Conditions for Rusting

A series of free IGCSE Chemistry Activities and Experiments (Cambridge IGCSE Chemistry).

In these lessons, we shall learn about conditions for rusting to take place.

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Conditions for Rusting
Iron and steel rust when they come into contact with water and oxygen. They rust faster in salty water or acid rain. Aluminium, on the other hand, does not corrode easily, because its surface is protected by a layer of aluminium oxide.

The following experiment investigates the conditions necessary for rusting to occur.

Fill up test tubes as follows:
Test tube A is filled with boiled water and an oil layer so that there is no oxygen.
Test tube B has calcium chloride which will dry the air.
Test tube C has regular tap water that has oxygen.
Place an iron nail in each of the three test tubes.
Cover each test tube and let it stand for a couple of days.
Compare the conditions of the nails in each test tube.

Prevention and treatment for rust
Rusting is an oxidation reaction. The iron reacts with water and oxygen to form hydrated iron(III) oxide, which we see as rust. This is the word equation for the reaction:
iron + water + oxygen → hydrated iron(III) oxide

Salt and acid acts as catalysts to speed up the reaction.

How to prevent rust?

  1. Painting
  2. Adding oil or grease
  3. Galvanizing - The iron or steel object is coated in a thin layer of zinc. This stops oxygen and water reaching the metal underneath and the zinc also acts as a sacrificial metal. Zinc is more reactive than iron, so it oxidises in preference to the iron object.

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