# Hydrochloric acid

This article relates to hydrogen chloride in solution. For information concerning the gas chloride hydrogen, to see the article Chloride hydrogen.

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The hydrochloric acid is a aqueous Solution of Chlorure of hydrogen H Cl. Its chemical formula is (H3O++ Cl-) and not HCl which is the chemical formula of the gas Chlorure of hydrogen. It is a Strong acid (it ionizes in aqueous solution completely), principal constituting gastric acid . It is an acid usually used as chemical reagent in the Industrie. The hydrochloric acid being a Liquid very corrosive, it must be handled with precaution. The concentrated hydrochloric acid can have a pH lower than 1.

The hydrochloric acid, also known in the history under the name of muriatic acid (this name former to is discovered Chlore and Chemical formula HCl) was discovered by the alchemist Jabir ibn Hayyan in the vicinity of the year 800. It is chemicals which were frequently used in the history since the beginnings of the Chimie. With the the Middle Ages, it was used by the alchemists in their search of the Philosopher's stone (under the name of “spirit of dirtied salt” or acidum ). It was then used by many scientists, among whom Glauber, Priestley or Davy, which contributed to establish modern chemistry.

During the Industrial revolution, the hydrochloric acid became an important industrial chemical reagent used in many applications, in particular for the production with large scales of made up organics like vinyl the Chlorure for PVC, or like the 4,4 ' - MDI/Diisocyanate of toluene for the Polyuréthane, like applications to more small scales like the production of Gélatine or the treatment of the Cuir. The production of hydrochloric acid is close at present to 20 million ton S per annum.

## History

The hydrochloric acid was discovered in the vicinity of the year 800 by the alchemist arabo - Yemeni Jabir ibn Hayyan, which obtained it by mixing salt (NaCl) and Vitriol (Acid sulphuric H2SO4 in solution). Jabir discovered or invented a great number of chemicals, and reported its discoveries in more than twenty works which allowed the propagation of its knowledge on hydrochloric acid and other chemicals during several centuries. Its invention of the Eau levels, mixture of hydrochloric acid and of Acid nitric making it possible to dissolve the Or, took part in the search of the Philosopher's stone.

With the the Middle Ages, the European alchemists knew hydrochloric acid under the name of spirit of dirtied salt or acidum . The vapor, the Chloride hydrogen, was called Gaz marine Acide . The old name muriatic acid has the same origin ( muriatic means " belonging to salt or the Water of mer"), and the name is sometimes still used. Basilius Valentinus, the abbot-alchemist of the Abbey of Erfurt (Germany), produced an significant amount at the 15th century of it.

With the XVII {{E}} century, Johann Rudolf Glauber of Karlstadt amndt Hand (Germany) used salt (NaCl) and sulphuric Acid to prepare Sulfate of sodium (Na2SO4), thus producing Chlorure of hydrogen gas (HCl). Joseph Priestley of Leeds prepared Chlorure of pure hydrogen in 1772, and in 1818 Humphry Davy of Penzance (the United Kingdom) showed that these chemicals consist of Hydrogène and of Chlore.

During the Industrial revolution, the request for substances Alcalin be, and in particular by Sodium carbonate, strongly increased in Europe, and the new industrial process developped at the point by Nicolas Leblanc (originating in Issoudun) allowed a cheap production large scales. In the Proceeded Leblanc, salt is transformed into Sodium carbonate, by using like reagents of the sulphuric Acid , the Craie and the coal, with also a secondary production of hydrogen gas chloride. Until the promulgation in 1863 of the Alkali Act prohibits it with the the United Kingdom, the hydrogen chloride was slackened in the air. Following this prohibition, the producers of Sodium carbonate were constrained to dissolve gas in water, thus producing hydrochloric acid on an industrial scale.

When the Procédé Leblanc was replaced at the beginning of the 20th century by the Procédé Solvay, without secondary production of hydrochloric acid, this one had been essential right now like an important chemical reagent for a great number of applications. Its commercial interest contributed to the emergence of other techniques of production, which are always used at present (see in the continuation).

The hydrochloric acid is quoted like a precursor in Table 2 of the Convention against the illicit traffic of narcotics and psychotropic substances of 1988 against the drug trafficking, because of its use in the synthesis of Héroïne and Cocaïne.

