✔ 最佳答案
Case I: NO is formed when adding the solution of an iron(II) salt to concentrated nitric acid
The solution contains water. When the solution is added to the concentrated HNO3, the concentrated HNO3 is diluted to become moderately concentrated HNO3 or even dilute HNO3. When moderately concentrated HNO3 or dilute HNO3 acts as an oxidizing agent, nitrogen monoxide gas (NO) is formed.
Half equations:
Fe2+(aq) → Fe3+(aq) + e-
4H+(aq) + NO3-(aq) + 3e- → 2H2O(l) + NO(g)
Overall equation:
3Fe2+(aq) + 4H+(aq) + NO3-(aq) → 3Fe3+(aq) + 2H2O(l) + NO(g)
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Case II: NO2 is formed when adding the solid of an iron(II) salt to concentrated nitric acid
When the solid is added to the concentrated HNO3, the solid is dissolved in the water (solvent) of the concentrated HNO3. This does not affect the concentration of the acid, and it is still concentrated HNO3. When concentrated HNO3 acts as an oxidizing agent, nitrogen dioxide gas (NO2) is formed.
Half equations:
Fe2+(aq) → Fe3+(aq) + e-
2H+(aq) + NO3-(aq) + e- → H2O(l) + NO2(g)
Overall equation:
Fe2+(aq) + 2H+(aq) + NO3-(aq) → Fe3+(aq) + H2O(l) + NO2(g)
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