The ammonia formula is commonly known as the nitrogen trihydride formula or the azane formula. The formula for ammonia is \(NH3\). The molecular formula is derived from the chemical structure of ammonia, which has three hydrogen atoms and a trigonal pyramidal shape. 

On the other hand, the nitrogen atom has a single electron pair. Ammonia reacts with carbon dioxide at 200∘C200∘C and an atmospheric pressure of 200200 to produce urea. Read the article to know more about the structure and formula and the physical and chemical properties of ammonia. 

What is Ammonia?

Ammonia is the simplest inorganic base that is also an important Nitrogen sourcefor many applications. It is also known as azane or nitrogen trihydride.

Structure and Formula of Ammonia

Ammonia is a compound of Hydrogen and Nitrogen with the chemical formula \({\rm{N}}{{\rm{H}}_3}\)

Molar Mass of Ammonia

Molar mass of ammonia = Atomic mass of nitrogen \( + 3 \times \left( {{\rm{Atomic}}\,{\rm{mass}}\,{\rm{of}}\,{\rm{hydrogen}}} \right) = 14.0067\,\,{\rm{u + 3}} \times \left( {{\rm{1}}.{\rm{0078}}\,{\rm{u}}} \right){\rm{ = 17}}.{\rm{03}}\,{\rm{g/mol}}.\)

Hybridization of Ammonia

Hybrid orbitals of the Nitrogen atom \( = \) Number of atoms attached \( + \,\) Lone pairs

\( = 3\,\, + 1 = 4\)

The nitrogen atom in ammonia is \({\rm{s}}{{\rm{p}}^{\rm{3}}}\) hybridised \([1(2{\rm{s}}) + 3(2{\rm{p}}) = 4{\rm{s}}{{\rm{p}}^3}]\) This means the atomic orbitals of the nitrogen atom undergo intermixing to form \(4{\rm{s}}{{\rm{p}}^3}\) hybridised orbitals.

The \(3\) half-filled \({\rm{s}}{{\rm{p}}^{\rm{3}}}\) hybrid orbitals of Nitrogen overlap with three \(1\,{\rm{s}}\) orbitals of hydrogen atoms to form sigma bonds. The fourth \({\rm{s}}{{\rm{p}}^3}\) hybridized orbital contains the lone pair of electrons.

Molecular Geometry of Ammonia

The \({\rm{s}}{{\rm{p}}^3}\) hybrid orbitals repel each other and are directed towards four corners of a regular tetrahedron. Hence the geometry should be tetrahedral. But the bond pairs suffer repulsion from the lone pair and distort the tetrahedral geometry to trigonal pyramidal or distorted tetrahedral structure.

The nitrogen atom is at the centre and the three hydrogen atoms are from the base of the pyramid. The lone pair forms the apex of the pyramid.

Bond Angle of Ammonia

As the nitrogen atom in Ammonia is \({\rm{s}}{{\rm{p}}^3}\) hybridised, the geometry should be tetrahedral with a bond angle of \(109.5^\circ .\) But the bond pair-lone pair repulsion distorts the tetrahedral angle to \(107^\circ .\)

Dipole Moment of Ammonia

The charge separation present in a molecule of a polar covalent compound is called a dipole moment.

There are \(3\) polar \({\rm{N}}\,{\rm{ – }}\,{\rm{H}}\) bonds in ammonia molecule, each carrying a dipole moment of \(0.9\) Debyes. The resultant dipole moment is experimentally found to be \(1.46\) Debyes. This shows that the hydrogen atoms in the ammonia molecule are not aligned symmetrically with the nitrogen atoms. At the same time, the high value of dipole moment suggests the molecule to be triangular pyramidal.

Lewis Structure of Ammonia

The central nitrogen atom has five valence electrons. It needs \(3\) more electrons to complete its valence shell. Hence, three additional electrons from the hydrogen atom complete the octet of Nitrogen. Besides three bond pairs, Ammonia has only one lone pair.

