The kinetics of disproportionation of elemental iodine to iodide and iodate ions has been studied in basic aqueous media using Raman and uv-visible spectroscopy. The I 0 stretching vibrations for 10-and 120H-were observed at 430 i 2 and 560 + 2 cm-', respectively. The totally symmetric stretching vibration for 107 was observed at 685 i 2 c m l . The Raman results indicate that 120H-is a linear molecule with a stronger 1-0 bond than 1 0 . The rate expression at 25°C in 1 mol d m 3 NaOH was found to be whereThe reaction is primarily a reaction of thc iodine + 1 oxidation-state species 10-and 120H-. It proceeds through the t 3 oxidation-state species 1 0 7 . The following equilibrium and rate constants were determined:
Spectroelectrochemistry at an optically transparent electrode, in conjunction with controlled potential coulometry, has been used to study the Tc(IV)/Tc(III) redox couple in aqueous bicarbonate solutions. The complexation provided by bicarbonate/carbonate ions was found to stabilize both Tc(IV) and Tc(III). The uv–visible absorption spectra for technetium(III) and technetium(IV) carbonate complexes are described. The redox potential for the Tc(IV)/Tc(III) couple, as well as the number of electrons, the number of carbonate groups, and the number of hydroxyl groups exchanged during the redox process in bicarbonate media are reported.
The freezing-point depressions of aqueous solutions of the homologous series RNH3Br, where R varies from ethyl to n-octyl, and of sodium decanoate were determined and used to calculate osmotic and mean activity coefficients. In the case of the surfactants octylamine hydrobromide and sodium decanoate, the pre- and post-micellar regions were covered. Activity data at higher temperatures were calculated using previously published thermochemical data. Some difficulties arise in the critical micellar region of sodium decanoate at high temperatures as a result of the large concentration and temperature dependence of the heat capacity data. The activities from freezing point data are compared with those obtained from specific electrodes.
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