Sacrificial Protection

Summary: Sacrificial protection prevents rusting by attaching a more reactive metal (e.g. zinc, magnesium) to iron or steel. The more reactive metal corrodes in preference to the iron, sacrificing itself. Galvanising (zinc coating) is the most common example. Tags: igcse chemistry definition metals corrosion Created: 2026-07-14 Last Updated: 2026-07-23

Sacrificial protection is a method of preventing rusting where a more reactive metal is placed in contact with iron or steel. The more reactive metal loses electrons in preference to the iron — it is oxidised instead of the iron — thereby “sacrificing” itself to protect the iron.

How It Works

1. Two metals in contact in the presence of water and oxygen form an electrochemical cell
2. The more reactive metal has a greater tendency to lose electrons (form positive ions)
3. Electrons flow from the more reactive metal to the iron
4. The more reactive metal is oxidised (corrodes) while the iron is protected from oxidation
5. As long as some sacrificial metal remains, the iron will not rust

Why It Works Even When Scratched

This is the key advantage over barrier methods:

• If galvanised steel is scratched → zinc is exposed alongside iron
• Zinc is more reactive than iron → zinc loses electrons preferentially
• Electrons from zinc flow to the exposed iron → iron remains as Fe atoms (does NOT form Fe³⁺)
• The zinc corrodes, the iron does not

This is why galvanising is superior to simple barrier methods — it provides continuous protection even after damage.

Galvanising

Galvanising is the most common form of sacrificial protection:

1. Steel is coated with a layer of zinc
2. Zinc is applied by dipping in molten zinc (hot-dip galvanising) or by electroplating
3. The zinc layer provides BOTH:
   • Barrier protection (physical coating)
   • Sacrificial protection (zinc corrodes instead of iron)

Sacrificial Protection in Terms of Electron Loss

The more reactive metal (e.g. Zn) loses electrons more readily:

• Zn → Zn²⁺ + 2e⁻ — zinc is oxidised (corrodes)
• Fe → Fe²⁺ + 2e⁻ — this does NOT happen because zinc supplies electrons preferentially

The iron accepts electrons from the sacrificial metal, keeping it in its metallic (reduced) state.

Other Examples

Key Facts

• Sacrificial protection uses a more reactive metal to protect iron
• The more reactive metal loses electrons in preference to iron
• Continues to protect even when scratched (unlike barrier methods)
• Galvanising = coating steel with zinc → barrier + sacrificial protection
• Zinc is oxidised: Zn → Zn²⁺ + 2e⁻
• Iron is protected from oxidation (does NOT form Fe²⁺/Fe³⁺)
• Explained by the reactivity series — Zn is more reactive than Fe

See Also

• Rusting of Iron
• Barrier Method
• Galvanising
• Reactivity of Metals
• Redox Reactions
• IGCSE-Chem-Index

This is a key term definition page — part of the IGCSE Chemistry (0620/0971) keyword glossary.