Electromotive
Electromotive (or Displacement) Series, a listing of chemical elements, usually of metals, in order of their decreasing ability to give up electrons when immersed in an electrically conducting solution. The order of some common elements in the electromotive series is potassium, sodium, magnesium, aluminum, zinc, chromium, iron, nickel, tin, lead, copper, mercury, silver, platinum, and gold.
If an element is immersed in a solution containing another element lower in the electromotive series, the higher element will pass into solution and displace the lower element from the solution. For example, if a piece of zinc is immersed in a lead sulfate solution, zinc will displace the lead to produce zinc sulfate and free lead will collect around the zinc as sludge.
The principle of the electromotive series is used in the manufacture of electric cells (batteries). The two electrodes of a cell are made of different elements, and are therefore at different points in the electromotive series. The farther apart in the series they are, the greater is the voltage that the cell is able to produce.