Question

What happen when iron is added to fuming nitric acid?

Answer 1

Reacting iron powder with dilute nitric acid will produce Iron III Nitrate, nitrous oxide & water (the nitric acid oxidising the iron to the Fe3+ cation). The reaction proceeds slowly.

Fe + 4 HNO3 → Fe(NO3)3) + NO + 2H2O

Concentrated nitric acid renders the iron passive though - a small amount of Fe2O3 is formed and coats the metal, but that cannot be oxidised any further and the reaction then stops.