In natural water and waste water, the forms of nitrogen of greatest interest are nitrate, nitrite, a — Organic Chemistry Chemistry Question

In natural water and waste water, the forms of nitrogen of greatest interest are nitrate, nitrite, ammonia, and organic nitrogen. All these forms of nitrogen, as well as nitrogen gas, are biochemically interconvertible and are components of the nitrogen cycle. The macro Kjeldahl method, in combination with a titration method, is often used in the determination of organic nitrogen in wastewater. In the first step, H₂SO₄, K₂SO₄, and HgSO₄ are added to the sample solution. After digestion, the solution is neutralized by the addition of concentrated NaOH. The gas liberated by the treatment is then distilled into a solution of excess boric acid and the latter subsequently titrated with 0.01 M^-H₂SO₄.

Nitrite is known to cause the illness methemoglobinemia in infants. In the laboratory, nitrite can be determined by a colorimetric method. The method requires the preparation of a series of standard nitrite solutions. However, nitrite is readily oxidized in the presence of moisture and hence standardization of the stock nitrite solution is required in order to achieve high accuracy in the subsequent analysis. The standardization is carried out by adding a known excess of standard KMnO₄ solution and H₂SO₄ solution are added into the nitrite stock solution. The purple color of the solution due to the presence of excess permanganate was subsequently discharged by the addition of a known quantity of Na₂C₂O₄ and the mixture back titrated with standard permanganate solution.