The “iodine clock” reaction involves the mixing of two colorless solutions to produce a solution which remains colorless for a precise amount of time, then suddenly changes to a deep purple-blue color (as seen in the demonstration below). The time is controlled by the temperature and/or the concentrations of the reactants.
Demonstration of iodine clock reaction
The reaction you will study involves the oxidation of iodide ion (I-) to dissolved tri-iodide ion (I3-):
6 H+ + IO3- + 8 I- →→ 3 I3- + 3 H2O
Triiodide ion combines with starch indicator to produce the characteristic purple-blue color. Timing how long it takes for the blue color to appear allows the rate of the reaction to be measured.
EXPERIMENTAL GOALS
In this lab simulation, your goals will be to:
Determine the rate law for the iodine clock reaction by using the method of initial rates to determine the reaction order for each reaction (IO3-, I- and H+) and the rate constant for the reaction.
Determine the activation energy for the iodine clock reaction by measuring the rate constant for the reaction at different temperatures.
Use the experimentally determined rate law to examine the plausibility of proposed mechanisms for the iodine clock reaction.