Properties
Appearance	Colourless gas
Odour	strong pungent odour
Density	\(0.68\,\frac{{\rm{g}}}{{{\rm{c}}{{\rm{m}}^{\rm{3}}}}}\)
Melting Point	\(- 77.73\,^\circ {\rm{C}}\)
Boiling Point	\(- 33.34\,^\circ {\rm{C}}\)
Solubility	soluble in water, chloroform, ether, ethanol, methanol
Acidity \(({\rm{p}}{{\rm{K}}_{\rm{a}}})\)	\(32.5\)
Basicity\(({\rm{p}}{{\rm{K}}_{\rm{b}}})\)	\(4.75\)
Conjugate acid	Ammonium
Conjugate base	Amide

Occurrence of Ammonia

Naturally, it exists in the body; the kidneys secrete them to neutralize excess acid. Moreover, we can find its small amount in rainwater, volcanic areas, and even in the atmosphere. Ammonia likewise is present in the soil as ammonium salts.

Preparation of Ammonia

The preparation of ammonia are given below:

Haber’s Process

Haber’s process is the industrial method to manufacture Ammonia. In this process, Ammonia is produced by the direct mixing of Nitrogen and Hydrogen.

This reaction follows Le Chatelier’s principle and is, \(({\rm{a}})\) exothermic, \(({\rm{b}})\) reversible, and \(({\rm{c}})\) proceeds with a decrease in volume. The ideal conditions for the production of Ammonia are:

1. Low Temperature: The temperature required for the maximum yield of Ammonia for the reaction is about \(500\,^\circ {\rm{C}}.\)
2. High Pressure: In Haber’s process, a low volume favors the forward reaction. Hence, high pressure of \(200\)\( – \,900\) atmospheres supports forward reaction.
3. Catalyst: Finely divided iron-containing molybdenum or alumina is used as a catalyst. Molybdenum or alumina \({\rm{(A}}{{\rm{l}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}{\rm{)}}\) acts as a promoter to increase the efficiency of the catalyst used.

Physical Properties of Ammonia

1. Ammonia is a colorless gas.
2. It has a sharp pungent odor with a soapy taste. It brings tears to eyes.
3. It is lighter than air and thus collected by the downward displacement of air.
4. It is very soluble in water due to hydrogen bonding. Because of its high solubility, ammonia gas cannot be collected over water.

5. It melts at room temperature by applying a pressure of around \(8 – 10\) atmospheres.
6. Liquid Ammonia boils at \(239.6\,{\mkern 1mu} {\rm{K }}\left( {{\rm{ – 33}}.{\rm{5}}\,^\circ {\rm{C}}} \right)\) under one-atmosphere pressure.
7. It has a high value of the latent heat of vaporization (\(1370\,{\mkern 1mu} {\rm{J}}\) for each gram) and hence is used as a coolant in refrigerators.
8. Liquid Ammonia solidifies to a white crystalline substance at \(195.3\,{\mkern 1mu} {\rm{K}}\left( {{\rm{ – 77}}.{\rm{8}}\,^\circ {\rm{C}}} \right).\)

Chemical Properties of Ammonia

The chemical properties of ammonia are explained below:

Thermal Stability

Ammonia disintegrates into Hydrogen and Nitrogen on heating with metallic catalysts or by passing an electric current through it.

\(2{\rm{N}}{{\rm{H}}_3} \to {{\rm{N}}_2}\, + \,3{{\rm{H}}_2}\)

Combustibility

Ammonia is flammable and burns in the presence of oxygen.

\({\rm{4N}}{{\rm{H}}_3} + 3{{\rm{O}}_2} \to 2{{\rm{N}}_2}\, + \,6{{\rm{H}}_2}{\rm{O}}\)

Ammonia reacts with air in the presence of platinum-rhodium catalyst at \(800\,^\circ {\rm{C}}\)

Basic Character

Ammonia turns red litmus blue and acts as a Lewis base. It can readily donate its lone pair of electrons to the Nitrogen atom to form an ammonium ion.

