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The experimental densities of a local anesthetical drug, tetracaine hydrochloride (TC·HCl) in aqueous binary (H2O + TC·HCl) solutions and aqueous ternary electrolytic solutions (H2O + NaCl/KCl + TC·HCl) are reported at 288.15, 293.15, 298.15, 303.15 and 308.15 K in the dilute concentration region. The densities, were used to calculate apparent molar volumes ( $$V_{\phi }$$ ) at the finite concentrations of TC·HCl at the studied temperatures. The coefficient of thermal expansion (α) of solutions and the apparent molar expansivity ( $$E_{\phi }$$ ) of the solute, at 293.15, 298.15 and 303.15 K are also obtained. The limiting apparent molar volume ( $$V_{\phi }^{0}$$ ) and limiting apparent molar expansivity ( $$E_{\phi }^{0}$$ ) of TC·HCl were estimated using extrapolation methods. It is noted that the solute expansivity goes through a minimum in water as a function of temperature and at lower concentrations of electrolytes. By using the $$V_{\phi }^{0}$$ data of the studied binary and ternary systems, the values of transfer volumes, that is, volume changes due to transfer ( $$\Delta_{{{\text{tr}}}} V_{\phi }^{0}$$ ) from aqueous to mixed electrolyte solutions, are estimated. The observed $$\Delta_{{{\text{tr}}}} V_{\phi }^{0}$$ values are found to be both temperature and concentration dependent. The excess molar volume of mixing ( $$\Delta_{\text{m}} V^{{\text{E}}}$$ ) are also calculated at 298.15 K. The volume changes due to micellization are small and the sign and magnitude depend upon the structure making and breaking abilities of the salt. It is suggested that the micelles involved are of the stacking type and not in the form of linear aggregates. The hydration shell water structure around the cations seems to be controlled by temperature and the nature of the perturbing ions. The results are explained in terms of unique stacking type interaction, akin to micelles but differing in details on the mode of interactions.

Experimental measurements of the speed of sound, density and osmotic vapour pressure are reported for binary 18-Crown-6 (18C6) + CH3OH, KBr + CH3OH and ternary KBr + 18C6 + CH3OH solutions at 298.15 K. The density and compressibility data were processed to obtain the apparent molar volume (o V ) and apparent molar isentropic compressibility ( $$\phi _{K_S } $$ ) of the solutes in methanol. Expansivity data were obtained for the 18C6 + CH3OH system from density data at different temperatures and were used for calculation of the isothermal compressibility values at 298.15 K. The isothermal compressibility and expansivity data are further used to obtain the apparent molar isothermal compressibility ( $$\phi _{K_T } $$ ) and apparent molar expansivity (o E ) of 18C6 in methanolic solutions and as well as the energy-volume coefficient parameter (∂ U/∂ V) T in methanol solutions. The volume and compressibility changes due to complexation of KBr with 18C6 are obtained at infinite dilution for o V and o K . The results are compared with the similar data obtained by us previously for aqueous and CCl4 solutions. The osmotic coefficient data were used to calculate activities and activity coefficients of each component at 298.15 K as a function of the concentration of binary and ternary methanolic solutions containing KBr and 18C6. The activity and activity coefficient data are used to evaluate the pair and triplet interaction parameters by making appropriate use of the McMillan-Meyer theory of solutions. The calculation of the thermodynamic equilibrium constant (K) is made using the pair interaction parameter, g NE (non-electrolyte – electrolyte pair interaction), for the complexation equilibria. The nature of interactions present in the CH3OH solutions is discussed.