Corrosion and Prevention

Study the conditions for rusting and investigate various prevention methods

Equation

4Fe(s) + 3O₂(g) + 2nH₂O(l) → 2Fe₂O₃·nH₂O(s)

Conditions & Ionic Half Equations

Rusting requires water (H₂O) and oxygen (O₂).

Anode: Fe(s) → Fe²⁺(aq) + 2e⁻

Cathode: O₂(g) + 4H⁺(aq) + 4e⁻ → 2H₂O(l)

Formula

Fe₂O₃ · nH₂O

Full Name

Hydrated Iron(III) oxide

HKDSE Tip

Essential conditions: $Both water (H₂O) and oxygen (O₂) are required for rusting.$
Factors accelerating rusting: $Soluble ionic substances (e.g. NaCl), acidic pollutants, high temperature, and scratches on the iron surface all speed up rusting.$
Sacrificial protection: $Connect iron to a more reactive metal (e.g. Zn, Mg). The more reactive metal loses electrons and corrodes instead of the iron.$
Common protection methods: $Cathodic protection, electroplating, tin-plating, plastic coating, oiling, and using stainless steel alloys can all slow down or prevent corrosion.$

Lab Guide

1
Choose Condition
Select a control or a specific rusting/prevention condition.
2
Observe Changes
Observe color changes on the nail until it is fully rusted or the observation period ends.
3
Understand Principle
Read the explanation to understand why some conditions accelerate or prevent rusting.

Please select a condition first