Hydrochloric Acid

Hydrochloric Acid Chemical Formula and Properties

Formula: HCl

Molar mass: 36.46 g/mol

Appearance: Colourless, transparent liquid

It is a simple diatomic molecule consisting of a hydrogen atom and a chlorine atom connected with a covalent single bond. Since the chlorine atom is much more electronegative than the hydrogen atom, the covalent bond between the atoms is polar.


  • • Hydrochloric acid is a strong corrosive acid

  • • A solution of hydrogen chloride in water is known as hydrochloric acid. Its chemical formula is HCl

  • • It has a unique pungent smell

  • • One of its common application is that it is commonly used a laboratory reagent

  • • It is used both in its aqueous and gaseous form

  • Occurrence

    It is a major component of the gastric juice also referred to as the gastric acid.

    Preparation of hydrochloric acid

    Hydrochloric acid is prepared by dissolving hydrogen chloride and water. When hydrogen chloride gas enters the water, the water molecules take the hydrogen atom in HCl(g) and pull it away from the chlorine atom. This is the dissolution process, which makes hydrochloric acid.

    HCl + H2O ----> H3O+ Cl-

    Hydrogen chloride is also generated as by-products from industrial-scale production of other chemicals. Industrially it is prepared by the combustion of hydrogen in chlorine. Due to evaporation, the high concentration of HCl is hard to prepare.

    Uses of hydrochloric acid

  • • Hydrochloric acid is a strong acid as it is completely disassociated in water.

  • • It can be used to prepare salts containing Cl- ions called chlorides.

  • • It is also used in titration for determining the number of bases as it is a strong acid and will give more precise results.

  • • Hydrochloric acid is also used to prepare samples in chemical analysis.

  • • Concentrated hydrochloric acid can dissolve a variety of metals to form hydrogen gas and oxidized metal chlorides.

  • What makes HCl an excellent acidifying agent?

    It is a pure reagent and least hazardous to handle. It consists of non-corrosive and non- reactive chloride ion.

    Physical properties of hydrochloric of acid

    The physical properties like boiling and melting points, density, and pH, of hydrochloric acid, varies depending on the concentration of hydrochloric acid in water. It is colorless with a highly pungent odor.

    Chemical properties of HCl

  • • HCl is a strong acid.

  • • It is monoprotic therefore it can only release one proton (H+). In water; it completely dissociates to form hydrogen and chloride ions. The reason hydrochloric acid dissociates into hydrogen and chloride ions are because it is a polar covalent compound and therefore when added to water it ionizes.

  • • Concentrated hydrochloric acid can dissolve metals and form oxidized metal chlorides and hydrogen gas

  • • HCl is very corrosive it attacks many metals like mercury, gold, platinum, tantalum, silver, and certain alloys are an exception.

  • • Non-corrosive in presence of glass.

  • Applications

    Hydrochloric acid is a strong inorganic acid that is used in a variety of industrial processes.


    Fe2O3+ Fe + 6 HCl -> 3 FeCl2 + 3 H2O

    This is a process in which dilute hydrochloric acid is used to remove rust or iron oxide from iron or steel before processing it further wire production, a coating of sheet and strip, and tin mill products. This is required for all steel products that need further processing.

    2) Cleaning agent

    Hydrochloric acid can be used to clean any material that can withstand its effects as it is extremely powerful. It is also used to neutralize swimming pools if the pH level is high. This is done by pouring it into the pool while the pool pump is on.

    3)To regulate pH

    Hydrochloric acid is also used to regulate the acidity pH of solutions. It is used to regulate the pH in a variety of manufacturing and treatment processes such as pharmaceuticals, swimming pools, drinking water, beverages, and food.

    4)Production of inorganic compounds

    Many inorganic compounds can be produced from simple acid-based reactions resulting in inorganic compounds.
    Some of them are listed below:

    Water treatment chemicals such as iron (III) chloride and polyaluminium chloride (PAC) are also included in the list.
    Fe2O3 + 6 HCl → 2 FeCl3 + 3H20

  • • Both PAC and iron (III) chloride are used as coagulation and flocculation agents in drinking water production, wastewater treatment, and paper production.

  • • Zinc chloride for galvanizing industry and battery production

  • • Calcium chloride and nickel (II) chloride for electroplating

  • CaCO3 + 2 HCl -> CaCl2 + CO2 + H2O

    5) Production of organic compounds

    Hydrochloric acid is used in the production of organic compounds like vinyl chloride and dichloromethane which are used to produce PVC (polyvinyl chloride). Other than this hydrochloric acid is used to produce a variety of organic compounds like ascorbic acid and pharmaceutical products.

    6) Gastric acid

    Hydrochloric acid is an important part of gastric juice produced in the body which helps in digestion. In the stomach, inactive pepsinogen is converted into active pepsin by HCl which then helps digestion by breaking the bonds linking amino acids, a process known as proteolysis.

    Hazards of hydrochloric acid

    If a small amount of hydrochloric acid is inhaled, it results in eye, nose, respiratory tract irritation and inflammation in humans, oral exposure can result may cause damage to the mucous membranes, stomach, oesophagus etc. However continuous exposure to hydrochloric acid can result in gastritis, chronic bronchitis etc

    Difference between hydrogen chloride and hydrochloric acid

    Both hydrogen chloride and hydrochloric acid have the same formula. The difference is in the physical states they exist in. Hydrogen chloride is in a gaseous state while hydrochloric acid is in an aqueous solution.
    So, this is all about hydrochloric acid. Applications of hydrochloric acid are one of the most aspects of this section.