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Hydrogen Chloride – Definition, Preparation, Properties, Uses

  • Last Updated : 19 Jan, 2022

As a hydrogen halide, the compound hydrogen chloride has the chemical formula HCl. It is a colourless gas at ambient temperature that emits white fumes of hydrochloric acid when it comes into contact with air-water vapour. In technology and industry, hydrogen chloride gas and hydrochloric acid are critical. Hydrochloric acid, an aqueous solution of hydrogen chloride, is also known as HCl.

Dissolving gaseous hydrogen chloride in water yields hydrochloric acid. Because of the acid’s corrosive nature, ceramic, glass, or occasionally tantalum apparatus is usually employed. Hydrochloric acid is often sold as a solution containing 28–35 % hydrogen chloride by weight, sometimes known as concentrated hydrochloric acid. Although anhydrous liquid hydrogen chloride is accessible, its application is limited due to the large and expensive containers necessary to store it.

Below mentioned is the structure of HCl:

Structure of HCl

Preparation of HCl

  • Glauber created hydrogen chloride for the first time in 1648 by heating sodium chloride with concentrated H2SO4. Davy demonstrated in 1840 that HCl is a combination of chlorine and hydrogen. Muriatic acid is another term for hydrochloric acid. Warming NaCl crystals with concentrated H2SO4 produces muriatic acid (Sulphuric acid).


  • As a byproduct, we obtain sodium bisulphate, which is insoluble. As a result, we add additional sodium chloride to it. This mixture must be heated to a higher temperature of around 823K. It produces soluble sodium sulphate and HCl gas. This HCl is dried by treating it with strong sulphuric acid. HCl is not dried in the presence of phosphorus pentoxide or vigorous lime. This is due to the fact that it reacts with both of these molecules.

NaHSO4 + NaCl → Na2SO4 + HCl

  • Typically, the majority of the hydrogen chloride/hydrochloric acid produced is a byproduct of other chemical reactions. The chlorination of hydrocarbons also produces HCl.
  • Dissolving gaseous hydrogen chloride in water yields hydrochloric acid. Because of the acid’s corrosive nature, ceramic, glass, or occasionally tantalum apparatus is usually employed.

Chemical Properties of HCl

  • In an aqueous solution, the chemical dissociates extensively into a hydronium ion (H3O+) and a chloride ion (Cl-).
  • Because it is monoprotic, it can only emit one proton.
  • In water, it can entirely dissociate to generate hydrogen and chloride ions.
  • Noble metals react at a 1:3 ratio with a mixture of nitric acid and hydrochloric acid. This is referred to as aquaregia.
  • The salts of weaker acids react with hydrochloric acid. Sodium carbonate, sodium bicarbonate, and other salts are examples.
  • When hydrochloric acid combines with sodium carbonate and sodium bicarbonate, it produces sodium chloride, carbon dioxide, and water.
  • It also converts sodium sulphate to sodium chloride, sulphur dioxide, and water.
  • Reaction with Sodium Carbonate

Na2CO3 + 2HCl → 2NaCl + CO2↑ + H2O

  • Reaction with Sodium Bicarbonate

NaHCO3 + HCl → NaCl + CO2↑ + H2O

  • Reaction with Sodium Sulphate

Na2SO3 + 2HCl → 2NaCl + SO2↑ + H2O

Physical Properties of HCl

  1. Hydrogen chloride is a colourless, pungent-smelling gas.
  2. The gas smells in damp air due to its high solubility.
  3. Dissociation is essentially complete in dilute liquids. As a result, hydrochloric acid is a powerful acid.
  4. Hydrochloric acid is a hydrogen chloride aqueous solution.
  5. It liquefies at 189K to create a colourless liquid and freezes at159K to form a white solid.
  6. Hydrochloric acid is non-corrosive in the presence of glass.
  7. Hydrochloric acid is extremely corrosive, attacking metals such as platinum, gold, silver, mercury, tantalum, and others.

