Kinetic studies on the reactions of indium(I) with iron(III), iodine and oxygen in aqueous solutions

Abstract

The reaction of indium(I) with iron(III), In^I+ 2Fe^III→ In^III+ 2Fe^II, has been studied in air-free conditions µ= 0·7M(LiClO₄). Variation of the hydrogen-ion concentration was limited to the range [H⁺]= 0·01–0·04M in order to reduce the effectiveness of the reaction of indium(I) with H⁺-ions. The data obtained fit the rate law, –d[Fe^III]//_dt= 2k₁k_a[In^I][Fe^III]//_[H⁺] where k₁ is the rate constant for the reaction of In⁺ with FeOH²⁺, and K_a is the first acid dissociation constant for Fe³⁺. At 25°k₁= 1·1 × 10³ l mol^–1 s^–1, ΔH₁^‡= 6·2 ± 0·6 kcal mol^–1 and ΔS₁^‡=–23 ± 2 e.u. With iodine (present as I₃^–) the reaction, In^I+ I₃^–→ In^III+ 3l^–, is too fast to follow using the stopped-flow technique (k₂ > 2 × 10⁸ l mol^–1 s^–1 at 10°). The stoicheiometry of this reaction is 1 : 1 even with [H⁺]= 2·0M. Formation of a red precipitate of lnl (k₃∼ 3 l mol^–1 s^–1 at 10°) is observed when an excess of indium(I) is used. The reaction of indium(I) with oxygen has been studied at [H⁺]= 0·0025M. Assuming a first-order dependence on [O₂]k₄= 1·7 × 10³ l mol^–1 s^–1, at 10° and µ= 0·0025M.