# Chemistry of Gold

On average, a million tons of earth contain just ten pounds of gold. This scarcity, as well as its beauty and chemical properties account for its high value from ancient times. The name for the element is of Anglo-Saxon origin and the symbol comes from the Latin aurum, meaning "shining dawn".

Gold metal has a distinctive yellow color and is incredibly malleable and ductile. A single ounce of pure gold can be beaten out to a sheet that is about 300 feet square!! Pure gold is easily cut with a knife. Few elements react with gold under normal conditions and so most gold is recovered as small flakes of the pure element.

Gold is a very good conductor and is often used to plate electrical contacts since it resists corrosion so well. It also is a good reflector of heat-carrying infra-red radiation.

The world's oceans contain billions of tons of gold but it is too widely dispersed to be recovered (two-tenths of an ounce per million tons of water).

Gold will not react with either $$H_2SO_{4(aq)}$$ or $$HNO_{3(aq)}$$, rather it will react with what is called aqua regia, which is one part $$HNO_3$$ and three parts $$HCl$$. For example,

$Au_{(s)} + 4H^+_{(aq)} + NO^-_{3(aq)} + 4Cl^-_{(aq)} \rightarrow [AuCl_4]^-_{(aq)} + 2H_2O_{(l)} + NO_{(g)}$

Note: The group 11 metals do not react with hydrochloric acid.

## References

• Kebbekus, Barbara B. "A Chemical-Medical Mystery: Gold Jewelry and Black Marks on Skin." J. Chem. Educ. 2000, 77, 1298.

## Contributors

Stephen R. Marsden (ChemTopics)