Electrode Potential And EMF

Standard Electrode Potential

Chemical reactions do change the way of life, a close intervention on the contribution of one of the most  common reactions in chemistry i.e. oxidation and reduction reaction gives us the insight on its contribution to  batteries, which without any qualms is considered one of the most pivotal unit for our gadgets and power contribution.

One of the prototype of these cells were Voltaic cell, which lies in the category of electrochemical cells. These cells are made from copper and zinc placed in the solution of their sulphates. The electron from the zinc is passed to the copper during the process of oxidation- reduction reaction which thereby leads to the generation of electric current. Nevertheless, the intensity of the current produced is very much dependent on the standard electrode potential, which in simple terms is nothing but the magnitude of energy per unit charge obtainable from oxidation and reduction reactions, in terms of two halves reaction i.e. reduction half reaction and oxidation half reaction.

The electromotive force or EMF is a contribution from the anode, which is how easily it can lose electrons also called as oxidation potential. However, the reduction potential of the cathode electrode is dependent on the ability of cathode to gain electrons. The cell or the standard electrode potential is the summation of both these components. And can be expressed in terms of a simple mathematical equation as follows:

E (cell) = reduction potential(Ecathode) +oxidation potential(Eanode). ……………………………… (1)

If we can find the two components of potential  for each pair of cathode and anode, we can determine the standard electrode potential. Nevertheless even formulating one or the other is sufficient as oxidation potential of a half-reaction is just the negative of the reduction potential for the reverse of that reaction.

electrode potential

Some hurdles in measuring electrode potential are as follows:

  • It can only be determined in reactions with some other electrode and not in isolation.
  • The dependence of electrode potential on concentration of the materials, pressure and temperature.

In laboratory the first hurdle is superseded by using standard hydrogen electrode as the bench mark for measuring potential. This is implemented as it is the “potential difference” that holds an importance whereas zero of potential is illogical.

The second hurdle is overcome by selecting a thermodynamically standard environment for standard electrode potential measurement. This is the condition when the concentration of solute is 1 molar, 1 atmosphere of gas pressure at standard temperature of 295.15 Kelvin.

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Practise This Question

The EMF of cell Ni|Ni2+||Au3+|Au is:
Given that E=0.25V for Ni2+|Ni;E=1.5V for Au3+|Au