Identify oxidation and reduction in redox reactions

What is a Redox Reaction?

A redox (reduction‑oxidation) reaction is a chemical change where electrons are transferred between substances. One reactant loses electrons (oxidised) and another gains electrons (reduced).

Think of it like a game of “give‑and‑take”:

• 🧑‍🔬 Oxidation – the player who gives away electrons.
• 🧑‍🔬 Reduction – the player who receives electrons.

Oxidation Numbers – The Quick Check

Oxidation numbers (ON) help us spot who’s losing or gaining electrons.

1. Assign the ON to each element in the reaction.
2. Compare the ON of each element in reactants vs. products.
3. Change in ON tells you oxidation or reduction.

Rule of thumb: Higher ON → Oxidised, Lower ON → Reduced.

Step‑by‑Step: Identify Oxidation & Reduction

1. Write the balanced equation.
2. Assign oxidation numbers.
3. Spot changes.
4. Label the species:
   • Oxidised species: ↑ ON
   • Reduced species: ↓ ON

Example Reaction

Equation: $\ce{Zn + Cu^{2+} -> Zn^{2+} + Cu}$

Exam Tips 📚

• Always balance the equation first before assigning oxidation numbers.
• Check that the total charge on each side is the same.
• Remember: Oxidation = loss of electrons, Reduction = gain of electrons.
• Use the “give‑and‑take” analogy to explain quickly in your answer.
• When in doubt, write the half‑reactions – it clarifies the electron flow.