WHY DO ABSOLUTE VALUE OF ELECTRODE POTENTIAL CAN NOT BE DETRMINED?
It is because practically we fail to determine electrode potential of a half cell consisting of an electrode dipped in its own salt solution. We, can measure only the difference between two half - cell potentials. that gives emf of the cell . If we arbitrarily choose the potential of one of the electrode ( half cell ) then that of the other can be determined with respect to this. Therefore , we need to set up a galvanic cell consisting of two half cells , and measuring out its EMF. This is possible only when we construct a cell with two half cells & calculate its EMF ( in volts ) using the expression
Eo cell = EoR - EoL
Hence , electrode potential of one of the half cells must be known . As per IUPAC norms Hydrogen electrode has been chosen under standard conditions (ie. H2 with 1 bar press . ,[ H+ ] = 1 M & at 298 K ) with its arbitrarily fixed electrode potential as equal to zero.
So , the reduction electrode potentials of all the different electrodes have been determined and reported as electrode potential relative to that of hydrogen electrode .Thanks (0)