Mistake Master
Galvanic and electrolytic cells
An electrochemical cell splits a redox reaction in two and makes the electrons travel through a wire to get from one half to the other. Which way they travel — and whether they need a push — is the whole story.
§1
Two cells, one set of rules.
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A cell separates a redox reaction into two half-reactions at two electrodes. A galvanic (voltaic) cell runs a spontaneous reaction (ΔG < 0) to produce electrical energy; an electrolytic cell uses an external power source to drive a nonspontaneous one (ΔG > 0).
In both, the rules for the electrodes are the same: oxidation happens at the anode, reduction at the cathode ("an ox, red cat"). Electrons flow through the external wire from anode to cathode.
The salt bridge carries ions, not electrons, to keep each half-cell electrically neutral. Electrons never travel through the salt bridge — they go through the wire.
§2
Wiring the cell.
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Assign each role, then route the charge.
- Split the redox reaction. One half-reaction oxidizes, the other reduces.
- Assign the electrodes. Oxidation at the anode, reduction at the cathode (in both cell types).
- Route the electrons. Through the external wire, from anode to cathode.
- Route the ions. Through the salt bridge, to keep each half-cell neutral.
- Check for a power source. Galvanic runs on its own; electrolytic needs an external supply.
§3
The pieces you'll meet.
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The parts of an electrochemical cell.
§4
Worked example: tracing a galvanic cell.
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Anode. The metal being oxidized (losing electrons) is the anode — say Zn → Zn²⁺ + 2e⁻.
Cathode. The reduction half (gaining electrons) is the cathode — say Cu²⁺ + 2e⁻ → Cu.
Electrons. Flow through the external wire from the Zn anode to the Cu cathode.
Ions. The salt bridge lets ions migrate to balance charge; no electrons pass through it. Because the reaction is spontaneous, no power source is needed — this is galvanic.
§5
Mistakes that cost real points.
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"Electrons travel through the salt bridge."
Electrons flow through the external wire; the salt bridge carries ions to keep the half-cells neutral. Routing electrons through the salt bridge misrepresents how the circuit works — the wire is the electron path.
Fix. Send electrons through the wire and ions through the salt bridge.
"Reduction happens at the anode."
Oxidation happens at the anode and reduction at the cathode, in both galvanic and electrolytic cells ("an ox, red cat"). Swapping the electrode roles reverses the entire analysis. Anode = oxidation, cathode = reduction.
Fix. Fix the roles: oxidation at the anode, reduction at the cathode.
"An electrolytic cell runs on its own, like a battery."
An electrolytic cell drives a nonspontaneous reaction (ΔG > 0), so it requires an external power source to push the electrons. Only a galvanic cell runs spontaneously. Assuming electrolysis is self-driving misses the required power supply.
Fix. Remember electrolytic cells need an external power source; only galvanic cells are spontaneous.
§6
Skill Check.
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Ten scenarios. Pick the chips that match your answer, then check. A scenario marks complete the first time every part is right. Progress saves on this device.