Page 39 - Curriculum Visions Dynamic Book

REACTIVITY SERIES
Element Reactivity
potassium most reactive sodium
calcium
magnesium
aluminium manganese chromium zinc
iron
cadmium
tin
lead
copper
mercury
silver
gold
platinum least reactive
The disadvantage of using tin plate
Tin is plated onto iron or steel to protect it from corrosion, but it is only good if it remains unscratched. The reason you often see rusting cans is that tin is below steel (iron) in the reactivity series, so that when the steel is exposed by scratching, the steel corrodes at the expense of the tin, and the tin doesn’t protect the steel at all. This is an important reason why aluminium containers have replaced tin- plated ones in recent years.
 A nail with a small tin collar has
been placed in water. After a few days the nail is heavily rusted, but the tin is unaffected. This shows that tin speeds up the corrosion of steel and shows why tin- plated objects are only protected provided the tin remains unscratched.
Also...
Tin-plating is not the ideal way of protecting food. However, it was the best way for
150 years given the technology available until recently. Thus tin cans dominated the food- preservation market for 150 years because aluminium could not be produced cheaply.
corrosive: a substance, either an acid or an alkali, that rapidly attacks a wide range of other substances.
plating: adding a thin coat of one material to another to make it resistant to corrosion.
 Metals can be placed in order
of how vigorously they react in a list called a reactivity series. Tin is below iron in the reactivity series. Therefore exposed iron will always corrode when placed in a damp environment with tin. This is why steel cans rust badly as soon as they become scratched. It is not just the iron rusting; it is also encouraged to rust faster by the presence of the tin.
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