Dimerization Constants from Acoustic Measurements: Solutions of Benzene, Cyclohexylamine and Aniline in Cyclohexane.

A model assuming that the formation of dimers determines the acoustic properties of liquid mixtures, in the inert solvent cyclohexane, was applied to describe the observed dependences of sound speed on composition. The dimerization constants were estimated. The results allow one to propose that the solutes tend to form associates larger than dimers in concentrated solutions, while in dilute systems solute-solvent interactions play an important role.

Ultrasonic and densimetric titration applied for acid-base reactions.

Classical acoustic acid-base titration was monitored using sound speed and density measurements. Plots of these parameters, as well as of the adiabatic compressibility coefficient calculated from them, exhibit changes with the volume of added titrant. Compressibility changes can be explained and quantitatively predicted theoretically in terms of Pasynski theory of non-compressible hydrates combined with that of the additivity of the hydration numbers with the amount and type of ions and molecules present in solution.

Peculiarity of aqueous solutions of 2,2,2-trifluoroethanol.

Aqueous solutions of 2,2,2-trifluoroethanol appear to show a structural transition at alcohol mole fraction equal to x(TFE) = 0.05, which can be concluded from a discontinuity of the speed of sound. At the same concentration, a discontinuity was observed in the parameters of the long-living component of the positron annihilation spectrum.

Hydration of amino acids from ultrasonic measurements.

In this paper the results of compressibility of aqueous solutions of amino acids in water and in aqueous HCl and NaOH solutions at 25 °C are presented. The effect of the charged protonated amino groups and deprotonated carboxylic groups on the hydration number was tested. The idea of additivity of the hydration number with the constituents of the solute molecule was successfully applied and discussed.

Compressibility of aqueous solutions of nonelectrolytes: an equilibrium model.

In this paper the parabolic-shaped dependences of compressibility kappa(S) of a nonelectrolyte in water solvent on concentration are explained and described semiquantitatively in terms of hydrate formation equilibrium reaction. It was demonstrated that only two fitted parameters, the hydration number n(h) and the formation constant of the hydrate K, are sufficient to reproduce satisfactorily the experimental data, in particular the characteristic minimums of kappa(S) versus composition observed at low contents of solutes.