Question

For the reaction, $M^{n+}(a q)+n e^{-} \longrightarrow M(s)$, select the best suitable representation of Nernst equation, when the solid $M$ is taken.

• A. $E_{M^{n+} / M}=E_{\left(M^{n+} / M\right)}^{\circ}-\frac{R T}{n F} \ln \frac{[M]}{\left[M^{n+}\right]}$
• B. $E_{M^{n+} / M}=E_{M^{n+} / M}^{\circ}-\frac{R T}{n F} \ln \frac{1}{\left[M^{n+}\right]}$
• C. $E_{M^{n+} / M}=E_{M^{n+} / M}^{\circ}-\frac{R T}{n F} \ln \frac{\left[M^{n+}\right]}{[M]}$
• D. $E_{M^{n+} / M}=E_{M^{n+} / M}^{\circ}-\frac{R T}{n F} \ln \left[M^{n+}\right]$

Answer 1

Answer: (B)

Electrode potential of an electrode is measured with respect to standard hydrogen electrode by the expression
$E_{M^{n+/ M}}=E_{M^{n+/ M}}^{\circ}-\frac{R T}{n F} \ln \frac{[M]}{\left[M^{n+}\right]}$
but concentration of solid $M$ is taken as unity
So, $E_{M^{n+/ M}}=E_{M^{n+} / M}^{\circ}-\frac{R T}{n F} \ln \frac{1}{\left[M^{n+}\right]}$