The iodine clock reaction is a classical chemical clock demonstration experiment to show chemical kinetics in action. It was discovered by Hans Heinrich Landolt in 1886. Two color solutions are mixed and at first there is no visible reaction. Then you'll see the solutions changing to clear or cloudy white color.
The iodine is mixed with starch to make a dark blue-black color solution. Then the solution of vitamin C is added to make it clear.
How does it work? Iodine has two different “oxidation states” – one where the iodine molecules have a negative charge (I-) and the other where they have no electric charge (I0) Only the iodine with no electric charge can combine with starch to make the blue-black color. Certain chemical reactions (called oxidation and reduction reactions) can make iodine shift back and forth between these two states when it is mixed with Vitamin C solution.
