Suppose that a solution is tested for NO2 ion by adding 3M H2SO4 and heating, repeating this process until no further reaction occurs. This solution
is then analyzed for NO3 ion by adding FeSO4 solution and more H2SO4, heating the test tube and its contents. The NO3 ion reaction is positive. In this case, is it accurate to state that NO3 ion was present in the original solution? Briefly explain. Write appropriate equations to support your answer.

The correct equation will be "[Fe(H2O)5]²⁺ + NO → Fe(H2O)5NO]²+ (brown ring) ".

Explanation:

For NO₂, the addition of H₂SO₄ forms HNO₂ comprising NO gas as well as HNO₂, the equation will be:

⇒  NO₂⁻ + 2H⁺ →  HNO2

⇒  HNO₂ + H₂O + H⁺  →  HNO₃ + NO

For NO₃⁻,

NO₃⁻, Fe₂+ oxidized to Fe₃ + then releases NO gas in the existence of H₂SO₄

⇒  3Fe₂⁺ + 4H⁺ + NO₃⁻  →  3Fe₃⁺ + NO + 2H₂O

Brown ring forming establishes NO3- presence in the initial test sample,

⇒  [Fe(H2O)5]²⁺ + NO  →  Fe(H2O)5NO]²+ (brown ring)