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.

Written by: R. Sasini Manoja Perera, (undergraduate), last modified: 30/05/2021

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.

Brown Ring Test equation

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.

Brown Ring Test disturbance due to bromide ions Br-

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.

Brown Ring Test disturbance due to iodide ions I-

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.

Al powder, NaOH, NO3- ion test

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.

Devardas Alloy Test for NO3- ion

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.