Testing Ammonium Salts and Ammonium Cation

There are lot of ammonium compounds in this planet and ammonium cation has the chemical formula of NH4+. There are tests to identify ammonium cation from other cations. As an example, Ammonium salts release ammonia gas when heated with aqueous alkali solutions like NaOH. Ammonium chloride can be tested by aqueous NaOH solution. In this tutorial, we will study how ammonium salts are identified from other salts or compounds.


Content

  • Testings to identify ammonium salts by experiments
    • Reaction of aqueous strong base and an ammonium salt
    • Decomposition of ammonium salt compounds
  • Example and examination questions for ammonium salt identification


Testings to identify ammonium salts by experiments

There are lot of ways to test and identify ammonium cation and we are going to look one by one in this tutorial.

  • Reaction of aqueous strong base and an ammonium salt
  • Decomposition of ammonium salt compounds
    • Ammonium nitrate (NH4NO3)
    • Ammonium nitrite (NH4NO2)
    • Ammonium hydroxide (NH4OH)
    • Ammonium sulfate ((NH4)2SO4 )
    • Ammonium phosphate ((NH4)3PO4)
    • Ammonium carbonate ((NH4)2CO3)
    • Ammonium dichromate ( (NH4)2Cr2O7
    • Heating ammonium chloride and potassium dichromate mixture
    • Ammonium perchlorate (NH4ClO4)
    • Ammonium halides (NH4Cl, NH4Br, NH4I)


Test 01: Add aqueous strong base to compounds contains ammonium cation

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.

NH4Cl + NaOH → NH3 + NaCl + H2O

NH4NO3 + NaOH → NH3 + NaNO3 + H2O



Mechanism of ammonium salt and aqueous strong base reaction

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.

Ammonium salts and hydroxides reaction mechanism

Decomposition of ammonium salt compounds

In this section we will see how ammonium salt are decomposed under heating.



Heating ammonium nitrate (NH4NO3)

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


Heating ammonium nitrite (NH4NO2)

Nitrogen (N2) gas and water are produced when ammonium nitrite is heated.

NH4NO2 → N2 + H2O


Decomposition of ammonium hydroxide (NH4OH)

When ammonium hydroxide (NH4OH) is heated, it decomposes to NH3(g) and H2O(g).

NH4OH → NH3 + H2O


Heating ammonium sulfate

When ammonium sulfate ( (NH4)2SO4) is heated, it decomposes to ammonia gas molecules and sulfuric acid molecules.

(NH4)2SO4 → NH3 + H2SO4


Decomposition of ammonium phosphate

Ammonia and H3PO4(g) are produced due to the decomposition of ammonium phosphate ( (NH4)3PO4 ).

(NH4)3PO4 → NH3 + H3PO4



Heating ammonium carbonate

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


Decomposition of ammonium dichromate

Ammonium dichromate ( (NH4)2Cr2O7 ) will decompose into nitrogen (N2) gas, chromium oxide ( Cr2O3 ) and water. Chromium oxide is green colour and it is an amphoteric oxide.

(NH4)2Cr2O7 → N2 + Cr2O3 + H2O


Heating a mixture of ammonium chloride and potassium dichromate

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



Heating ammonium perchlorate

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


Decomposition of ammonium halides

Now we are going discuss decomposition of halides ( Cl- , Br- , I- ) of ammonium cation.


Decomposition of ammonium iodide (NH4I)

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 (NH4Br)

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 (NH4Cl)

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



Example and examination questions for ammonium salt identification


Identify ammonium chloride and Sodium chloride? Both compounds exist as solids. Give testing steps in detail.

  1. Add both solids separately to two distilled water containers.
  2. Then add aqueous NaOH solution to both solutions and heat each solution.
  3. Do ammonia gas testings for both containers.
  4. You can see positive signs of ammonia gas presence for one container. As we studied earlier, that container should have the ammonium chloride solution.





Have Questions?



How do I identify ammonium chloride and sodium chloride?

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.



How to identify ammonium sulfate and ammonium phosphate?

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.



Colour of product when NH4NO3 is heated?

When NH4NO3 is heated, it decomposes to N2O and H2O. N2O is colourless. No colourful product is given in this reaction.



How to identify ammonium carbonate and ammonium nitrate ?

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.


Write chemical reaction of ammonium salt with a known alkali

Ammonium salt reacts with alkali and release ammonia gas. As alkalis, NaOH, KOH, Ba(OH)2can be used.

NH4Cl + NaOH → NH3 + NaCl + H2O


Green colour product that gives as a result when ammonium salt heats?

Ammonium dichromate gives a green colour Cr2O3 when heating.




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