Electrode potential and cell e.m.f. sign convention

2 Electrode potential and cell e.m.f. sign conventions In the past the question of signs which are to be given to electrode potentials and cell e.m.f. s has caused great confusion on account of differing conventions. The convention adopted by the International Union of Pure and Applied Chemistry (I.U.P.A.C.) is the one which should be used and which will be used throughout this book. 

By the electrode potential of the half-cell M /M is implied the e.m.f. of the cell formed by coupling the latter with a hydrogen half-cell. Since the potential of the latter is zero under standard conditions, the e.m.f. determined is the electrode potential of the M /M couple. The cell may be represented by 

Other hand, if the hydrogen electrode becomes the negative pole, taking up electrons as hydrogen ionizes, the unknown electrode potential is positive and again equal to the e.m.f. developed by the cell. A table of International Standard Electrode Potentials on the hydrogen scale is given below (Table 5.1). 

In performing calculations on such cells, it is a useful practice to write down all the information, including electrode reactions, known about the two halfcells to the left and right as follows. 

Left-hand electrode Negative pole of cell Oxidation process occurs Zn Zn + + 2 e 

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