On the Mechanism of the Reduction Process of the Hydrogen Ion at the Dropping Mercury Electrode. III. Experimental Part —The Half-wave Potential, Log-plot Analysis and the Reversibility of the Wave

Abstract

Abstract Various properties of the current-voltage curve of the reduction wave of the hydrogen ion were studied in the system of the dil. HCl in 0.1 n KCl solution. It was found out that the log-plot of the reduction wave is not linear and that the half-wave potential shifts to be more negative with the increase of the limiting current. The temperature coefficient of the half-wave potential was obtained to be about 3 millivolts per degree over the temperature range of 0 to 50°. This value of the temperature coefficient is much larger than the value which is expected when the reduction process of the hydrogen ion proceeds under the condition of the diffusion-controlled type. The Kalousek’s methods were applied to the hydrogen wave in order to test the reversibility of the reduction process and it was shown that this process is one of the irreversible type. These experimental results were satisfactorily explained by assuming the reduction process of the hydrogen ion as follows: First, the hydrogen ion is adsorbed on the surface of the D.M.E., and, next, the adsorbed hydrogen ion is neutralized to the hydrogen atom under the condition of the activation-controlled process. In this case it was assumed that the equilibrium state represented by the Freundlich adsorption isotherm exists between the hydrogen ion in the neighborhood of the electrode surface and the adsorbed hydrogen ion in the adsorbed layer. The value of the free energy of activation of the overall discharge process of the hydrogen ion was calculated.