Question

At 298 K, the standard electrode potentials of Cu²⁺/Cu, Zn²⁺/Zn, Fe²⁺/Fe and Ag⁺/Ag are 0.34 V, - 0.76 V, - 0.44 V and 0.80 V, respectively.
On the basis of standard electrode potential, predict which of the following reaction cannot occur?

• A. CuSO₄(aq) + Zn(s) → ZnSO₄(aq) + Cu(s)
• B. CuSO₄(aq) + Fe(s) → FeSO₄(aq) + Cu(s)
• C. FeSO₄(aq) + Zn(s) → ZnSO₄(aq) + Fe(s)
• D. 2CuSO₄(aq) + 2Ag(s) → 2Cu(s) + Ag₂SO₄(aq)

Answer 1

The Correct Option is D

To predict which reaction cannot occur based on standard electrode potentials, we need to consider the concept of spontaneity in redox reactions. A reaction can spontaneously occur if the standard cell potential, \( E_{\text{cell}}^\circ \), is positive. For a redox reaction: \[ \text{Cell Potential}: E_{\text{cell}}^\circ = E_{\text{cathode}}^\circ - E_{\text{anode}}^\circ \]

The given standard electrode potentials are:

• \( \text{Cu}^{2+}/\text{Cu}: 0.34 \, \text{V} \)
• \( \text{Zn}^{2+}/\text{Zn}: -0.76 \, \text{V} \)
• \( \text{Fe}^{2+}/\text{Fe}: -0.44 \, \text{V} \)
• \( \text{Ag}^{+}/\text{Ag}: 0.80 \, \text{V} \)

We'll analyze the reactions:

1. \(\text{CuSO}_4(\text{aq}) + \text{Zn(s)} \to \text{ZnSO}_4(\text{aq}) + \text{Cu(s)}\)

   • \( E_{\text{cell}}^\circ = 0.34 - (-0.76) = 1.10 \, \text{V} \, (\text{positive}) \) - Could occur.

2. \(\text{CuSO}_4(\text{aq}) + \text{Fe(s)} \to \text{FeSO}_4(\text{aq}) + \text{Cu(s)}\)

   • \( E_{\text{cell}}^\circ = 0.34 - (-0.44) = 0.78 \, \text{V} \, (\text{positive}) \) - Could occur.

3. \(\text{FeSO}_4(\text{aq}) + \text{Zn(s)} \to \text{ZnSO}_4(\text{aq}) + \text{Fe(s)}\)

   • \( E_{\text{cell}}^\circ = -0.44 - (-0.76) = 0.32 \, \text{V} \, (\text{positive}) \) - Could occur.

4. \(2\text{CuSO}_4(\text{aq}) + 2\text{Ag(s)} \to 2\text{Cu(s)} + \text{Ag}_2\text{SO}_4(\text{aq})\)

   • \( E_{\text{cell}}^\circ = 0.34 - 0.80 = -0.46 \, \text{V} \, (\text{negative}) \) - Cannot occur.

The reaction \( 2\text{CuSO}_4(\text{aq}) + 2\text{Ag(s)} \to 2\text{Cu(s)} + \text{Ag}_2\text{SO}_4(\text{aq}) \) cannot occur spontaneously due to its negative cell potential.