Answer
Reduction of Copper(II) and Zinc(II) Ions in Water
🔬 Standard Electrode Potentials (E°):
| Half-Reaction | E° (V) |
|---|---|
| Cu²⁺(aq) + 2e⁻ → Cu(s) | +0.34 V |
| Zn²⁺(aq) + 2e⁻ → Zn(s) | −0.76 V |
| 2H₂O + 2e⁻ → H₂ + 2OH⁻ (alkaline) | −0.83 V |
| 2H⁺ + 2e⁻ → H₂ (acidic) | 0.00 V |
✅ Can Copper(II) Be Reduced in Water?
The standard potential for Cu²⁺/Cu is +0.34 V, which is higher than the potential required to reduce water. This means copper(II) ions can be reduced to solid copper in aqueous solution.
✔️ Copper(II) ions can be reduced to metallic copper in water.
🧪 This agrees with experimental electrochemistry.
🧪 This agrees with experimental electrochemistry.
❌ Can Zinc(II) Be Reduced in Water?
The standard potential for Zn²⁺/Zn is −0.76 V, which is close to the reduction potential of water (−0.83 V in alkaline solution). As a result, water is more likely to be reduced to hydrogen gas instead of Zn²⁺.
❌ Zinc(II) ions cannot be easily reduced in water.
⚠️ Water is preferentially reduced, so H₂ forms instead of Zn metal.
⚠️ Water is preferentially reduced, so H₂ forms instead of Zn metal.
📚 Does This Match Background Knowledge?
Yes, this agrees with what is known in electrochemistry:
- Copper is often electroplated or recovered from water-based solutions.
- Zinc is typically reduced in non-aqueous systems or molten salts to avoid hydrogen evolution.
✅ Final Summary:
| Ion | Can It Be Reduced in Water? | Reason |
|---|---|---|
| Cu²⁺ | ✔️ Yes | Higher E°, reduced before water |
| Zn²⁺ | ❌ No | Lower E°, water is reduced first |