Ionic association and thermodynamic parameters for solvation of vanadyl sulfate in ethanol-water mixtures at different temperatures Esam A. Gomaa, Reham M. Abu-Qarn ⁎ Chemistry Department, Faculty of Science, Mansoura University, 35516-Mansoura, Egypt abstract article info Article history: Received 18 November 2016 Received in revised form 13 February 2017 Accepted 16 February 2017 Available online 22 February 2017 Conductance measurements of vanadyl sulfate have happened in binary mixed solvent with alcohol mass frac- tion 0%, 30% and 50% (W/W) (EtOH-H 2 O) at different temperatures from 298.15 to 313.15 K (with a step of 5 K). The experimental data have been analyzed by using the Fuoss-Hsia-Fernández-Prini (FHFP) equation. Molar conductance (Λ m ), limiting molar conductance (Λ 0 ), Walden product (Λ 0 η 0 ), ion-pair association constant (K A ), the activation energy for the transport process (E a ) and the standard thermodynamic parameters for asso- ciation (ΔG ° A , ΔH ° A and ΔS ° A ) were estimated and discussed. The effect of formation hydrogen bond in solution also has been studied. The obtained results show that the association constant was increased as the relative per- mittivity of the solvent decreased while the molar conductance and the limiting molar conductance values were decreased. Furthermore, as the temperature increased, the association constant values were increased indicating the association process is endothermic. © 2017 Elsevier B.V. All rights reserved. Keywords: Molar conductance Ion-pair association constants Binary mixed solvents Walden product Hydrodynamic radii Vanadyl sulfate 1. Introduction To obtain information on the intermolecular interactions and geometrical effects in the systems, thermo-physical and bulk properties of solutions are very useful. Accurate knowledge of thermodynamic properties of solution mixtures has great important in theoretical and applied areas of research. Studying the transport properties (conduc- tance, viscosity, ionic mobility) of electrolytes in aqueous and partially aqueous media are very useful to obtain information about ion-ion and ion-solvent interactions in these solutions [1–6]. In recent years, Scientists made important theoretical progress by developing chemical models of electrolyte solutions, the low-concentration chemical model (lcCM), mean spherical approximation (MSA, and their extensions). The Fuoss-Hsia-Fernández-Prini (FHFP) equation is one of the mathe- matic conductivity theories, which has been successfully used by many researchers to investigate many electrolytes in solutions [7–13]. The physical properties of the binary mixed solvents like the viscosity and the relative permittivity can be varied over a wide range making them a favorite solvent system for the study of ion association and ion mobility. Recently, a study of the properties of vanadium compounds attracts tremendous attention due to its importance in many fields such as biochemistry, medicinal chemistry and industry [14–16]. It forms numerous inorganic compounds as vanadyl sulfate. Vanadium compounds exhibit antitumor or carcinogenic properties. Vanadyl Sulfate (vanadium (IV) oxide sulfate) is a known inorganic compound of vanadium, which has a high physiological and industrial importance [17–22]. Vanadyl sulfate used in industry as vanadium battery, which has many advantages such as longer life, better stability, higher efficien- cy and easy operation. Thermodynamic properties of vanadyl sulfate are very important to get data, which can be used in many fields [23–25]. The present article show the effect of relative permittivity, viscosity and the hydrogen bonding on the transport properties of vanadyl sul- fate in a binary mixed solvent with alcohol mass fraction 0%, 30% and 50% (W/W) (EtOH-H 2 O) at different temperatures from 298.15 to 313.15 K (with a step of 5 K). By applying the Fuoss-Hsia-Fernández- Prini (FHFP) conductivity equation [26]. 2. Experimental 2.1. Chemicals Bidistilled water was used in the preparation of mixed solvent with a specific conductivity of 0.07 μS cm −1 at 298.15 K. Ethanol (EtOH, 99.5%), Vanadyl sulfate trihydrate (VOSO 4 ·3H 2 O, ≥ 99.9%) were purchased from Sigma-Aldrich and also were used as such without further purification. Potassium chloride (KCl, ≥ 99%) was purchased from Sigma-Aldrich and was dried in an oven for 5 h before use at 378.15 K. 2.2. Solutions Binary mixed solvent of ethanol –water with the alcohol mass fractions of 0%, 30%, and 50% were chosen to be the solvent media Journal of Molecular Liquids 232 (2017) 319–324 ⁎ Corresponding author. E-mail address: reham.magdy20@mans.edu.eg (R.M. Abu-Qarn). http://dx.doi.org/10.1016/j.molliq.2017.02.085 0167-7322/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq