Nitrate ions are not oxidizing under alkaline conditions. In this case, a metathesis reaction occurs, and the product is barium sulfite precipitated and sodium nitrate. When hydrogen ions are present in the solution, the hydrogen ions will combine with the nitrate to form nitric acid and become oxidizing, in which case the sulfite will be oxidized to sulfate. In the presence of hydrogen ions, nitrate is unstable. With the combination of hydrogen ions and nitrate, the stability of nitrate is rapidly broken, and then the highly active oxygen is decomposed under the induction of sulfite. An atom that oxidizes sulfite to sulfate.