1 Journal of Chemical & Engineering Data 54 (2) (2009) 566-573. doi: 10.1021/je8005002 You can ask full-text to the first author: https://www.researchgate.net/profile/Kouissi_Taoufik2 KCl-Induced Phase Separation of 1, 4-Dioxane + Water Mixtures Studied by Electrical Conductivity and Refractive Index. Kouissi T. 1 , Ouerfelli N. 2 and Bouanz M. 1,3,* 1. Laboratoire de Physique des Liquides et d’Optique Non Linéaire, Département de Physique, Faculté des Sciences de Tunis, Campus Universitaire, 2092 El Manar Tunisia. 2. Laboratoire de Chimie Analytique et Electrochimie, Département de Chimie, Faculté des Sciences de Tunis, Campus Universitaire, 2092 El Manar Tunisia. 3. Laboratoire de Physique des Liquides Critiques, Département de Physique, Faculté des Sciences de Bizerte, 7021 Zarzouna Tunisia. * To whom all correspondences should be addressed; e-mail: Moncef.Bouanz@fsb.rnu.tn (M. Bouanz). Abstract Salt-induced phase separation of 1, 4-dioaxane (D) + water (W) with KCl has been investigated by measuring the electrical conductivity  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 refractometer.By visual method the lower critical temperature T c was determined as (311.032 ± 0.015) K, give the mole fraction of dioxane: x D = n D /(n D + n W ) = 0.295 ± 0.002. Conductivity and refractive index were carried out in the range 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 curves data were analyzed to determine the critical exponent β associated with the coexistence curve. The results show that those ( 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 agree 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. Keywords: water-dioxane; ternary; ionic system; critical exponent; order parameter; electrical conductivity; refractive index. 1. Introduction Physical and physical-chemical properties of liquid mixtures are important for understanding the thermodynamic behavior. One of the most important of which is that these properties many provide information about intermolecular, ion-ion and ion-molecular interactions, also for association, pair-formation and clustering phenomena. We have been investigating and reporting data for the critical isobutyric acid + water (IBAW) mixture for many years: Transport phenomena, 1 ionic structures, 2 solvation phenomena in the binary fluid, 3 the effect of ions on mixture 4 and phase equilibrium properties occurring in the presence of added ions. 5-7 The electrical conductivity of (IBAW) mixtures has been also studied. 8-12 In this context, we have investigated conductivity () and refractive index (n) along the coexisting curve of the system 1, 4-dioxane + water + potassium chloride (DWKCl) and in the one-phase region near and far away from the critical temperature. We note that 1, 4-dioxane and water (DW) is miscible in all proportions at all temperature. The addition of salt to a homogeneous (DW) mixture causes at a certain composition a phase separation, giving then two conjugate phases. 14-22 Note that progressively introducing electrolytes in water + dioxane mixtures, at a low dielectric constant, gives evidence on the progressive association on ions pairs. 23 Also, the study of different physico-chemical properties in all the domains of compositions shows the existence of different regions with distinct behavior. 23 Ion-solvent and solvent-solvent interactions have been investigated. 24-25 In fact, some recent structural studies show that the dioxane and water both proton acceptors that will be a significant degree of H-bonding, leading to strong correlation between the molecules. 26-30 When the concentration of a electrolytes increases a phase separation in ternary system (DWKCl) is often observed. With the aim of a better understanding of the critical behavior of ionic systems, we present in this paper experimental conductivity and refractive index data along the coexistence curve of the salt-saturated (DWKCl) system. This ternary system was studied at atmospheric pressure as a function of the temperature. In the one-phase region, we have also determined experimental data of the conductivity and refractive index for a fixed critical composition (on a salt-free basis) as a function of temperature. On the basis of previous remarks, we propose the order parameter for (DWKCl) system, when the critical behavior of ionic system is analyzed in terms of that choice, Ising behavior is obtained in extend region, up to 5.10 -2 in reduced temperature. For higher distances to the critical temperature, deviations from Ising behavior is observed and effective exponent β eff are presented and discussed for this system. Experimental procedure Sample preparation The 1, 4-dioxane was provided by Merck. The purity was stated to be 99.99 %. The water was obtained from deionised and three times distilled water, and has a specific conductivity of about 10 -6 Ω -1 .cm -1 or less. The guaranteed purity of the potassium chloride (Merck product) is better than 99.5 %.