The Effect of High Acid Concentration

In higher acidity, the rate constant may correlate better with (the Hammet-Deyrup acidity scale) than with the stoichiometric concentration of H+. Since nearly all the studies involve hydrolysis reactions, the depletion of the reagent water may be an important consideration also. 

These points are illustrated nicely in the study of the aquation of CrNj in 1-11 M HC104. The loss of CrN monitored at 270 nm is first-order (rate constant = k). The — log k vs —Hq (log/tg) profile is reproduced in Fig. 1.16. It is marked by a linear dependence at lower acidities, a short plateau, and a decrease in k with increasing acidity at [HCIO4] 8.0 M, at which point there is decreasing value for the activity of water. This behavior conforms to a rate law of the form 

The k2 term must be included since a k ), has a positive intercept ( j) at = is plot of A (if, -t- hf) h vs although linear (slope 0. A simple mechanism consistent with this rate law  

Information on the kinetics of complex ion reactions in high acid is sparse, partly because of the instability problems, but also because of the difficulties in the interpretation of results in such a complex medium. 

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