Question

Set up the cell constiting of $H_{\left(aq\right)}^{+}|H_{2g)}$ and $P{b}_{\left(aq\right)}^{2+}|P{b}_{\left(s\right)}$ electrodes. Calculate the emf at $25℃$ of the cell if $\left[P{b}^{2+}\right]$ = 0.1 M, $\left[H^{+}\right]=0.5M$ and hydrogen gas is at 2 atm pressure, $E^{o}Pb=-0.126V$.

• A. 0.1178 V
• B. 0.1278 V
• C. 0.1378 V
• D. 0.1478 V

Answer 1

The correct option is B 0.1278 V

$2H^{+}+Pb\to H_2+P{b}^{2+}$

Here, $n=2=Changeinoxidationnumber$

By Nernst Equation,

$E_{cell}=E_{cell}^{\circ }-\frac{0.059}{2}\log \frac{\left[P{b}^{2+}\right]\cdot P{H}_2}{[H^{+}{]}^2}$

$=0.126-\frac{0.059}{2}\log \frac{0.1\times 2}{0.25}$

$\approx 0.1278V$