WHAT IS ELECTRODE POTENTIAL? When a metal is placed in a solution of its ions, the metal acquires either a positive or negative charge with respect to the solution. On account of this, a definite potential difference is developed between the metal and the solution. This potential difference is called electrode potential.
Following two changes occur when a metal rod is dipped in its salt solution, 
The metal ion Mn+ may collide with the strip, gain n electrons and get converted   into metal atom, i.e., the ion is reduced.
                                        Mn+ + ne  → M      (Reduction)
The metal atom on the strip may lose n electrons and enter the solution as Mn+ ion, i.e., metal is oxidised.
                                        M → Mn+  + ne      (Oxidation)
Hence, the magnitude of the electrode potential of a metal is a measure of its relative tendency to lose or gain electrons, i.e., it is a measure of the relative tendency to undergo oxidation (loss of electrons) or reduction (gain of electrons).
It is not possible to measure the absolute value of the single electrode potential directly. Only the difference in potential between two electrodes can be measured experimentally.  It is, therefore, necessary to couple the electrode with another electrode whose potential is known. This electrode is termed as reference electrode. The EMF of the resulting cell is measured experimentally. 
Emf of the cell = E Anode + E Cathode 
                           = Oxidation potential of anode + Reduction potential of cathode

The value of the electrode potential depends upon:-
1.     Nature of the electrode
2.     Concentration of the ions in solution
3.     Temperature
In order to compare the electrode potentials of various electrodes, it is necessary to specify the concentration of the ions present in solution in which the electrode is dipped and the temperature of the half-cell. The potential difference developed between metal electrode and the solution of its ions of unit molarity (1M) at 25°C is called standard electrode potential. According to the IUPAC convention, the reduction potential alone be called as the electrode potential (EO), i.e., the given value of electrode potential be regarded as reduction potential unless it is specifically mentioned that it is oxidation potential.
Oxidation potential is the tendency of the electrode to lose electrons and reduction potential is the tendency of the electrode to accept electrons.
Oxidation potential can be converted into reduction potential by changing the sign only
Standard reduction potential = - (Standard oxidation potential)
Standard oxidation potential = - (Standard reduction potential)

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