaction parameters. The cross square rule is valid over the entire temperature range although the deviations are larger at higher temperatures. Pitzer θ ^v_NaK and $\theta _{ClSO_4 }^v$ parameters were determined from the common ion mixtures. The values of θ ^v_NaK were small and not strongly dependent upon temperature. The values of $\theta _{ClSO_4 }^v$ were also small and changed considerably with temperature.