Reference electrodes

Every oxidation needs to be accompanied by reduction — the occurrence of only oxidation or only reduction is not possible (refer to the Std. XI Chemistry Textbook, Chapter 6). In a galvanic cell oxidation and reduction occur simultaneously, and the potential associated with the redox reaction can be experimentally measured. For the measurement of potential, two electrodes need to be combined together where the redox reaction occurs.

What would happen if the potential of one of the electrodes in a galvanic cell were zero? Can we measure the potential of such a galvanic cell? There are two electrodes combined together, and a redox reaction results. The measured cell potential is the algebraic sum of the two electrode potentials; if one electrode potential is zero, the measured cell potential is equal to the potential of the other electrode.

From the foregoing arguments it follows that it is necessary to choose an arbitrary standard electrode as a reference point. The chemists have chosen the hydrogen gas electrode — consisting of $\mathrm{H_2}$ gas at 1 atm pressure in contact with a 1 M $\mathrm{H^+}$ ion solution — as the primary reference electrode. The potential of this electrode has arbitrarily been taken as zero; the electrode is called the standard hydrogen electrode (SHE). …