WHAT IS ELECTRODE POTENTIAL
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)
OR