9.5 Corrosion of Metals
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28. State the two conditions required for the rusting of iron and steel.
The continuous simultaneous presence of both oxygen (from the air) and water.
29. What is the chemical name for the product formed when iron rusts?
Hydrated iron(III) oxide (represented chemically as Fe2O3•xH2O).
30. List three common barrier methods used to prevent the rusting of iron.
Painting, greasing/oiling, and coating with plastic layer shields.
31. How do barrier methods prevent iron from rusting?
They construct a physical blockade that excludes atmospheric oxygen and water from reaching the surface of the underlying iron metal.
32. Describe the use of zinc in preventing the corrosion of iron.
Zinc is applied via galvanizing. It acts as an external physical barrier and provides long-term sacrificial protection if the surface is scratched.
33. Explain sacrificial protection in terms of the reactivity series.
A more reactive metal (such as zinc or magnesium) is attached to the iron structure. Because it is higher in the reactivity series, it reacts with oxygen and water in preference to the iron.
34. Explain sacrificial protection in terms of electron loss.
The more reactive sacrificial metal loses electrons more easily than iron (Zn → Zn2+ + 2e-), meaning it is oxidized instead of the iron. The iron remains reduced in its elemental state.