This is called The iodine clock reaction | Amazing Facts

The iodine clock reaction is a classic chemical clock demonstration experiment aimed at displaying chemical kinetics in action; it was discovered by Hans Heinrich Landolt in 1886[1],[2]. The iodine clock reaction exists in several variations, each involving iodine species (iodide ion, free iodine, or iodate ion) and redox reagents in the presence of starch. Two colorless solutions are mixed and, at first, there is no visible reaction. After a short time, the liquid suddenly changes to a dark blu