Overview
This lecture explains the structure, function, and notation of galvanic cells, emphasizing oxidation-reduction reactions and the flow of electrons to generate electrical energy.
Galvanic Cell Fundamentals
- A galvanic cell uses two beakers: one for oxidation (anode) and one for reduction (cathode).
- Oxidation occurs at the anode, where a metal loses electrons to form ions.
- Reduction occurs at the cathode, where ions gain electrons to form metal.
- The two electrodes are connected by a wire and a voltmeter to measure total cell potential.
- Electrons flow from the anode (negative) to the cathode (positive).
Electrochemical Potentials and Standard Conditions
- Each half-reaction has a standard reduction potential found in data tables.
- The standard cell potential is the sum of the cathode and (reversed) anode potentials.
- Standard conditions: 1 mol/L solutions, 298 K (25°C), and 1 atmosphere pressure.
- Deviations from standard conditions affect the measured potential.
Salt Bridge and Charge Balance
- The salt bridge contains mobile cations and anions, maintaining electric neutrality in solutions.
- Cations (e.g., Na⁺) flow into the cathode half-cell; anions (e.g., NO₃⁻) flow into the anode half-cell.
- The salt bridge keeps charge balance, allowing continuous electron flow.
Observations in Galvanic Cells
- At the anode: electrode mass decreases, and ion concentration in solution increases.
- At the cathode: electrode mass increases due to metal deposition.
- Solution color may change based on ion concentration.
Notation (Cell Representation)
- Cell notation lists the oxidation half-cell (anode | ion) first, followed by the reduction half-cell (ion | cathode), separated by || for the salt bridge.
- Single vertical lines (|) separate different phases; commas separate same-phase species.
- Indicate ion concentrations in standard cell notation if known.
Example Problem: Nickel-Zinc Cell
- Oxidation: Zn(s) → Zn²⁺(aq) + 2e⁻; zinc is the anode.
- Reduction: Ni²⁺(aq) + 2e⁻ → Ni(s); nickel is the cathode.
- Electrons flow from zinc (anode) to nickel (cathode).
- Total standard cell potential: 0.76 V (Zn) – 0.24 V (Ni) = 0.52 V.
- Salt bridge: Na⁺ flows into the cathode, NO₃⁻ flows into the anode.
- Notation: Zn(s) | Zn²⁺(aq) || Ni²⁺(aq) | Ni(s).
Key Terms & Definitions
- Oxidation — Loss of electrons from a species.
- Reduction — Gain of electrons by a species.
- Anode — Electrode where oxidation occurs (negative in galvanic cells).
- Cathode — Electrode where reduction occurs (positive in galvanic cells).
- Salt Bridge — Allows ions to flow and maintain charge balance between half-cells.
- Standard Cell Potential — Measured voltage under standard conditions (1 M, 1 atm, 25°C).
- Cell Notation — Shorthand representation of a galvanic cell setup.
Action Items / Next Steps
- Review and memorize cell notation rules and standard conditions.
- Practice constructing and analyzing galvanic cells using standard potential tables.
- Complete any assigned problem sets or textbook readings on electrochemical cells.