Given the half‑reactions and their respective standard reduction potentials 1. Cu 3 + + 2 e − ⟶ Cu + E ∘ 1 = + 1.28 V 2. Cu 2 + + e − ⟶ Cu + E ∘ 2 = + 0.15 V 3. Cu 2 + + 2 e − ⟶ Cu ( s ) E ∘ 3 = + 0.34 V 4. Cu + + e − ⟶ Cu ( s ) E ∘ 4 = + 0.52 V calculate the standard reduction potential for the reduction half‑reaction of Cu ( III ) to Cu ( II ) . Cu 3 + + e − ⟶ Cu 2 +