Rust and Corrosion

RUSTING

In the end of this lesson, you will be able to:

1.6.1 describe metal corrosion process as redox reaction through activities.

1.6.2 experiment to prevent rusting.

Poll

Is corrosion of metals similar to rusting of iron?

• YES

• NO

RUSTING OF IRON

Rusting of iron is a chemical process that occurs when iron is exposed to oxygen and water, and undergoes a redox reaction.

CORROSION OF METAL

Corrosion of metal is a redox reaction where the metal is oxidised spontaneously when the metal atoms release electrons to form metal ions.

The more electropositive the metal is, the easier it is for the metal to corrode

e.g corrosion of iron, Fe is faster than copper, Cu.

Multiple Choice

Which of the following is the correct half equation for oxidation of magnesium?

Multiple Select

What are the conditions for rusting? (You can tick more than 1 answer)

• carbon dioxide

• oxygen

• nitrogen

• water

The surface of the iron in the middle of the water droplet where the concentration of oxygen is low serves as the anode (negative terminal).

Iron atom, Fe loses electrons and undergoes oxidation to form iron(II) ions, Fe2+.

Fe ==> Fe²⁺ + 2e

Electrons flow through the iron, Fe to the end of the water droplet where the concentration of oxygen is higher. The iron, Fe surface at that part becomes the cathode (positive terminal), where reduction occurs.

 Oxygen, O₂ that dissolves in water accepts electrons and undergoes reduction to form hydroxide ion, OH⁻.

 O₂ + 2H₂O + 4e⁻ → 4OH⁻ 

The iron(II) ion, Fe²⁺ produced reacts with hydroxide ion, OH⁻ to form iron(II) hydroxide, Fe(OH)² .

Fe²⁺ + 2OH⁻ → Fe(OH)₂

Iron(II) ion, Fe2+ is green but rust is brown because iron(II) hydroxide, Fe(OH)2 undergoes continuous oxidation with oxygen to form hydrated iron(III) oxide Fe2 O3 .xH2 O (rust). x is an integer that has various values.

Fe(OH)₂ ==> Fe₂ O₃ .xH₂ O

Multiple Select

State the characteristics of rust

• Green

• Brown

• Brittle

• Permeable

Multiple Select

Which of the followings are ways of protecting rusting?

• Use of protective surface such as paint, grease and tin plating

• Sacrificial protection

• Alloying

• None of the above

Multiple Choice

Your mother would not buy dented canned food. Explain why?

• Not good for health

• As soon as the can is dented, iron underneath is exposed to air and water. Rusting of iron will occurs faster because iron is more electropositive than tin.

• As soon as the can is dented, iron underneath is exposed to air and water. Rusting of iron will occurs faster because iron is less electropositive than tin.