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Electrochemistry: Balancing by Ion Electron Method and the Oxidation Half Reaction

Balancing by Ion Electron Method

This method is based on the principle that electrons lost during oxidation half reaction is equal to the electrons gained in the reduction half reaction.

Following steps involved are:

  • Write the skeleton equation.
  • Write the oxidation number of all the atoms above their symbols in the skeletal equation.
  • Find the atoms undergoing change in Oxidation Number. Thus, find out the species getting oxidized and reduced, respectively.
  • Split the whole (net) equation into two half reactions i.e.. oxidation half reaction and reduction half reaction.
  • Balance the atoms, undergoing change in oxidation number in each half reaction.
  • Calculate the total change in oxidation number in each half reaction which is equal to the total number of electron transfer.
  • Add total number of electron transfer as calculated above on the reactant side in reduction half and on the right-hand side on the oxidation half reaction.
  • Balance the charges by adding (for reactions in acidic medium) or (reactions basic medium) either on left or right of equation.
  • Finally balance and by adding on the required side of the reaction.
  • Add the two half reactions such that total number of electrons cancel out on both sides. To do so half reactions may be required to multiplied by some numbers to make the number of electrons equal on both sides.

Example:

in acid medium

Balance the following equation by Ion Exchange method

Step I and II:

Write the oxidation number of the atoms above their symbol in the skeletal equation

Step III:

Oxidation number of is increasing; therefore, it is undergoing oxidation and oxidation number of is decreasing so it is undergoing reduction.

Step IV:

Split the reactions in two half reactions:

Reduction Half Reaction

Oxidation Half Reaction

Balance the first reduction half reaction

Step V:

Balance the atoms undergoing change in Oxidation Number.

Step VI & VII:

Write the total number of electron transfer taking place. Here each atom undergoes change in by therefore two atoms undergoes change in Oxidation Number by 6.

Step VIII:

Balance the charge by adding on the left side

Step IX:

Balance the H and O by adding on either side

Balancing the Oxidation Half Reaction

According the steps as followed for reduction half reaction

Atoms are balanced on both side, so we go to next step, that is number of electron transfer taking place.

Balance the charge and it is balanced.

Step X:

Add the two half reactions

Electrolytic Conduction

  • The chemical substances whose aqueous solutions conduct electricity are called electrolytes and those which do not conduct current are called as non-electrolytes.
  • The phenomenon of conduction of current through a solution is called electrolytic conduction.
  • Electrolytic conduction takes place due to the movement of cations and anions in a solution.

The electrical conductance of a solution, depends upon:

  • Nature of solute
  • Valency of its ion
  • The concentration in solution
  • The temperature