There are lot of ammonium compounds in this planet and ammonium cation has the chemical formula of NH4+. In this tutorial, ammonium salts and ammonia testing experiments, reactions and characteristics are discussed. As an example, some ammonium compounds can release ammonia gas when those relevant compounds are heated.
There are lot of ways to test and identify ammonium cation and we are going to look one by one in this tutorial.
Add aqueous strong base to any ammonium salt and heat the mixture. Ammonia gas will be released and there are several tests to identify ammonia gas. some of them are explained in detail in the below of this tutorial. But, notice that never try to smell the odour of ammonia gas because ammonia is highly toxic gas can harm humans as a ammonia testing method.
Several examples with chemically balanced equations are given below.
Hydrogen atoms in NH4+ ion molecule are positively charged because electronegativity of nitrogen atom is higher than hydrogen. In OH- ion, electron density around O atom is high. So, that electrons around oxygen atom in OH- attacks a hydrogen atom (positively charged) of NH4+ ion. As a result, one N-H bond breaks and form NH3 molecule and H2O molecule as products.
In this section we will see how ammonium salt are decomposed under heating.
Nitrous oxide (N2O) and water are formed as products when ammonium nitrate is heated. Nitrous oxide is one of the oxide of nitrogen and also it is a gas at room temperature.
NH4NO3 → N2O + H2O
NH4NO2 → N2 + H2O
When ammonium hydroxide (NH4OH) is heated, it decomposes to NH3(g) and H2O(g).
NH4OH → NH3 + H2O
When ammonium sulfate ( (NH4)2SO4) is heated, it decomposes to ammonia gas molecules and sulfuric acid molecules.
(NH4)2SO4 → NH3 + H2SO4
Ammonia and H3PO4(g) are produced due to the decomposition of ammonium phosphate ( (NH4)3PO4 ).
(NH4)3PO4 → NH3 + H3PO4
When ammonium carbonate ( (NH4)2CO3 ) is heated, it decomposes to ammonia, carbon dioxide and water. Ammonium carbonate is a solid compound. But all products are in gaseous phase and you cannot see a solid after the complete decomposition of ammonium carbonate.
(NH4)2CO3 → NH3 + CO2 + H2O
(NH4)2Cr2O7 → N2 + Cr2O3 + H2O
Heating a mixture of ammonium chloride and potassium dichromate also gives nitrogen (N2) gas, chromium oxide ( Cr2O3 ) and water as products as early reaction.
NH4Cl + K2Cr2O7 → N2 + Cr2O3 + H2O
When ammonium perchlorate (NH4ClO4) is heated above 2000C, it decomposes to nitrogen (N2) gas, chlorine (Cl2) gas, oxygen (O2) gas and water.
NH4ClO4 → N2 + Cl2 + O2 + H2O
Now we are going discuss decomposition halides ( Cl- , Br- , I- ) of ammonium ion.
Decomposition of ammonium iodide give ammonia and hydrogen iodide (HI). But hydrogen iodide is not stable to heat. Therefore, under heating hydrogen iodide readily decomposes to hydrogen gas (H2) and iodine (I2) vapor. I2 is a purple colour vapor.
NH4I → NH3 + HI
HI → H2 + I2
Decomposition of ammonium bromide gives ammonia and hydrogen bromide (HBr). But HBr is not stable to heat. Therefore, under furthermore heating HBr readily decomposes to H2 and Br2 gases. Br2 is a brown colour gas.
NH4Br → NH3 + HBr
HBr → H2 + Br2
Decomposition of ammonium chloride give NH3 and HCl. HCl is stable to heat and does not decompose furthermore like HBr an HI.
NH4Cl → NH3 + HCl
The difference in two compounds is cations. Just you have to do a simple test of adding strong base to two compounds. In one compound, you can observe a gas emission and it is related to ammonium chloride. There is no, specific observation in sodium chloride. Like that, you can identify ammonium ion and sodium ion.
Because anions of both compounds are different, we can do a sulfate ion testings and phosphate ion testing. Add aqueous NaOH to both solutions. It will give sodium sulfate and sodium phosphate solutions. Then, add magnesium nitrate solutions to sodium sulfate and sodium phosphate solutions. The one which gives a precipitate with magnesium nitrate is identified as relavnt to ammonium phosphate.
When NH4NO3 is heated, it decomposes to N2O and H2O. N2O is colourless. No colourful product is given in this reaction.
Both compounds have ammonium ion.
Add both compounds to aqueous barium chloride solution.
One compound forms a white precipitate. It is barium carbonate. That is related to the ammonium carbonate.
Ammonium salt reacts with alkali and release ammonia gas. As alkalis, NaOH, KOH, Ba(OH)2can be used.
NH4Cl + NaOH → NH3 + NaCl + H2O
Ammonium dichromate gives a green colour Cr2O3 when heating.