Standard Potential of the Copper Half-Cell

Copper sits comfortably above hydrogen in the electrochemical series, which is why it does not dissolve in hydrochloric acid no matter how concentrated — there is no thermodynamic driving force for Cu → Cu²⁺ + H₂. It takes an oxidising acid such as nitric, where the nitrate ion rather than the proton does the work, to attack it. That nobility is also why copper plumbing survives decades in water that would eat steel in months.

The same +0.3419 V is why copper refining works. Electrolytic refining dissolves impure anode copper and redeposits it at the cathode at 99.99 % purity, leaving gold, silver and platinum behind in the anode slime — a by-product stream valuable enough that it often pays for the refining. But the noble potential has a cost in mixed-metal plumbing: copper coupled to steel or aluminium drives galvanic corrosion of the less noble metal, which is why a dielectric union belongs at every such joint.