found on the periodic table
CAS Registry ID
at 298 K
: gold is available in many forms including wire, foil, and bars.
Gold is usually alloyed
to give it more strength, and the term carat
describes the amount of gold present (24 carats is pure gold). It is estimated that all the gold in the world, so far refined
, could be placed in a single cube 60 ft. on a side. It is metallic
, with a yellow colour when in a mass, but when finely divided it may be black, ruby, or purple.
It is the most malleable
metal; 1 ounce (28 g) of gold can be beaten out to 300 square feet. It is a soft metal
and is usually alloyed to give it more strength. It is a good conductor
of heat and electricity
, and is unaffected by air and most reagents
The most common gold compounds
are auric chloride (AuCl3) and chlorauric acid (HAuCl4). A mixture of one part nitric acid with three of hydrochloric acid is called aqua regia (because it dissolved gold, the King of Metals). It is unaffected by air and most reagents. It is found free in nature and associated with quartz
and other minerals
. Two thirds of the world's supply comes from South Africa
, and 2/3 of USA
production is from South Dakota
. Gold is found in sea water, but no effective economic
process has been designed (yet) to extract it from this source.
It would not normally be necessary to make gold in the laboratory as it is readily available commercially. The most romantic way to extract gold is by panning it out from a stream in some pleasant valley but most such sources are now depleted
. Panning relies upon the density
of gold (which is very high) being much greater than that of the sand and other particulates
. It therefore settles to the bottom of the pan.
Today, more often than not, gold is extracted
from ores. These ores often contain relatively little gold. Some of these processes cause environmental
concern. The ore is crushed to a powder so as to expose the small gold particles. These are dissolved by treatment of the rock
with cyanide solution in air. The result of this is a gold cyanide complex. Addition of zinc powder to the resulting solution precipitates
out the gold.
4Au + 8NaCN + O2 + 2H2O 4NaAu(CN)2
+ Zn 2NaCN + Zn(CN)2 + Au (s)