The ultrasonic speeds (3 MHz) and densities in pseudo-binary mixtures of the three different systems: ClCH2CONH2-H2O-ZnCl2, ClCH2CONH2-H2O-ZnBr2, CH3CONH2-H2O-ZnCl2 with the ratio (electrolyte + amide)/water = 1/55 have been measured. From these data, various thermodynamical parameters such as adiabatic compressibility, molar volume and their excess functions have been calculated. In addition, the pH values of the solutions and the isobaric molar heat capacity have been measured. All these parameters have been discussed to explain solute-solvent interactions, especially the effect of the presence the Cl atom in the acetamide molecules and the replacement of Zn by Br atom in the process of complexation. On the basis of the excess function, the complex ions with participation of amides have been detected. The effect of solvolysis has been also observed. (C) 2004 Elsevier B.V. All rights reserved.