Page 6 - Curriculum Visions Dynamic Book

Iron
Iron is a dense, silvery-grey metal.
It is the most widely used of all the metal elements because it is common, is cheap to produce from its ores,
can be bent while cold, and is strong.
However, some of its properties are less welcome. For example,
it is quite reactive, especially
with air and water, a process called corrosion. You can see why this happens by looking at the demonstrations below.
The reactivity of iron
Some metals are more reactive than others.
Gold, for example, hardly reacts at all, which is
why it stays bright and does not tarnish (develop
a dull oxide coating). On the other hand, some metals, like potassium, react vigorously with oxygen (corrode) as soon as they are placed in the air.
Metals can be placed in order of how vigorously they react, in a list called a reactivity series
(see right).
Copper is near the bottom of the reactivity series,
while iron is higher up. Therefore iron will always corrode when placed in a solution containing a copper compound such as copper sulphate. On the other hand, iron is below magnesium, which is why magnesium will always corrode when placed next to iron. This is shown in the picture on the right, where a small strip
of magnesium has been wrapped around the shank of an iron nail and placed in a bottle containing water and an indicator.
 Iron filings (the dark material) are placed in a small pile in a dish. Copper sulphate (the blue solution) is added.
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The red colour is caused by an indicator in the water. The clear water shows a neutral reaction. As the magnesium corrodes it produces magnesium hydroxide, an alkali, which turns the region near the corroding magnesium red.