Question

What is a standard hydrogen electrode?

Answer 1

Hint: We know that in an acid solution hydrogen gas is bubbling and forms an hydrogen electrode. Now we can write a equation for hydrogen electrode is as follows:
     ${{\text{H}}^{\text{ + }}}\left( {aq} \right) + {e^ - } \rightleftharpoons \dfrac{1}{2}{{\text{H}}_{\text{2}}}\left( g \right)$

Complete step by step answer:
With respect to the hydrogen ion this electrode is reversible. Hydrogen gas is non-conducting towards platinum or some other metals that are not attracted by acids. We also know that hydrogen gas easily comes into equilibrium with hydrogen and it is used for making electrical contact in circuits. Therefore we can represent hydrogen electrode as Pt; ${{\text{H}}_2}\left( g \right),\,{{\text{H}}^{\text{ + }}}$ . We also know that hydrogen electrode is a gas electrode.

As we know in a reversible hydrogen electrode, the potential in which hydrogen gas at one atmospheric pressure is bubbled over a solution of hydrogen ions of one unit activity that has been fixed as zero. We know this electrode as standard hydrogen electrode (SHE) and we can represent standard hydrogen potential as
     ${\text{Pt;}}{{\text{H}}_{\text{2}}}\left( g \right)$ (1 atm), ${{\text{H}}^{\text{ + }}}\left( {aq} \right)$ (c =1M)
With respect to standard hydrogen electrodes we can measure all other single electrode potential that is referred to as potentials on the hydrogen scale.

Additional Information: Chlorine and oxygen electrodes are also well known gas electrodes.

Note:
As we know electrode potential is the tendency of an electrode which gains or loses electrons when it is in touch with its own ion in solution. To decide experimentally that potential of a single electrode is not possible.