Page 11 - Curriculum Visions Dynamic Book

(Above) Silver tarnishes quickly when exposed to air. Air has turned this fork from a shiny grey-white
to a dark yellow-black. The upper left corner of the fork has had the tarnish removed using silver polish. The tarnish is caused by reactions with chemicals in the air, principally with hydrogen sulphide gas.
temperatures. As a result, when metals get hot, they react more readily. Some chemicals, such as water,
also have a dramatic effect on the oxide film. This is especially true of iron and steel, whose oxide coat keeps breaking down in the presence of air and
water. We see this oxide as rust.
The presence of a metal speeds up many chemical
reactions even though the metal takes no part in
the reaction. This is called a catalytic effect. For example, finely divided platinum is used to make the gases coming from car exhausts less polluting. Carbon monoxide and unburned fuel are changed efficiently
in the presence of platinum into carbon dioxide and water. That is why the box next to the muffler is called a catalytic converter.
(Below) Lead is a relatively unreactive metal, so it does not corrode. That is why it has traditionally been used to fix glass into window frames.
(Below) An iron chain readily rusts. The zinc-plated chain on the left is not affected.
(Below) Although gold is expensive, it is an excellent conductor of electricity and also a relatively unreactive metal. That makes it suitable for specialized applications in electrical circuits.
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