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Hydrochloric acid +(aq) Cl(aq) or H3O+ Cl also known as muriatic acid, is an
aqueous solution An aqueous solution is a solution Solution may refer to: * Solution (chemistry) Image:SaltInWaterSolutionLiquid.jpg, upMaking a saline water solution by dissolving Salt, table salt (sodium chloride, NaCl) in water. The salt is the solute an ...
of
hydrogen chloride The compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with d ...

hydrogen chloride
( ). It is a colorless solution with a distinctive
pungent Pungency is the condition of having a strong, sharp smell or flavor Flavor (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the Engli ...
smell. It is classified as a
strong acid Acid strength is the tendency of an acid An acid is a or capable of donating a (hydrogen ion H+) (a ), or, alternatively, capable of forming a with an (a ). The first category of acids are the proton donors, or s. In the special ca ...

strong acid
. It is a component of the
gastric acid Gastric acid, gastric juice, or stomach acid, is a digestive fluid formed within the stomach lining. With a pH between 1 and 3, gastric acid An acid is a or capable of donating a (hydrogen ion H+) (a ), or, alternatively, capable of for ...
in the digestive systems of most animal species, including humans. Hydrochloric acid is an important laboratory reagent and industrial chemical.


History

In the early tenth century, the Persian physician and alchemist Abu Bakr al-Razi ( 865–925, Latin: Rhazes) conducted experiments with
sal ammoniac Salammoniac, also sal ammoniac or salmiac, is a rare naturally occurring mineral composed of ammonium chloride, NH4Cl. It forms colorless, white, or yellow-brown crystals in the isometric-hexoctahedral class. It has very poor cleavage and is brit ...
(
ammonium chloride Ammonium chloride is an inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. However, the distinction is not clearly defi ...

ammonium chloride
) and
vitriol Vitriol is the general chemistry, chemical name encompassing a class of chemical compound comprising sulfates of certain metalsoriginally, iron or copper. Those mineral substances were distinguished by their color, such as green vitriol for hydra ...

vitriol
(hydrated
sulfates The sulfate or sulphate ion is a polyatomic anion An ion () is a particle, atom or molecule with a net electric charge, electrical charge. The charge of the electron is considered negative by convention. The negative charge of an ion is ...
of various metals), which he distilled together, thus producing the gas hydrogen chloride. In doing so, al-Razi came very close to discovering hydrochloric acid, but it appears that he disregarded the gaseous products of his experiments, concentrating instead on the color changes that could be effected in the residue. Drawing on al-Razi's experiments, the ''De aluminibus et salibus'' ("On Alums and Salts", an eleventh- or twelfth century Arabic text falsely attributed to al-Razi and translated into Latin in the second half of the twelfth century by
Gerard of Cremona European depiction of the Persian physician Rhazes, in Gerard of Cremona's ''Recueil des traités de médecine'' 1250–1260. Gerard de Cremona translated numerous works by Arab scholars. Gerard of Cremona (Latin Latin (, or , ) is a classical ...
, 1144-1187) described the heating of metals with various salts, which in the case of
mercury Mercury usually refers to: * Mercury (planet) Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. It is named after the Roman g ...

mercury
resulted in the production of
mercury(II) chloride Mercury(II) chloride or mercuric chloride (historically also known as corrosive sublimate) is the chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) comp ...

mercury(II) chloride
(corrosive sublimate). In this process, hydrochloric acid actually started to form, but it immediately reacted with the mercury to produce corrosive sublimate. Thirteenth-century Latin alchemists, for whom the ''De aluminibus et salibus'' was one of the main reference works, were fascinated by the chlorinating properties of corrosive sublimate, and they soon discovered that when the metals are eliminated from the process of heating vitriols, alums, and salts, strong
mineral acids A mineral acid (or inorganic acid) is an acid An acid is a molecule or ion capable of donating a proton (hydrogen ion H+) (a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid), or, alternatively, capable of forming a covalent bond ...
can directly be distilled. One important invention that resulted from the discovery of the mineral acids is ''
aqua regia ''Aqua regia'' (; from Latin, "regal water" or "Royal water") is a mixture of nitric acid and hydrochloric acid, optimally in a molar concentration, molar ratio of 1:3.The relative concentrations of the two acids in water differ; values could be ...

aqua regia
'', a mixture of
nitric acid Nitric acid (), also known as ''aqua fortis'' (Latin for "strong water") and spirit of niter, is a highly corrosive mineral acid. The pure compound is colorless, but older samples tend to acquire a yellow cast due to decomposition into nitroge ...

