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For the reaction
Calculate the potential or voltage if the [Cu+2] is 1 x 10-4 and the [Al+3] is 1 x 10-3.
Solution:
From the given chemical equation above
Aluminum lost six electrons and copper gained six electrons. The chemical equation is already balanced including the ions.
From Table of Common Standard Reduction Potentials for Al, E0 = 1.662 V since aluminum lost three electrons and oxidation takes place in the reaction. If you multiply any of half-reactions with a coefficient, then the value of reduction potential is still the same. We don't multiply the reduction potential with any coefficients and we change only the sign if the half-reaction is reversed.
Again, from Table of Common Standard Reduction Potentials for Cu, E0 = 0.3419 V since copper gained two electrons and reduction takes place in the reaction.
The reduction potential of the reaction is the sum of the reduction potential of two half-reactions. Hence, the reduction potential is
If the concentration of metal ions are given, then we can calculate the voltage of the reaction by using Nernst Equation as follows
where n is the number of electrons lost or gained in the reaction. Hence, the voltage for the reaction is
For any whole or pure metals in half-reactions, their concentration is 1 M. In this case, the concentration of Al and Cu is 1 M. Therefore, the voltage for the reaction is
