Testing NO₃^- ion | Identify NO₃^- (Nitrate) ions

Every metal nitrate (NO₃^-) compounds dissolve in the water. Therefore, it is easy to make aqueous solution of nitrate ions. There are some tests such as brown ring test, Al + NaOH, Devarda's alloy test to identify NO₃^- ion. Examples of testing NO₃^- ions are explained in detail in this tutorial.

Brown Ring Test

First the ion solution is taken into the test tube. Then newly made FeSO₄ {iron(ii)sulphate(vi)} solution is added into the solution. After that concentrated H₂SO₄ is added slowly and carefully along the wall of the tube. Then a brown ring occurs where the both solutions contact.

The reactions happen here as follows.

Special Notes:

Note 1: Disturbance given by nitrite ions (NO₂^-)

Nitrite ions (NO₂^-) ions also make the brown ring. Therefore, to ensure is important that there are no NO₂^- ions in the test tube.

Note 2: Bromide (Br^-) and iodide (I^-) ions should not be in the testing tube.

Bromide (Br^-) ions make liquid bromine (Br₂) and dissolve in the solution. Then the solution is converted into a brown color. Therefore, it may be difficult to identify that the brown color occurs due to the Br^- ions or NO₃^- ions.

Iodide (I^-) ions are converted into iodine (I₂) and that iodine links with extra I^- ions in the solution. I₃^- ions are made up and they dissolve in the aqueous solution. I₃^- ions depict brown color in the test tube.

Aluminium and NaOH with nitrate ion test

First aluminium (Al) powder and NaOH solution are added into an aqueous solution which may have NO₃^- ions. Then the tube is heated. NO₃^- ions can be identified by testing of releasing ammonia (NH₃) gas.

How to identify NH₃ gas:

• Ammonia has a characteristic smell and colorless gas.
• Ammonia gas converts humid red litmus into blue color.
• Ammonia gives yellow-brown precipitate when reacts with Nessler's reagent.
• Ammonia makes NH₄Cl white fumes when reacts with HCl.

Devarda's Alloy Test

Above test is done using Devarda's alloy (Al=45%, Zn=5%, Cu=50%) except Aluminum powder.

Special Notes:

• NO₂^- ions also give ammonia gas in this test. Therefore, NO₂^- ions should not be in the test tube
• Ammonium (NH₄⁺) ions emit ammonia gas in this test. Therefore, NH₄⁺ ions should not be in the test tube.