Iodine Clock Reaction
The reaction used in this experiment is a classic example of a chemical clock. The term, chemical clock, refers to a reaction where the concentration of one of the chemical components undergoes an abrupt change in concentration after a time period and leads to a sudden change in color. The reaction in this experiment is termed an iodine clock reaction, because it is the molecular iodine (I2) that undergoes the sudden concentration change. When the iodine concentration increases, it reacts with the starch in the solution to form a complex, turning it a deep purple.
As iodine was introduced, the solution turned a deep purple as expected.