Production of E.M.F. By Chemical Action

Production of E.M.F. By Chemical Action Points : Production of E.M.F. By Chemical Action A chemical cell is a device that uses the electric charges displaced by chemical action to produce an e.m.f. In this method two dissimilar metal plates (known as electrodes) are immersed in a solution called electrolyte. When these electrodes are externally connected by means of wires chemical action takes place inside the electrolyte. Thus a potential different is created between the two electrodes, which causes the flow of current in the external circuit through the connecting wires. The plate through which current leaves the cell to the external circuit is known as positive plate and the plate from which current enters the cell is known as negative plates. If the plates are of like material there is no e.m.f. produced. If the plates are of different materials e.m.f. is produced.

To explain the chemical action that occurs in battery consider a voltaic cell. (a). In an insulating container there is a solution of sulphuric acid H₂ SO₄. In this solution electrodes of copper and zinc are immersed. In solution molecules of H₂ SO₄ separate into H⁺ and SO₄ — ions. The action of this cell generating an e.m.f. is illustrated in various step as shown in Fig. (b), (c), (d), (e).

Now suppose a piece of metallic 7inc (Zn) inserted into the solution as indicated in (c) some of the Zn atoms from Zn⁺⁺ Ions and enter the solution, In the ionization Zn joins the SO4 — ions and forms zinc sulphate ZnSO₄ Each atom of Zn ionized therefore losses two electrons. These electrons are left on the zinc electrode as excess making that electrode negative w.r.t. the solution.

Now suppose a copper (Cu) electrode separated from zinc electrode is added. (d). Some of the H ions pick up one electron each from the copper become neutral gaseous hydrogen, which forms bubbles on the copper electrode. The loss of these electrons to the H ions causes copper electrode to have positive charge. Now when the circuit is completed as shown. (e) electrons flow from the ionized zinc through the zinc electrode to the external circuit, the copper plate and back to charge more H ions to gaseous hydrogen.