What happens to iodine when mixed with cornstarch?

Iodine, when mixed with cornstarch, creates a dark blue or black solution due to the formation of an iodine-starch complex. Cornstarch, composed of amylose and amylopectin, is a polymer containing abundant hydroxyl groups that form hydrogen bonds with the iodine molecules. These hydrogen bonds create a helical structure, causing the absorption of visible light in the red-orange spectrum, leading to the observed dark blue or blackish color. Depending on the concentration of iodine, the intensity of the coloration may vary. This reaction serves as a qualitative test for the presence of starch in a substance.