No abstract

The rate of oxygen exchange between 0 ' 8 enriched CrOd2-, HCr04-, Cr2072-and solvent water has been measured as a function of pH and total chromium(V1) concentration. The exchange can be explained in terms of the dimerization equilibria HCrOa-+ C r 0 4 2 -e Cr2072-+ OH-and 2HCr04-Cr2Ol2-+ Hz0 except a t high pH, where slow pH-independent exchange is observed. Rate constants for the reactions of the dimerization equilibria have been evaluated from the exchange results, and are in agreement with values obtained by a variety of other methods.

The reaction of carbon dioxide with water and hydroxide ions has been studied by measuring the rate of oxygen exchange between sodium carbonate and bicarbonate and oxygen-18 enriched water as a function of pH, ionic strength, and carbonate-bicarbonate concentration. I t has been shown that these reactions are catalyzed by carbonate and bicarbonate ions. Rate constants for the uncatalyzed and catalyzed reactions have been evaluated.

A method is described for rapid mixing and sampling in the application of the isotopic dilution technique to the study of ionic hydration. The behavior of solutions of various salts has been compared with that of solutions containing a hydrated cation of known formula, namely Cr(H2O)6+ + +. The holdback of water per ion of Al+ + + is the same (within 0.4 molecules of H2O as that of Cr+ + +, and t½ for the exchange of Al(H2O)6+ + + with H2O is >0.02 sec. at 25°·t½ for the exchange of water between Ni+ + (aq) or Fe+ + + (aq) and solvent is less than 0.02 sec.

Bis nahezu 80% des vollständigen Austausches aller fünf Wasserrnoleküle wird die Geschwindigkeit dieses Austausches für die Ionen (I) gemessen.