Iron, even in the form of steel, is prone to rust. This is a slow reaction that takes place when the iron is in contact with both water and oxygen. It is quite easy to show that water and oxygen are both needed for rusting by setting up a simple controlled experiment.
Things you need to know…
- deionised water is purified/distilled water
- over time, oxygen from the air will dissolve into water
- boiling the water makes all the dissolved oxygen evaporate
- anhydrous calcium chloride absorbs water
Set up three tubes as shown below…
Tube A is the control tube. The iron nail will be in contact with water and dissolved oxygen. The other two tubes will be compared with this tube.
Tube B only has water in it because the oil prevents any oxygen from the air touching the water.
Tube C has only air and no water because any moisture is absorbed by the calcium chloride.
The tubes are left for a week before being carefully observed again. How will they have changed?
Tube A – the iron nail should be coated in rust. This is the control tube – the one with which the other two can be compared.
Tube B – there will be no rusting because there is water but no oxygen.
Tube C – there will be no rusting because there is oxygen (from the air) but no water.
Questions…
- What evidence is there that rusting is a chemical process not a physical one?
- How does steel differ from iron?
- Name a material you might use to coat iron to prevent rusting.
- Suggest two physical properties shared by all metals.
- Suggest one chemical property of metals.
- In an experiment, what is meant by a control?
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