Question

For the cell reaction $Mg_{(s)} + Zn^{2+}_{(aq)} (1M) \longrightarrow Zn_{(s)} + Mg^{2+}_{(aq)} (1M)$ The emf has been found to be 1.60 V, $E^o$ of the cell is :

• A. -1.60 V
• B. 1.60 V
• C. 0.0098 V
• D. 1.36 V

Answer 1

Answer: (B)

1.60 V

Answer 2

The Nernst equation is $E = E^o - \frac{RT}{nF} \ln Q$. For the given reaction, $n=2$ and $Q = \frac{[Mg^{2+}]}{[Zn^{2+}]} = \frac{1M}{1M} = 1$. Since $Q=1$, $\ln Q = 0$, so $E = E^o$. Given $E = 1.60$ V, $E^o = 1.60$ V.