ELECTRODE POTENTIAL

#. ELECTRODE POTENTIAL : 

When an electrode is in contact with the solution of its ions in a half cell , it has tendency to lose or gain electrons which is known as Electrode Potential. It is expressed in Volts. It is an intensive property i.e., independent of amount of species in the reaction.

• OXIDATION POTENTIAL :

The tendency to lose electron in the above case is known as Oxidation Potential. Oxidation potential of a half cell is inversely proportional to the concentration of ions in the solution.

• REDUCTION POTENTIAL :

The tendency to gain electron in the above case is known as Reduction Potential. According to IUPAC convention, the reduction potential alone be called as the electrode potential unless it is specifically mentioned.

                                                 E°_red = – E°_oxidalion

_{#. STANDARD ELECTRODE POTENTIAL :}

The potential difference developed between metal electrode and solution of ions of unit molarity (1M) at 1 atm pressure and 25°C (298 K) is called standard electrode potential.

It is denoted by E°.

@.Reference Electrode

The electrode of known potential is called reference electrode. It may be primary reference electrode like hydrogen electrode or secondary reference electrode like calomel electrode.

Standard hydrogen electrode (SHE) Standard hydrogen electrode (SHE). also known as normal hydrogen electrode (NHE), consists of platinum wire, carrying platinum foil coated with finely divided platinum black. The wire is sealed into a glass tube placed in beaker containing 1 M HCl. The hydrogen gas at 1 atm pressure is bubbled through the solution at 298K. Half-cell is pt H₂ (1 atm) H⁺ (1 M)

In SHE. at the surface of plantinum, either of the following reaction can take place

2H⁺(ag) + 2e^– → H₂G Reduction

H₂(g) → 2H⁺(ag) + 2e^– Oxidation

The electrode potential of SHE has been fixed as zero at all temperatures.Its main drawbacks are

1. It is difficult to maintain 1 atm pressure of H₂ gas.
2. It is difficult to maintain H⁺ ion concentration 1 M.
3. The platinum electrode is easily poisoned by traces of impurities.

Hence, calomel electrodes are conveniently used as reference electrodes, It consists of mercury in contact with Hg₂ Cl₂ (calomel) paste in a solution of KCl.