Question

Define standard electrode potential. Calculate the standard electrode potential of the following cell:
Zn / Zn$^{2+}$ $\;\;||\;\;$ Cu$^{2+}$ / Cu when
$E^{0}_{(Zn^{2+}/Zn)} = -0.76 \, V$ and $E^{0}_{(Cu^{2+}/Cu)} = +0.34 \, V$.

Hint:

Always identify the cathode (higher $E^0$) and anode (lower $E^0$) correctly before applying the formula $E^0_{\text{cell}} = E^0_{\text{cathode}} - E^0_{\text{anode}}$.

Answer 1

Definition:
The standard electrode potential of an electrode is the potential difference developed between the electrode and the standard hydrogen electrode (SHE) when the electrode is in contact with its ions at unit concentration (1 M), at 1 atm pressure, and 298 K.

Step 1: Write the given cell.
The cell is: \[ \mathrm{Zn \;|\; Zn^{2+}(1M) \;\;||\;\; Cu^{2+}(1M) \;|\; Cu} \]

Step 2: Identify anode and cathode.
- For Zn$^{2+}$/Zn: $E^{0} = -0.76 \, V$ (more negative, so Zn acts as anode).
- For Cu$^{2+}$/Cu: $E^{0} = +0.34 \, V$ (more positive, so Cu acts as cathode).

Step 3: Formula for standard cell potential.
\[ E^{0}_{\text{cell}} = E^{0}_{\text{cathode}} - E^{0}_{\text{anode}} \]

Step 4: Substitute values.
\[ E^{0}_{\text{cell}} = \big(+0.34 \, V\big) - \big(-0.76 \, V\big) \] \[ E^{0}_{\text{cell}} = +0.34 + 0.76 = +1.10 \, V \] \[ \boxed{E^{0}_{\text{cell}} = +1.10 \, V} \]