Cast antimony electrode is one of the few indicator electrodes convenient for continuous control of the pH of pulps during flotation of various ores. The wide application of this electrode in production conditions is hindered to some extent by the lack of clear ideas about the mechanism of action of electrodes, because without this it is very difficult to establish the conditions of their normal operation. On the basis of the values of experimentally obtained potentials, as well as chemical properties of elements of arsenic subgroup, an attempt has been made to elucidate chemical processes occurring on metal-oxide electrodes (elements of arsenic subgroup) in aqueous solutions. As a result, electrode reactions (interaction of hydrate film on the electrode with ions of aqueous solution) are given. The influence of temperature on the readings of arsenic, antimony and visutite electrodes was determined and the heat effects of chemical processes occurring at these electrodes were calculated. The obtained values of thermal effects confirm the correctness of the proposed electrode reactions.