ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
Manganese and copper voltaic cell. Copper (right) and manganese (left) half cells joined by a salt bridge. When a stick of copper (Cu) is inserted in a copper salt solution it loses electrons according to the reaction, Cu<-->Cu2+ + 2e- . So Cu metal and Cu2+ ion form a redox couple with Cu2+ as the oxidant and Cu as the reductant. The same occurs for manganese (Mn) metal and manganese salt. The copper half cell produces electrons at a faster rate than the manganese so there is a potential difference between them. When the two half cells are joined by a saturated salt "bridge" and the metals are joined by a wire, a current flows.
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