Electrochemical behaviour of molybdenum electrodes in various aqueous and buffered solutions and their use in titrations

Abstract The open circuit potential of Mo electrodes has been followed as a function of time in various aqueous solutions until steady state values Est were obtained. These varied with the logarithm of the molar concentration C as Est = a + b log C. The rate of oxide film thickening was determined from the linear relationship between the open circuit potential of Mo E and the logarithm of immersion time t as E = a1 + b1 log t. A plot of the final steady state potential of Mo as a function of the pH of buffered solutions fits the linear relationship Est = a2 - b2 pH. The oxide film formed on Mo provides the opportunity to use the metal-metal oxide as an indicator electrode for potentiometric acid–base and precipitation titrations. In the case of redox titrations, the Mo electrode could not be used successfully on its own, but when coupled with platinum as a bimetallic pair electrode, excellent results were obtained when used as an indicator electrode for oxidation–reduction reactions.