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Science

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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.

Steel and aluminium have advantages and disadvantages when used to make cars, which are recycled to re-use valuable materials and cut down on waste.

Rusting

Iron and steel rust when they come into contact with water and oxygen. Both water and oxygen are needed for rusting to occur. In the experiment below, the nail does not rust when air - containing oxygen - or water is not present:

Calcium chloride absorbs water in the sealed right-hand test tube, so there is air but no water, and so no rusting. In the central test tube a nail is inside boiled water which is sealed by oil, so there is no oxygen, and so no rusting. In the left test tube there is water and oxgen with the nail, and it rusts.

Calcium chloride absorbs water in the right-hand test tube

Salt dissolved in water does not cause rusting, but it does speed it up, as does acid rain.

Aluminium does not rust - corrode. Its surface is protected by a natural layer of aluminium oxide. This prevents the metal below from coming into contact with air and oxygen.

Unlike rust, which can flake off the surface of iron and steel objects, the layer of aluminium oxide does not flake off.

Rusting - higher

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

iron + water + oxygen    →    hydrated iron(III) oxide

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