Page 24 - Curriculum Visions Dynamic Book

Making use of the reactivity of aluminium
Aluminium is the most reactive metal in common use. All metals more reactive than aluminium (calcium, sodium, etc.) are unstable and need special handling.
The reactivity of aluminium has advantages and disadvantages. One advantage is that it readily reacts with oxygen from the air, forming a gastight and invisible oxide layer on its surface that protects the metal from environmental corrosion.
On the other hand, being so reactive, the metal is very difficult to separate out from its ore and the costs of manufacture are high.
Aluminium and the reactivity series
Each metal reacts with the environment differently. Some, like potassium, are highly reactive; others, like gold, are very stable.
When two different metals are placed in a conducting solution (an electrolyte such as
salt water), a natural battery is formed. In a battery, one of the electrodes (the anode)
always corrodes, while the other (the cathode) becomes plated (or coated) with material from the corroding electrode.
Which electrode corrodes, and which is protected (becomes plated) depends on the positions of the metals in the reactivity series. Metals above those in the table become corroded; those lower down are protected.
Aluminium is more reactive than, for example, iron, so when aluminium and iron are placed together in salt water, for example, the aluminium will corrode rather than the iron (see opposite).
The reactivity table also helps to explain why aluminium is so difficult to extract from its ores compared with many other common metals. The higher up the table, the more energy it takes to separate the metal from its ores. For example, iron (in the middle of the table) can be smelted (a chemcial reaction involving heat and a reducing agent) whereas aluminium (near the top of the table) can only be refined using large amounts of electrical energy.
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