Why freshly prepared FeSO4 subjected NO2 gives brown black colour?

Answer 1

When freshly prepared FeSO4 is subjected to NO2, a reaction occurs where the iron(II) ions in FeSO4 are oxidized to iron(III) ions. This oxidation reaction results in the formation of a complex between iron(III) ions and NO2, which is responsible for the brown-black color observed. The complex formed absorbs certain wavelengths of light, leading to the perception of the brown-black color.

Answer 2

When freshly prepared FeSO4 is exposed to NO2 gas, it forms a complex compound known as iron(II) nitrate. This complex has a characteristic brown-black color due to the formation of iron(II) nitrate-Nitrogen dioxide complex. The color change is a result of the interaction between the iron ions and the NO2 gas, leading to the formation of this colored compound.

Answer 3

Brown ring test:

NO2- + H+ = NO

NO + FeSO4 = [Fe(NO)]SO4