Uses of hydrogen chloride

Hydrogen chloride is an important chemical in chemistry. Generally, hydrogen chloride and chlorine are taught together because of the close relationship. Chlorine is a co-product most of the time while producing HCl. Therefore it is important to study these two concepts together. Here, you will learn about hydrogen chloride, its uses, its preparation, and other important topics.

Hydrogen chloride

Hydrogen chloride is a compound of chlorine and hydrogen and the symbol HCl denotes it. Hydrogen chloride is a gas under normal conditions of air pressure and temperature. When dissolved in water, hydrogen chloride gas is known as hydrochloric acid. Hydrogen chloride is an example of a polar covalent compound.
Hydrogen chloride was prepared for the first time in 1648 by a German-Dutch chemist and alchemist, Glauber. He formed hydrogen chloride by bringing sodium chloride to heat up and concentrated H₂SO₄. In the year 1840, Davy showed that hydrogen chloride is a compound of hydrogen and chlorine.

How to prepare hydrogen chloride

There are several uses of hydrogen chloride gas, but it’s important to understand how hydrogen chloride is prepared before we discuss it.

Direct synthesis

Pure hydrogen chloride can be made by combining hydrogen and chloride. Here is the chemical reaction of combining hydrogen and chlorine :
Cl₂ + H₂ → 2 HCl
Note that this reaction is exothermic. The hydrogen chloride gas obtained in this process is imbibed in ionised water, making hydrochloric acid. This process gives very pure hydrochloric acid, which is used in many industries like the food industry.

Organic synthesis

The industrial production of hydrogen chloride is a different process. Hydrogen chloride is formed by the integration of chlorinated and fluorinated organic compounds, for instance, PVC, CFCs, Teflon, Freon and chloroacetic acid as well.
In the chemical reaction, the hydrogen atoms in the hydrocarbons are substituted by chlorine atoms, the hydrogen atoms that are released then combine with the idle atoms released from chlorine molecules and hence hydrogen chloride is formed. Here are chemical reactions:
R-H + Cl₂ → R-Cl + HCl
R-Cl + HF → R-F +HCl
The hydrogen chloride produced is absorbed in water, which gives hydrochloric acid of the technical or industrial grade.

Use of hydrogen chloride

There are many uses of hydrogen chloride gas in several industries like the food industry. Here are some of the uses of hydrogen chloride:

• It is used in the production of chlorine and chlorides.
• It is used in tanning industries.
• It is used in dyeing calico printing.
• It is used in several medicines.
• It is an essential reagent in the labs.
• It is used in the production of glucose through the hydrolysis of starch.
• It is used in pickling before galvanising, electroplating and tinning.
• It is used in making aqua regia that is used in dissolving metals such as gold.

Properties of hydrogen chloride

Here are some of the properties of hydrogen chloride:

• Hydrogen chloride is a colourless gas.
• It has a pungent smell
• Hydrogen chloride is soluble in water.
• When hydrogen chloride is liquified at 189 K temperature, a colourless liquid is produced
• Hydrogen chloride can freeze at 159 K temperature. When frozen, hydrogen chloride appears as a white solid substance.

Chemical properties of hydrogen chloride

Here are some chemical properties of hydrogen chloride:

Reaction with litmus

Dry hydrogen chloride gas has no reaction on litmus. The aqueous solution of hydrogen chloride turns the litmus from blue to red which indicates it is acidic.

Oxidation

Hydrogen chloride is oxidised by atmospheric oxygen in cuprous chloride’s presence to produce chlorine.
4HCl + O₂ → 2H₂O + 2Cl₂

Acidic properties of HCl

The aqueous form of hydrogen chloride is acidic and it is almost completely ionised in H₂O.
H₂O + 4HCl → H₃O⁺ + Cl^–
Hydrogen chloride in aqueous form is known as hydrochloric acid. Hydrochloric acid shows all the properties of acid.

As a reducing agent

Hydrogen chloride acts as a reducing agent as it can be oxidised to chloride with the help of oxidising agents such as potassium permanganate, potassium dichromate and manganese dioxide:
2KMnO₄ + 16HCl → 2KCl +
2MnCl₂ + 8H₂O + 5Cl₂
K₂Cr₂O₇ + 14HCl → 2 KCl + 2 CrCl₃ + 7 H₂O + 3Cl₂
MnO₂+ 4HCl → MnCl₂ + 2H₂O + Cl₂

Reaction with fluorine

When reacted with fluorine, it displaces chloride from HCl. Here is a chemical reaction: 2HCl + F₂ → 2HF It is important to note here that iodine and bromine don’t react with hydrogen chloride.

Making of aqua regia

3 parts of hydrochloric acid in concentrated form is mixed with one part of nitric acid in concentrated form to form what is called aqua regia.
To form nascent chlorine, Hydrochloric acid is oxidised by nitric acid in aqua regia. Here is a chemical reaction:
3HCl + HNO₃ →NOCl + 2H₂O + 2Cl
Aqua regia is known to dissolve noble metals such as platinum and gold. Here is a chemical reaction:
Au + 3Cl → AuCl₃
Au + 4H⁺+ NO₃¯ + 4 Cl¯ → AuCl₄¯ + NO + 2 H₂O
3Pt + 16 H+ + 4NO₃‾ + 18 Cl¯ → 3 [PtCl₆]²¯ + 4 NO + 8 H₂O

Chlorine

The atomic number of chlorine is 35. Group 17, period 3 in the modern periodic table, is occupied by this compound. Chlorine is represented by the symbol Cl₂. It has a pungent smell and is greenish-yellow. The nature of this gas is poisonous. Chlorine boils at 239.11 K and its melting point is 171.6 K. When dissolved in water, chlorine takes the form of chlorine water and is known as hypochlorous acid. This acid is yellow, which is very unstable and thus, it decomposes and forms nascent oxygen.

Conclusion

Hydrogen chloride, when dissolved in water, is known as hydrochloric acid or muriatic acid. When in gaseous state, hydrogen chlorine does not react with litmus. However, when in liquid, hydrogen chloride turns the litmus from blue to red, depicting that it is acidic. There are multiple uses of hydrogen chloride. For instance it acts as a solvent while dissolving noble metals such as platinum and gold. Also there are multiple physical and chemical property of hydrochloric acid which we have discussed in this article.