Electrode Potential

Metal atoms have tendency to lose electrons and go into solution as metal ions. Electrode potential is a measure of the tendency of metal atoms to gain or loose electrons when in contact with a solution of its own ions.

When a metal strip M is immersed in a solution of its salt containing ions (Mⁿ⁺), one of the processes can occur:

1. The dissolution process where atoms of metal electrode M may loose some electrons to the electrode and enter the solution as Mⁿ⁺. The metal electrode gets negative charge and the solution gets extra positive charge.

M → Mⁿ⁺ + ne^– (metal is oxidized)

2. The deposition process where metal cations Mⁿ⁺ from the solution may come in contact with the metal strip, gain some electrons and get converted into metal atoms M, which get deposited on the surface of metal strip. Separation of charges take place and a potential is developed called electrode potential.

Mⁿ⁺ + ne^– → M (the ion is reduced)

The electrode reaction reaches an equilibrium:

M (s) ⇄ Mⁿ⁺ (aq) + ne^-

Electrode potential is the potential developed at the interface between metal and its salt solution when a metal is dipped in its own salt solution.

Standard Electrode Potential

An electrode is said to be in the standard state if the concentration of the electrolyte is one molar and the temperature is 298 K. Then its electrode potential is called standard electrode potential and denoted by Eº. If any gas is used to make the electrode then the pressure of the gas should be 1 bar.