Ultrasonic Absorption Study of Ion Association in Aqueous Copper(II) Formate, Acetate, and Propionate

Article abstract of DOI:10.1021/j100390a029

The ultrasonic absorption of aqueous copper(II) formate at 20, 35, and 50 deg C and copper(II) propionate at 20 deg C was measured in the concentration range 0.0062-0.1 M with a pulsed, variable-path-length apparatus over the frequency range 10-143 MHz.The ultrasonic absorption of 0.0016-0.025 M copper(II) acetate at 20 deg C was measured from 1 to 21 MHz in a differential cell.The single relaxation observed in all cases was attributed to ion association.The steady-state approximation was applied to the concentration of the solvent-separated ion pairs.The rate constant at 20 deg C for the substitution of water by a carboxylate ion around Cu²⁺ is (3.4+/-1.2)x10⁸ s^-1.The enthalpy of activation for the substitution process is 10+/-1 kcal/mol for copper formate.The overall volume change due to ion association is 13-17 cm³/mol.