The equilibrium constant at \(298\,{\rm{K}}\) for this reaction is \(1.8 \times {10^{ – 5}}.\)

Reaction with Metal Oxides

Ammonia, when heated with metal oxides, gets oxidized to Nitrogen.

\(3\,{\rm{CuO}}\,{\rm{ + }}\,{\rm{2}}\,{\rm{N}}{{\rm{H}}_3} \to \,2\,{{\rm{H}}_2}{\rm{O + }}\,{{\rm{N}}_2} + 3\,{\rm{Cu}}\)

\(3\,{\rm{PbO}}\,{\rm{ + }}\,{\rm{2}}\,{\rm{N}}{{\rm{H}}_3} \to \,2\,{{\rm{H}}_2}{\rm{O + }}\,{{\rm{N}}_2} + 3\,{\rm{Pb}}\)

Reaction with Iodine

Ammonia reacts with iodine to form a dark-coloured precipitate of Nitrogen triiodide.

\({\rm{2}}\,{\rm{N}}{{\rm{H}}_3} + 3{{\rm{I}}_2} \to \,\,{\rm{N}}{{\rm{H}}_3}{\rm{N}}{{\rm{I}}_3}{\rm{ + }}\,3\,{\rm{HI}}\)

Reaction with Carbon Dioxide :(formation of urea)

Ammonia on heating with \({\rm{C}}{{\rm{O}}_2}\) under pressure produces urea.

Reaction with Alkali Metals

A blue-coloured solution is formed when alkali metals react with liquid Ammonia. The blue colour of these solutions is a result of the presence of solvated electrons \({\rm{(e – (N}}{{\rm{H}}_{\rm{3}}}{\rm{)n)}}\) For Example, with sodium

\({\rm{Na}}\, + 2{\rm{N}}{{\rm{H}}_3} \to \mathop {2{\rm{NaN}}{{\rm{H}}_2}}\limits_{{\rm{Sodamide}}}  + {{\rm{H}}_2}\)

Formation of Complex Compounds

Ammonia reacts with soluble salts of copper, silver, etc., to form complex compounds. In reaction with copper sulfate solution, it gives a deep blue coloured complex compound, tetraamminecopper \({\rm{(II)}}\) sulphate.

Uses of Ammonia

1. In the production of urea and rayon and certain fertilisers such as ammonium nitrate, urea diammonium phosphate, ammonium sulfate and so on.
2. Ammonia has a high heat of vaporization, hence is used as a refrigerant in ice plants.
3. \({\rm{N}}{{\rm{H}}_3}\) is used in the production of nitric acid by Ostwald’s procedure.
4. In the production of sodium carbonate by Solvay’s procedure.

Tests of Ammonia

Ammonia can be confirmed by the following tests-

1. The pungent odour of Ammonia is a characteristic test to detect its presence.
2. Ammonia is a strong Lewis base, hence turns wet red litmus blue and moist turmeric paper to brown.
3. Thick white fumes of ammonium chloride are formed when a glass rod dipped in concentrated \({\rm{HCI}}\) is brought near ammonia gas.
4. A blue-coloured solution is obtained when added to a solution of copper sulfate.
   \({\rm{N}}{{\rm{H}}_{\rm{3}}}{\rm{ + CuS}}{{\rm{O}}_{\rm{4}}}{\rm{ + n}}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to {\rm{[Cu(N}}{{\rm{H}}_{\rm{3}}}{{\rm{)}}_{\rm{4}}}{{\rm{(}}{{\rm{H}}_{\rm{2}}}{\rm{O)}}_{\rm{n}}}{\rm{]S}}{{\rm{O}}_{\rm{4}}}\)
5. Ammonia gives brown precipitate when added to Nessler’s Reagent.
   \({\rm{NH}}_4^ + {\rm{ + 2}}{\left[ {{\rm{Hg}}{{\rm{I}}_4}} \right]^{2 – }}{\rm{ + }}{\mkern 1mu} {\rm{4O}}{{\rm{H}}^ – } \to {\rm{HgO}}.{\rm{Hg}}{\mkern 1mu} \left( {{\rm{N}}{{\rm{H}}_2}} \right){\rm{I + 7}}{{\rm{I}}^ – } + 3{{\rm{H}}_2}{\rm{O}}\)

