Overview
This lecture explains how galvanic (voltaic) cells use chemical reactions—specifically oxidation-reduction reactions—to produce electricity, detailing their setup, operation, and key concepts.
What is a Voltaic Cell?
- Voltaic (galvanic) cells convert chemical energy into electricity using oxidation-reduction (redox) reactions.
- Batteries are everyday examples of voltaic cells.
Basic Structure of a Voltaic Cell
- The cell consists of two beakers: one with zinc sulfate solution and a zinc metal strip, the other with copper sulfate solution and a copper metal strip.
- The metals are connected by a wire, allowing electrons to flow from zinc to copper, generating electricity.
- A salt bridge (U-shaped tube with salt solution) connects the two solutions to maintain electrical neutrality.
Electron Flow and Redox Reactions
- Electrons move from zinc (which loses electrons) to copper (which gains electrons).
- Zinc becomes Zn²⁺ and dissolves; copper ions (Cu²⁺) gain electrons, become neutral copper atoms, and deposit on the copper electrode.
- Over time, the zinc electrode shrinks and the copper electrode grows.
Oxidation and Reduction Sites
- Oxidation (loss of electrons) occurs at the zinc electrode (anode).
- Reduction (gain of electrons) occurs at the copper electrode (cathode).
- Half-reactions describe the redox events at each electrode.
Writing Half-Reactions and Cell Notation
- Oxidation half-reaction at anode: Zn(s) → Zn²⁺(aq) + 2e⁻
- Reduction half-reaction at cathode: Cu²⁺(aq) + 2e⁻ → Cu(s)
- Cell notation summarizes the cell: Zn(s) | Zn²⁺(aq) || Cu²⁺(aq) | Cu(s)
Role of the Salt Bridge
- The salt bridge allows ions to move between solutions, balancing charge buildup during the redox process.
- Na⁺ ions move toward the cathode (negative buildup), Cl⁻ ions toward the anode (positive buildup).
Key Terms & Definitions
- Voltaic/Galvanic Cell — Device converting chemical energy into electrical energy via redox reactions.
- Redox Reaction — Chemical reaction involving transfer of electrons (oxidation and reduction).
- Anode — Electrode where oxidation (loss of electrons) occurs.
- Cathode — Electrode where reduction (gain of electrons) occurs.
- Half-Reaction — Equation showing either the oxidation or reduction process separately.
- Salt Bridge — Tube allowing ion transfer to maintain charge balance between half-cells.
- Cell Notation — Shorthand representation of a voltaic cell and its reactions.
Action Items / Next Steps
- Review example half-reactions and practice writing cell notation for similar voltaic cells.
- Prepare for upcoming discussion or lab on constructing and observing a voltaic cell in action.