Hydrochloric Acid (HCl)

What is Hydrochloric Acid?

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4 min readDec 20, 2022


Hydrochloric acid also called muriatic acid is an aqueous solution of hydrogen chloride with the chemical formula HCl. It is a strong corrosive acid that is formed when a hydrogen and chlorine atom are connected with a single covalent bond.

Hydrochloric Acid (HCl) structure, properties, facts and uses

Hydrochloric acid is a strongly acidic and simple diatomic molecule that has a distinctively pungent smell. It is widely used in laboratories as a reagent and processing or production of leather and gelatin. It is a component of gastric acid in our digestive system.


The physical properties such as boiling and melting points, density, and pH of hydrochloric acid depend on the concentration or molarity of the aqueous HCl solution. The most common properties of HCl are given below,

  • Chemical formula: HCl(aq)
  • Molecular Weight/ Molar Mass: 36.458 g/mol
  • Appearance: Colorless liquid that fumes in the air when concentrated
  • Odor: Pungent smelling
  • Melting point: Depends on the concentration of HCl
  • Boiling point: Depends on the concentration of HCl
  • Acidity (pKa): −5.9 for HCl gas
  • CAS Number: 7647–01–0
  • ChemSpider: 307

Gaseous hydrogen chloride is a diatomic molecule that has a covalent bond between the hydrogen and chlorine atoms. In aqueous solutions, it formed chloride ions and hydrated hydrogen ions or hydronium ions. Gaseous hydrogen chloride is a dry and completely unreactive chemical compound.

HCl can be oxidized by potassium permanganate or potassium dichromate to liberate chlorine gas. It also reacts with carbonates and sulfites to form carbon dioxide and sulfur dioxide gases respectively.

Facts about Hydrochloric Acid

  • At room temperature, hydrogen chloride is a colorless to slightly yellow, corrosive, nonflammable gas that contacts water to form hydrochloric acid. Both these forms are corrosive in nature.
  • Hydrochloric acid is produced industrially by dissolving hydrogen chloride in water. Hydrogen chloride used for this purpose may be obtained by the chloralkali process which produces hydroxide, hydrogen, and chlorine. After the production of these chemicals hydrogen and chlorine combined to produce hydrogen chloride.
  • Hydrochloric acid is toxic to humans and other animals. Acute or short-term inhalation exposure in humans may cause eye, nose, and respiratory tract irritation and inflammation, and pulmonary edema. Chronic or long-term exposure to HCl may cause gastritis, chronic bronchitis, dermatitis, and photosensitization in humans.
  • Aldehydes and epoxides in the presence of HCl may readily polymerization but alcohol and glycols in the presence of HCl lead to dehydration.
  • It is corrosive to living tissue and too many materials but not to rubber. Therefore, we use rubber protective gloves and related protective gear for handling concentrated hydrochloric acid solutions.
  • Gastric acid is one of the main secretions of the stomach that contain mainly hydrochloric acid. HCl may acidify our stomach content to a pH of 1 to 2.
  • A mixture of conc. HCl and conc. HNO3 in the ratio of 3:1 by volume is called Aqua regia which may be used to dissolve noble metals such as gold and platinum.

Uses of Hydrochloric Acid

Hydrochloric acid is an important laboratory reagent and industrial chemical that uses widely in laboratories and industrial processing. The most common uses of hydrochloric acid are,

  • The most important application of hydrochloric acid in the industry is in the pickling of steel, to remove rust or iron oxide scale from iron or steel.
  • Hydrochloric acid may be used to maintain the pH of solutions that are used in food, pharmaceutical, and drinking water system.
  • Many chemical reactions involving HCl are used for the production of food, food ingredients, and additives.
  • HCl is an important material in the production of chlorides.
  • High-quality hydrochloric acid is used in analytical chemistry for the regeneration of ion exchange resins. The acid is used to remove the cations from the ion exchange resins by replacing them with hydrogen ions.
  • It is strong mineral monoprotic acid in chemistry that interferes with various oxidation-reduction reactions. In the chemistry laboratory, HCl is the preferred choice in titration for determining the amount of bases.
  • It is used in polymers and fertilizers industries for the production of rubber and artificial fertilizer.
  • It is an effective chemical reagent used in the manufacture of polyvinyl chloride (PVC) for plastics and other industrial processes.
  • It is used widely for the processing of leather, cleaning of household products, and building construction.
  • In textile industries, HCl is used in the manufacture of dye.
  • The oil production process may be stimulated by injecting hydrochloric acid into the rock of an oil well by dissolving a portion of the rock and formation of a large-pore structure.


Hydrochloric acid — Wikipedia

Hydrochloric Acid — Formula, Uses, Solution, Function — Priyamstudycentre.com

Hydrochloric Acid | HCl — PubChem — NIH



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