## Chemistry

The hydrogen chloride (HCl) is a monoacide, which dissociates (ionizes) to give a Ion H+ (a Proton). The other ion formed during dissociation is the ion Chlorure Cl-. In aqueous Solution, the ion H+ binds to a water molecule to form an ion Hydronium H3O+.

$HCl + H_2O \ longrightarrow H_3O^+ + Cl^-$

The hydrochloric acid can thus be used to prepare salts known as chlorides , such as for example sodium chloride NaCl. The hydrochloric acid is a strong acid: it is completely dissociated in water.

The monoacides have only one constant acid dissociation, Ka, which is related to the rate of dissociation of the acid in water. For a strong acid like HCl, Ka is very high (>1). Attempts were made to assign a Ka constant with HCl. When a chloride salt as NaCl is added to aqueous HCl, it does not have practically any effect on pH, which indicates that the ion Cl- is a combined Base extremely weak and that HCl is completely dissociated in aqueous solution. For concentrated or intermediate hydrochloric acid solutions, the assumption that the Molarity of the H+ ions is equal to the molarity of HCl is excellent, with an agreement of four significant figures.

Among the strong acids current in chemistry, all inorganic, the hydrochloric acid is the monoacide least likely to undergo a parasitic reaction of oxydoreduction. It is one of the acids less dangerous to be handled: in spite of its acidity, it produces ions chloride very little Réactif S and not toxic. The fairly concentrated hydrochloric acid solutions are stable and their concentration does not vary in time. These properties, allied with the fact that it is available like pure reagent, make hydrochloric acid a very good acid reagent or a very good acid for the Titrage of basic solutions of unknown concentrations. The strong acids are useful for titration because they give more marked points of equivalence, making the results more precise. The hydrochloric acid is frequently used in chemical Analyze or to dissolve samples for analysis. The concentrated hydrochloric acid solutions can dissolve some metals by forming metallic oxide chlorides and Hydrogène gas. It is also used like acid Catalyseur in certain chemical reactions.

### Physical properties

The physical properties of hydrochloric acid, such as the points of boiling or fusion, depend on the concentration or the molarity of HCl in aqueous solution. They vary since the physical properties of the Eau for 0% of HCl until those of hydrochloric acid smoking for fractions higher than 40% of HCl.

Les Temperature and Pression of reference for the values given in the table is 20°C and 1 atmosphere (101 kPa).

The hydrochloric acid as a binary mixture of HCl and H2O has a Azéotrope in boiling with 108.6°C for a fraction of 20.2% HCl. In crystallization, it has four Eutectique S to form the crystals of HCl·H2O (68% HCl), HCl·2H2O (51% HCl), HCl·3H2O (41% HCl) and HCl·6H2O (25% HCl) and of ice (0% HCl).

## Production

### Direct synthesis

The production with hydrochloric acid large scales is almost always related to other industrial productions of chemical compounds. For example, in the production of Chlorine, a solution of salt (NaCl) is electrolyzed to produce the Chlore, as well as Soude and Hydrogène. Chlorine gas can be recombined with hydrogen, which leads to the production of pure hydrogen HCl chloride gas. This reaction being Exothermic, the installation is called furnace with HCl.

$Cl_2 + H_2 \ longrightarrow 2HCl$

The formed hydrogen chloride is dissolved in demineralized water, which makes it possible to produce pure hydrochloric acid.

### Organic synthesis

The major part of the production of hydrochloric acid is integrated in made up generating stations of chlorinated organics or Fluor be, for example the Téflon, the freon or others CFC, the chloride acyle derived from the acetic Acid or PVC. It is often about a production integrated, with a direct re-use on the site. During the chemical reaction, Atome S of Hydrogène of the starting organic compounds are replaced by atoms of Chlore resulting from the molecule of Cl2, while the hydrogen atoms thus released recombine with the second atom of the molecule of Dichlore (Cl2) leading to the hydrogen chloride formation.

$R-H + Cl_2 \ longrightarrow R-Cl + HCl$

Fluoridation is then a reaction during which chlorine is substituted by Fluor what leads again to the hydrogen chloride formation.

$R-Cl + HF \ longrightarrow RF + HCl$

The hydrogen gas chloride obtained either is re-used directly, or dissolved in water to form hydrochloric acid.

### Industrial market

The hydrochloric acid is produced in solution until concentrations of 38  % HCl. Higher concentrations are possible from a chemical point of view, but the evaporation is then important and so much the storage which handling require of the additional precautions, such of the low Température S or the Pression. The solutions produced for industry thus have concentrations close to 30  % with 34  % HCl, optimized for transport so as to limit the losses evaporation. The solutions for a use domesticates (mainly in the maintenance products) generally have concentrations about 10  % with 12  % HCl, for which it however is recommended to dilute again before use.

