which in turn fades the solution colour. This reaction sequence goes on until all the
thiosulfate ions (present in a small quantity) have been consumed. Only then does the
reaction between triiodide and starch take place forming the dark blue complex.
The aim is to study the kinetics of reaction (2), i.e. to establish the dependence of
the reaction rate on reactant concentrations, and possibly to get insight into the
reaction mechanism.
The kinetics of a reaction transformed into a clock reaction is easily investigated
by the initial rates method. All one has to measure is ∆t i.e. the time elapsed from the
mixing of the two solutions to a sudden colour change (sending out a signal) (4−6).
From the stoichiometry of the reactions (1−4), one can deduce the following
expression for the initial rate of reaction