Hydrochloric Acid overview
8 min read
Published on:October 29th, 2023

Hydrochloric acid with the chemical formula HCl, which consists of two elements, hydrogen and chlorine, is a clear liquid with a very pungent smell, which was first discovered in around 800 AD by mixing common salt with sulfuric acid by Jaber bin Hayyan.

After that, in the 15th century, hydrochloric acid was produced using the reaction of rock salt and green vitriol by Valentius as muriatic acid, but this chemical substance was widely used in scientific experiments by chemists such as Glauber, Davy and Priestley.

Hydrochloric acid, which is also known by other names such as hydrochloric acid, muriatic acid, salt essence and hydronium chloride, is structurally linear and its molecular weight is 36.5 g/mol. Hydrochloric acid has very high acidity and its pH is between 0 and 2 at room temperature. Figure (1) shows the molecular structure of this acid.

Molecular structure of hydrochloric acid

Fig (1): Molecular structure of hydrochloric acid

Hydrochloric acid soluble in water is called hydrogen chloride, and the physical properties of this strong acid, including density, melting point, and boiling point, depend on the concentration of hydrogen chloride dissolved in water.

As mentioned above, hydrochloric acid is a very strong acid with the chemical formula of HCl, but hydrogen chloride is a gas with the chemical composition of HCl. So the only difference between these two is their physical state. Figure (2) is a simple diagram of the production process of hydrogen chloride gas from hydrochloric acid solution.

production process of hydrogen chloride gas

Fig (2): Simple diagram of the production process of hydrogen chloride gas from hydrochloric acid solution

Hydrochloric acid production process

Hydrochloric acid is produced both industrially and naturally.

Hydrochloric acid is produced in the industry using various processes, including:

  • The reaction of burning chlorine in hydrogen
  • Reaction of sulfuric acid with sodium chloride

As a side product in the chlorination process of organic compounds (this process is usually used in the industry.
In the electrolysis process, a solution containing sodium chloride, which is usually called brine, as a raw material in an electrolysis cell, using an electric current, chloride ions are separated from the solution and combined with hydrogen ions (H+) and hydrochloric acid. it is produced.

In another method, chlorine gas (Cl2) turns into hydrochloric acid in contact with water. In one process, chloride compounds such as sodium chloride (NaCl) or hydrogen chloride (HCl) are contacted with strong heat sources, such as copper sulfate (CuSO4), then in this process, chloride compounds are decomposed and chlorine (Cl2) is released with water. It is combined and hydrochloric acid is produced.

In another process, hydrogen gas (H2) combines with chlorine gas (Cl2) and under the influence of a metal catalyst such as palladium (Pd) or platinum (Pt) leads to the formation of hydrochloric acid.

It should be noted that the industrial production of hydrochloric acid may be done using other methods and any method may be used depending on the needs and environmental conditions for the production of this chemical.

Hydrochloric acid reactions

Hydrochloric acid participates in a wide range of reactions and the by-products produced by the decomposition of this acid are:

  • Hydrogen chloride
  • Sodium Chloride
  • Chlorine
  • Carbon monoxide
  • carbon dioxide
  • Hydrogen gas

Following are some of the most important and common reactions of hydrochloric acid.

Reaction of hydrochloric acid with active metals


Reaction of hydrochloric acid with bases

Hydrochloric acid reacts with various bases such as metal oxides and hydroxides. The products of these reactions, which are known as neutralization reactions, are water and salt. Some of these reactions are given below:


Reaction of hydrochloric acid with metal carbonates and bicarbonates
Hydrochloric acid reacts with metal carbonate compounds or bicarbonates and releases carbon dioxide gas, some of these reactions are given below:


Reaction with metal sulfides

The reaction product of hydrochloric acid and metal sulfides is oxygen sulfide. Below are two examples of these reactions:


Reaction with silver nitrate

The product of the reaction between hydrochloric acid and silver nitrate is a white precipitate called silver chloride. This reaction is given below:


Reaction with lead nitrate

Hydrochloric acid reacts with lead nitrate and produces a chalky white precipitate called lead chloride. This reaction is given below:


Applications of hydrochloric acid

1-pH control and regulation

Hydrochloric acid is used to adjust the acidity of solutions and also to control the pH of pharmaceutical products, water and foods.

