Ammonia or NH3 is one of the attractive compounds to learn about. It has an aromatic smell and a colorless, fire-resistant gas. It is formed up of one nitrogen atom and three hydrogen atoms. The sharing of electrons in Ammonia is asymmetric, which makes it a polar molecule. It has a trigonal bipyramidal molecular geometry and is one of the common components in agriculture as it is broadly used as a fertilizer. Ammonia is also used in construction dyes, pesticides, and other such chemicals.

It is basic to know whether this molecule is a base or an acid to figure out its chemical properties further. Commonly, a molecule is analyzed as a base or acid by looking at its pH. Ammonia is disparate from other molecules, and hence one-word answer for this question wouldn’t satisfy. Keep reading this article to find out if NH3 is an acid or base. 

Is NH3 (Ammonia) An Acid Or A Base?

NH3 also recognized as Ammonia is a pungent-smelling gas compound that comprises 1 atom of Nitrogen and 3 atoms of Hydrogen. Ammonia has a low boiling temperature at -33 degrees celsius and is lighter than air. Often students speculate about whether NH3 is an acid or base. In this article, you’ll get to know about the acidity and basicity of NH3 in detail.

Is NH3 A Lewis Acid Or Base
Is NH3 A Lewis Acid Or Base

So, is NH3 an acid or base? NH3 is a weak base with pH 11 ( at standard conditions) but it is also looked at as amphoteric which implies it can act as both acid and base under disparate conditions. NH3 under advisable condition act as a weak base and accepts H+ and forms its conjugate acid NH4+ and under disparate condition NH3 will act as an excessively weak acid and give away H+ ion to form its conjugate base NH2-.

However, conferring to Lewis’s assumption of acids and bases, NH3 due to the existence of a lone pair of electrons is examined as a Lewis base.

What is NH3 (Ammonia)?

NH3 (Ammonia) is a fire-resistant colorless gas that is lighter than the air. It has a very aggressive bad odor and is recognized as a pungent-smelling gas due to its manufacturing by bacterial decomposition of urea. It is an extremely toxic gas that can cause lung damage or even death due to continued exposure to Ammonia.

In industries, Ammonia is commonly used for the formation of fertilizers, disinfectant chemicals, refrigerants, and many other nitrogen-based organic and inorganic aggregates.

Ammonia’s chemical formula is NH3 and has a trigonal pyramidal shape with a Nitrogen atom on the pyramid top and 3 hydrogen atoms at the 3 base edges. The atomic number of Nitrogen is 7 and 5 electrons in its valence shell. This implies that after the construction of 3 bonds with Hydrogen, Nitrogen brings a lone pair of electrons.

The molar mass of NH3 is around 17.03g and has a bond angle of 107.5 degrees which is slightly fewer than that in tetrahedral (109.5 degrees). The lone pair brings some repulsion to bonds due to which the angle is marginally less than the tetrahedral.

Is NH3 Acidic Or Basic?

As clarified earlier, although NH3 is a weak base and classic solution of ammonia has a pH of 11 but still, it is amphoteric in nature which implies it can act as both acid as well as a base under disparate conditions.

When NH3 acts as a base, it will devote its lone pair to a proton H+ and construct its conjugate acid NH4+ whereas when NH3 acts as an acid, it can give out H+ ion and constructs a conjugate base as NH2-.

Reactions are delivered below:

(Acting as a Lewis Base) NH3 + H+ → NH4+

(Acting as a Lewis Acid) NH3 → NH2- + H+

Why Does NH3 Acts As A Lewis Base?

Lewis’s explanation of Base is that any chemical compound that has the capability to devote lone pairs to other chemical species can act as a lewis base. We know that, in NH3, Nitrogen(N) has 5 electrons in its valence shell with the composition of (1s2, 2s2, sp3), and Hydrogen has only 1 electron with the configuration of (1s1).

NH3 is sp3 hybridized and it shares 3 (sp3) hybridized electrons to build bonds with 1s electrons of all 3 hydrogen atoms and the result of which 1 (sp3) electron pair on N remain unpaired.

It implies the Nitrogen atom is left with one lone pair of electrons, which can contribute to a proton in an applicable medium, and thus NH3 can act as a Lewis base.

Let us take an example of NH3 reacting with H+ ion. When NH3 reacts with the H+ ion, it donates its lone pair to the H+ ion and forms NH4+ as conjugate acid.

Chemical Properties of NH3 (Ammonia)

Structure

NH3 Lewis Structure
NH3 Lewis Structure

Conferring to the VSEPR theory, the chemical structure of Ammonia is trigonal pyramidal with bond angles of 107.5 degrees. Nitrogen has one lone pair of electrons left after participating 3 electrons to form bonds with 3 hydrogen atoms.

This trigonal pyramidal configuration brings the molecule with a dipole moment and makes it a polar molecule. Due to the existence of a lone pair, it has the capability to form hydrogen bonds in water.

Amphoteric Nature

As clarified earlier, NH3 is a weak base and reacts with acids to form salts. Although NH3 is a weak base, it also acts as a weak acid under definite situations and reacts with bases. It can lose H+ ions and form Amides (NH2-). One of the examples of such reaction is when Lithium performs with NH3 to form Lithium Amide.

(NH3 acting as a weak acid) Li + NH3 → LiNH2 + H2

Redox Reaction (Self Disconnection)

NH3 also complete self dissociation and brings out redox reaction under certain conditions. Below is the reaction where NH3 constructs its conjugate acid and conjugate base together.

NH3 → NH4+ + NH2-

Combustion

NH3 experiences exothermic combustion to produce Nitrogen gas and water vapor. Below is the combustion reaction of NH3.

NH3 + O2 → N2 + H2O ( enthalpy change of this reaction is −1267.20 kJ/mol)

Although Nitrogen oxides are insecure with respect to N2 still we can compose Nitrogen oxides with the cooperation of some catalysts. An example of such a reaction is:

NH3 + O2 → NO + H2O

The combustion of NH3 is always done in the existence of a catalyst due to the high heat of vaporization and ignition temperature. Platinum gauze is one of the catalysts used in the NH3 combustion reaction.

NH3 Acts As A Weak Base In Water

When put in water, NH3 readily associates with water due to its polar nature and capability to form hydrogen bonds in water. It helps in the dissociation of H2O molecules in (Hydrogen ions) H+ and (Hydroxyl ions) OH- ions and forms bonding with H+ ions.

NH3 on associating with H+ ions form NH4+ and leaves OH- ions in the solution. Since OH- ion concentration advances, it derives from the increase in pH and hence conveys basicity to the solution.

Also, the formed ammonium ion (NH4+) keeps breaking into NH3 and H+ ions, and hence not all ammonia results in the formation of OH- ions, and thus NH3 is known as a weak base.