Identify redox reactions as reactions involving gain and loss of oxygen

Chemical Reactions – Redox

Objective

Identify redox reactions as reactions involving the gain and loss of oxygen atoms.

Exam Tip

When you see a reaction, count the oxygen atoms on each side. If the number changes, it’s a redox reaction. Also, check the oxidation states of the main elements.

Analogy: Oxygen as a Traffic Cop

Think of oxygen atoms as traffic cops directing electrons. In a redox reaction, the traffic cop (oxygen) moves from one vehicle (atom) to another, causing one to lose electrons (become oxidised) and the other to gain electrons (become reduced).

Common Redox Examples

  • Combustion of methane: CH₄ + 2O₂ → CO₂ + 2H₂O (Oxygen is added to carbon and hydrogen).

  • Rusting of iron: 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃ (Iron loses electrons to oxygen).

  • Displacement reaction: 2Na + Cl₂ → 2NaCl (Oxygen not involved, but check oxidation states to confirm redox).

Oxidation States Cheat Sheet

ElementCommon Oxidation State
Oxygen (O₂)0 (in elemental form)
Oxygen in oxides-2
Iron (Fe)0, +2, +3
Carbon (C)-4, +2, +4

Exam Tip

Always write the oxidation states of the key atoms before and after the reaction. If they change, you’ve spotted a redox process.

Quick Check List

  1. Count oxygen atoms on both sides.

  2. Check oxidation states of the main elements.

  3. Look for electron transfer (gain/loss).

  4. Confirm that the total charge is balanced.

Final Thought

Remember: In redox reactions, oxygen is often the “traffic cop” that moves between atoms, causing one to lose electrons (oxidise) and another to gain electrons (reduce). Keep an eye on the oxygen count, and you’ll always know when a redox reaction is happening! 🚗⚡️