The principal hydrochloric acid manufacturers in the world are in particular Dow Chemical with 2 million ton S per annum, like Formosa plastics, Georgia GULF corporation, Tosoh corporation, Akzo Nobel and Tessenderlo with productions ranging between 0,5 and 1,5 million of tons per annum. The total worldwide production is estimated at 20 million tons per annum, whose approximately 3 million tons per direct synthesis and the complement like produces secondary organic reactions. Most of the production is used directly by the producer: the “external” worldwide market is estimated at 5 million tons per annum.

## Uses

The hydrochloric acid is an inorganic acid extremely used in a great number of industrial processes. The quality of the product used generally depends on the application considered.

### Productions of organic compounds

The major part of hydrochloric acid is used for the production of made up organics such as vinyl the Chlorure for PVC or the 4,4 ' - MDI/Diisocyanate of toluene for the Polyuréthane. This use frequently functions on a captive mode, i.e. with a use of hydrochloric acid locally manufactured. Among the others made up organics whose manufacture requires hydrochloric acid, one can quote the Bisphénol has for the Polycarbonate S, the Activated carbon and the Ascorbic acid (vitamin C), as well as many medicinal products.

### Regeneration of ion exchangers

An important use of hydrochloric acid of high-quality is the regeneration of exchanging resins of ions. The exchange of Cation S is usually used to withdraw Ion S of which in particular Na+ or Ca2+ of aqueous solutions to produce demineralized water:

$Na^+$ is replaced by $H_3O^+$

$Ca^ \left\{2+\right\}$ is replaced by $2H_3O^+$

The exchanging resins of ions and demineralized water thus obtained are very much used in chemical industry, the production of drinking water or the Agribusiness industry.

### Neutralization and control of the pH

The hydrochloric acid is usually used to control the acidity (pH) of solutions:

$OH^- + HCl \ longrightarrow H_2O + Cl^-$

In industries requiring a high Purity (drug company, agroalimentary, or of production of drinking water), the control of pH of the water used in the processes is carried out with hydrochloric acid of high-quality. In less significant industries, hydrochloric acid of technical quality is used to neutralize rejected water, or for the treatments of swimming pools.

### Scouring of steels

The Décapage is a crucial step in the surface treatment of a Métal, generally of the Fer or Acier, to withdraw the layer of Oxyde before making him undergo a Extrusion, a Galvanisation or any other process. The reagent most usually used for the scouring of the carbon steels is the hydrochloric acid of technical quality of concentration generally close to 18% HCl.

$Fe_2O_3 + Fe + 6HCl \ longrightarrow 3FeCl_2 + 3:00 _2O$

The product of the reaction was re-used a long time as a solution of Chlorure of iron (II), but the important concentrations of Heavy metals tend to make disappear this use.

Metallurgical industry developed in the last years a process of regeneration of hydrochloric acid making it possible to recover the acid used during scouring. One of the process of regeneration most current is the Procédé Dependeg:

$4FeCl_2 + 4:00 _2O + O_2 \ longrightarrow 8HCl+ 2Fe_2O_3$

In this manner, the hydrochloric acid is used in closed circuit. The iron oxide produced by the process of regeneration in addition constitutes a secondary product which may undergo beneficiation in industry.

The hydrochloric acid is not a reagent of scouring usually used in the case of the stainless steels.

### Production of inorganic compounds

The hydrochloric acid can be used to produce a great number of inorganic compounds during reactions of the acido-basic type, in particular of the products of water treatment such as the Chlorure of iron (III) or the Chlorure of aluminum (CAP).

$Fe_2O_3 + 6 HCl \ longrightarrow 2 FeCl_3 + 3:00 _2O$

The Chloride iron (III) and the CAP are used as agents coagulant or flocculating in waste processings, the production of drinking water or the production of Papier.

Among others inorganic compounds produced with hydrochloric acid, one can quote the Calcium chloride (CaCl2) for the salting of the roads, the Chlorure of nickel (II) (NiCl2) for the electrodeposition, or the Chlorure of zinc (ZnCl2) for the Galvanisation or the production of batteries.

