Question

At 298K temperature, a hydrogen gas electrode is made by dipping platinum wire in a solution of $HCl$ of pH = 10 and by-passing hydrogen gas around the platinum were at one atm pressure. The potential of electrodes would be?
(A)- 0.59V
(B)- 0.118V
(C)- 1.18V
(D)- 0.059V

Answer 1

The standard hydrogen electrode (SHE), is a redox electrode which forms the basis of thermodynamic scale of the oxidation-reduction potentials. Its absolute electrode potential is estimated to be $4.44$ $\pm$ $0.02 V$ at room temperature ($25$ $^oC$), but to form a basis for comparison with all other electrode reactions, hydrogen's standard electrode potential (denoted by ${E^o}$) is declared to be zero volts at any given temperature.

Complete step by step solution:
You might be thinking how a hydrogen gas electrode works? Let’s have a brief discussion in order to make it clear.
Hydrogen electrode is based on the redox half-cell reaction:
$2{H^ + }(aq) + 2{e^ - } \to {H_2}(g)$
This redox reaction occurs with platinum electrodes. The electrode is dipped in an acidic solution and pure hydrogen gas is bubbled through it. Both the concentration of reduced form and oxidized form is maintained at unity i.e. 1. This implies that the pressure of hydrogen gas is 1 bar and the activity coefficient of ions of hydrogen in the solution is unity. The activity of hydrogen ions is their concentration.
There are many reasons for choosing platinum electrodes for the formation of standard hydrogen electrodes. Platinum is an inert element i.e. it does not corrode and not is very less reactive. It has the capability to catalyze the reaction of proton reduction and it also has a high intrinsic exchange current density for proton reduction on platinum.
There are also different types of hydrogen electrodes and they are as follows:
- NHE (Normal Hydrogen Electrode): In NHE, potential of a platinum electrode is measured in 1M acid solution.
- SHE (Standard Hydrogen Electrode):In SHE, potential of a platinum electrode is in a theoretical ideal solution (the standard for zero potential for all temperatures)
- RHE (Reversible Hydrogen Electrode):In RHE, we use a practical hydrogen electrode whose potential depends on the pH of the solution.
Now, for hydrogen electrode, oxidation half reaction is:
${H_2} \to 2{H^ + } + 2{e^ - }$
given pH = 10
therefore, ${H^ + } = 1 \times {10^{ - pH}} = 1 \times {10^{ - 10}}(As\,the{\text{ of pH is 10}})$
Now. by using Nernst equation for hydrogen electrodes, we get:
${E_{cell}} = {E^0}_{cell} - \dfrac{{0.0591}}{2}\log (\dfrac{{{{[{H^ + }]}^2}}}{{{P_{{H_2}}}}})$
For hydrogen electrodes, ${E^0}_{cell}$=0
${E_{cell}} = 0 - \dfrac{{0.0591}}{2}\log (\dfrac {{{{[{{10}^{ - 10}}]}^2}}}{1}) = 0.591$

Therefore, the correct answer to the given question is (A)- 0.59V.

Note: Remember that whenever the potential of any other electrodes compared with that of the standard hydrogen electrode at the same temperature, the standard electrode potential of hydrogen electrode will be taken as 0.