Valency of Ions Formed during Anodic Dissolution of Metals in Acids

Abstract

The charge of cations of active metals, going anodically into solution in acid or alkaline electrolytes, can be computed from the current applied and the total hydrogen evolution rate after the initial, self‐dissolution rate has been subtracted. However, under such conditions an ionic charge, experimentally not provable, of much higher or lower value than the normal one is calculated. Evidently this charge is apparent and corresponds to the true one only then, if the self‐dissolution rate does not change when the anodic current is applied.It can be shown (by measuring the total hydrogen volume developed) that calculated abnormal valencies result when the change of self‐dissolution rate (difference effect) due to the anodic current is disregarded. In the case of the positive effect, high charges and, in the case of the negative effect, low (apparent) cationic charges are computed. The impossibility of the calculated high cationic charges proves in turn that the positive effect cannot be explained by the expulsion of such cations by the anode. Since it was shown at least in the case of Be (which also might be true with Mg) that the metal partially disintegrated into tiny metal particles under the influence of the anodic current, the need for the assumption of Be+ formation is removed. The appearance of the negative A effect can be explained in a better way.All the phenomena occurring in the anodic compartment in acidic as well as neutral solutions can be explained readily by the consequences of the altered self‐dissolution rates, especially if the activation of the dissolving surface of the anodic metal, the breakdown of the protective films, and the formation of metal fragments by the anodic current are considered.