Single Electrode Potential

Electrode pontential is the potential build between metal electrode and its solution.

Lets assume an electrode made up of Cu metal is dipped in aqueous solution, Ex. CuSO₄. Then there can be two possibilities such as Cu will deposite from solution to electrode or from electrode it will dissolve to solution. hence there are two electrode potential possible:

Type of Electrode Potential:
   (1) Oxidation Potential
   (2) Reduction Potential

Oxidation Potential :
It is the tendency of an electrode to loose electron on its own solution and get oxidized.

In above image,Lets assume initially the Cu will dissolve into the solution and when the equilibrium is achieved then there will exist a potential between the surface of electrode and solution. And this potential is known as Single Oxidation Potential.

Reduction Potential :
It is the tendency of an electrode to gain electrone from its own solution and get reduced.

In above image,Lets assume initially the Cu starts depositing on electrode surface fron the solution and when the equilibrium is achieved then there will exist a potential between the surface of electrode and solution. And this potential is known as Single Reduction Potential.

Standard Electrode Potential

While measuring electrode potential, if the concentration of ions is 1M. the temperature is 25^oC, and for cell reaction where gases are involved, the pressure is 1 atm then the electrode potential will called as standard electrode potential.

How do we measure equilibrium standard electrode potential
Measuring single electrode potential is not possible as we need other half reaction to complete the curcuit and measure electrode potential. So when a probe then it will develop another electrode potential and the potential we measure will be difference between the potential between metal and the probe.
So for practical purpose we assume probe's single electrode potential as zero and , measure standard electrode potential of any metal with respect to that probo which is fixed.

(1) To generalized it we use referance hydrogen electrode. The standard potential for the half cell reaction
H₂ ----> 2H⁺ + 2e^- is assumed to be zero.
(2) Since it is practically not possible to make an electrode out of hydrogen gas. An inert gas (H₂) electrode is used because of its inertness and ease at which e^- transfer occures on its surface.
(3) The hydrogen electrode is setup by using a platinized platinum wire immerse in HCl solution.
(4) H₂ gas free from O₂ and CO is bubbled close to the platinized platinum surface maintaining 1 atm pressure.
(5) And standard electrode potenial is measure on voltmeter (or Electrometer).

Electromotive force (EMF) or Cell potential of a cell
The difference of the electrode potential beetween the two electrodes i.e., cathode and anode in a electrochemical cell is known as cell potential or Electromotive force of cell

EMF or Cell Petential, E_cell = Reduction potential of cathode - Reduction potential of anode
EMF or Cell Petential, E_cell = E_cathode - E_anode

Note : If E_cell is +ve means reaction will be spontaneous and will occure without any external source. If E_cell is -ve means reaction is non-spontaneous may need external source to carry out the reaction.