The tendency to metal to lose electrons or tendency of its ions to gain electrons depends upon the concentration of the ions in solution. At the same time, the tendency to lose or gain electrons is expressed in terms of electrode potentials. The value of electrode potential, thus, varies with the variation in the concentration of the ions. The quantitative relationship between the concentration of ions and electrode potentials is given by Nerst equation. For a common electrode reaction:
Mn^{+} + ne^{-} M The nerst equation can be written in the two ways as + (RT/nF) In [Mn^{+}]/[M] Or, - (RT/nF) In [Mn^{+}]/[M]
In the present aspect, only the first form will be used in the further discussion. Converting natural logarithm (In) to log10 in the first expression, we get + (2.303 RT/nF) log [Mn^{+}]/[M], Where, = electrode potential
= standard electrode potential with reference to SHE when concentration of Mn^{+} is 1 mol L^{-1} R = 8.314 JK^{-1} mol^{-1}; T = temperature [Mn^{+}] = molar concentration of ions; n = number of electrons gained F = Faraday constant 96500 C mol^{-1}; [M] = concentration of metal Substituting these values, we get log [Mn^{+}]/[M] = + (0.059/n) log [Mn^{+}]/[M] In general, for any electrode, E_{red} = + (0.059/n) log [oxidized state]/[reduced state]