The Photochemical Chlorate-Iodide Clock Reaction
Romulo O Pires1, Roberto B Faria1
1Instituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, 21941-909 Rio de Janeiro, Brazil.
Abstract:
Mixing iodide and perchloric acid solutions with an excess of chlorate inside a diode-array spectrophotometer led to the observation of an abrupt decrease of the absorbance at the 215 nm isosbestic point after an induction period. The clock time decreases by increasing the initial concentrations of chlorate and acid, but increasing the initial iodide concentration has an opposite effect. The proposed mechanism simulates the experimental results and considers the interaction of UV light with iodide, producing iodine and triiodide ion. The autocatalytic core of this mechanism is the same as that employed to explain the autocatalytic behavior of chlorine dioxide-iodine reaction, but considering H2IO+ as the reactive species rather than HOI, being a more realistic mechanism for acid conditions.
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