Purpose
To help students understand the principles of a galvanic cell and the importance of a salt bridge in maintaining electrical conductivity.
Materials Needed
- Voltmeter
- Beakers of 1 M zinc sulfate
- Beakers of copper (II) sulfate
- Copper strip
- Zinc strip
- Paper towel
- Safety equipment (as needed)
Procedure
- Setup: Introduce the voltmeter, zinc sulfate solution, copper sulfate solution, and metal strips.
- Student Engagement: Ask students how to arrange the metal strips in the solutions to produce a positive voltage reading on the voltmeter.
- Assembly:
- Allow students to suggest placing the strips in opposing solutions. Follow their suggestions and observe the results.
- Note the brief voltage reading and explain why it drops quickly.
- Demonstrate copper plating onto zinc and explain the concept of short-circuiting.
- Electrolyte Explanation:
- When students suggest placing each metal in its respective solution without a salt bridge, discuss the missing component.
- Use your fingers as a salt bridge to illustrate electron flow and charge balance.
- Mention the safety of the demonstration based on the MSDS and emphasize handwashing afterward.
- Alternative Salt Bridge: Show the use of a paper towel soaked in zinc sulfate as a salt bridge.
Chemical Equations
| Half-Reaction | Equation | Standard Reduction Potential (E°) |
|---|---|---|
| Copper Reduction | Cu²⁺(aq) + 2e⁻ → Cu(s) | E° = +0.34 V |
| Zinc Oxidation | Zn(s) → Zn²⁺(aq) + 2e⁻ | E° = -0.76 V |
| Overall Cell Reaction | Cu(s) + Zn²⁺(aq) → Zn(s) + Cu²⁺(aq) | E°cell = -1.1 V |
Conclusion
This demonstration illustrates the crucial role of the salt bridge in maintaining the flow of ions and electrons in a galvanic cell, highlighting the principles of electrochemistry.