Nitric acid: oxidation-reduction reactions
Reaction with gold
A gold leaf is introduced in a a mixture of nitric and chlorhydric acid (aqua regia)...
A reaction starts.
Gold is "dissolved" (transformed to a soluble salt)
The solution is poured on a watch glass.
During evaporation yellow crystals appear.
A gold leaf is introduced in a a mixture of nitric and chlorhydric acid (aqua regia)...
$Au$ $-$ $3e^-$ $+$ $4Cl^-$ $\longrightarrow$ $AuCl_4^-$
$HNO_3$ $+$ $3e^-$ $+$ $3H^+$ $\longrightarrow$ $NO$ $+$ $2H_2O$
$Au$ $+$ $HNO_3$ $ +$ $4Cl^-$ $+$ $3H^+$ $\longrightarrow$ $AuCl_4^-$ $+$ $NO$ $+$ $2H_2O$
