Question
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 wire at $$1$$ $$atm$$ pressure. The oxidation potential of electrode would be
A.
0.059$$\,V$$
B.
0.59$$\,V$$
C.
0.118$$\,V$$
D.
1.18$$\,V$$
Answer :
0.59$$\,V$$
Solution :
For hydrogen electrode, oxidation half reaction is
$$\eqalign{
& \mathop {{H_2}}\limits_{\left( {1\,\,atm} \right)} \to \mathop {2{H^ + }}\limits_{\left( {{\text{At}}\,pH\,10} \right)} + 2{e^ - } \cr
& {\text{If}}\,\,pH = 10 \cr
& {H^ + } = 1 \times {10^{ - pH}} = 1 \times {10^{ - 10}} \cr
& {\text{From Nemst equation,}} \cr
& {E_{cell}} = {E^ \circ }_{cell} - \frac{{0.0591}}{2}{\text{log}}\frac{{{{\left[ {{H^ + }} \right]}^2}}}{{{p_{{H_2}}}}} \cr
& {\text{For hydrogen electrode,}}\,{E^ \circ }_{cell} = 0 \cr
& {E_{cell}} = - \frac{{0.0591}}{2}{\text{log}}\frac{{{{\left( {{{10}^{ - 10}}} \right)}^2}}}{1} \cr
& = + \frac{{0.0591 \times 2}}{2}{\text{log}}\frac{1}{{{{10}^{ - 10}}}} \cr
& = 0.0591\,{\text{log}}\,{10^{10}} \cr
& = 0.0591 \times 10 \cr
& = 0.591\,V \cr} $$