Ammonium Ion

The ammonium ion has the chemical formula \({\rm{NH}}_4^ + .\) It is a positively charged polyatomic ion commonly known as the ammonium cation.

Fumes from hydrochloric acid and Ammonia forming a white cloud of ammonium chloride

The ammonium ion is generated when Ammonia, a weak base, reacts with Brønsted acids (proton donors):

\({\rm{N}}{{\rm{H}}_3}{\rm{ + }}{{\rm{H}}^ + } \to {\rm{NH}}_4^ + \)

The ammonium ion is mildly acidic, reacts with Brønsted bases to form uncharged ammonia molecule:

\({\rm{NH}}_4^ + {\rm{ + }}{{\rm{B}}^ – } \to {\rm{HB}}{\mkern 1mu} {\rm{ + }}{\mkern 1mu} {\rm{N}}{{\rm{H}}_3}\)

When Ammonia is dissolved in water, a tiny amount of it converts to ammonium ions:

\({\rm{N}}{{\rm{H}}_3} + {{\rm{H}}_2}{\rm{O}}{\mkern 1mu} \to {\mkern 1mu} {\rm{NH}}_4^ + + {\rm{O}}{{\rm{H}}^ – }\)

The extent of the ammonium ion formation depends on the \({\rm{pH}}\) of the solution.

1. The equilibrium shifts to the right with low \({\rm{pH}}\): more ammonia molecules are converted into ammonium ions.
2. The equilibrium shifts to the left with high \({\rm{pH}}\): the hydroxide ion abstracts a proton from the ammonium ion, generating Ammonia.

Structure and Bonding

The lone pair of electrons on the nitrogen atom \(({\rm{N}})\) in Ammonia forms a coordinate covalent bond with a proton \(({{\rm{H}}^ + })\). The bonding in Ammonia is as shown below:

1. The hydrogen atom shown in red in the ammonium cation is the fourth hydrogen atom attached by a coordinate covalent bond to the ammonia molecule. Once the coordinate covalent bond is formed, no difference lies between the coordinate covalent and the ordinary covalent bonds. All hydrogens are equivalent in the molecule, and the extra positive charge carried by the hydrogen ion is distributed throughout the molecule.
2. The ammonium ion has a tetrahedral structure and is isoelectronic with \({\rm{C}}{{\rm{H}}_4}\) and methane. In terms of size, the ammonium cation \(({{\rm{r}}_{{\rm{ionic}}}} = 175\,{\rm{pm)}}\) resembles the caesium cation \(({{\rm{r}}_{{\rm{ionic}}}} = 183\,{\rm{pm)}}.\)

Properties
Chemical Formula	\({\rm{NH}}_{_4}^ + \)
Molar mass	\(18.039\,{\rm{g}}/{\rm{mol}}\)
Acidity	\(9.25\)
Conjugate Base	Ammonia
Shape	Tetrahedral

Ammonia Solution Formula

Ammonia solution, also known as ammonium hydroxide, ammoniacal liquor, ammonia liquor, aqua ammonia, aqueous Ammonia, is a solution of Ammonia in water. It can be denoted by the symbols \({\rm{N}}{{\rm{H}}_3}({\rm{aq}})\) Its molecular formula is \({\rm{N}}{{\rm{H}}_4}{\rm{OH}}\) and is composed \({\rm{N}}{{\rm{H}}_4}^ + \) and \({\rm{O}}{{\rm{H}}^ – }\) ions.

