Rusting – Lesson Objectives

• Understand how salt water affects rusting.• Understand that rusting is an oxidation reaction

(iron reacts with oxygen forming an oxide).• Construct the word equation for rusting• Explain why aluminium does not corrode in moist

conditions.

What has caused this iron to turn red? Can you guess why it happened?

When iron rusts…Rusting

… it reacts with oxygen and turns back to the iron oxide it was made from.

But things are not that simple.

Iron does not rust in the desert, even though there is plenty of oxygen in the air.

Rusting also needs water.

Iron + Oxygen + Water Hydrated Iron (iii) Oxide

Redox Reactions

• Redox is a short way of saying:Reduction and

oxidation

Oxidation meant adding Oxidation meant adding oxygen to a substance.oxygen to a substance.

Rusting (iron becoming iron oxide) is an example of oxidation.

Reduction meant taking Reduction meant taking oxygen away.oxygen away.

Extracting iron from iron oxide in the blast furnace is reduction.

• Early on in chemistry these words had very straightforward meanings.

Redox reactions: oxidation and ions

• Whenever metals react with oxygen they form ionic compounds and the metal loses electrons to form positively charged ions.

• Eg. When magnesium burns to form magnesium oxide magnesium atoms (no charge) become magnesium ions (2+ charge) by losing 2 electrons to oxygen atoms.

Mg O2 e- to give Mg2+ O2-

Oxidation involves loss of electrons.

Redox Reactions: oil rig

An easy way of remembering this is “Oil RigOil Rig”!

O oxidationO oxidation

II isis

L lossL loss

R reductionR reduction

II isis

G gainG gain

of electrons

Prevention

• Cover in oil

• Paint

• Galvanise – coat with Zinc

• Stainless steel – mixture of Fe and C and Chromium (Cr)

Here’s a puzzle

iron mystery metal

identical nut and bolt in identical conditions!

identical except that one is made of iron and the other is made from a mystery metal

the mystery metal is aluminium

aluminium does not corrode in moist conditions

so it is suitable for window frames

…. and other things that get wet

How does it happen?• aluminium reacts

quickly with the oxygen in the air

• a layer of aluminium oxide forms

• no more oxygen can reach the metal

What is rust? – Write and answer in your book.

• E/F – Rust requires both air AND water. It is and Orange/brown substance.

• C/D - Rust is ‘Iron Oxide’

• B/C - Iron + Oxygen + Water Hydrated Iron (iii) Oxide