Oxidation & Reduction

Rusting iron and burning wood are both oxidation, bonding with oxygen. More broadly, losing electrons is oxidation and gaining electrons or losing oxygen is reduction, and the two always happen together. Paint and plating slow rust by blocking oxygen, while smelting metals is reduction that removes oxygen from ore. Here you can switch oxygen-bond and electron-transfer views and slide the rust progress.

What is Oxidation?

🔥 Gain Oxygen or Lose Electrons → Oxidation!

①Iron rusting = Fe + O → iron oxide (slow oxidation)

②Wood burning = C + O → CO₂ (fast oxidation)

③Broader sense: losing electrons = oxidation

④Opposite: losing oxygen or gaining electrons = reduction

Visualizing Redox Reactions

Definition of Redox

Oxidation: gain O / lose e⁻ ↔ Reduction: lose O / gain e⁻

Oxidation and reduction always happen together

Oxidation in Everyday Life — Rust

Oxidation Progress40%

💡 How to Prevent Rust

①Painting → blocks direct contact with O₂

②Oiling → blocks water and O₂

③Galvanizing → zinc is oxidized first (sacrificial)

④Stainless → chromium forms a protective layer

Applications of Redox

Metal Smelting (Reduction)

CuO + C → Cu + CO₂

Strip O from copper oxide (reduction) → pure copper

Combustion (Fast Oxidation)

CH₄ + 2O₂ → CO₂ + 2H₂O + Energy

Fast oxidation of fuel (methane) → releases heat

Summary

Core Idea of Redox

Oxidation (O↑ e⁻↓) ↔ Reduction (O↓ e⁻↑) — together

When one side is oxidized, the other must be reduced

🎯 Exam Points

①Oxidation = gain O = lose electrons

②Reduction = lose O = gain electrons

③Oxidation and reduction always occur together

④Combustion (fast) and rust (slow) follow the same principle

⑤Smelting = reduction (extracting metal from ore)

Examples and Unit Test

Example 1

When iron rusts into iron oxide, and when oxygen is taken from copper oxide to get copper, which is oxidation and which is reduction?

Oxidation is combining with oxygen or losing electrons; reduction is losing oxygen or gaining electrons.

Iron combining with oxygen to form iron oxide is oxidation, and copper oxide losing oxygen to become copper is reduction.

▸ Iron → iron oxide = oxidation / copper oxide → copper = reduction

Combining with oxygen is oxidation; losing oxygen is reduction.

Example 2

When copper oxide and carbon are heated, copper and carbon dioxide form. Do oxidation and reduction happen separately or together?

When one substance loses oxygen (reduction), another substance combines with that oxygen (oxidation).

Copper oxide loses oxygen and is reduced, while carbon combines with oxygen and is oxidized. So oxidation and reduction always happen together.

▸ They happen together (copper = reduction, carbon = oxidation)

Oxidation and reduction always happen at the same time.

Unit-test style

Which statement about oxidation and reduction is correct?

①Losing oxygen is called oxidation

②Oxidation and reduction always happen together

③Gaining electrons is called oxidation

④Painting iron speeds up its oxidation

⑤Combustion is a reduction reaction that loses oxygen

▸ ② Oxidation and reduction always happen together

When one side loses oxygen (reduction), the other gains oxygen (oxidation), so oxidation and reduction always happen together.

Losing oxygen is reduction (①), gaining electrons is reduction (③), painting blocks oxygen and prevents oxidation (④), and combustion is an oxidation reaction that combines with oxygen (⑤).

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Atomic Model

Exothermic / Endothermic

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