The ultrasonic absorption in aqueous solutions of a number of 2–2 electrolytes including the sulfates of the bivalent transition metal ions has been measured in the frequency range 105–109 Hz at temperatures between 5 and 50°C. Generally, three relaxations can be separated in this frequency range if the structural absorption of the electrolytic solution is properly taken into account. Relaxation times and corresponding maximum absorption per wavelength are allocated to the normal coordinates of a three-step association or dissociation mechanism. In order to be applicable to the new experimental results, the existing theory of the stepwise association had to be extended to a more general form. By means of suitable transformations the normal coordinates can then be expressed in terms of kinetic and thermodynamic parameters of the individual reaction steps. Values of the rate constants, equilibrium constants, reaction volumes, and activation energies calculated on the basis of the extended theory are presented for the individual reaction steps.