### Other uses

The hydrochloric acid is fundamental chemicals used also in a great number of applications to small scales, such as the treatment of the Cuir or construction, or as cleaning domestic. Moreover, the production of Pétrole can be facilitated by injecting hydrochloric acid in the rock formations constituting the oil well, which makes it possible to dissolve part of the rock and to form a porous structure . The acidification is a process usually used for the oil production in the North Sea.

Many chemical reactions implementing of hydrochloric acid are also used for the production of ingredients Aliment food additive surfaces or . One can in particular quote the Aspartame, the Fructose, the citric Acid , the Lysine, the Protéine S hydrolized and the Gélatine. The hydrochloric acid used is then extra-pure quality.

## Hydrochloric acid and living organisms

### Physiology

The hydrochloric acid is the principal one constituting gastric acid . It is thus present in the Estomac where it contributes to the Digestion of food. It is secreted by the parietal cells (also known under the name of oxyntic cells) during a complex mechanism bringing into play a quantity of important energy. These cells contain an important network of secretion (called canaliculi), since which the hydrochloric acid is secreted in the Estomac. They belong to the epithelial glands of the stomach.

### Pathophysiology and pathology

The mechanisms which prevent the damage of the digestive epithelium by hydrochloric acid are the following:
• a negative Feedback of secretions of acid

• a fine layer of Mucus covering the gastric epithelium
• the secretion of Bicarbonate of sodium by the epithelial cells of the Stomach and the Pancreas
• the structure even of the gastric epithelium
• an surge adequate Blood uin
• prostaglandins (they stimulate secretions of Mucus and of bicarbonate, maintain the integrity of the epithelial barrier, allow the adequate blood surge and stimulate the repair of the damaged mucous membranes)

When these protection mechanisms do not function, it can develop heartburn or a Ulcère. Drugs called Inhibiteur of the pump with protons make it possible to prevent the excessive production of acid in the stomach, while Antiacide S make it possible to neutralize the acids present.

In certain cases, the production of hydrochloric acid in the stomach can be insufficient. This pathological state is known under the name of Hypochlorhydrie or Achlorhydrie. It can potentially lead to Gastro-entérite S.

### Chemical weapons

During the First World War, the Phosgène (COCl2) was a Chemical weapon usually used. The principal effect of phosgene results from dissolution from gas in the mucous membranes from the Poumon S where it east converts by carbon Hydrolyze into Dioxide and out of hydrochloric acid. This one contributes to break the alveolar membranes and the lungs fill of fluid (pulmonary edema).

The hydrochloric acid is also partly responsible for the effects of the Mustard gas. In the presence of water, for example to surface of the eyes or in the lungs, the mustard gas reacts by forming hydrochloric acid.

## Safety

### Reference UNO for the Transport of dangerous matters

• Class: 8
• number: 1789 (Hydrochloric acid)

### Safety

Hydrochloric acid strongly concentrated form of the vapor S acids. These vapors and the acid solution have both a corrosive effect on the human tissue S, and can damage the respiratory bodies, the eyes, the Peau and the Intestin S. the dichlore, a very toxic gas, is produced when the hydrochloric acid is mixed with current oxidizing chemicals such as the Bleach (NaClO) or the Permanganate of potassium (KMnO4). To minimize the risks during the use of hydrochloric acid, it is advisable to take the suitable precautions. For example, one never should add water in the acid: to avoid boiling, it is advisable to add the acid in water. It is also recommended always to carry Lunettes of safety and gloves.

## References

• Chemicals Economics Handbook, Hydrochloric Acid , International SRI, 2001, p. 733.4000A-733.3003F
• Van Dorst, W.C.A., and Al , technical product booklet Hydrochloric Acid , Akzo Nobel Bases Chemicals, 2004 (public document)
• Van Dorst, W.C.A., various technical papers , Akzo Nobel Base Chemicals, 1996-2002 (not for open publication)
• Lide, David, NIST, CRC Handbook off Chemistry and Physics , CRC Close, 61st edition, 1980-1981
• Aspen Technology, Aspen Properties , binary mixtures modelling software, calculations by Akzo Nobel Engineering, 2002-2003
• Evison D, Hinsley D, Rice P. Chemical let us weapons. 2002; 324 (7333): 332-5. PMID 11834561
• Arthur C., M.D. Guyton, John E. Hall, Textbook off Medical Physiology , W.B. Saunders Company; 10th edition (August 15,2000), ISBN 072168677X

## External bonds

• toxicological Card (INRS)

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