A kinetic study of the reaction between vanadium(V) and iodide ions

Abstract

The kinetics of the reaction between vanadium(V) and iodide ions have been studied in the absence of oxygen and in a range of acidity such that all quinquevalent vanadium is converted into hydroxovanadium(V) ion. The rate equation, obtained by a statistical treatment of the results is (i) where k_1,5=(1·20 ± 0·04)× 10^–2 l² mol^–2 s^–1, -d[H₄VO₄⁺]/dt=k_1,5[H₄VO₄⁺][l^–][H⁺]+k_2,5[H₄VO₄⁺][l^–][H⁺]²+k_4,5[H₄VO₄⁺][l^–]²[H⁺]²(i)

k _2,5 =(5·9 ± 0·4)× 10^–2 l³ mol^–3 s^–1, and k_4,5=(4·7 ± 0·4)× 10^–1 l⁴ mol^–4 s^–1 at 25 °C and at ionic strength 0·4M (NaClO₄). Equation (i) is found to fit the results of previous workers as well. A mechanism for the reaction is suggested, which is based on replacement in the co-ordination shell of the vanadium(V) atom before the redox process takes place.