conc.HNO3

Fe3+ will be formed eventually

NO3- + 2H+ + e- -->NO2 + H2O Ecell = +0.8V
Fe-->Fe2+ + 2e- Ecell = -0.44V
Fe + 4HNO3-->Fe(NO3)2 + 2NO2 + 2H2O
Ecell = +0.8-(-0.44)=+1.24V

NO3- + 4H+ + 3e- -->NO + 2H2O Ecell = +0.96V
Fe2+ -->Fe3+ + e- Ecell = +0.77V
3Fe(NO3)2 + 4HNO3-->3Fe(NO3)3 + NO + 2H2O
Ecell = +0.96-0.77=+0.19V

Since concentrated nitric acid is a strong oxidizing agent.

It will oxidize iron into iron (III) directly and give brown nitrogen dioxide gas.


Equation:

Fe (s) + 6HNO3 (aq) ---} Fe(NO3)3 (aq) + 3NO2 (g) + 3H2O (l)



More-to-know:

Dilute nitric acid and concentrated sulphuric acid also perform similar reactions.





Hope my explanations help.

it oxidize iron to iron(ll)
NO3^ - + 2H^+ + e^ - →NO2 +H2O
Fe → Fe^2+ + 2e^ -

4HNO3 +Fe → 2NO2 + 2H20 + Fe(NO3)2