NH4Cl has an acidic or basic pH.

NH4Cl is the chemical formula for ammonium chloride. It occurs naturally in the form of the mineral sal ammoniac.

This substance is an inorganic salt of ammonia. It occurs as a white, crystalline salt that is extremely soluble in water (about 37 percent ).

So, is NH4Cl a basic or an acid? NH4Cl is an acidic salt. NH4Cl has a pH value between 4.5 and 6 and a pKa value of 9.24; thus, it is mildly acidic. It is a salt of hydrochloric acid and ammonia, which are strong acids and weak bases, respectively. As the acidity or basicity of a salt’s constituent constituents determines its pH, NH4Cl is acidic.

Let us read this in further depth.

What makes NH4Cl an acidic salt?

Neutralization is the reaction between an acid and a base that produces a salt whose properties are derived from its constituents, i.e. acid and base.

The intensity of the acid and base that combine to make a particular salt determines whether it is acidic or basic.

By comprehending the nature of its combining compounds, it is also possible to determine the acidity or basicity of salt, i.e.

Acid and weak base are known to combine to generate acidic salt.

The formation of basic salt requires the combination of a weak acid and a strong base.

The final product of the reaction between a strong acid and a strong base is neutral salts.

The following is the reaction for preparing NH4Cl:

As is evident from the preceding chemical equation, NH4Cl is the neutralisation product of hydrogen chloride, a strong acid that almost entirely ionises in water to generate protons, and ammonia, a recognised weak base.

As previously mentioned, the combination of a strong acid and a weak base produces an acidic salt.

Why is an NH4Cl aqueous solution acidic?

When an acid or base is dissolved in an aqueous solution, its molecules dissociate, resulting in the creation of ions; hence, the acidity or basicity of a material in an aqueous solution can be determined by constructing its dissociation equation.

The dissociation equation for NH4Cl can be expressed as follows:

NH4Cl (aq) —–> NH4+ + Cl –

NH4+ is the conjugate acid of ammonia, while Cl- is its conjugate base.

We will recollect at this juncture that:

A powerful acid yields a weak conjugate base.

Strong bases generate weak conjugate acids.

A weak acid yields a powerful conjugate base.

A weak base yields a powerful conjugate acid.

Consequently, NH4+ is a powerful conjugate acid, whereas Cl- is a weak conjugate base. Ammonium chloride is hence an acidic salt.

This can also be explained by recognising the additional hydrolysis of these ions. Since Cl- is a weak conjugate base, it cannot receive additional protons.

In contrast, the NH4+ ion donates its proton to the water molecule to generate the hydronium ion.

The response can be expressed as:

According to Arrhenius’ theory of acids and bases, acids are substances that, upon dissociation in an aqueous solution, produce hydrogen or hydronium ions.

As observed in the preceding equation, the hydrolysis of ammonium ions results in the release of hydronium ions when NH4Cl is dissolved in water.

These hydronium ions are accountable for the acidity of the ammonium chloride solution in water.

The pH of NH4Cl

A substance’s pH value indicates the acidity or alkalinity of its aqueous solution. It is the concentration of hydrogen ions present in a solution.

On the pH scale, pH values for different substances range from 1 to 14, with a neutral solution having a pH value of 7.

All chemicals with a pH value less than 7 are acidic, whereas all substances with a pH value more than 7 are basic.

We already know that NH4Cl is an ionic salt generated by the neutralisation of a strong acid and a weak base.

Consequently, NH4Cl’s pH should be less than 7.

pH calculation for a 1 M NH4Cl Solution

Calculation of the concentration of hydrogen ions:

[H+] = √Ka X M

As the value of Ka = NH4Cl at 25°C is 5.6 x 10-10

Also, we are computing the concentration of hydrogen ions in a 1 M NH4Cl solution.

Consequently, [H+] = 5.6 x 10-10 x 1

= 2.3 X 10-5

The pH of a 1 M solution of NH4Cl can be calculated as follows:

pH = – log [H+]

= − log [2.3 X 10-5]

= – [log 2.3 – 5 log 10]

= 4.63

Since the pH of ammonium chloride is less than seven, NH4Cl is acidic.

