Describe a test that a student could carry out to show the presence of nitrate ions in a solution of a sample?
Answer:
Nitrate is almost impossible to test for with a single test unless it is the only anion present and the solution is not colored. If it is the only thing present,
1. Add the sample to a test tube.
2. Add 10 drops of 18M sulfuric acid. Mix thoroughly and cool.
3. Carefully add 3-4 drops of 0.2M FeSO4 so it floats on top of the rest of the solution.
4. Allow to stand for 1-2 minutes.
5. A brown color at the junction of the solutions shows the presence of nitrate.
The major inteferences are bromides, iodides, and chromates, other colors.
Instrumental methods include ion chromatography and ion selective electrodes. These require specialized equipment.
In wastewater, it is normally done by reducing the nitrate to nitrite with cadmium, complexing it to get a colored solutions, and running standard curves by visible spectrophotometry. This test is not simple and also requires advanced instruments to do properly. A web search for "cadmium reduction" and nitrate will find you the detailed procedure.
The test for nitrateion can be done by 2 ways. the test solution should be first testedfor the presence of nitrite ion.if the solution tested negetive then reduce the nitrate solution to nitrite by using Zn(dust) then add dilute HCl and aniline then pour the mixture to beta naphthol.A red dye confirms the presence of nitrate.Nitrates also liberate reddish brown NO2 when treated with Cu turningsand concentrated sulphuric acid only and not with dilute sulphuric acid(distinction from Nitrites).
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