Physicochemical characteristics of 1-ethyl- and 1-butyl-3-methylimidazolium chloroaluminate ionic liquids

•Molar concentrations of ions were calculated in the acidic ILs.•Cation concentration is the main reason for the conductivity change in the acidic ILs.•Activation energy for conduction does not change in the acidic ILs.•“Relay-race” mechanism of conductivity in acidic ILs was proposed. Density, viscosity and specific conductivity of 1-ethyl-3-methylimidazolium and 1-butyl-3-methylimidazolium chloroaluminate ILs (AlCl3–[EMIm]Cl and AlCl3–[BMIm]Cl) are systematically measured for the compositions with the molar ratio of aluminum chloride to the organic salt (N) from 0.8 to 2.0 and at temperatures from 273 to 373 K. Additivity of the densities and molar volumes of the mixture has been confirmed for the acidic ILs: [R]AlCl4 and [R]Al2Cl7 (where [R] = [EMIm]+ or [BMIm]+). Molar concentrations of ions in the acidic ILs have been calculated. The viscosity of the IL decreases sharply with the growth of N in the basic ILs and less sharply in the acidic ILs. Equimolar mixtures exhibit the highest specific conductivity. The decrease in the molar concentration of [R]+ cations is the main factor inducing the decrease in the specific conductivity of the acidic ILs. The activation energy for conduction does not change within the measurement error in the acidic AlCl3–[EMIm]Cl and AlCl3–[BMIm]Cl ILs and is 14.8 ± 0.3 and 17.7 ± 0.4 kJ·mol−1, respectively. The electrical conductivity in the acidic ILs confirms the supposition about equal mobilities of AlCl4– and Al2Cl7– anions in the ILs and about the probable “relay-race” mechanism of electrical conductivity.