Page 11 - Curriculum Visions Dynamic Book

 All iron and steel objects have to be painted or protected in some other way against rust. Most vehicles are coated in a number of protective layers during manufacture and given several coats of paint before they leave the factory.
electrode: a conductor that forms one terminal of a cell.
electrolysis: an electrical–chemical process that uses an electric current to cause the break up of a compound and the movement of metal ions in a solution. The process happens in many natural situations (as for example in rusting) and is also commonly used in industry for purifying (refining) metals or for plating metal objects with a fine, even metal coating.
electrolyte: a solution that conducts electricity.
oxidation/reduction: a reaction in which oxygen is gained or lost. (Also... More generally oxidation involves the loss of electrons.)
EQUATION: The rusting of iron
Iron + water + oxygen ➪ ferric hydroxide ➪ ferric oxide + water 4Fe(s) + 6H2O(l) + 3O2(g) ➪ 4Fe(OH)3(s) ➪ 2Fe2O3(s) + 6H2O(l)
 This rusting horseshoe shows
two forms of rust.
The light brown rust patches are recently formed ferric hydroxide or Fe(OH)3. In contrast, the darker-brown rust patches are the final solid state of ferric oxide, or Fe2O3, shown in the equation above.
If a wetted iron surface is exposed either by being uncoated or because the paint on the surface has been chipped, oxygen atoms are able to enter the water through its surface
skin. In this water one of the world’s tiniest batteries forms.
The water is oxygen rich and the iron forms an electrode, one terminal of a battery. The oxygen-poor region in the scratch, and thus farther from the air, forms the other electrode. The water forms the electrolyte. A minute electric current now flows, and iron
is carried in solution to the oxygen-rich water, where it is oxidised and deposited.
Thus, iron is removed from one part of the metal and deposited as an oxide or hydroxide nearby. This explains why rusty
material is often both pitted and lumpy. (To find out more
about the way electrolysis and electroplating work, see page 37.)
Rust
Also...
How iron becomes pitted
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