Ultrasonic Relaxation of C11SO₄ in H₂O Ethylene Glycol Mixtures at 25°C

Measurements of ultrasonic absorption of CuSO₄ solutions in H₂O at 20 °C and 25 °C and in ethylene glycol mixtures at 25 °C are reported for the frequency range 15 to 275 MHz. A single relaxation, shifting to lower frequency with increasing concentration, of ethylene glycol is observed. The high frequency value of the sound absorption for the electrolyte solutions is however larger than the one for the corresponding solvent mixtures. This is discussed either in terms of the possible existence of other relaxations at higher frequencies or in terms of a change or the absorption of the solvent upon addition of the electrolyte at high frequency. The observed relaxations are interpreted as due to a process of ionic association between Cu⁺² and SO₄ ⁻². A model utilizing two steps seems to represent satisfactorily the data. The rate constants of the ligand penetration in the first coordination sphere of the metal decrease as the glycol concentration increases. This is interpreted as due to the formation of Cu⁺²-glycol complexes in accord with well known findings of inorganic chemistry.