Investigation of Adiabatic Compressibility and Ultrasonic Relaxation in Aqueous Solutions of N, N-Diisopropylacetamide and Zinc Acetate

Measurements of velocity at frequency of 1 MHz and absorption coefficient of ultrasonic waves within the range 3-50 MHz in aqueous solutions of N,N-diisopropylacetamide (D-i-PA) and zinc acetate ((CH3$\text{}_{C}$OO)$\text{}_{2}$Zn) were made. Additionally, the density of the solutions was measured. The adopted method for making the solutions helped to change the ratio of the number of non-electrolyte molecules to that of electrolyte molecules, with a constant number of water molecules. Measurements of the velocity of ultrasonic waves in the solutions under study were conducted by means of an impulse-phase interferometer. Measurements of the absorption coefficient of ultrasonic waves were conducted by means of an ultrasonic high frequency system, type Matec Instruments (USA) Model 7700. All the measurements were conducted at a constant temperature of 20°C. On the basis of the analysis of excess functions of the molar volume and the adiabatic compressibility, the formation of solvatomers composed of [(D-i-PA)$\text{}_{2}$Zn(H$\text{}_{2}$O)$\text{}_{2}$]$\text{}^{2+}$ and [(D-i-PA)Zn(H$\text{}_{2}$O)$\text{}_{3}$]$\text{}^{2+}$ was found. Also the complex [Zn(CH$\text{}_{3}$COO)$\text{}_{4}$]$\text{}^{2-}$ can be recognised. The results of measurements of sound absorption indicate the occurrence of the relaxation process in the solutions under study and the frequency range used. On the basis of the relaxation theory, relaxation parameters of the process under study were calculated. The relaxation processes discovered in the system (D-i-PA)-H$\text{}_{2}$O(CH$\text{}_{3}$COO)$\text{}_{2}$Zn were assigned to the formation and disintegration of solvatomers composed of [(D-i-PA)Zn(H$\text{}_{2}$O)$\text{}_{3}$]$\text{}^{2+}$ and probably complexes mentioned before.