In an aqueous solution, Ammonia deprotonates a small fraction of the water to give ammonium ion and hydroxide ion. At equilibrium :

\({\rm{N}}{{\rm{H}}_3} + {{\rm{H}}_2}{\rm{O}} \to {\rm{NH}}_4^ + + {\rm{O}}{{\rm{H}}^ – }\)

In a \(1\,{\rm{M}}\) ammonia solution, about \(0.42\% \) of the Ammonia is converted to an ammonium ion. The base ionization constant is-

\({{\rm{K}}_{\rm{b}}} = \frac{{[{\rm{NH}}_4^ + ][{\rm{O}}{{\rm{H}}^ – }]}}{{{\rm{N}}{{\rm{H}}_3}}} = 1.77 \times {10^{ – 5}}\)

Ammonium Hydroxide Chemical Formula

The chemical formula of ammonium hydroxide is \({\rm{N}}{{\rm{H}}_4}{\rm{OH}}.\) The ammonium ion has a charge of \( + 1,\) and the hydroxide ion has a charge of \( – 1.\) When they react, they both cancel each other out and balance automatically in the end.

Properties
Chemical Properties	\({\rm{N}}{{\rm{H}}_{\rm{4}}}{\rm{OH}}\)
Molar Mass	\({\rm{35}}{\rm{.04}}\,{\rm{g/mol}}\)
Appearance	Colourless liquid
Odour	Fishy
Density	\({\rm{0}}{\rm{.86}}\frac{{\rm{g}}}{{{\rm{c}}{{\rm{m}}^3}}}\)
Melting Point	\(- 91.5\,^\circ {\rm{C}}\)
Boiling Point	\(24.7\,^\circ {\rm{C}}\)
Solubility	Miscible

Ammonium Hydroxide Structural Formula

The ionic structure of ammonium hydroxide is shown below:

Summary

Ammonia is an important compound in the world of chemistry. It acts as a strong Lewis Base. Ammonia and the ammonium ion are vital components of metabolic processes. It plays an essential role in the manufacture of fertilisers. We learned the formula, properties, and structure of ammonia molecules through this article. We also learned about ammonium hydroxide and ammonium ions.

FAQs

Q.1. Why \({\rm{NH}}_4^ + \) called Ammonium?
Ans: Ammonia, when protonated, forms an ammonium ion. It is a positively charged species with tetrahedral geometry.

Q.2. How is \({\rm{N}}{{\rm{H}}_3}\) formed?
Ans: Ammonia has formed from \(3\) atoms of Hydrogen and \(1\) atoms of Nitrogen. Hence, three hydrogen atoms each share their \(1\) electron with Nitrogen to form three covalent bonds and make an ammonia molecule \(({\rm{N}}{{\rm{H}}_3}).\)

Q.3. What’s the difference between Ammonia and Ammonium?
Ans: Ammonia contains one Nitrogen and three Hydrogen, whereas Ammonium contains one Nitrogen and Four Hydrogen. Ammonia is a weak base and is un-ionized. On the other hand, Ammonium is ionized.

Q.4. Is Ammonia acidic or basic?
Ans: Ammonia solution is said to be a weak base. This is because the Ammonia’s nitrogen atom has an electron pair that easily accepts a proton. When Ammonia is in water, it can readily gain hydrogen ions to form hydroxide and ammonium ions.

Q.5. What is the scientific name for Ammonia?
Ans: The scientific name of Ammonia is nitrogen trihydride.

Q.6. Which is more toxic, Ammonia or Ammonium?
Ans: When \({\rm{pH}}\) is high un-ionized Ammonia is the toxic form. The ammonium ion is relatively nontoxic and predominates when \({\rm{pH}}\) is low. In general, less than \(10\) percent of Ammonia is in the toxic form when \({\rm{pH}}\) is more than \(8.0.\)

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