LESSON 23 Rusting of Metals: Brown Village Roofs
Grade Level: 7-10

1. Grades 7-10

2. Overview Rusting is a chemical process that, can take place in metals exposed to the atmosphere. Not all metals however rust. Rusting is common with the metal, iron. Certain conditions in the air around a metal have to be present for iron to rust. Iron rust which, generally appears brown, is itself a chemical compound quite different from the iron itself. The rusting of iron can be prevented. In towns and large cities where iron sheets are used for roofing houses, rusting can also take place if the iron sheets are not protected from rusting.

3. Purpose When an iron sheet rusts, it forms a new coating around the iron itself. The purpose of this lesson is to show that the brown corrugated iron roofs in some villages is as a result of the rusting of the iron in the sheets. Rusting can be prevented.

4. Objectives Students will be able to:

i. Identify what is iron rust.
ii. Demonstrate how a piece of iron can be made to rust
iii. Show that rusting in iron can be prevented.

5. Resources/materials

  • Strips of different metals-iron, copper, aluminium, tin
  • Test tubes, iron nails
  • World map showing iron ore deposits
  • Wall charts showing iron and its uses.

6. Activities and Procedures Iron and its allied product, steel are important in the development of many countries. Iron ore, the raw material for the manufacture of iron is found as mineral deposit in some countries of the world. Here the teacher should guide the students to search and study the iron mineral deposits in the world.

When metals are exposed to the atmosphere over a long period, they change their appearance. Some get duller and less bright while some like iron develop a coating over its surface. The words tarnish and rust are then applied. Iron is known to rust while a metal like aluminium tarnishes. This lesson should help to explain the following:

  • What is iron rust?
  • How is iron rust formed?
  • Is iron rust useful?
  • How can iron rust be prevented?

This lesson offers good opportunity for the students to carry out simple experiments on rusting with simple materials. This study of rusting will involve some bit of chemistry. Iron rust is a compound of iron. It is formed when iron reacts with the oxygen of the air in the presence of moisture (water) to form a brown substance known as iron oxide. The process is a chemical reaction, which takes place over a period of time. It should be noted that oxygen and water are necessarily present for iron to rust.

Iron + oxygen + water ====== Iron rust.

The conditions for iron to rust can then be easily deduced. The rusting of iron is at times referred to as slow burning. Why?

Rusting of iron affects the quality of the iron. It is like the decay of the iron. Rusting costs the community a great deal of money. It has to be prevented otherwise articles made of iron will decay away. The students should then be guided to search for cases of iron rusting in their environment. What materials rust and where are they found. An abandoned car on the road side over a long time get covered with a brown substance-rust. The students should explain this. That discussion can lead to the observation of old brownish iron roofs found in many villages and towns.

The teacher should now perform the simple experiments with the iron nails. Then the methods applied for preventing rusting should be discussed-painting, greasing, electroplating and galvanising should be studied.

7. Tying it all together Rusting is a term appropriately applied to the behaviour of iron under certain conditions. When iron rusts, a new substance is formed. The rusting of iron affects the iron and it could be costly. So it has to be prevented.

8. Assessment The students should deduce how iron can be distinguished from other metals.

9. Author(s) S. T. Bajah stan@alpha.linkserve.com

10. References STAN (1998) Nigerian Integrated Science Project. Book Two. Ibadan: Heinemann Educational Books (Nigeria) Limited.