摘要:
A new method of analysis for the ultrasonic absorption of systems involving multiple coupled equilibria is described. The method consists of calculating the relaxation frequencies and amplitudes under a postulated reaction mechanism using trial values of the rate constants and volume changes and of comparing the computed absorption α/f2 (absorption coefficient over frequency squared) directly with the experimental one. Application of this method to the ultrasonic absorption study of aqueous zinc(II)-thiocyanate solutions reveals that the relaxation absorption is ascribed to the successive complex formation equilibria Zn(SCN)3−nn−1 +SCN−(kn⇄k−n)Zn(SCN)2−nn, n=1–4. The rate constants and volume changes of the above reactions are determined. The method proves to be especially effective when the absorption spectra are associated with multiple coupled equilibria and accordingly too broad to be separated to discrete relaxation processes by the usual method of analysis.