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Mechanics lessons
Water on Earth
Changes of state in the nature: the water cycle
Water in human body
Test for water
Properties of water in different states
States of matter
States of matter and its changes
Boiling water
Water: freezing and melting
Changes of state: mass and volume
Molecules in different states of matter

Mixtures and solutions
Heterogeneous mixtures
Homogeneous mixtures
Vaporization of water
Dissolving a solid in water
Conservation of mass on dissolving
Miscibility in water

Mass and volume
Volume and its units
Measuring volume with a graduated cylinder
Mass and its units
Measuring the mass of a liquid
Mass of a liter of water
Volumetric mass density
Air and atmosphere
Earth's atmosphere protect us
Threats to the Earth's atmosphere
Composition of air
Air and life
Atoms and molecules
Molecules in mixtures and pure substances
Molecules and states of matter
Composition of molecules
Constituents of the atoms
The electrical neutrality of the atom

Basics of combustion
The combustion of carbon
The combustion of butane
Atoms and chemical reactions
Chemical reactions
Chemical equations
Law of conservation of mass
Chemical synthesis

Most common metals

How to distinguish metals ?

Corrosion of metals

Electrical conductivity of solid materials

Electrons and free electrons

Electric current in metals
The conductivity of aqueous solutions
Aqueous solutions and ions
The direction of movement of ions
Formation of ions
Tests for ions
Acidic and basic solutions
pH of aqueous solutions
Ions in acidic and basic solutions
Dilution of acids and bases
Composition of hydrochloric acid
Chemical reaction between iron and hydrochloric acid

Electrochemical cells and chemical energy
Chemical reaction beteween a copper sulphate solution and zinc
Copper sulfate and zinc battery
Basics of electrochemical cell



Corrosion of metals

1) What is corrosion ?

The corrosion of a matter is its degradation.
It may have mechanical causes such as frictions or chemical causes.
In the open air, metals are in contact with dioxygen, water, carbon dioxide and gaseous pollutants that can cause a chemical transformation in which the metal is one of the reactants. The latter is then consumed and some products are formed.

2) Corrosion of gold

Gold is one of the few metals to be free from corrosion. It thus preserves its shine and color despite prolonged exposure to air.
It is said that gold is unalterable and this is one of properties that makes it a precious metal.



3) Copper corrosion

Copper corrodes in contact with air: it is covered with a greenish layer called verdigris.
This layer is impermeable and isolates copper from air and reactants responsible for its corrosion.
Copper corrosion stops as soon as verdigris forms.
Copper corrosion remains superficial, it only modifies its appearance.
Example: The Statue of Liberty is covered with verdigris

4) Corrosion of iron

The iron reacts with dioxygen and water to form some reddish rust. This porous layer of rust lets air and water pass: they can reach iron and keeps reacting with it until it is completely transformed into rust.
An iron object can deeply corrode and may even totally disappear.
The iron must then be protected with a layer of paint or varnish which isolates it from the water and air.

5) Corrosion of silver

Silver oxidizes on contact with dioxygen from the air: it darkens by covering with a layer of silver oxide. This impermeable layer prevents corrosion from spreading.

6) Corrosion of aluminum and zinc

The corrosion of the zinc and aluminum is the same type as that of copper and silver: it only attacks the metal surface on which is formed an oxide layer (zinc oxide or aluminum oxide ).
However, the layers that form in both cases are greyish. It is therefore difficult to distinguish them from metal they cover.