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Density, Speed of Sound, and Refractive Index Measurements for the Binary Mixture (1, 4-Dioxane + Isobutyric Acid) at T = (295.15, 298.15, 301.15, 304.15, 307.15, 310.15, and 313.15) K ABSTRACT: Density, speed of sound, and refractive index for the binary mixture (1,4-dioxane (1) + isobutyric acid (2)) were measured over the whole composition range at temperatures T = (295. 15, 298.15, 301.15, 304.15, 307.15, 310.15, and 313.15) K and at the atmospheric pressure. From the experimental data, excess molar volume V E , excess isentropic compressibility κ S E , excess speed of sound c E , excess refractive index n E , molar refraction R, and deviation in molar refraction ΔR were calculated. These results have been fitted to the Redlich−Kister polynomial equation. The excess molar volume, excess isentropic compressibility, and deviation in molar refraction were found to be negative, whereas excess speed of sound and excess refractive index were found to be positive for all temperatures. The thermodynamic properties have been discussed in terms of nature of molecular interactions between the components of the mixture.a Standard uncertainties (u) are u(ρ) = 0.00005 g.cm −3 , u(n) = 0.0001, u(c) = 0.2 m.s −1 , u(T) =0.01 K and u(p) = 0.05 kPa.

Salt-induced phase separation of 1,4-dioxane (D) + water (W) with KCl has been investigated by measuring the electrical conductivity (κ) and the refractive index (n) along the coexisting curve in the vicinity and far from the lower critical solution temperature (LCST) using a conductometer and a refractometer. By visual method, the lower critical temperature (T c ) was determined to be (311.032 ( 0.015) K with the mole fraction of dioxane on a salt-free basis: x′ D ) n D /(n D + n W ) ) 0.295 ( 0.002. The conductivity and refractive index were carried out in the range of 0.010 K < (T -T c ) < 17.500 K. Critical values were fitted and compared with those predicted by models proposed in the literature. The electrical conductivity and refractive index coexistence curve data were analyzed to determine the critical exponent (β) associated with the coexistence curve. The results show that those (κ and n) constitute good order parameters as valid as the volume fraction. In the neighborhood of the LCST (T/T c -1 < 3 • 10 -2 ), the critical exponent obtained by the two techniques agrees with the scaling law prediction. The KCl salt at the saturation facilitates the formation of the molecular correlations, and the phase separation takes place in the electrolyte.

The ternary critical mixture of 1,4-dioxane (1) + water (2) + saturated KCl (3) has a lower critical point. The viscosity η and electrical conductivity κ of this system have been measured as function of temperature for nine critical mixtures along the coexistence curve below the temperature of phase transition. The water mole fraction in free basis x′ 2 in the mixtures extends from (0.550 to 0.880) and the molality m of KCl from (0.47 to 2.039) mol • kg -1 . The viscosity was found to decrease with an increase in temperature, water mole fraction, and the molality of KCl, while the electrical conductivity increases with an increase in temperature, with the water mole fraction and molality of salt. The viscosity and electrical conductivity represented anomalies near the critical temperature T c . The critical electrical conductivity κ c varies with water mass fraction w 2 as a second degree polynomial and with the molality m of salt as a third degree polynomial. The variation of critical composition in water and in the molality of salt varied the temperature of separation of phase, T t . The activation energy E a (κ) for ionic conduction decreased with increasing x′ 2 and consequently with molality, but they are not influenced in the activation energy E a (η) for viscous flow.