Redox reaction: electron transfer, oxidising and reducing agents

Watch electrons move from the reducing agent to the oxidising agent in Zn + Cu²⁺, Mg + H⁺, Cu + Ag⁺, Na + Cl₂ and Fe + Cu²⁺, with the oxidation numbers, the half reactions and a reaction that does not happen. Free for every student.

Also searched as: redox reaction class 11 · redox reaction class 11 · oxidising and reducing agent · oxidation and reduction · electron transfer reaction · half reactions

About this experiment

Aim

To see that oxidation and reduction go together as a transfer of electrons, to identify the oxidising and reducing agents with the help of oxidation numbers, and to predict whether a displacement reaction happens.

Theory

Oxidation is loss of electrons (the oxidation number increases) and reduction is gain of electrons (the oxidation number decreases): OIL RIG, oxidation is loss, reduction is gain. They always happen together, so the reaction is called a redox reaction. The number of electrons lost by one species equals the number gained by the other.

The species that gives electrons is oxidised and is the reducing agent. The species that takes electrons is reduced and is the oxidising agent. In Zn + Cu²⁺ → Zn²⁺ + Cu zinc is oxidised (0 → +2) and acts as a reducing agent, and Cu²⁺ is reduced (+2 → 0) and acts as an oxidising agent.

A reaction can be split into two half reactions: the oxidation half Zn → Zn²⁺ + 2e⁻ and the reduction half Cu²⁺ + 2e⁻ → Cu. Their sum is the net ionic equation, in which the electrons cancel.

Formulas used

• oxidation: A → Aⁿ⁺ + n e⁻ (oxidation number increases)
• reduction: Bᵐ⁺ + m e⁻ → B (oxidation number decreases)
• E°cell = E°(oxidising agent couple) − E°(reducing agent couple)
• reaction is spontaneous if E°cell > 0

Procedure: what to do in the virtual lab

1. Choose Zn + Cu²⁺ and slowly drag the progress slider. Watch the electrons travel from Zn to Cu²⁺.
2. Read which species is oxidised and which is reduced, and note the oxidation numbers before and after.
3. Check the two half reactions and the total number of electrons.
4. Try the other reactions. In Na + Cl₂ identify the oxidising agent.
5. Choose the last one (Cu + Zn²⁺). Why does nothing happen?

Observations to make

• The species that loses electrons gets a more positive oxidation number.
• The electrons lost always equal the electrons gained.
• A metal with a more negative E° displaces the ion of a metal with a more positive E°, never the other way.

What you can change in this experiment

• Reaction: Zn + Cu²⁺ → Zn²⁺ + Cu / Mg + 2 H⁺ → Mg²⁺ + H₂ / Cu + 2 Ag⁺ → Cu²⁺ + 2 Ag / 2 Na + Cl₂ → 2 Na⁺ + 2 Cl⁻
• Progress of the electron transfer

Viva questions on Redox reaction

Questions an examiner may ask in the Class 11 chemistry practical. Run the experiment in the lab to find the answers yourself, then check them in the Learn tab.

1. What are oxidation and reduction in terms of electrons?
2. What is an oxidising agent? Give an example.
3. Why does zinc displace copper from copper sulphate solution but copper does not displace zinc?
4. What are half reactions?

Frequently asked questions

Syllabus: Class XI Chemistry, Chapter 7 — Redox Reactions, §7.1 (classical idea and electron transfer), §7.2 (redox reactions in terms of electron transfer)

What you do in the lab

Change the controls and watch the chemistry behave in real time in 3D. Live readouts and graphs show the numbers behind it, and the Learn tab has the theory, procedure, observations and viva questions. Works on a phone or a laptop, in English and Hindi.

Topics: redox reaction · oxidation and reduction · oxidising agent · reducing agent · electron transfer · half reaction · displacement reaction · activity series · redox reactions

More from this unit

• Galvanic cell: Mg | Mg²⁺ || Cu²⁺ | Cu
• Galvanic cell: Zn | Zn²⁺ || Ag⁺ | Ag
• Copper with concentrated nitric acid
• Dichromate oxidises iron(II)
• Fractional oxidation number: S₄O₆²⁻, C₃O₂, Fe₃O₄ and Pb₃O₄
• Iodometric titration of copper(II)
• Iron nail in copper sulphate
• Redox titration: KMnO₄ vs Mohr's salt

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