Page 41 - Curriculum Visions Dynamic Book

The reactivity of gold
Gold is near the bottom of the reactivity series because it almost unreactive. Gold will
not react with the air to form oxides. Traditionally only a mixture of concentrated nitric
acid and concentrated hydrochloric acid (called aqua regia) would dissolve gold.
Gold and coinage
The first use of metal as a form of currency goes back to the ancient Egyptians about six thousand years ago. Gold, silver and copper were most often used, hence their grouping into the coinage metals. The metals were poured into moulds to produce blank discs called planchets. Markings were stamped on their faces by pressing them between two bronze dies. The coins usually had their
value on one side and the head of the ruler on the other as a guarantee.
Gold will not stand up to handling unless it is alloyed with other metals. For example, in the United States gold
coins (made until 1933) were
90% gold and the remainder silver and copper.
Gold was once used as a worldwide currency reserve, and was held in vaults as a guarantee of the paper money in circulation. This system no longer operates, and gold can be bought and sold on the open market. However, it
is still true that when people feel nervous about a currency they buy gold, thus forcing up gold prices.
There are still large reserves of gold, the largest being at Fort Knox, Kentucky, USA, which contains both bullion (bars) and coins.
electrolysis: an electrical– chemical process that uses
an electric current to cause the break up of a compound and
the movement of metal ions in
a solution. The process happens in many natural situations
(as for example in rusting) and
is also commonly used in industry for purifying (refining) metals
or for plating metal objects with
a fine, even metal coating.
ion: an atom, or group of atoms, that has gained or lost one or more electrons and so developed an electrical charge.
reactivity: the tendency of a substance to react with other substances. The term is most widely used in comparing the reactivity of metals. Metals are arranged in a reactivity series.
 A Krugerrand, one of the world’s most famous gold coins.
REACTIVITY SERIES
Element
Reactivity
potassium sodium calcium magnesium aluminium manganese chromium zinc
iron cadmium tin
lead copper mercury silver gold platinum
most reactive
least reactive
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