Chemical World Investigating the conditions needed for rusting
Plan, design, carry out and write up an investigation to show that both oxygen and water are necessary for iron to rust. Hints:
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Calcium chloride is a compound that can be used to remove moisture from air.
Remove dissolved oxygen from water by boiling the water.
Placing a layer of oil on top will keep the oxygen out of the water.
1. What variables will stay the same in this investigation? What variable will change?
2. What is a suitable controlled variable in this investigation? z
Fig. 14.2.5 Rust on a metal door
Corroded metals are weaker and can be expensive to replace.
Ways to prevent corrosion include: z z
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Painting the metal will protect cars and large structures such as bridges.
Covering the metal with a plastic coating prevents exposure of the metal to oxygen and water.
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Greasing the moving parts of the metal with oil.
Plating (covering) the metal with a thin coating of another metal that does not rust. Chromium plating gives an attractive, shiny effect. Zinc is also used in plating. If the metal coating on the iron is zinc, then the iron is said to be galvanised. Zinc will protect iron even when it gets scratched.
Preventing corrosion
Plan, design, carry out and write up an investigation to examine the effectiveness of three ways of preventing the corrosion of an object containing iron.
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Galvanising a metal roof will prevent corrosion
Steel is a form of iron that corrodes easily. However, the oxides formed by some metals protect them from corrosion.
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The oxide of aluminium acts as a barrier and protects the aluminium from reacting further with water and oxygen.
Gold, silver and platinum are unreactive and will never corrode. They remain shiny and this is one of the reasons why they are so valuable.
