Redox Reactions: Oxidation and Reduction Explained (2024)

What are Redox Reactions?

Redox reactions involve the transfer of electrons between substances. The name comes from REDuction and OXidation happening simultaneously.

Remember: OIL RIG

Oxidation Is Losing electrons
Reduction Is Gaining electrons

Oxidation

• Loses electrons
• Oxidation state increases
• The substance is oxidized
• Acts as a reducing agent
• Example: Na → Na⁺ + e⁻

Reduction

• Gains electrons
• Oxidation state decreases
• The substance is reduced
• Acts as an oxidizing agent
• Example: Cl₂ + 2e⁻ → 2Cl⁻

Oxidation States (Numbers)

Oxidation states help us track electron transfer. They're like "bookkeeping" for electrons in compounds.

Rules for Assigning Oxidation States:

1. Free elements = 0 (Na, O₂, Cl₂)
2. Monatomic ions = charge (Na⁺ = +1, Cl⁻ = -1)
3. Oxygen usually = -2 (except in peroxides)
4. Hydrogen usually = +1 (except in metal hydrides)
5. Group 1 metals = +1, Group 2 = +2
6. Sum of all oxidation states = total charge

Examples:

H₂O: H = +1, O = -2

CO₂: C = +4, O = -2

SO₄²⁻: S = +6, O = -2

NH₃: N = -3, H = +1

MnO₄⁻: Mn = +7, O = -2

💡 Pro Tip:

If oxidation states change during a reaction, it's a redox reaction!

How to Identify Redox Reactions

1️⃣

Assign Oxidation States

Calculate oxidation numbers for all elements

2️⃣

Compare Changes

Look for elements that change oxidation states

3️⃣

Identify Agents

Find what's oxidized and what's reduced

Example: Zn + CuSO₄ → ZnSO₄ + Cu

Oxidation States:

Zn: 0 → +2 (increases)
Cu: +2 → 0 (decreases)

Conclusion:

Zn is oxidized (loses e⁻)
Cu²⁺ is reduced (gains e⁻)

Common Types of Redox Reactions

Combustion Reactions

Organic compounds react with oxygen. Carbon is oxidized, oxygen is reduced.

CH₄ + 2O₂ → CO₂ + 2H₂O
C: -4 → +4 (oxidized)
O: 0 → -2 (reduced)

Key Points:

• Always involves O₂
• Produces CO₂ and H₂O
• Releases energy (exothermic)
• Carbon gets oxidized

Metal Displacement

More reactive metal displaces less reactive metal from its compound.

Fe + CuSO₄ → FeSO₄ + Cu
Fe: 0 → +2 (oxidized)
Cu: +2 → 0 (reduced)

Activity Series:

Most reactive: K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Ag, Au :Least reactive

Corrosion (Rusting)

Metals react with oxygen and water in the environment.

4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃
Fe: 0 → +3 (oxidized)
O: 0 → -2 (reduced)

Prevention:

• Galvanization (zinc coating)
• Paint or oil barriers
• Cathodic protection
• Alloying (stainless steel)

Balancing Redox Equations

Half-Reaction Method:

Oxidation Half-Reaction:

Zn → Zn²⁺ + 2e⁻

Shows electron loss

Reduction Half-Reaction:

Cu²⁺ + 2e⁻ → Cu

Shows electron gain

Overall Reaction:

Zn + Cu²⁺ → Zn²⁺ + Cu

Key Rule: Electrons must balance!

The number of electrons lost in oxidation must equal the number gained in reduction.

Practice Redox Reactions

Master electron transfer and oxidation states with our interactive tools!

Balance Redox Equations Practice Problems

Redox Reactions Oxidation & Reduction