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Q.
The pressure of $H_{2}$ required to make the potential of hydrogen electrode zero in pure water at 298 K is:
NTA AbhyasNTA Abhyas 2022
Solution:
$Pt , \frac{ H _{2( g )}}{ H ^{+}}$Hydrogen electrode $E _{ H _{2} / H ^{+}}^{0}=0.0 Volt$
$H _{2( g )} \rightarrow 2 H _{( aq )}^{+}+2 e ^{-}$
$\left[ H ^{+}\right]=10^{-7} M$ at $25^{\circ} C$ (for Pure water)
$E =\frac{-0.0591}{2} \log \left(\frac{\left[ H ^{+}\right]^{2}}{ P _{ H _{2}}}\right)$
$E =0=\log \frac{\left[ H ^{+}\right]}{ P _{ H _{2}}}=0$
$\therefore\left[ H ^{+}\right]^{2}= P _{ H _{2}}=\left(10^{-7}\right)^{2}$
$\therefore P _{ H _{2}}=10^{-14} atm$