Home – Home – Jornals – Journal of Structural Chemistry 2008 number 5

Isoentropy compressibilities of aqueous magnesium chloride and sulfate were determined based on precision measurements of ultrasound velocity, density, and isobaric heat capacity at low to high concentrations at 278.15-323.15 K. The hydration numbers h and the molar parameters of volume and compressibility were calculated based on thermodynamically correct equations for hydration complexes (V_h, β_hV_h), water in the hydration shell (V_1h, β_1hV_1h), and the void containing a stoichiometric mixture of ions (V_2h, β_2hV_2h). The h and β_hV_h values were found to be independent of the temperature; the molar compressibility of the hydration sphere (β_1hV_1h) and the stoichiometric mixture of ions without a hydration shell (β_2hV_2h) were independent of the concentration under the stated conditions. The effect of the electrostatic field of ions on the temperature dependence of the molar volume of water in the hydration sphere was more significant than the effect of pressure on the temperature dependence of the molar volume of bulk water. This is attributed to changes in the dielectric constant of water in the vicinity of the electrolyte ions.