Q.

What pressure (bar) of H2 would be required to make emf of hydrogen electrode zero in pure water at 25°C           [2024]

1 10-7  
2 10-14  
3 0.5  
4 1  

Ans.

(2)

                2H+(aq)+2e-H2(g)

                By Nernst equation at 298K

                EH+/H2=EH+/H2-0.059nlog10PH2[H+]2

               For pure water [H+]=10-7M and EH+/H2=0

               0=0-0.0592log10PH2[10-7]2

              log10PH2[10-7]2=0

              PH2[10-7]2=1

              PH2=10-14bar