Adding aluminum to copper sulfate in the presence of water results in the following redox reaction: 2Al(s) + 3Cu2+ (aq) = 2Al3+ (aq) + 3Cu(s). This reaction forms aluminum chloride and elemental copper.
Adding aluminum to a copper chloride solution causes the formerly blue-green solution to turn almost colorless, to warm and then to form a colored solid. Sprinkling copper chloride powder on a thin sheet of aluminum foil and spraying with water causes holes to form in the foil and a rusty solid to form. In both examples, the copper ions transform to elemental copper, and the aluminum metal becomes aluminum ions. In the solution, copper ions have the blue-green color, but aluminum ions are colorless. With the aluminum foil, the same reaction causes the formation of holes in the sheet and the deposition of elemental copper as the rust colored substance. Recovering the newly formed solid and melting in a very hot flame forms copper metal in a recognizable form. In redox reactions, more active metals gain electrons to become ions, and less active metals donate ions and return to their elemental form. Redox reactions are important in many different areas, ranging from biological function to the operation of an automobile.