9.5 and 9.6 - Extraction and Corrosion of Metals

What are the conditions required for iron to rust?

Water and oxygen are required. Salt and acid rain increase the rate of rusting.

How do barriers prevent rusting?

They stop oxygen and water from reaching the metal surface.

Name some common barrier methods to prevent rusting.

Painting, oiling/greasing, plastic coating, electroplating.

How does painting prevent rusting?

Paint forms a protective layer, keeping oxygen and water away from metal.

How do oiling and greasing prevent rusting?

They create a thin film that blocks oxygen and moisture.

How does plastic coating protect metal?

A plastic layer (e.g., PVC) acts as a waterproof and airtight barrier.

How does electroplating protect metals?

A thin layer of a non-reactive metal (e.g., tin, chromium) covers the iron, preventing rust.

What is galvanising?

Coating iron or steel with zinc to prevent rusting.

How does zinc protect iron in galvanising?

Acts as a barrier and through sacrificial protection — zinc corrodes instead of iron.

What is sacrificial protection?

Using a more reactive metal (like zinc or magnesium) to corrode instead of iron.

Why does the more reactive metal in sacrificial protection corrode first?

It loses electrons more easily, preventing iron from oxidising.

How does the reactivity series relate to metal extraction?

Metals low in the series are easy to extract; high reactivity metals are harder and need electrolysis.

How are metals like iron, zinc, and lead extracted?

By chemical reduction with carbon (because they are mid-reactivity).

How are metals like aluminium, sodium, and magnesium extracted?

By electrolysis, as their compounds are very stable.

What is the main ore of iron and aluminium?

Iron: hematite (Fe₂O₃) , Aluminium: bauxite (Al₂O₃)

Write the reaction of carbon burning in a blast furnace.

C + O₂ → CO₂

How is carbon monoxide formed in a blast furnace?

CO₂ + C → 2CO

How is iron reduced from Fe₂O₃ in a blast furnace?

Fe₂O₃ + 3CO → 2Fe + 3CO₂

What happens when limestone is heated in a blast furnace?

CaCO₃ → CaO + CO₂

How is slag formed?

CaO + SiO₂ → CaSiO₃

Why is cryolite used in aluminium extraction?

Lowers melting point of Al₂O₃, saving energy.

Why do carbon anodes in aluminium electrolysis need replacement?

They react with oxygen to form CO₂ and gradually wear away.

What is the cathode reaction in aluminium electrolysis?

Al³⁺ + 3e⁻ → Al (reduction)

What is the anode reaction in aluminium electrolysis?

2O²⁻ → O₂ + 4e⁻ (oxidation)C + O₂ → CO₂