Gold

Gold, Au, is a soft yellow malleable transition metal element, found in Group Ib of the periodic table.

Atomic Number : 79
Relative Atomic Mass : 197
Melting Point : 1064 degC
Boiling Point : 2807 degC
Relative Density : 19.32

Discovery

Gold was known from ancient times, and it was probably used as money.

Occurrence

Gold is very widely distributed in nature at concentrations too low for it to be extracted profitably. It is found

in Quartz veins as "Reef Gold" and
on alluvial gravels as "Alluvial Gold".

Gold has been found as large nuggets in California.

Extraction

Gold is extracted from other matter by "Panning" when it is present as free particles.

Gold is extracted from crushed gold-bearing quartz by forming a complex with sodium cyanide.
4 Au + 8 NaCN + H2O + O2
==> 4 NaOH + 4 NaAu(CN)2

The gold is subsequently recovered from the complex by precipitation with zinc dust.
NaAu(CN)2 + Zn ==> Na2Zn(CN)2 + 2 Au

Preparation

Manufacture

Properties

Gold is

a bright lustrous metal which has a characteristic yellow colouration,
highly malleable and ductile (extremely thin sheets have been made),
an excellent conductor of heat and electricity.

Reactions

Gold is stable and not oxidised in air.

Gold is not attacked by nitric acid, sulphuric acid, or hydrochloric acid.

Gold is attacked by boiling ferric chloride solution.

Uses

Gold is the standard for the world's currency.

Gold is widely used in jewellery, where it is used in admixture with other metals, usually copper. Pure Gold is 24-Carat.

Detection and Analysis

Gold is detected in solution by the addition of a dilute solution of stannous chloride when a precipitate of colloidal gold is formed, which has a characteristic colouration of "Purple of Cassius".

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