nitric acid
and hydrochloric acid in a 1:3 proportion, capable of dissolving gold. This was first described in
pseudo-Geber Pseudo-Geber (or "Latin pseudo-Geber") refers to a corpus of alchemical writings dating to the late 13th and early 14th centuries, attributed to Geber (, died ), an early of the . The most important work of the Latin pseudo-Geber corpus is '' ...
's ''De inventione veritatis'' ("On the Discovery of Truth", after c. 1300), where ''aqua regia'' was prepared by adding ammonium chloride to nitric acid. However, the production of hydrochloric acid itself (i.e., as an isolated substance rather than as already mixed with nitric acid) depended on the use of more efficient cooling apparatus, which would only develop in subsequent centuries. Thus, recipes for the production of hydrochloric acid only appear in the late sixteenth century, the earliest being found in
Giovanni Battista Della Porta Giambattista della Porta (; 1535? – 4 February 1615), also known as Giovanni Battista Della Porta, was an Italian scholar, polymath A polymath ( el, πολυμαθής, ', "having learned much"; Latin Latin (, or , ) is a classical la ...

Giovanni Battista Della Porta
's (1535–1615) ''Magiae naturalis'' ("Natural Magic") and in the works of other contemporary chemists like
Andreas Libavius Andreas Libavius or Andrew Libavius was born in Halle, Germany c. 1550 and died in July 1616. Libavius was a renaissance man who spent time as a professor at the University of Jena The University of Jena, officially the Friedrich Schiller Uni ...

Andreas Libavius
(c. 1550–1616), Jean Beguin (1550–1620), and Oswald Croll (c. 1563– 1609). The knowledge of mineral acids such as hydrochloric acid would be of key importance to seventeenth-century chemists like Daniel Sennert (1572–1637) and
Robert Boyle Robert Boyle (; 25 January 1627 – 31 December 1691) was an Anglo-Irish Anglo-Irish () is a term which was more commonly used in the 19th and early 20th centuries to identify an ethnic group An ethnic group or ethnicity is a group ...

Robert Boyle
(1627–1691), who used their capability to rapidly dissolve metals in their demonstrations of the composite nature of bodies.


Etymology

Because it was produced from
rock salt Halite ( or ), commonly known as rock salt, is a type of salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its natural form as a cry ...

rock salt
according to the methods of
Johann Rudolph Glauber Johann Rudolf Glauber (10 March 1604 – 16 March 1670) was a German-Dutch alchemist Depiction of Ouroboros from the alchemical treatise ''Aurora consurgens'' (15th century), Zentralbibliothek Zürich, Switzerland Alchemy (from Arabic: ...
, hydrochloric acid was historically called by European alchemists ''spirits of salt'' or ''acidum salis'' (salt acid). Both names are still used, especially in other languages, such as german: Salzsäure, nl, Zoutzuur, sv, Saltsyra, es, Salfumán, tr, Tuz Ruhu, pl, kwas solny, hu, sósav and cs, kyselina solná Gaseous HCl was called ''marine acid air''. The name ''muriatic acid'' has the same origin (''muriatic'' means "pertaining to brine or salt", hence '' muriate'' means
hydrochlorideIn chemistry, a hydrochloride is an acid salt resulting, or regarded as resulting, from the reaction of hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution ...
), and this name is still sometimes used. The name ''hydrochloric acid'' was coined by the French chemist
Joseph Louis Gay-Lussac Joseph Louis Gay-Lussac (, , ; 6 December 1778  – 9 May 1850) was a French chemist and physicist. He is known mostly for his discovery that water is made of two parts hydrogen and one part oxygen (with Alexander von Humboldt Friedric ...

Joseph Louis Gay-Lussac
in 1814.


Industrial developments

During the
Industrial Revolution The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe Continental Europe or mainland Europe is the contiguous continent A continent is any of several large landmasse ...
in Europe, demand for
alkaline In chemistry, an alkali (; from ar, القلوي ''al-qaly'' "ashes of the saltwort") is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...

alkaline
substances increased. A new industrial process developed by
Nicolas Leblanc Nicolas Leblanc (6 December 1742 – 16 January 1806) was a French chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist A scientist is a person who conducts Scienti ...
of Issoudun, France enabled cheap large-scale production of
sodium carbonate Sodium carbonate, ·10, (also known as Natrium Carbonate, washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield modera ...

