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Chemistry · 6. Redox and electrochemistry

Electrons, oxidation states and electrochemical cells

Track electron transfer from displacement reactions to current in cells.

40 minutesContent version: 2.1
Start the interactive pathwayOpen the virtual experiment

Driving question

How can we identify electron donors and explain how chemical energy produces current?

Curriculum coverage

Vietnam Chemistry 10–12; IGCSE electrochemistry and metals.

Model scope and limitations

School electrode-potential models assume stated conditions; real cells have polarisation and internal resistance.

Learning objectives

  • Identify oxidation, reduction and agents.
  • Write half-equations and balance electrons.
  • Explain electron and ion flow in a cell.

Prerequisite knowledge

  • Ions, charge and reactivity series.

Core knowledge

Oxidation

Oxidation is electron loss; reduction is electron gain.

Displacement

A more reactive metal can reduce ions of a less reactive metal.

Cell

Electrons travel externally from oxidation to reduction; ions maintain charge balance.

Worked example

Fe + Cu²⁺ → Fe²⁺ + Cu: Fe → Fe²⁺ + 2e⁻ is oxidation; Cu²⁺ + 2e⁻ → Cu is reduction.

Misconceptions to avoid

  • The oxidising agent is reduced; the reducing agent is oxidised.
  • Electrons do not cross the salt bridge; ions do.

Virtual experiment procedure: Iron and copper(II) sulfate

  1. Record initial colour and metal mass/area.
  2. Place Fe in CuSO₄ and observe coating and colour over time.
  3. Write and combine the two balanced half-equations.

Safety and cautions

  • Copper salts are environmentally harmful; do not pour real solutions down drains.

Evidence to collect

  • Coating evidence, colour change and a net ionic equation.
Open the virtual experiment

Diagnostic check

1. Oxidation is?

  1. Loss of electrons
  2. Gain of electrons
  3. No electron change
Show answer and explanation

Correct answer: Loss of electrons

Remember OIL: oxidation is loss.

2. In Fe + Cu²⁺ → Fe²⁺ + Cu, what is reduced?

  1. Cu²⁺
  2. Fe
  3. Cu
Show answer and explanation

Correct answer: Cu²⁺

Cu²⁺ gains two electrons to become Cu.

3. Where do electrons travel in a cell?

  1. External circuit
  2. Salt bridge
  3. Solvent as protons
Show answer and explanation

Correct answer: External circuit

The external conductor carries electrons.

Application practice

1. Correct oxidation half-equation for Zn?

  1. Zn → Zn²⁺ + 2e⁻
  2. Zn²⁺ + 2e⁻ → Zn
  3. Zn → Zn²⁻
Show answer and explanation

Correct answer: Zn → Zn²⁺ + 2e⁻

Loss of two electrons forms Zn²⁺.

2. What does an oxidising agent do?

  1. Accepts electrons and is reduced
  2. Donates electrons and is reduced
  3. Does not participate
Show answer and explanation

Correct answer: Accepts electrons and is reduced

It oxidises another species by accepting electrons.

3. What is the salt bridge role?

  1. Allow ions to maintain neutrality
  2. Short-circuit electrons
  3. Create new metal
Show answer and explanation

Correct answer: Allow ions to maintain neutrality

Ions prevent charge build-up in half-cells.

Academic references

  1. OpenStax Chemistry 2e — peer-reviewed general chemistry
  2. IUPAC Gold Book — authoritative chemical terminology
  3. BIPM — SI Brochure, 9th edition

This lesson is maintained against the cited sources below. Simulations are learning models and do not replace supervised physical-laboratory safety procedures.

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WebLab STEM
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Đức Tiến — Control & Automation Engineer