Direct contact between zinc and Cu²⁺ transfers electrons at the interface and often releases heat. Separating Zn/Zn²⁺ and Cu²⁺/Cu into half-cells permits the same net reaction to drive an external circuit. This is a galvanic cell during spontaneous discharge.

Oxidation occurs at the anode and reduction at the cathode by definition. In the discharging Zn/Cu cell, zinc is the negative anode and copper the positive cathode. Zn → Zn²⁺ + 2e⁻ supplies electrons, and Cu²⁺ + 2e⁻ → Cu consumes them. Electrons flow externally Zn → Cu; conventional current in the wire is opposite. Zinc loses mass and copper gains deposited metal under this ideal reaction.

The salt bridge or suitable separator allows ions to migrate and limits charge buildup while keeping the solutions usefully separated. For this cell, anions migrate toward the zinc compartment as Zn²⁺ accumulates, and cations toward copper as Cu²⁺ is consumed. Electrons do not travel through the salt bridge. The anode/cathode reaction definitions always hold, but their signs reverse between galvanic and electrolytic operation.

Galvanic Zn/Cu: Zn | Zn²⁺ || Cu²⁺ | Cu; anode oxidation, cathode reduction

Worked example

For every mole Zn dissolved, two moles electrons pass through the circuit and one mole Cu²⁺ is reduced. Both half-cell charges would otherwise become unbalanced, so ion migration is required for sustained current.

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NEET Method

Label half-reactions first, then electrode names, galvanic signs, external electron direction and compensating ions.

NCERT Trap

Anode always means oxidation, but “negative anode” specifically describes galvanic discharge. The salt bridge conducts ions, not electrons.

Redox Reactions

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