sodium carbonate
(soda ash). In this
Leblanc process The Leblanc process was an early industrial process Industrial processes are procedures involving chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that c ...
, common salt is converted to soda ash, using sulfuric acid, limestone, and coal, releasing hydrogen chloride as a by-product. Until the British Alkali Act 1863 and similar legislation in other countries, the excess HCl was often vented into the air. An early exception was the Bonnington Chemical Works where, in 1830, the HCl began to be captured and the hydrochloric acid produced was used in making sal ammoniac (
ammonium chloride Ammonium chloride is an inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. However, the distinction is not clearly defi ...

ammonium chloride
). After the passage of the act, soda ash producers were obliged to absorb the waste gas in water, producing hydrochloric acid on an industrial scale. In the 20th century, the Leblanc process was effectively replaced by the
Solvay process The Solvay process or ammonia-soda process is the major industrial process for the production of (soda ash, Na2CO3). The ammonia-soda process was developed into its modern form by the Belgian chemist during the 1860s. The ingredients for this are ...

Solvay process
without a hydrochloric acid by-product. Since hydrochloric acid was already fully settled as an important chemical in numerous applications, the commercial interest initiated other production methods, some of which are still used today. After the year 2000, hydrochloric acid is mostly made by absorbing by-product hydrogen chloride from .


Structure and reactions

Hydrochloric acid is the salt of the and chloride. Its ions are often written as H3O+ Cl, although the cation is in fact often bonded to other water molecules. A combined IR, Raman, X-ray, and neutron diffraction study of concentrated hydrochloric acid revealed that the primary form of H+(aq) in these solutions is H5O2+, which, along with the chloride anion, is hydrogen-bonded to neighboring water molecules in several ways. (See
Hydronium In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in th ...

Hydronium
for further discussion of this issue.)


Acidity

As a strong acid, hydrogen chloride has a large ''K''a. Theoretical estimates suggest that the p''K''a of hydrogen chloride is −5.9. However, it is important to distinguish between hydrogen chloride gas and hydrochloric acid. Due to the
leveling effect Leveling effect or solvent leveling refers to the effect of solvent on the properties of acids and bases. The strength of a strong acid is limited ("leveled") by the basicity of the solvent. Similarly the strength of a strong base is leveled by t ...
, except when highly concentrated and behavior deviates from ideality, ''hydrochloric acid'' (aqueous HCl) is only as acidic as the strongest proton donor available in water, the aquated proton (popularly known as "hydronium ion"). When chloride salts such as NaCl are added to aqueous HCl, they have only a minor effect on , indicating that Cl is a very weak
conjugate base A conjugate acid, within the Brønsted–Lowry acid–base theory The Brønsted–Lowry theory (also called proton theory of acids and bases) is an acid–base reaction An acid–base reaction is a chemical reaction A chemical reactio ...
and that HCl is fully dissociated. Dilute solutions of HCl have a pH close to that predicted by assuming full dissociation into hydrated H+ and Cl.


Physical properties

Physical properties A physical property is any Property (philosophy), property that is Measurement, measurable, whose value describes a state of a physical system. The changes in the physical properties of a system can be used to describe its changes between momenta ...
of hydrochloric acid, such as
boiling Boiling is the rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point, the temperature at which the vapour pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding atmosphere. Ther ...
and
melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can b ...

melting point
s,
density The density (more precisely, the volumetric mass density; also known as specific mass), of a substance is its per unit . The symbol most often used for density is ''ρ'' (the lower case Greek letter ), although the Latin letter ''D'' can also ...

density
, and , depend on the
concentration In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in t ...

concentration
or
molarity Molar concentration (also called molarity, amount concentration or substance concentration) is a measure of the concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types ...
of HCl in the aqueous solution. They range from those of water at very low concentrations approaching 0% HCl to values for fuming hydrochloric acid at over 40% HCl. Hydrochloric acid as the binary (two-component) mixture of HCl and H2O has a constant-boiling
azeotrope An azeotrope () or a constant boiling point mixture is a mixture In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that m ...

azeotrope
at 20.2% HCl and 108.6 °C (227 °F). There are four constant-
crystallization Crystallization or crystallisation is the process by which a solid Solid is one of the four fundamental states of matter 4 (four) is a number A number is a mathematical object A mathematical object is an abstract concept arising ...

crystallization
eutectic points for hydrochloric acid, between the
crystal A crystal or crystalline solid is a solid Solid is one of the four fundamental states of matter (the others being liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformatio ...

crystal
form of 3Ol (68% HCl), 5O2l (51% HCl), 7O3l (41% HCl), 3Ol·5H2O (25% HCl), and ice (0% HCl). There is also a metastable eutectic point at 24.8% between ice and the 7O3l crystallization. They are all Hydronium salts.


