Question

The reduction potential of hydrogen electrode will be negative if:

• A. $P_{H_2}=1atm;\left[H^{+}\right]=2.0M$
• B. $P_{H_2}=1atm;\left[H^{+}\right]=1.0M$
• C. $P_{H_2}=2atm;\left[H^{+}\right]=1.0M$
• D. $P_{H_2}=2atm;\left[H^{+}\right]=2.0M$

Answer 1

Answer: (A)

$P_{H_2}=1atm;\left[H^{+}\right]=2.0M$

For hydrogen electrode,

${2H}^{+}+2e^{-}\to H_2$

$E_{cell}=E^0-\frac{0.059}{2}log\left[\frac{P_{H_2}}{{\left(H^{+}\right)}^2}\right]$

$E^0=0$

$E_{cell}=\frac{0.059}{2}log\left[\frac{{\left(H^{+}\right)}^2}{P_{H_2}}\right]$

for $E_{cell}$ to be negative

$\frac{{\left(H^{+}\right)}^2}{P_{H_2}}<1$

i.e, $P_{H_2}>\left[H^{+}\right]$

Hence $P_{H_2}=2atm,\left[H^{+}\right]=1.0m$