What is the Test for Ammonium Ions is an interesting question in the field of chemistry. It can be answered in the following manner. There are various qualitative methods to identify ammonium ions. The easiest method is reacting with sodium hydroxide to evolve ammonia gas. There are different methods to identify ammonia gas. This article explains those methods in detail. Ammonia is a complex forming agent with metal ions; metal complexes give a characteristic colouration to the reaction mixture. These reactions can be used to identify ammonium ions. In some cases, ammonium ions form precipitates with some of the chemical reagents. Ammonium ions can act as an oxidizing agent and reducing agent. Therefore, it involves in so many chemical reactions. Some of these reactions involved formation of precipitates, changes in colour in the reaction and evolution of gases. They are used as tests to identify ammonium ions. Moreover, there are some sensitive methods to identify ammonium ions. These methods allow to identify ammonium ions even if they are present in trace quantities.
Test for ammonium ions
1. Sodium hydroxide solution
Ammonia gas is evolved when warming. There are few ways to identify the evolved gas.
NH4+ + OH- —> NH3 (g) + H2O
• By its characteristic odor: Smelling the odor of the vapour cautiously, removing the test tube from the flame.
• By a glass rod moistened with concentrated Hydrochloric acid is held in the vapour forms the white fumes of ammonium chloride.
NH3(g)+ HCl —> NH4Cl(g)
(White fume)
• By its ability to turn filter paper moistened with mercury(I) nitrate to black. In this test, a mixture of mercury(II)amidonitrate (white) and mercury (black) precipitates is formed.
2NH3+ Hg22++ NO3– —> Hg(NH3)NO3(s) + Hg + NH4+
(White) (Black)
• By its ability to change moistened red litmus paper to blue or turmeric paper brown.
• By a filter paper moistened with a solution of manganese (II) chloride and Hydrogen peroxide gives a brown colour. This is due to the oxidation of Manganese(II) to Manganese(IV) oxide by alkaline solution formed.
2NH3 +Mn2++ H2O2+ H2O —> 2NH4++ MnO(OH)2(s)
(Brown)
2. Sodium hexanitritocobaltate (III)
When an ammonium solution is treated with Sodium hexanitritocobaltate (III), (Na3[Co(NO2)6], it gives a yellow precipitate of ammonium hexanitrocobaltate. This is similar to that produced with potassium ions.
3NH4+ + [Co(NO2)6]3- —> (NH4)3[Co(NO2)6] (s)
(Yellow)
3. Perchloric acid or sodium perchlorate solution
No precipitate is formed with ammonium ions. This test is a distinction from potassium ions.
4. Nessler’s reagent: alkaline solution of potassium tetraiodomercurate(II)
In the presence of ammonium ions with Nessler’s reagent, it forms a precipitate of mercury (II) amido-iodide. The colour of the precipitate varies from yellow to brown, depending on the quantity of ammonium ions.
NH4+ + 2[HgI4]2-+ 4OH– —> HgO. Hg(NH2I (s) +7I– +3H2O
(Yellow or brown)
This test can be used to identify traces of ammonia present in the drinking water.
**Note:All metals except sodium or potassium must be absent to carry out this test.
5. P-Nitrobenzene-diazonium chloride reagent
This reagent yields a red colouration with an ammonium salt in the presence of sodium hydroxide solution.
6. Hexachloraplatinic(IV) acid: H2[PtCl6]
With this reagent a yellow precipitate of ammonium hexachloplatinate(IV) is formed.
2NH4+ + [PtCl6]2- —> (NH4)2[PtCl6](s)
(Yellow)
The characteristics of this precipitate are similar to that is formed with potassium salt. However, can be distinguished by decomposing with sodium hydroxide, with the evolution of ammonia gas when warming.
7. Tannic acid – silver nitrate test
The chemistry behind this test is the reduction of tannic acid upon the silver ammine complex [Ag(NH3)2]+, to yield black silver. In here silver precipitates in the presence of ammonia, but not from a slightly acidic silver nitrate solution.
Procedure:Mix two drops of 5% tannic acid solution with two drops of 20% silver nitrate solution. Place the mixture upon drop reaction paper (or upon a little cotton wool). Hold the paper in the vapour produced by heating an ammonium salt with sodium hydroxide solution.
A black stain formed on the paper (or upon the cotton wool).
**Note:This test is a sensitive one.
What is the Test for Ammonium Ions – Summary
All ammonium salts decompose to ammonia upon heating. The evolved gas of ammonia has a characteristic smell, turns the moistened red litmus blue and changes the universal litmus paper into blue. These qualitative observations can be used as an identification test method for ammonia. Ammonium salts form coloured metal complexes with some of the d -block elements. These chemical reactions used to identify ammonium ions in an unknown mixture. Ammonium ions involve in many redox reactions, including the formation of precipitates and changes in colour. Reactions that involve in visual observations are used as test methods to identify ammonium ions.
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