Question

For the electrode $H_{(a q)}^{+} \mid H_{2_{(g)}}$, if $pH$ is decreased by one unit at $25^{\circ} C$, then the cell potential

• A. decreases by 59.1 mV
• B. increases by 59.1 mV
• C. remains unchanged
• D. becomes zero

Answer 1

Answer: (B)

increases by 59.1 mV

Answer 2

From Nernst equation, $E=\frac{-R T \log _{10} p H}{F}$
This equation tells us that every decrease in $pH$ of one unit, the potential of hydrogen electrode increases by
$\frac{R T \log _{10}}{F}(\approx 59.1\, mV$ at $298\, K )$.
The Nernst equation has thus given us the $pH$ dependence of any reaction involving hydrogen ions.