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Chemistry

State why aqua regia dissolves gold, which is insoluble in all other acids.

Hydrogen Chloride

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Answer

Aqua regia : 1 part of conc. HNO3 and 3 parts of conc. HCl

Nitric acid present in aqua regia oxidizes HCl to chlorine.

HNO3 + 3HCl ⟶ NOCl + 2H2O + 2[Cl] [nascent chlorine]

This nascent chlorine reacts with noble metals like gold forming the corresponding soluble chloride.

Au + 3[Cl] ⟶ AuCl3 [Gold (III) Chloride]

Hence, aqua regia dissolves noble metals like gold and platinum which are insoluble in all other acids.

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