Iodine oxidation by hydrogen peroxide in acidic solutions, Bray-Liebhafsky reaction and other related reactions

Abstract

The kinetics of the iodine oxidation by hydrogen peroxide is a complicated function of the concentrations of iodine, hydrogen peroxide, perchloric acid and iodate. A proposed model in eight steps explains the new experimental results. It explains also the effect of the concentrations at the steady state of the hydrogen peroxide decomposition catalyzed by iodine and iodate. Without iodate added initially, the iodine oxidation by hydrogen peroxide is preceded by an induction period that depends on the oxygen concentration. A simple extension of the proposed model gives a semi-quantitative explanation of the oxygen effect and allows simulations of the Bray-Liebhafsky oscillations at 25 degrees C.

Iodine oxidation by hydrogen peroxide and Bray–Liebhafsky oscillating reaction: effect of the temperature

“…11 In acidic solutions, its complicated rate law can be reduced to the form given in Table 2. The rate r À4 of the reverse reaction decreases when [H + ] increases and we have shown 7 that it can control the rate of reaction (O) at high acidities. Relation (4) was experimentally verified at 251 when the acidities are sufficiently high for H 2 O 2 concentrations in the vicinity of the maximum of k exp .…”

“…Trying to isolate reaction (R5), Liebhafsky had fixed the iodide ions concentration using the equilibrium TlI(s) " Tl + + I À and the IOH concentration using the equilibrium I 2 (s) " IOH + I À + H + . This technique seemed more or less successful at 251 and our analysis 7 of his measurements gave the mean value We have shown 7 that the effect of the acidity on k exp implies that reaction (R6) is catalyzed by H + : k 6 = k 3 which is an adjustable parameter of the model. For reaction (R7) we use the rate constants obtained by Liebhafsky. 2c,21 Reactions (R8a)-(R8c) were introduced in the model for reasons explained in our previous paper 7 and replaced for the numerical simulations by (R8) with the rate Reaction (R11) was added to the first simple version of our mechanism 4a because it allows good simulations of the oxygen effect on the oscillations.…”

“…This is a consequence of the quasistationarity of [I 2 O]. 7 The mentioned values of k À3 is an adjustable parameter of the model. The mechanism of reaction (R4) has been discussed before.…”

“…6 New kinetic results for this reaction led us to propose 7 a new variant of our model for the BL reaction with a set of rate constants at 251. The first aim of this work is to extend this set at higher temperatures.…”

“…We also discuss further effects that may affect seriously the BL oscillations. They are mainly related with the effect of the produced oxygen [7][8][9] and ignoring them can lead to erroneous conclusions about the mechanism.…”