[en] Highlights: • Three selected inorganic hydrated salts in water and methanol solutions were acoustically and spectroscopically investigated. • All investigated electrolytes are strong in aqueous solutions but weak in methanol. • Substantial differences of the coordination abilities of the cations are manifested, especially in acoustic properties. - Abstract: Hydrated salts, MgCl_2·6H_2O, CuCl_2·2H_2O and EuCl_3·6H_2O when dissolved in methanol, conserve their original coordination numbers, probably dissociating two chloride anions (magnesium chloride), stepwise in equilibrium reactions (copper chloride) or probably only one Cl"− (europium chloride). Water hydrating molecules are almost fully removed from the coordination shell only in the case of MgCl_2·6H_2O. The above conclusions were drawn from analyzing the acoustic and densimetric properties of the title systems and confirmed by conductivity tests. The results are also compared to those in aqueous solutions. The emission and excitation spectra obtained for europium chloride were applied as spectroscopic probes of solution structure, as well as of the number of existing species and their symmetries.

[en] We report the results of acoustic and positron annihilation measurements in aqueous solutions of acetonitrile (CH₃CN). Hydrophobicity of the solute is discussed, as well as the possibility of describing the title system in terms of hydrophobic solvation. A new method of calculating the 'ideal' positronium lifetimes is proposed, based on the mean volume of cavities (holes) in liquid structure available for positronium pseudoatom. The results are almost identical with those obtained from molar volumes using the concept of Levay et al. On the other hand, the same calculations performed using the 'bubble' model of annihilation yield very different results. It seems that either acetonitrile forms with water clathrate-like hydrates of untypical architecture, or it is too weak hydrophobic agent to form clathrate-like hydrates at all. The former interpretation seems to be more probable