The electrode potential of the Tc(IV)-Tc(VII) couple

A redetermination of the standard potential for the Tc(VII)-Tc(IV) redox couple was completed because there is disagreement among published values of E0. Using electrodeposited technetium oxide, potentials were measured as a function of pH and technetium concentration. The slopes of the plots of electrode potential vs. pH and activity of TcO4- were measured to be 0.0773 ± 0.0023 V/(pH unit) and 0.021 ± 0.0050 V/(log unit), respectively. These values agree with the theoretical values of 0.0788 V/(pH unit) and 0.0197 V/(log unit) within the standard deviations of our measurements. The value of E0 was determined to be 0.747 ± 0.004 V. Within the limits of error, this agrees with the value E0 = 0.741 ± 0.004 V determined by Cartledge and Smith. (orig.)