Ammonium Nitrate (NH₄NO₃)

What is Ammonium Nitrate?

Ammonium nitrate is an ionic salt made up of the ammonium cation (NH₄)⁺ and the nitrate anion (NO₃)^–. The chemical formula of this compound is NH₄NO₃.

Since Ammonium Nitrate contains half of the nitrogen (N) in the nitrate form and half in the ammonium form, ammonium nitrate is a widely used fertiliser. The nitrate form is easily transported to the roots with the help of soil moisture and is thus instantly available for plant absorption.

Table of Contents

• Structure of Ammonium Nitrate – NH₄NO₃
• Preparation of Ammonium Nitrate – NH₄NO₃
• Properties of Ammonium Nitrate
• Uses of Ammonium Nitrate
• FAQs

Structure of Ammonium Nitrate

This compound features an ionic bond between an ammonium ion and a nitrate ion. The structure of an NH4NO3 molecule is illustrated below.

The pi electrons in the nitrate ion are delocalized due to resonance. The net charge on this ion is -1 (since the nitrogen atom holds a charge of +1 and each oxygen atom holds a charge of -⅔). Therefore, only one NH4+ ion can form an ionic bond with one NO3– ion.

Chemical Data

Preparation of Ammonium Nitrate

Ammonium nitrate readily dissolves in water by dissociating into its constituent ions. This salt is acidic in nature since it is derived from a weak base (NH3) and a strong acid (HNO3).

NH₄NO₃ can be prepared from the acid-base reaction between nitric acid and ammonia, described by the following chemical equation:

NH₃ + HNO₃ → NH₄NO₃

This reaction is highly exothermic and proceeds violently. Ammonium nitrate is also known for its oxidizing powers. It is widely used in many explosives used in the mining and construction sectors. NH₄NO₃ is also one of the key components of ANFO, one of the most popular choices of industrial explosives.

Ammonium Nitrate Properties

Physical Properties

• Ammonium nitrate is a crystalline solid having a white/grey colour.
• It has a trigonal crystal structure.
• It is quite soluble in water; its solubility at 20^oC is 150g/100ml. The solubility increases to 1024g/100ml when the temperature is raised to 100o
• The dissolution of NH₄NO₃ in H₂O is highly endothermic.
• This compound has very low shock and friction sensitivities.

Chemical Properties

• When NH₄NO₃ is reacted with the hydroxides of alkali metals, the nitrates of alkali metals are formed along with ammonia.
• Upon heating, this compound decomposes to form nitrous oxide (N₂O) and water.
• When exploded, this compound yields N₂, O₂, and water as the byproducts.
• Despite being a component of many explosives, ammonium nitrate is not an explosive by itself. It must be mixed with a primary explosive such as an azide to form an explosive mixture.

Ammonium Nitrate as Fertilizer

Since nitrogen is an essential component of both the NH₄ (ammonium) and NO3 (nitrate) components of the molecule, ammonium nitrate is a widely used fertiliser. In addition to plants being able to absorb nitrogen directly from the molecule in its nitrate form, soil microorganisms can also progressively change the ammonium part of the complex into nitrate. Due to these advantages, ammonium nitrate is a preferred nitrate source for plant nutrition by many vegetable farmers. Ammonium nitrate is used by animal farmers for fertilising pasture and hay since urea-based fertilisers have a tendency to volatilize from the soil before the plants can absorb them. Additionally, it is very soluble, making it a good choice for irrigation systems.

Uses of Ammonium Nitrate

Some important applications of this ionic salt are listed below.

• NH4NO3 is a key component of many fertilizers since it is quite rich in nitrogen (34%).
• Another advantage of this compound is that it doesn’t lose its nitrogen to the atmosphere, as is the case with urea.
• When mixed with fuel oil, it forms an explosive known as ANFO, which is one of the most popular industrial explosives.
• The dissolution of this compound in water is quite endothermic, making it an ideal choice of material in instant cold packs.
• It is also used in the mining and construction industry as a component of explosives.

Despite its numerous applications, the use of this compound is being slowly phased out by the governments of many countries due to its scope for misuse. Ammonium nitrate was one of the key ingredients of the explosives that were used in the 2011 Delhi bombings and the 2013 blasts in Hyderabad.

To learn about other ionic compounds of the nitrate anion, such as potassium nitrate, register with BYJU’S and download the mobile application on your smartphone.