Chemistry - Gold

Introduction

• Gold is a bright, reddish yellow, soft, dense, malleable, and ductile metal naturally found in the earth’s crust.

• The symbol of gold is ‘Au’ and atomic number is ‘79.’

• Gold is (chemically) a transition metal and belongs to group 11 of the periodic table.

Salient Features of Gold

• Gold, which remains in a solid state under standard conditions, is the least reactive element.

• Gold is resistant to most of the acids.

• Gold does dissolve in aqua regia; aqua regia is a mixture of nitric acid and hydrochloric acid.

• However, gold is insoluble in nitric acid.

• Gold usually dissolves in alkaline solutions of cyanide.

• Cyanide solutions are commonly used in mining and electroplating.

• Gold also dissolves in mercury and forms ‘amalgam alloys.’

• Gold does not react with oxygen at any temperature.

Occurrence of Gold

• Gold commonly occurs as a free element i.e. in the natural form.

• Gold occurs as nuggets or else found in in rocks, grains, in veins, and in some other alluvial deposits.

• Gold also occurs in a solid solution forms with the native element such as silver (as electrum).

• At some places, gold also naturally alloyed with copper and palladium.

Alloys of Gold

• Following are the major alloys of gold −

  • Colored gold

  • Crown gold

  • Electrum

  • Rose gold

  • Tumbaga

  • White gold

Compounds of Gold

• Following are the major compounds of the gold −

  • Gold (III) chloride - AuCl₃

  • Gold (I) chloride - AuCl

  • Cyanide - CN

  • Chloroauric acid - HAuCl₄

  • Gold (III) oxide - Au₂O₃

  • Gold bromide - AuBr

  • Aqua regia - HNO₃+3HCl

  • Gold bromide - AuBr₃

  • Gold (III) hydroxide - AuH₃O₃

  • Gold fluoride - AuF₃

  • Gold (V) fluoride - AuF₅

  • Gold sulfide - Au₂S

  • Fulminating gold

  • Gold salts

  • Gold heptafluoride

Uses of Gold

• Gold is one of the oldest elements that human being have been using for thousands of years.

• As it is highly precious and provides a beautiful look, hence it is characteristically used in making ornaments.

• As per the recent trend (of the world), about 50% gold is used in making jewelry, 40% used in investments, and remaining 10% is used in industry.