The Influence of Supporting Electrolytes on Ionic Equilibria. The Hydrolysis of the Dichromate Ion

Abstract

The influence of supporting electrolytes on the equilibrium has been investigated with a view to comparing this influence with that exerted on the rate s of reactions of similar charge-types. Neither the influence on the equilibrium constant nor that on the rate constant of the back reaction was fonnd to be uniquely determined by the principle of ionic strength. These results, together with examples from the literature, show that there seems to be nothing special about environmental influence on the kin e tic s of reactions. It is suggested that what makes prediction difficult is the fact that in both cases activity coefficients appear in a combination which is different from that encountered in the mean activity coeffic tent, A spectrophotometric method is employed. The value of the equilibrium constant at zero ionic strength has been found equal to 4,4 x 10-2 ; the heat of reaction is 3.8 Kcal mol-I. The discrepancies between these values and those reported in the literature are discussed.

UV−Vis Spectroscopic Determination of the Dissociation Constant of Bichromate from 160 to 400 °C

“…UV−vis spectroscopy is limited to equilibria involving species containing appropriate chromophores. , Recently, stable pH indicators have been developed for temperatures up to 400 °C. − Hexavalent chromium appears to be an ideal candidate for direct spectrophotometric study without an indicator, since all the Cr(VI) species absorb light in the UV and visible regions − and others − have been used to study acid−base equilibria of Cr(VI) at 20 °C or slightly elevated temperatures. However, the potentiometric study by Palmer and co-workers 50 is the only high-temperature study (to 175 °C) of Cr(VI) equilibria.…”