# Conc.HNO3 can be transported in aluminium containers.Explain why?

Oct 1, 2016

The position of Al in the Elechtro-chemical series shows that Al is stronger reducing agent than Hydrogen. When Al metal is added to dilute $H N {O}_{3}$containing higher concentration of ${H}^{+}$ ions, it reduces the ${H}^{+}$ ions in the solution to hydrogen gas and itself gets oxidized to $A l {\left(N {O}_{3}\right)}_{3}$

$2 A l \left(s\right) + 6 H N {O}_{3} \left(\mathrm{di} l\right) \to 2 A l {\left(N {O}_{3}\right)}_{3} + 3 {H}_{2} \uparrow$

But when Al is dipped in conc . $H N {O}_{3}$ where the concentration of ${H}^{+}$ ions is very low, it reduces Nitrogen of $H \stackrel{+ 5}{N} {O}_{3}$ molecule to $N {O}_{2}$and itself gets oxidized to $A {l}_{2} {O}_{3}$ which forms very thin invisible protective layer on the metal. It then resists further oxidation of Al atom below the protective layer of $A {l}_{2} {O}_{3}$.

This occurs when concentrated $H N {O}_{3}$ is kept in Aluminium container and makes transportation of conc. $H N {O}_{3}$ in Aluminium container possible.

The equation of possible oxidation reaction occurred during formation of the protective layer of $A {l}_{2} {O}_{3}$

$2 A l \left(s\right) + 6 H N {O}_{3} \left(c o n c\right) \to A {l}_{2} {O}_{3} \left(s\right) + 6 N {O}_{2} \left(g\right) + 3 {H}_{2} O \left(l\right)$