Iodine Clock Reaction Lab Report

Title: The effect of concentration on reaction rates

Introduction: - Chemical kinetics is the branch of chemistry that is concerned with the mechanisms and rates of chemical reactions. The mechanism of a chemical reaction is a description of what happens to each molecule at a very detailed level—which bonds are broken, which new bonds are formed, and how the three-dimensional shapes of the chemicals changes during the course of the reaction. The rate of the reaction is a measure of its speed. The iodine clock reaction is a favorite demonstration in chemistry classes because it has an element of drama. Two clear solutions are mixed, producing a new clear solution. Then, after a period of several seconds, the solution turns dark blue. As mentioned, chemical kinetics measures how fast a reaction is occurring.

To perform the iodine clock reaction in this science fair project, you will mix potassium iodide, hydrochloric acid, starch, thiosulfate and hydrogen peroxide. The time it takes for the reaction mix to turn blue will be measured with a stopwatch. For the procedure, you will vary the amount of hydrogen peroxide to see how this affects the time the mixed chemicals stay clear before turning blue.

The reactions that form the basis for the iodine clock reaction are shown below.

Equation 1:

H2O2 + 3 I- + 2 H+ → I3- + 2 H2O

• H2O2 = Hydrogen peroxide

• I- = Iodide ion (from potassium iodide)

• H+ = A proton, from hydrochloric acid (HCL)

• I3- = Triiodide

• H2O = Water

Equation