Chemistry 30

Overview

The Iodine Clock Reaction is a “classic” experiment demonstrating the effects of concentration and temperature on reaction rate.

In this experiment two solutions are mixed. The reaction takes place in two steps.

Step 1: IO₃^–_(aq) + 3HSO₃^–_(aq) → I^–_(aq)+3SO₄^2–_(aq) + 3H^+;_(aq)

Step 2: 5I^–_(aq) + 6H⁺_(aq) + IO₃^–_(aq) → 3I_{2 (aq)} + 3 H₂O_(l)

The iodine, I₂, produced in Step 2 will react with starch (not shown in the equations), producing a deep blue-black solution.

The rate of the entire reaction can be measured by timing how long it takes before the blue color appears once the two solutions are mixed.

By altering the concentration of one of the reactants (Part A) and by changing the reaction temperature (Part B), the effects of these factors on reaction rate can be determined.