Conductometric studies of aqueous ionic liquids, 1-alkyl-3-methylimidazolium halide, solutions at T = 298.15–328.15 K

Abstract

Electrical conductances of aqueous ionic liquids, 1-butyl-3-methylimidazolium bromide, [BMIm]Br, 1-pentyl-3-methylimidazolium bromide, [PnMIm]Br, 1-hexyl-3-methylimidazolium bromide, [HMIm]Br, 1-butyl-3-methylimidazolium chloride, [BMIm]Cl, and 1-butyl-3-methylimidazolium iodide, [BMIm]I solutions at low concentrations of ionic liquids have been measured at ( T = 298.15–328.15 K). The ion association constants, K A , limiting molar conductivities, Λ 0 and distance parameters, R were obtained using low concentration Chemical Model (lcCM) conductivity equation for the investigated systems. The results show that the K A values decrease with lengthening alkyl chain and larger size of anion; i.e. Cl −< Br − < I −. Therefore, there is slight ion association effect in [BMIm]Cl at all experimental temperatures. Furthermore, the K A and Λ 0 values for the aqueous solutions of ionic liquids increase as the temperature increases. Thermodynamic functions such as Gibbs free energy, enthalpy and entropy of ion pair formation were calculated using K A values. Results also show that Δ H A 0 values exhibit weak dependence on the temperature this shows that ion pair formation of ionic liquids in water is the entropy driven process.