Nitric acid: oxidation-reduction reactions
Reaction with copper
Copper turnings...
..are treated with concentrated nitric acid.
A reaction starts..
A colourless gas ( NO ) is produced..
..and introduced in a glass cylinder.
NO gas is put in contact with air..
It reacts with oxigen to give a brown gas (NO2).
The solution is poured into a watch glass.
During evaporation blue crystals appear.
Copper turnings...
$Cu$ $-$ $2e^-$ $\longrightarrow$ $Cu^{2+}$
$HNO_3$ $+$ $3e^-$ $+$ $3H^+$ $\longrightarrow$ $NO$ $+$ $2H_2O$
$3Cu$ $+$ $2HNO_3$ $+$ $6H^+$ $\longrightarrow$ $3Cu^{2+}$ $+$ $2NO$ $+$ $H_2O$
$2NO$ $+$ $O_2$ $\longrightarrow$ $2NO_2$
