Why is NH3 (Ammonia) Soluble in Water? (+ 3 Things to Know)

Yes, ammonia (NH₃) is soluble in water. ¹ It is soluble in water because it can form hydrogen bonds with water molecules. The polarity of NH₃, with a lone pair of electrons on the nitrogen atom, allows it to interact with the partially positive hydrogen atoms of water through hydrogen bonding, resulting in its solubility.

Well, this was just a simple answer. But there are few more things to know about this topic which will make your concept super clear.

So let’s dive right into it.

Explanation: Why is NH3 soluble in water?

Ammonia (NH₃) is soluble in water due to its ability to form hydrogen bonds with water molecules. Hydrogen bonding occurs when a hydrogen atom, bonded to a highly electronegative atom (such as nitrogen in NH₃), interacts with a lone pair of electrons on a neighboring molecule. 

In the case of ammonia and water, the partially positive hydrogen atom in water can form a hydrogen bond with the lone pair of electrons on the nitrogen atom in ammonia. ² This interaction allows ammonia molecules to become surrounded by water molecules, resulting in the dissolution of ammonia in water.

The formation of hydrogen bonds between ammonia and water molecules helps to stabilize the resulting solution. These hydrogen bonds are relatively strong and can overcome the attractive forces between ammonia molecules, allowing the ammonia to mix uniformly with water.

Furthermore, the polar nature of both ammonia and water contributes to their mutual solubility. Ammonia is a polar molecule with a partial positive charge on the hydrogen atoms and a partial negative charge on the nitrogen atom. ³

Water is also a polar molecule, with a partial positive charge on the hydrogen atoms and a partial negative charge on the oxygen atom. ⁴ This similarity in polarity facilitates the interaction and mixing of ammonia and water molecules.

Overall, the ability of ammonia to form hydrogen bonds with water and its polarity enable it to dissolve in water and form a homogeneous solution.

What factors affect the solubility of NH3 in water?

The solubility of ammonia (NH₃) in water can be influenced by several factors:

1. Temperature: The solubility of NH₃ in water generally decreases with increasing temperature. This relationship is typical for most gases dissolved in liquids. ⁵ As the temperature rises, the kinetic energy of the gas molecules increases, leading to a decrease in the attractive forces between the ammonia and water molecules. Consequently, the solubility of NH₃ decreases.
2. Pressure: Unlike some gases, the solubility of NH₃ in water is not significantly affected by changes in pressure at normal conditions. ⁶
3. Concentration of NH₃: The solubility of NH₃ is also influenced by the concentration of NH₃ in the gas phase. According to Henry’s law, the solubility of a gas is directly proportional to its partial pressure above the liquid. Thus, an increase in the concentration of NH₃ in the gas phase will lead to an increase in its solubility in water.
4. pH: The presence of other substances in water, especially acidic or basic species, can influence the solubility of NH₃. ⁷ In an acidic solution, NH₃ can react with H+ ions to form (NH₄)+ ions, reducing the concentration of free NH₃. In a basic solution, NH₃ can act as a weak base and react with OH- ions to form (NH₄)+ and OH-. ⁸ The formation of (NH₄)+ ions reduces the concentration of free NH₃ and affects its solubility.
5. Presence of other solutes: The presence of other solutes in water can also affect the solubility of NH₃. ⁹ For instance, some salts can form complexes with NH₃, reducing its solubility. Additionally, the presence of other dissolved gases, such as carbon dioxide (CO₂), can compete for hydrogen bonding sites with NH₃, affecting its solubility.

It’s important to note that these factors can interact with each other, and their combined effect determines the overall solubility of NH₃ in water under specific conditions.

Can NH3 dissolve in other solvents besides water?

Yes, ammonia (NH₃) can dissolve in solvents other than water. While water is a common solvent for ammonia due to its ability to form hydrogen bonds, ammonia can also dissolve in various organic solvents.

Organic solvents that are polar or have polar functional groups, such as alcohols (e.g., methanol, ethanol), ethers (e.g., diethyl ether), and amines, can dissolve NH₃ to some extent. ^{10 11 12 13} These solvents can interact with ammonia through hydrogen bonding or dipole-dipole interactions, allowing for dissolution.

Nonpolar solvents, on the other hand, are generally not suitable for dissolving ammonia because they lack the necessary polar interactions. Examples of nonpolar solvents include hydrocarbons like hexane or toluene.

It’s important to note that the extent of solubility and the behavior of NH₃ in different solvents can vary. Factors such as solvent polarity, temperature, pressure, and the presence of other solutes can all influence the solubility and behavior of ammonia in various solvents.

Further reading

Why is Methanol (CH3OH) Soluble in Water?
Why is Acetone Soluble in Water?
Is Hexane Soluble in Water?
Why is Ethanol Soluble in Water?
Is Phenol Soluble in Water?

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