When iodine reacts with starch, it is trapped in the starch's helical structure forming a blue-black precipitate. Iodine is not very water soluble, so in making an iodine solution, potassium iodide (KI) is added. This results in the formation of a triiodide complex, which is completely soluble in water.
An electron transport chain pumps protons across a membrane while transferring electrons from one chemical to another.
