Ammonium Chloride

Ammonium chloride is an inorganic chemical compound with the formula NH₄Cl. This inorganic compound is the sal ammoniac that literally means the salt of ammonia and hydrogen chloride. Ammonium chloride is formed as the by-product in the manufacturing process of sodium carbonate. Ammonium chloride has diuretic effects. It is found as a white crystalline solid in its purest form. It also shows expectorant effects. Ammonium chloride is mildly acidic in nature due to the presence of chloride ion in it.

A 5% solution of ammonium chloride when mixed with water gives a pH of 4.6 to 6. This inorganic compound is highly soluble in polar solvents, especially water. Ammonium chloride can also be formed as a result of the reaction between ammonium sulfate and sodium chloride. It is useful in veterinary medications. This compound helps in the prevention of urinary stones in animals like goats, sheep and cattle.

Preparation of Ammonium Chloride

Ammonium chloride is the by-product of the Solvay process. This process is useful to produce sodium carbonate. Along with the production of ammonium chloride, this process is also useful in some industrial operation. These operations require ammonia release to be minimized. Ammonia is consumed with sodium chloride, water and carbon dioxide to give sodium carbonate and ammonium chloride as products. The chemical reaction for Solvay’s process is

\(CO_{2} +NH_{3}+2NaCl+H_{2}O \rightarrow 2NH_{4}Cl+Na_{2}CO_{3}\)

The commercial production of ammonium chloride is done by combining ammonia with hydrochloric acid. It also gives the same reaction with hydrogen chloride gas.

\(NH_{3}+HCl \rightarrow NH_{4}Cl\)

The compound of ammonium chloride naturally occurs in regions witnessing volcanic activities. It is found on the volcanic rocks located near the fume-releasing vents. These vents are fumaroles. The crystals of the compound directly deposit from the gaseous state. These crystals tend to be short-lived because they dissolve easily in water.

For the preparation of pure ammonium chloride, pure diluted hydrochloric acid and pure ammonium hydroxide are combined. One part of ammonium hydroxide reacts slowly with 2 parts of hydrochloric acid along with the constant stirring of the solution. This solution is then heated until the crystallization process starts. The ammonium chloride crystals appear and then they are dried and cooled separately.

If we want to obtain 200gm of pure ammonium chloride, we dissolve 300gm of crude ammonium chloride in 300ml of boiling water. 10gm of chlorine water is added to this solution and the solution is heated for about 20 minutes with stirring the solution properly. Eventually, 10g of 10% ammonium hydroxide solution is added and the final solution is evaporated. The solution is evaporated until granulation and then thoroughly dried.

By this method, we obtain pure ammonium chloride. Pure ammonium chloride crystals are colourless or white salts. This salt is soluble in 3 parts of water at a temperature of 15⁰ C. This compound is nearly insoluble in alcohol. We need to stop heating once granulation starts. Otherwise, strong heating leads to decomposition. Decomposition produces ammonia and hydrochloric acid again.

Properties of Ammonium Chloride

1. Physical Properties –
   1. Ammonium chloride is a white crystalline solid. It does not have a characteristic odour.
   2. The melting point of ammonium chloride is 338⁰ Boiling point of this inorganic compound is 520⁰ C.
   3. It has a density of more than water. Its density is 1.5274gm/ml.
   4. This compound has high solubility.
   5. It is soluble in polar solvents and is soluble in water, methanol, glycerol, and ethanol.
   6. It is also slightly soluble in acetone. But it is insoluble in non-polar or organic solvents. For example, it is insoluble in ethyl acetate.
2. Chemical Properties –
   1. Although ammonium chloride may appear sublime on heating, but eventually, on strong heating, it decomposes.
   2. This compound decomposes into ammonia and hydrogen chloride gas.

\(NH_{4}Cl \rightarrow NH_{3}+HCl\)

As the compound ammonium chloride is mildly acidic in nature, it reacts with strong bases. It reacts with a strong base sodium hydroxide to release ammonia gas, sodium salt and water. The sodium salt produced is sodium chloride.

\(NH_{4}Cl+NaOH \rightarrow NH_{3}+NaCl+H_{2}O\)

A 5% weight by weight aqueous solution of ammonium chloride has a peculiar pH range of 4.6 to 6.0. Ammonium chloride needs elevated temperatures in order to react with alkali metal carbonates. This reaction produces alkali metal chloride and also release ammonia gas.

\(NH_{4}Cl+Na_{2}CO_{3} \rightarrow 2NH_{3}+2NaCl+H_{2}O+CO_{2}\)

Ammonium also undergoes endothermic reactions. These reactions are with compounds like barium hydroxide. Dissolution in water is also an endothermic reaction for ammonium chloride. Although this process is endothermic, ammonium chloride readily dissolves in water. The reactions of ammonium chloride are of high industrial importance.

Applications of Ammonium Chloride

Ammonium chloride is majorly useful as a source of nitrogen for various kinds of fertilizers like chloro-ammonium phosphate. Rice and wheat are the crops that are mainly fertilized this way in Asia.

Ammonium chloride was also useful in the pyrotechnics industry in the 18^th century. But it was replaced by less hygroscopic and safer alternative chemicals. It fulfils the purpose of providing a chlorine donor to improve the green and blue colours in the flame of copper ions.

It is also useful to provide white smoke signals. But it readily performs double decomposition reaction with potassium chlorate. This generates highly unstable ammonium chlorate making its use very dangerous.

The compound of ammonium chloride also acts as a flux in the preparation of metals that are to be coated by tin or undergoing galvanization.

FAQs about Ammonium Chloride

Q.1. What role does ammonium chloride play in archaeology?

Ans. The vapours of ammonium chloride are deposited on the fossils. This leads to the formation of a white inert layer of tiny crystals. These are fairly harmless crystals which can easily be removed. This helps to cover up any sort of colouration in the fossil. If this layer is lighted at an angle, it immensely enhances the contrast in the photographic records of specimens that are three-dimensional in nature. This technique is also useful to eliminate reflection on the glass and to provide similar specimens for photographic documentation.

Q.2. How is ammonium chloride helpful in food production?

Ans. Ammonium chloride is useful as a food additive under the name of sal ammoniac or salmiak. It works as a nutrient for yeast in the process of breadmaking and also as an acidifier. Also, it is an important supplement in the cattle feed. It acts as an ingredient in the nutritive sources of yeasts and many other microorganisms. In the subcontinent countries like India, Pakistan, Tajikistan, this compound is Noshader. It is useful to enhance the crispness of local snacks like jalebi and samosa.

Q.3. Can ammonium chloride act as a buffer solution?

Answer. A buffer solution is a solution that resists the change in the pH of the solution when a short amount of acid or base is added. Sodium chloride forms a buffer solution with sodium hydroxide. Ammonium chloride is a strong electrolyte which undergoes complete dissociation. Ammonium hydroxide on the other hand is a weak electrolyte. The presence of ammonium ions due to dissociation of ammonium chloride further suppresses sodium hydroxide’s dissociation. Thus, this solution forms a basic buffer. The pH of this buffer is around 9.25. The addition of small amounts of acid or alkali in this solution does not impact the pH of the solution.