2-Food industry

Hydrochloric acid is used in the food industry in products such as syrups, cookies, crackers, sauces, soft drinks, cereals and canned products to increase flavor and prevent spoilage.

3-Cleaning agent

Hydrochloric acid, which is also known as salt essence, is used as a chemical substance useful for removing stains, cleaning bathroom and kitchen tiles, and also for bleaching clothes in the textile industry due to its strong acidic properties.

4-Industrial washing and rust removal

Dilute hydrochloric acid is used to remove rust or iron oxide from steel and iron. Hydrochloric acid, due to its low pH, has a very high ability to scale and wash, and its cleaning is not related to household uses, for example, scaling tools and industrial pipes, opening sewage wells, scaling and cleaning tiles from Among the applications of hydrochloric acid in this field.

5-Production of organic and inorganic compounds

One of the basic reactions in the industry that leads to the production of chemicals is the acid-base reaction. Hydrochloric acid is used in the production of organic compounds such as vinyl chloride and dichloromethane, which are used to produce PVC. Hydrochloric acid is used in the preparation of compounds such as polyaluminum chloride and ferric acid, which are used in water purification. Hydrochloric acid also reacts with limestone and produces calcium chloride, which is widely used in various industries.

6-Application in military industries

Phosgene is a dangerous chemical that was used in the First World War. Phosgene is a colorless gas with a hay-like odor that is produced by the reaction between purified carbon monoxide and chlorine gas in the presence of activated carbon. When phosgene is used as a chemical weapon instead of chlorine gas, it penetrates deeply into the mucous membranes of the lungs and is hydrolyzed in the body. Then it turns into carbonic acid and hydrochloric acid and will destroy the internal organs. It is estimated that in World War I, 85% of deaths were due to phosgene inhalation.

7-Application of hydrochloric acid in building

In order to clean the surface of the walls of the building, the reaction between hydrochloric acid and calcium carbonate is used. This reaction will continue until one of the two reactants is exhausted. The following reaction represents this reaction:


Due to the very high corrosiveness of this material during use, in addition to the safety points, attention should also be paid to the damage to the texture of building materials. Figure (3) shows how the consumption of hydrochloric acid is distributed in different industries.

consumption of hydrochloric acid in different industries

Fig (3): distributnig the consumption of hydrochloric acid in different industries

Storage conditions and safety of using hydrochloric acid

If hydrochloric acid is stored in the right place and conditions according to the manufacturer’s instructions, its shelf life is about 5 years. The American Environmental Protection Agency has considered this substance as one of the corrosive and toxic substances and has mentioned the necessity of maintaining safety while working with it.

Hydrochloric acid is highly corrosive and its concentrated type leads to the release of very dangerous acid mists.
In case of inhalation, even a very small amount leads to inflammation in the nose, eyes and respiratory tract.
As a result of contact with the mouth, the mucous membrane of the mouth and stomach will be damaged. Long-term exposure to this acid can lead to gastritis.

If this acid comes into contact with the skin, immediately wash the area with water and change the contaminated clothes.

In case of eye contact, immediately wash the eyes with plenty of water for 15 minutes and consult a doctor immediately.

Industrial market or industrial hydrochloric acid

The production of hydrochloric acid with concentrations higher than 40% is chemically possible, but due to the high rate of storage evaporation and the special conditions of its use in these conditions, the grade of industrial hydrochloric acid is 30 to 35%, which balances the transportation efficiency. and product loss through evaporation is optimized.
The major producers of hydrochloric acid worldwide are:

  • DOW Chemical
  • Gerogia Gulf Corporation
  • Tosoh Corporation
  • Akzo Nobel

The total global production of hydrochloric acid is estimated to be about 20 million tons per year, of which about 3 million tons per year is produced from direct synthesis and the rest as a secondary product from organic and similar syntheses.