By Sunil Bhardwaj

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Explain the origin of single electrode potential? OR

Explain the Nernst theory of single electrode potential. OR

Explain De-electronation or electronation phenomenon.

Ans:

The tendency of metal to lose or gain electron is known as electrode potential. When it loses it is known as Oxidation potential and when it gains it is known as reduction potential. Nernst found that whenever any metal plate is in contact with its ions (electrolyte) two phenomenon are taking place simultaneously.

(1) The metal starts dissolving producing ions. The ions go in the solution and electrons are shielding on plate. $$ Zn \longrightarrow { Zn }^{ 2+ } + { 2e }^{ - }.$$ This tendency of the metal to lose the electron and ions go in the solution shielding the electrons on the metal is known as solution pressure \({ P }_{ S }\) of the metal and is also known as De-electornation.

(2) When the metal is in contact with metal ions. In this case ions (cation) from the solution go and get deposited on the surface of metal plate. $${ Zn }^{ 2+ } + { 2e }^{ - } \longrightarrow Zn.$$ This tendency of the ins of the solution to get deposited on the surface of plate as neutral product is known as Osmotic pressure \({ P }_{ O }\) of the solution. It is also known as Electronation.

Now there are three possibilities.

(1) If \({ P }_{ S } > { P }_{ O }\). It means solution pressure of ions of the metal is greater than the solution pressure of the ions. i.e. de-electronation phenomenon is greater than electronation, in that case the metal will be having -ve polarity and is written on LHS of the cell i.e. anode.

(2) If \({ P }_{ S } < { P }_{ O }\). It means electronation phenomenon is greater than de-electronation. It will be having positive charge and is written on RHS of the cell and is having positive polarity and is called cathode.

(3) If \({ P }_{ S } = { P }_{ O }\). It means the ability of loosing and gaining the electron is same for the metal. the metal in that case will not have polarity i.e. polarity is zero. such metals can not be used as the electrode in electrochemical cells and are known as Null electrode.