Ion-association and solvation behavior of ammonium and potassium thiocyanates in 2-methoxyethanol + water mixed solvent media at different temperatures

Abstract

The electrical conductances of the solutions of ammonium thiocyanate (NH4SCN), and potassium thiocyanate (KSCN) in 2-methoxyethanol+water mixed solvent media containing 0.25, 0.48, and 0.72 mole fractions of 2-methoxyethanol (x1) have been reported at (298.15, 308.15, 313.15, 318.15, and 323.15) K. Analyses of the conductance data have been made on the basis of the 1978 Fuoss conductance-concentration equation yielding the limiting molar conductance (Λ0), the association constant (KA) and the distance of closest approach of ions (R). These two electrolytes are found to be very weakly associated in the 2-methoxyethanol+water mixed solvent medium containing 0.25mole fraction of 2-methoxyethanol, whereas these are found be moderately associated in the media containing 0.48, and 0.72mole fractions of 2-methoxyethanol within the temperature range (298.15 to 323.15) K. The limiting molar conductances and the association constants of these electrolytes are found to increase with temperature. The results indicate a changing solvodynamic size of the constituting ions with the composition of the media. The solvation of ions is weakened as soon as the ion-pair is formed due to the release of solvent molecules from the ionic solvation sheaths. Noncoulombic interactions are found to play an important role in the ion-association processes for the present system.