Partial molar volumes and partial molal adiabatic compressibilities of

J. Phys. Chem. 1983, 87, 3161-3166

3181

Partial Molar Volumes and Partial Molal Adlabatic Compressibilities of Nitroamminecobalt(I I I ) Complexes in Water at 25 C Fumlo Kawalzuml;

Katwyukl Matsumoto, and Hlroyasu Nomura

DepaHment of Chemical Engln&ng, Facow of Engineering, Nagoya Unlversity, Chlkusa-ku, Nagoya-shi, 464 Japan (Received: September 2 1, 1982; I n Flnal Form: December 3 1, 1982)

Densities and ultrasonic propagating velocities of aqueous solutions of a series of nitroamminecobalt(III) complexes have been measured at 25 "C at concentrations less than 0.1 mol kg-l. Partial molar volumes, have been determined by extrapolation of the relationship between 4, - Svm1f2and m, where S, is the coefficient given by the Debye-Huckel (DH) theory. In this relationship, nearly horizontal slopes have been observed for all samples. Infinite-dilution values of partial molal compressibility, have been evaluated from the linear extrapolation of the empirical plot of 4b against " I 2 . The concentration dependence of 4b of these complexes is much higher than those observed for ordinary electrolytes of the same valency type. Values of and 4bo assigned to the complex ions [Co(N02),,(NH3),,13-" increase regularly with the number of the ligand NO2contained in the complex. Analysis of the observed variation of and $boof complex ions has shown that even for nonelectrolytic complex [CO(NO,)~(NH,),]~ electrostriction should occur in solution.

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Introduction About 15 years ago, using an ultrasonic interferometer and Ostwald-type pycnometer, we1v2determined the compressibilities of aqueous solutions of such cobalt complexes as [CO(NH,),& (X = Cl-, Br-, or NO