Why does NH4Cl not qualify as a base or basic salt?

There are three primary ideas for differentiating acids and bases. They are as follows:

• According to Lewis theory, a base is a molecule that donates an unshared pair of electrons to another molecule, whereas an acid is a molecule that absorbs those electrons.

• According to the Bronsted-Lowry theory, an acid is a molecule that rapidly gives up protons in an aqueous solution, whereas a base is a molecule that readily accepts protons from an acid.

A molecule that creates hydroxide ion (OH-) in a solution is a base, whereas a molecule that cannot produce hydroxide ions is an acid, according to the Arrhenius theory.

In light of the aforementioned ideas, it is evident that the properties of the ammonium chloride molecule do not match the definition of a base provided by any of these theories; consequently, NH4Cl is not a base.

Synthesis of NH4Cl

Ammonium Chloride occurs naturally as the mineral sal ammoniac. It creates volcanic rocks near fumaroles in the vicinity of volcanoes.

As a result of the gaseous eruption, crystals are created, but they do not stay long because they are water-soluble.

The majority of Ammonium Chloride is produced as a byproduct of the Solvay process, which is used to produce Sodium Carbonate.

The reaction of Ammonia, Sodium Chloride, and Carbon dioxide in water constitutes the process.

Once Sodium bicarbonate precipitates, it is removed from the solution via filtration. After separating, washing, and drying the ammonium chloride from the precipitate. Below is the reaction equation for the Solvay process:

CO2 + 2NH3 + 2NaCl + H2O —–> 2NH4Cl + Na2CO3

Ammonium Chloride is produced commercially by the interaction of ammonia and hydrogen chloride, commonly known as hydrochloric acid when dissolved in water.

The corresponding chemical equation is as follows:

NH3 plus HCl produces NH4Cl.

Upon contact with sodium chloride, the double breakdown of ammonium sulphate also leads in the creation of ammonium chloride.

When hydrogen chloride is readily available, ammonium chloride can be produced through a direct neutralisation process.

However, because ammonium chloride is readily available as a by-product of double decomposition reactions, the latter are preferred due to their lower cost.

Properties

• NH4Cl has a molecular mass of 53.49 grammes per mole

• It appears as a whitish, hygroscopic solid.

• It has no odour and a density of 1.519 g/cm3.

• Its pH ranges from 4.5 to 6, and its pKa value is 9.24

• Its refractive index at 20°C is 1.642.

• It is soluble in liquid ammonia, hydrazine, and acetone to a small degree.

• The ammonium chloride boiling point is 520°C.

• The melting point of NH4Cl is 338°C.

Applications of NH4Cl

• Ammonium chloride is mostly utilised in nitrogen-based fertilisers. Nearly ninety percent of the global production of NH4Cl is utilised to manufacture fertilisers.

• It is utilised in the preparation of metals for tin coating, where it is employed to remove metal oxides from metal surfaces.

• NH4Cl is utilised as an acidifying salt for urine because it helps regulate the pH and has a diuretic impact.

• It is also used to treat cough because it has an expectorant effect, i.e., it irritates the mucous membrane.

• Ammonium Chloride is also used as an acidity regulator as a food ingredient under the E number E510.

• It is also used as an animal feed additive.

• It is also utilised as an inhibitor of ferroptosis.

• It is utilised to lower the temperature in cooling baths.

Certain aquatic organisms use ammonium chloride to sustain buoyancy in seawater.

• The aqueous solution of ammonium chloride was utilised as the electrolyte in Leclanché cells.

Conclusion

The salt Ammonium Chloride is acidic. NH4Cl has a pH range between 4.5 and 6 and a pKa value of 9.24.

HCl is a strong acid, whereas NH3 is a weak base, and their neutralisation reaction produces NH4Cl. It is therefore an acidic salt.

Ammonium chloride’s aqueous solution is acidic because, upon dissociation, it produces hydronium.

NH4Cl is not a base since none of the acid-base theories—the Lewis theory, the Arrhenius theory, or the Bronsted-Lowry theory—provide a definition for base.

Read more: Is O2 Polar or Nonpolar?

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.

LEAVE A REPLY

Please enter your comment!
Please enter your name here

Read More

Recent