Production

Hydrochloric acid is usually prepared industrially by dissolving
hydrogen chloride The compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with d ...

hydrogen chloride
in water. Hydrogen chloride can be generated in many ways, and thus several precursors to hydrochloric acid exist. The large-scale production of hydrochloric acid is almost always integrated with the industrial scale production of other chemicals, such as in the
chloralkali process The chloralkali process (also chlor-alkali and chlor alkali In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, s ...
which produces
hydroxide Hydroxide is a diatomic anion with chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other sym ...
, hydrogen, and chlorine, the latter of which can be combined to produce HCl.


Industrial market

Hydrochloric acid is produced in solutions up to 38% HCl (concentrated grade). Higher concentrations up to just over 40% are chemically possible, but the
evaporation Evaporation is a type of vaporization Vaporization (or vaporisation) of an element or compound is a phase transition from the liquid phase to vapor. There are two types of vaporization: evaporation and boiling. Evaporation is a surface phe ...

evaporation
rate is then so high that storage and handling require extra precautions, such as pressurization and cooling. Bulk industrial-grade is therefore 30% to 35%, optimized to balance transport efficiency and product loss through evaporation. In the United States, solutions of between 20% and 32% are sold as muriatic acid. Solutions for household purposes in the US, mostly cleaning, are typically 10% to 12%, with strong recommendations to dilute before use. In the United Kingdom, where it is sold as "Spirits of Salt" for domestic cleaning, the potency is the same as the US industrial grade. In other countries, such as Italy, hydrochloric acid for domestic or industrial cleaning is sold as "Acido Muriatico", and its concentration ranges from 5% to 32%. Major producers worldwide include
Dow Chemical The Dow Chemical Company (TDCC) is an American multinational chemical corporation headquartered in Midland, Michigan, United States, and a subsidiary of Dow Inc. The company is among the three largest chemical producers in the world. Dow manu ...
at 2 million tonnes annually (Mt/year), calculated as HCl gas, Georgia Gulf Corporation,
Tosoh Corporation is a global chemical A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately ...
,
Akzo Nobel Akzo Nobel N.V., trading as AkzoNobel, is a Dutch Dutch commonly refers to: * Something of, from, or related to the Netherlands * Dutch people () * Dutch language () *Dutch language , spoken in Belgium (also referred as ''flemish'') Dutch ...
, and Tessenderlo at 0.5 to 1.5 Mt/year each. Total world production, for comparison purposes expressed as HCl, is estimated at 20 Mt/year, with 3 Mt/year from direct synthesis, and the rest as secondary product from organic and similar syntheses. By far, most hydrochloric acid is consumed captively by the producer. The open world market size is estimated at 5 Mt/year.


Applications

Hydrochloric acid is a strong inorganic acid that is used in many industrial processes such as refining metal. The application often determines the required product quality. Hydrogen chloride, not hydrochloric acid, is used more widely in industrial organic chemistry, e.g. for
vinyl chloride Vinyl chloride is an organochloride An organochloride, organochlorine compound, chlorocarbon, or chlorinated hydrocarbon is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that cov ...
and
dichloroethaneDichloroethane can refer to either of two isomer In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structur ...

dichloroethane
.


Pickling of steel

One of the most important applications of hydrochloric acid is in the
pickling Pickling is the process of preserving or extending the shelf life of food Food is any substance consumed to provide Nutrient, nutritional support for an organism. Food is usually of plant, animal or Fungus, fungal origin, and contains ess ...
of steel, to remove rust or
iron oxide Iron oxides are chemical compounds composed of iron and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, ...

iron oxide
scale from iron or steel before subsequent processing, such as
extrusion Extrusion is a process used to create objects of a fixed cross section (geometry), cross-sectional profile by pushing material through a Die (manufacturing), die of the desired cross-section. Its two main advantages over other manufacturing pro ...

extrusion
,
rolling Rolling is a type of motion that combines rotation A rotation is a circular movement of an object around a center (or point) of rotation. The plane (geometry), geometric plane along which the rotation occurs is called the ''rotation plane' ...
,
galvanizing Galvanization or galvanizing (American and British English spelling differences, also spelled galvanisation or galvanising) is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot- ...
, and other techniques. Technical quality HCl at typically 18% concentration is the most commonly used pickling agent for the pickling of
carbon steel Carbon steel is a steel Steel is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or frac ...
grades. : Fe3O4 + Fe + 8 HCl -> 4 FeCl2 + 4 H2O The spent acid has long been reused as
iron(II) chloride Iron(II) chloride, also known as ferrous chloride, is the chemical compound of formula FeCl2. It is a paramagnetic solid with a high melting point. The compound is white, but typical samples are often off-white. FeCl2 crystallizes from water as ...

