llltrasonic Absorption in Aqueous Calcium Acetate
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Ultrasonic Absorption in Aqueous Solutions of Calcium Acetate and Other Biwalent Metal Acetates ordon Atkinson,"' Mostafa M. Emara, and R. Fernander-Prini De)epat?rnentof Chemistry, University of Oklahoma, Norman, Oklahoma 73069 (Received July 27, 1973;Revised Manuscript Received April 11, 1974) Publication costs assisted by the National Science Foundation
Ultrasonic absorption measurements in aqueous solutions of calcium acetate in the concentration range 0.14-1.09 M , a t various temperatures, show one relaxation for the low-concentration solutions and two for the high concentrations. On the basis of these measurements and analogous ones on Mg2 b, Ba", and Ni2+ solutions, we conclude that the relaxations are due to the substitution of one or two waters in the inner coordination sphere of the Ca2+ ion by acetate. The scanty thermodynamic data available and the high concentration of some of the solutions hampered a thorough quantitative interpretation of the data. In magnesium and calcium acetate solutions more concentrated than 1.4 M , the ultrasonic absorption is not explicable in terms of discrete relaxation processes.
Introduction Since Bazulin" measured ultrasonic absorption in aqueous zinc acetate iolutions in 1939, many other acetate solutions have been studied by this technique. Stuehr and Yeager3 have (wrnmarized the results of ultrasonic investigations of aqueous acetate solutions. It may be concluded that (1) transption metal acetate solutions show an ultrasonic relaxation in the megahertz region due to a chemical process, (2) alkali metad acetate solutions show no significant excess sound absorption, (3) 0.05 M calcium acetate solutions were found by Kurtze and Tamm* to show significant excess absorption with a relaxation frequency above 40 MHz, and (4) other processes such as acetate ion hydrolysis and acetic acid dimerization do not contribute significantly to sound a bsorptdion in metal acetate aqueous solutions. We were partrcularly interested in studying alkaline earth acetate solutions, especially those of Ca2+,so that the
results could be compared with those obtained in previous measurements of calcium and magnesium polycarboxylates5 Furthermore, we felt that previous measurements in alkaline earth solutions had been affected by experimental artifact^.^ After the measurements reported here were completed, Purdie and Barlow6 published the results of ultrasonic measurements in aqueous magnesium and calcium acetate solutions. Their data, in general, agree with those presented here but are restricted to a narrower concentration range (
