A piece of zinc is placed in a solution containing copper ions. The zinc atoms on the surface of the metal transfer two electrons to each copper ion and become zinc ions. As the copper metal forms on the surface of the zinc the blue color of the copper solution disappears because the zinc ions are colorless.
The beaker on the left contains a strip of zinc, while the beaker on the right contains a strip of platinum in a solution of cupric chloride. The salt bridge contains sodium sulfate. When the reaction begins, zinc atoms give up two electrons each. These electrons travel through the wire connecting the two beakers and are transferred to copper ions. As the zinc loses electrons it becomes zinc ions and the cupric ions are converted to copper, which plates out on the platinum. In order to balance the positive charge in the left-hand beaker created by the zinc ions, sulfate ions migrate out of the salt bridge, and some zinc ions also migrate into the bridge. In the other beaker, chloride ions migrate into the salt bridge and sodium ions move from the bridge into the beaker.
A source of direct current is connected to electrodes immersed in molten sodium chloride. Sodium ion are attracted to the negative electrode on the right, where they pick up electrons and become sodium metal. Chloride ions are attracted to the positive electrode on the left, where they give up electrons are form diatomic chlorine molecules that leave the liquid.