Iodine clock reaction

The iodine clock reaction, sometimes called the Landolt reaction, is a classical chemical clock experiment that is performed as a mechanism to demonstrate chemical kinetics in action. It was first observed by Hans Heinrich Landolt in 1886. The iodine clock reaction exists in several variations, which each involve iodine species (iodide ion, free iodine, or iodate ion) and redox reagents in the presence of starch. Two colourless solutions are mixed and at first there is no visible reaction. After a short time delay, the liquid suddenly turns to a shade of dark blue due to the formation of a triiodide–starch complex. In some variations, the solution will repeatedly cycle from colorless to blue and back to colorless, until the reagents are depleted.