Q.The E°(M²⁺/M) value for copper is positive. Suggest a possible reason for this.

Step 1. Recall that E°(M²⁺/M) for copper is +0.34 V, the only positive value among the 3d-series M²⁺/M couples -- every other 3d metal from Ti to Zn shows a negative value.

Step 2. A positive reduction potential means the REDUCED (metallic) side of the equilibrium is thermodynamically favoured over the OXIDISED (Cu²⁺) side -- in other words, elemental copper metal is genuinely more stable, under standard conditions, than the Cu²⁺ ion in solution.

Step 3. A practical consequence follows directly: copper does NOT dissolve in dilute, non-oxidising acids (like dilute HCl or dilute H₂SO₄) to liberate hydrogen gas, unlike metals with negative E° values (e.g. zinc, iron), because copper is simply not thermodynamically inclined to lose electrons and go into solution as Cu²⁺ under those conditions -- copper requires an OXIDISING acid (such as concentrated or dilute HNO₃) to dissolve. …

Interpret the sign of E°(Cu²⁺/Cu) directly: a positive value means the metallic (reduced) form is thermodynamically favoured over the ionic (oxidised) form, and connect thi …

• Explaining copper's positive E° purely by citing its d¹⁰ or d⁹ configuration without connecting that fact to the actual THERMODYNAMIC consequence being asked about (el …