Page 37 - Curriculum Visions Dynamic Book

Magnesium oxide
Just as calcium carbonate (limestone) can be heated to produce calcium oxide (quicklime), so magnesium carbonate (dolomite rock) can be heated to release magnesium oxide.
Magnesium oxide, the most useful compound of magnesium, melts at a very high temperature (2800°C). It is
a good conductor of heat, but it conducts electricity poorly. These properties allow it to be used to insulate electric heating elements.
anode: the positive electrode of an electrolysis cell.
cathode: the negative electrode of an electrolysis cell.
corrosion: the slow decay of a substance resulting from contact with gases and liquids in the environment. The term is often applied to metals. Rust is the corrosion of iron.
electrode: a conductor that forms one terminal of a cell.
 When a piece of magnesium ribbon is placed in a dish and some copper sulphate solution is added,
the magnesium corrodes very rapidly indeed. This is because magnesium is more reactive than copper. Magnesium is also more reactive than iron and can be used to protect it.
 The reactivity of magnesium relative to iron is demonstrated here. The liquids in both bottles contain an indicator that turns purple when a reaction takes place. The left-hand bottle contains an iron nail with magnesium wrapped around it and the right-hand bottle contains a similar iron nail with tin wrapped around it.
In the left-hand bottle a reaction takes place
at the magnesium strip, causing the formation of magnesium hydroxide, an alkaline substance that makes the indicator turn purple. The iron nail is not corroded because magnesium is more reactive than iron.
By contrast, in the right-hand bottle the tin has not reacted and the iron nail has corroded (rusted). This is because iron is more reactive than tin.
 Oil storage tanks, and
other large steel structures,
are often protected from
corrosion by attaching them
to magnesium blocks buried in
the ground. The magnesium blocks corrode, while the steel is protected.
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