This is a chemical reaction during which the initially colorless solution rapidly changing in blue-black after a certain period of time (which is dependent on the concentration of the solution prepared by us).  The simplest clock iodine can be made based on readily available reagents such as: starch solution (1 tablespoon per 100ml boiling water), a solution of ascorbic acid (Vitamin C tablet dissolved in 25 ml water), iodine, hydrogen peroxide and the cold water used for cooling, to obtain better control of the reaction.

Our chemical clock based on solution metabisulfite, iodate and starch solution. Initially, we prepare a solution of iodate dissolved in water. This is prepared by us solution A, which is subsequently added to solution B composed of metabisulfite and starch solution.

 

In the initial stage metabisulfite reacts with iodate by reducing it to iodide, which in fact determines the speed the whole reaction. The resulting iodide is oxidized to free iodine, which in turn reacts with the starch solution to form a complex of iodine-starch. The creation of this complex makes our sudden change of color of the solution to navy blue-black. Additionally to control the time of such reaction in more accurate way is often used beaker cooling in which there is our process.