Theory — Electron Transfer in Redox
Theory — Electron Transfer and Energy
Oxidation and reduction
A redox reaction is one in which electrons are transferred. Oxidation is the loss of electrons and reduction is the gain of electrons; a useful reminder is OIL RIG, oxidation is loss, reduction is gain. The species that loses electrons is the reducing agent, and the one that gains them is the oxidizing agent. We track the electrons with oxidation numbers, assigned by a short set of rules.
Galvanic cells and cell potential
In a galvanic cell the two half-reactions are separated so the electrons travel through a wire, doing useful work. Oxidation happens at the anode and reduction at the cathode. Each half-reaction has a standard reduction potential; the half-cell with the higher value is reduced (the cathode), and the lower one is oxidized (the anode).
| Reduction half-reaction | E° (V) |
|---|---|
| Ag⁺ + e⁻ → Ag | +0.80 |
| Cu²⁺ + 2e⁻ → Cu | +0.34 |
| 2H⁺ + 2e⁻ → H₂ | 0.00 |
| Pb²⁺ + 2e⁻ → Pb | −0.13 |
| Ni²⁺ + 2e⁻ → Ni | −0.25 |
| Fe²⁺ + 2e⁻ → Fe | −0.44 |
| Zn²⁺ + 2e⁻ → Zn | −0.76 |
Track the electrons
Oxidation numbers reveal which atom loses electrons (oxidized) and which gains them (reduced).
Anode and cathode
Oxidation happens at the anode; reduction happens at the cathode.
Cell potential
E°cell = E°cathode − E°anode; a positive value means the cell drives current on its own.
Apparatus
The equipment a real electrochemistry experiment uses to build a galvanic cell and measure its potential. In the simulation these are modelled for you, but the readings correspond to what each instrument would measure.
Instructions — Running the Virtual Experiment
This is a predict, reveal, and compare lab. In every part you work out the answer yourself first, enter it, and only then does the simulation reveal the experimental value so you can check your work against it.
Simulation — The Electrochemistry Bench
| Compound | Element | Your value | Actual |
|---|---|---|---|
| Choose a compound, calculate, and check. | |||
Assign the oxidation number
Build the cell
Team Questions
Example Lab Report
A worked example showing the expected format and the calculate, reveal, and compare workflow.
Redox Reactions
Chemistry | Section: [Your Section] | Date: [Date]
Lab Members: [Names of all members present]
Objective
To assign oxidation numbers, identify the species oxidized and reduced in a galvanic cell, and find the standard cell potential from electrode reduction potentials.
Theory
Oxidation is loss of electrons and reduction is gain of electrons. In a galvanic cell oxidation occurs at the anode and reduction at the cathode, and the cell potential is E°cell = E°cathode − E°anode.
Results (worked example)
| Quantity | Value |
|---|---|
| Oxidation number of Mn in KMnO₄ | +7 |
| Zn–Cu cell: anode (oxidized) | Zn |
| Zn–Cu cell: cathode (reduced) | Cu |
| E°cell (0.34 − (−0.76)) | 1.10 V |
Zinc has the lower reduction potential, so it is oxidized at the anode while copper is reduced at the cathode, giving a cell potential of 1.10 V.
Conclusion
Oxidation numbers identified the electron transfer, and the measured cell potential matched E°cathode − E°anode, confirming the predicted spontaneous direction of the cell.
Practice Questions
Show all work. Use the oxidation-number rules and E°cell = E°cathode − E°anode. Reduction potentials are in the Theory table.