(i) Reaction of HNO₃ with copper:

(A) With not and concentrated HNO₃, copper react of give nitrogen peroxide, copper nitrate and water

Cu + 4HNO₃ → Cu(NO)₃ + 2NO₂ + H₂O

(B) With 50% concentrated nitric acid copper reacts to give copper nitrate, nitric oxide and water

3Cu + 8HNO₃ → Cu(NO₃)₂.2NO + 4H₂O

(C) With 20 - 25% dilute. HNO₃ copper reacts to give copper nitrate, nitrous oxides and water.

4Cu + 10NHO₃ → 4Cu(NO₃)₂ + N₂O

(D) On passing vapour of nitric acid on heated copper nitrogen gas and water vapour are obtained

5Cu + 2HNO₃ → 4CuO + N₂ + H₂O

(ii) Reaction of HNO₃ with Iron:

(A) With cold and dilute HNO₃ iron reacts to give ferrous nitrate and ammonium nitrate

4Fe + 10HNO₃ → NH₄NO₃ + 4Fe(NO₃)₂ + 3H₂O

(B) Hot & dill nitric acid reacts with iron and gives ferric Nitrate & No gas

2Fe + 8HNO₃ → 2Fe(NO₃)₂ + 2NO↑ + H₂O

Fe + 6HNO₃ → Fe(NO₃)₂ + 3NO₂ + 3H₂O

(C) With hot and conc. HNO₃ Iron reacts to give ferric nitrate and nitrogen dioxide gas.

Fe + 6HNO₃ → Fe(NO₃)₂ + 3NO₂ + 3H₂O