Organic Synthesis

The industrial manufacture of hydrogen chloride is frequently integrated by creating fluorinated and chlorinated organic chemicals, such as Freon, Teflon, and other CFCs, and chloroacetic acid, PVC, and so on. The manufacture of hydrochloric acid is frequently combined with its captive on-site consumption. In the case of chemical reactions, hydrogen atoms on the hydrocarbon can be replaced by chlorine atoms, and the freed hydrogen atom recombines with the spare atom from the chlorine molecule to form hydrogen chloride. Fluorination is defined as the following reaction of chlorine-replacement that results in the production of hydrogen chloride, with the chemical reaction being as follows:

R−H + Cl2 → R−Cl + HCl

R−Cl + HF → R−F + HCl

The resulting hydrogen chloride can be absorbed in water or reused immediately, yielding industrial or technical grade hydrochloric acid.

Uses of Hydrogen Chloride

  1. Chlorine, aqua regia, and other chlorides are all made using HCl.
  2. It’s used to dissolve noble gases as a solvent.
  3. In laboratories, it is used as a reagent.
  4. Pickling of steel is a procedure that uses weak hydrochloric acid to remove rust or iron oxide from steel or iron before it is processed into wire, sheet and strip coating, and tin mill products.
  5. Organic compound manufacturing: HCl is beneficial in the production of organic compounds such as vinyl chloride and dichloromethane, both of which are used to make PVC. It also manufactures organic substances such as ascorbic acid and pharmaceuticals.
  6. Inorganic compound synthesis: HCl is beneficial in the synthesis of compounds that can be used as water treatment chemicals. Polyaluminium chloride (PAC), ferric acid, and aluminium carbohydrate, for example, are effective in water treatment. It is also beneficial in the regeneration of ion-exchange resins, particularly in the precipitation of cations from the resins.
  7. Gastric Acid: Hydrochloric acid is an essential component of gastric juice in the body, which aids digestion. In the stomach, hydrochloric acid turns inactive pepsinogen into active pepsin, which aids digestion by disrupting the links that link amino acids. This is known as proteolysis. Gastric Acid: Hydrochloric acid is a vital part of gastric juice in the body that helps indigestion. Inactive pepsinogen converts into active pepsin by hydrochloric acid in the stomach which helps digestion by breaking the bonds linking amino acids. This process is Proteolysis.

Harmful effects of HCl

  1. The digestive fluids of the human stomach contain hydrochloric acid.
  2. Excessive acid secretion produces stomach ulcers, whereas a substantial deficit hampers digestion and is sometimes the primary cause of deficiency anaemias.
  3. A few minutes of exposure to 0.1% by volume hydrogen chloride gas in the environment can result in death.
  4. Burns and skin irritation are caused by concentrated hydrochloric acid.

Safety from HCl: When hydrogen chloride comes into touch with water in bodily tissue, it produces caustic hydrochloric acid. Inhaling the fumes can induce coughing, choking, nose, throat, and upper respiratory tract inflammation, and, in severe cases, pulmonary edoema, circulatory system failure, and death. Contact with the skin might result in redness, discomfort, and serious chemical burns. Hydrogen chloride can cause serious eye burns and lasting eye damage.

Sample Questions

Question 1:  Which acid is used in the preparations of hydrogen chloride gas?


In the production of Hydrogen Chloride gas, concentrated sulfuric acid is employed.

Question 2: Give two examples of colourless gases that mix to form a white solid.


When hydrogen chloride and ammonia combine, they form a white solid.

Question 3: Why can’t dilute hydrochloric acid be concentrated by boiling beyond 22.2%?


It cannot be concentrated further than 22.2 percent by boiling because the molecules of dilute hydrochloric acid HCl (g) combine with water vapour.

Question 4: What are the physical properties of hydrogen chloride gas?


  1. It is an odourless and colourless gas.
  2. It has a sour flavour and a strong odour.
  3. It dissolves readily in water and other non-polar solvents.
  4. HCl gas has a boiling point of -83°C and a melting point of -113°C.
  5. It is caustic in nature, causing irritation, pain, and inflammation, as well as coughing, sneezing, and choking sensations when inhaled.

Question 5: How to convert Hydrochloric acid to nascent chlorine? Explain with a balanced equation.


By combining three parts concentrated hydrochloric acid and one part concentrated nitric acid, hydrochloric acid can be transformed to nascent chlorine.

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