What will happen if you put iodine on confectioners sugar?

When iodine is mixed with white sugar, such as confectioners' sugar, it is used to test for starch.

When iodine reacts with starch, which may be found in sugar or other substances, it undergoes a chemical change in which the starch molecules' shape changes, enabling them to complex with the iodine molecules. The resultant complex has an intense blue-black colour.

When iodine reacts with regular sugar or sucrose, this particular reaction does not take place. Sucrose is a basic disaccharide and lacks starch, therefore adding iodine only changes its colour slightly.

It's important to remember that confectioners' sugar often includes corn starch to stop clumping. As a result, if you add iodine to confectioners' sugar, the starch molecules present will respond with the iodine, turning it blue-black, indicating the presence of starch.