Note 563 — Chapter XV · OXIDATION AND REDUCTION. II. OXIDATION BY OXYGEN, PERMANGANATES, ETC.; OXIDATION OF ORGANIC COMPOUNDS

Fredenhagen, Z. anorg. Chem., 29, 424 (1902), has brought interesting experimental evidence of the charging of an electrode with gaseous oxygen, when ferric-ion is the oxidizing agent in aqueous solutions. Whether the oxygen, which is liberated by the action of the ferric-ion on water, 4 Fe3+ + 4 HO− ⇄ 4 Fe2+ + O2 + 2 H2O, is always the intermediate product and the direct oxidizing agent in aqueous solution, can hardly be considered decided by the experiment—it may well be the product of a parallel action, which must take place to a certain extent, according to the laws of equilibrium, in a system containing both Fe3+ and HO− ions. The result hardly proves that oxygen must be the intermediate product in the main action, when ferric ions act as the oxidizing agent. We may consider, for instance, a solution containing an iodide and a ferric salt: iodide ions have a far smaller affinity for their negative charges (electrons) than hydroxide ions have, and, consequently, will transfer their negative charges (electrons) more readily to the ferric ions than the hydroxide ions would. The action, if oxygen were first liberated, would lead to the same ultimate result, but the observation made by Fredenhagen would not prove that the main action would not nevertheless go by the shorter direct path rather than through an intermediate formation of oxygen.