A cell that produces electricity is known as a galvanic cell or voltaic cell. It converts chemical energy into electrical energy through a spontaneous redox reaction. A common example of a galvanic cell is the Daniel cell, which uses zinc and copper electrodes.
Construction:
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Two half-cells: A galvanic cell consists of two half-cells, each containing an electrode and an electrolyte. One half-cell contains a zinc electrode immersed in a solution of zinc sulfate (ZnSO₄), while the other half-cell contains a copper electrode immersed in a solution of copper sulfate (CuSO₄).
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Salt Bridge: A salt bridge (often a U-shaped tube filled with an electrolyte like KCl or NaNO₃) connects the two half-cells. It allows the flow of ions to maintain electrical neutrality in the solutions.
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Electrodes: The zinc electrode is the anode (negative electrode), where oxidation occurs. The copper electrode is the cathode (positive electrode), where reduction occurs.
Working:
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Oxidation at the Anode: In the zinc half-cell, zinc metal (Zn) loses electrons to form zinc ions (Zn²⁺):
Zn(s)→Zn2+(aq)+2e−
The electrons flow through the external circuit from the anode to the cathode, generating an electric current.
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Reduction at the Cathode: At the copper half-cell, copper ions (Cu²⁺) in solution gain electrons to form copper metal (Cu):
Cu2+(aq)+2e−→Cu(s)
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Flow of Ions: To complete the circuit, the salt bridge allows ions to flow between the half-cells. This flow of ions prevents the buildup of charge that would otherwise stop the reaction.
Electrical Energy: The flow of electrons through the external circuit provides electrical energy, which can be used to power devices.