The electrochemical reduction of Sn(II) at the dropping mercury electrode from aqueous 1 M sulfuric acid and from 0.3 M phenolsulphonic acid and its inhibition by ensa-6

Abstract

By means of the demodulation technique for the first time the high reduction rate constant of the Sn(II) ion in sulfuric acid is obtained. From the value of the operational transfer coefficient it follows that a following, potential independent “chemical” step is rate determining. On the addition of an inhibitor at positive potentials the transfer of the first electron can be made slow because this process is inhibited much more strongly than the following chemical step. At high concentration of the inhibitor the first electron transfer is rate determining at all potentials. In phenolsulphonic acid as the base electrolyte it appears that an intermediate chemical step is rate controlling together with the following chemical step. The intermediate step could be made rate determining by adding a little of the inhibitor. With a high concentraton of the inhibitor the first electron transfer becomes rate controlling again. Also the reduction of Sn(II) from a practical plating bath is discussed.