The rate constant of the reaction between hydrogen peroxide and ferrous ions has been measured in sulfuric acid solutions, by direct spectrophotometric observations of the ferric salt produced at λ=304 mμ. It has been confirmed that the rate is independent of acidity (measurements were carried out from 0.05 N to 0.8 N H2SO4) and that the reaction is bimolecular within a wide range of the concentrations of the reactants; the hydrogen peroxide concentration was varied in the ratio 1:25 and the ferrous sulfate in the ratio 1:20. The rate constant, which has been measured within the temperature range of 15° to 40°C, can be represented by the equation k1=1.05×108×exp(−8460/RT)1 moles−1sec−1.

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The photochemistry of ferrous ions in aqueous solutions has been investigated, and it has been confirmed that irradiation in the quartz ultraviolet, in the absence of oxygen, leads to the formation of ferric salt and molecular hydrogen. It has been concluded further that the primary absorption of a light quantum results in the formation of excited ions, (Fe2+·H2O)*, a considerable proportion of which undergo processes of deactivation, while the remaining (about one-tenth) dissociate according to (Fe2+·H2O)*→Fe3++OH−+H, leading to the formation of hydrogen atoms. The latter can undergo back reactions of the type Fe3++H→Fe2++H+. Investigation of the pH dependence of the quantum yield has led to the assumption that hydrogen atoms can also react according to H+H(hydr)+⇌H2(hydr)+, leading to the formation of hydrated hydrogen molecular ions which intervene in this process according to the reaction Fe2++H2+→Fe3++H2. Other experimental evidence and some theoretical considerations which have led to the assumption of H2+ (hydr) in aqueous solution are referred to.