Volumetric properties and the ion-interaction parameters of the binary system (CsB5O8 + H2O) at temperatures from (283.15 to 363.15) K and 101 kPa

Highlights: • Densities of CsB₅O₈(aq) at (0.02526–0.08148) mol·kg⁻¹ were measured. • Apparent molar volume and coefficient of thermal expansion were obtained. • Pitzer single-salt parameters of CsB₅O₆(OH)₄ were obtained for the first time. • Temperature-dependence equations of Pitzer single-salt parameters were obtained. -- Abstract: This paper reports the densities of CsB₅O₈ (aq) in the range of salt concentrations from 0.02526 to 0.08148 mol·kg⁻¹, which were determined by an accurate Anton Paar Digital vibrating-tube densimeter at 5 K intervals from 283.15 to 363.15 K and 101 kPa. The apparent molar volume (V_ϕ), the coefficient of thermal expansion (α), apparent molar expansibility of the solute (ϕ_E) were calculated and variations of these properties against temperature and concentration were revealed minutely. According to Pitzer ion-interaction apparent molar volume model of aqueous electrolyte system, the Pitzer single salt parameters i.e. F_MX (${\beta }_{MX}^{\left(0\right)v}$, ${\beta }_{MX}^{\left(1\right)v}$ and $C_{MX}^v$, M = Cs⁺, X = [B₅O₆(OH)₄]^-), the temperature-dependence equation [F_MX (i, p, T) = a₁ + a₂ln(T/298.15) + a₃(T-298.15) + a₄/(620-T) + a₅(T-227), i = ${\beta }_{MX}^{\left(0\right)v}$, ${\beta }_{MX}^{\left(1\right)v}$ and $C_{MX}^v$] as well as their coefficients a_i (i = 1 to 5) in the binary system were obtained, which is not reported in the literature. The fitted results of single salt parameters ${\beta }_{MX}^{\left(0\right)v}$, ${\beta }_{MX}^{\left(1\right)v}$ and $C_{MX}^v$ were in good agreement with the experiment values, indicating that the single salt parameters and temperature relational coefficients for Cs[B₅O₆(OH)₄] obtained in this work are reliable.