Question

The pressure of $H_2$ required to make the potential of hydrogen electrode zero in pure water at 298 K is:

• A. $10^{-14}atm$
• B. $10^{-12}atm$
• C. $10^{-10}atm$
• D. $10^{-4}atm$

Answer 1

Answer: (A)

$Pt,\frac{H_{2(g)}}{H^{+}}$Hydrogen electrode $E_{H_2/H^{+}}^0=0.0Volt$
$H_{2(g)}\to 2H_{(aq)}^{+}+2e^{-}$
$\left[H^{+}\right]=10^{-7}M$ at $25^{\circ }C$ (for Pure water)
$E=\frac{-0.0591}{2}\log \left(\frac{{\left[H^{+}\right]}^2}{P_{H_2}}\right)$
$E=0=\log \frac{\left[H^{+}\right]}{P_{H_2}}=0$
$\therefore {\left[H^{+}\right]}^2=P_{H_2}={\left(10^{-7}\right)}^2$
$\therefore P_{H_2}=10^{-14}atm$