Page 53 - Curriculum Visions Dynamic Book

(Above) A piece of potassium burning on the surface of water.
(Below) Corrosion of iron requires the presence of both water and air. If an iron nail is placed in a small tube that is partly filled with distilled water and left open to the air, the part of the nail in the water will gradually corrode.
Although very reactive metals react in this violent way, less reactive metals also react. Most metals react in water containing dissolved oxygen. During the chemical reaction that takes place, the metal is oxidized and a surface coating produced. We call this corrosion.
The water and the air dissolved in it act as an electrical conducting solution. One of the metals most severely affected by this reaction is iron. The particular form of corrosion that occurs is called rust. It is also a chemical reaction.
However, not all metals react as quickly. There is,
in fact an order of reactivity (see chart on page 54). Magnesium is more reactive in water than iron, for example. The importance of this is that if a piece of magnesium is wrapped around a nail and the two placed in water, then the magnesium reacts with the water,
and the iron remains uncorroded. This is an extremely important result because it means that, for example,
if blocks of a reactive metal are placed on the hull of
a ship, it is the blocks of metal that corrode, while the hull remains undamaged. Such protection saves huge
(Right) However, if some similar new, clean nails are put in a desiccator,
an apparatus designed to keep the air completely dry, and if yet more nails are put in a tube that is then filled with freshly prepared distilled water
(which has been boiled in preparation and so contains no dissolved oxygen), little corrosion is seen even after many weeks in either case.
Distilled water in open container so that air can mix freely
Rust develops on nail within 24 hours.
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