iron(II) chloride
(also known as ferrous chloride) solutions, but high heavy-metal levels in the pickling liquor have decreased this practice. The steel pickling industry has developed hydrochloric acid regeneration processes, such as the spray roaster or the fluidized bed HCl regeneration process, which allow the recovery of HCl from spent pickling liquor. The most common regeneration process is the pyrohydrolysis process, applying the following formula: : 4 FeCl2 + 4 H2O + O2 -> 8 HCl + 2 Fe2O3 By recuperation of the spent acid, a closed acid loop is established. The
iron(III) oxide Iron(III) oxide or ferric oxide is the inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. However, the distinction is ...
by-product of the regeneration process is valuable, used in a variety of secondary industries.


Production of inorganic compounds

Akin to its use for pickling, hydrochloric acid is used to dissolve many metals, metal oxides and metal carbonates. The conversion are often depicted in simplified equations: : Zn + 2 HCl → ZnCl2 + H2 : NiO + 2 HCl → NiCl2 + H2O : CaCO3 + 2 HCl → CaCl2 + CO2 + H2O These processes are used to produce metal chlorides for analysis or further production.


pH control and neutralization

Hydrochloric acid can be used to regulate the
acidity An acid is a molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In phys ...
() of solutions. : OH^- + HCl -> H2O + Cl^- In industry demanding purity (food, pharmaceutical, drinking water), high-quality hydrochloric acid is used to control the pH of process water streams. In less-demanding industry, technical quality hydrochloric acid suffices for
neutralizing A neutralizing antibody (NAb) is an antibody that defends a cell (biology), cell from a pathogen or infectious particle by neutralizing any effect it has biologically. Neutralization renders the particle no longer infectious or pathogenic. Neutra ...
waste streams and swimming pool pH control.


Regeneration of ion exchangers

High-quality hydrochloric acid is used in the regeneration of ion exchange resins. is widely used to remove
ion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ...
s such as Na+ and Ca2+ from
aqueous An aqueous solution is a solution Image:SaltInWaterSolutionLiquid.jpg, Making a saline water solution by dissolving Salt, table salt (sodium chloride, NaCl) in water. The salt is the solute and the water the solvent. In chemistry, a solution ...
solutions, producing demineralized water. The acid is used to rinse the cations from the resins. Na+ is replaced with H+ and Ca2+ with 2 H+. Ion exchangers and demineralized water are used in all chemical industries, drinking water production, and many food industries.


Laboratory use

Of the six common strong
mineral acid A mineral acid (or inorganic acid) is an acid An acid is a molecule or ion An ion () is a particle In the Outline of physical science, physical sciences, a particle (or corpuscule in older texts) is a small wikt:local, localized ph ...
s in chemistry, hydrochloric acid is the monoprotic acid least likely to undergo an interfering reaction. It is one of the least hazardous strong acids to handle; despite its acidity, it contains the non-reactive and non-toxic chloride ion. Intermediate-strength hydrochloric acid solutions are quite stable upon storage, maintaining their concentrations over time. These attributes, plus the fact that it is available as a pure
reagent A reagent is a substance or compound added to a system to cause a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter ...
, make hydrochloric acid an excellent acidifying reagent. It is also inexpensive. Hydrochloric acid is the preferred acid in
titration Titration (also known as titrimetry and volumetric analysis) is a common laboratory method of quantitative chemical analysis Analytical chemistry studies and uses instruments and methods used to separate, identify, and quantify matter. In pr ...

titration
for determining the amount of bases. Strong acid titrants give more precise results due to a more distinct endpoint.
Azeotropic An azeotrope () or a constant boiling point mixture is a mixture of two or more liquids whose proportions cannot be altered or changed by simple distillation.Moore, Walter J. ''Physical Chemistry'', 3rd e Prentice-Hall 1962, pp. 140–142 This ha ...

Azeotropic
, or "constant-boiling", hydrochloric acid (roughly 20.2%) can be used as a
primary standard A primary standard in metrology 290px, alt=Man in white standing in front of a large machine, A scientist stands in front of the Microarcsecond Metrology (MAM) testbed. Metrology is the scientific study of measurement ' Measurement is the numb ...
in quantitative analysis, although its exact concentration depends on the
atmospheric pressure Atmospheric pressure, also known as barometric pressure (after the barometer A barometer is a scientific instrument that is used to measure air pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the ...
when it is prepared.


Other

Hydrochloric acid is used for a large number of small-scale applications, such as leather processing, household cleaning, and building construction.
Oil production The extraction of petroleum is the process by which usable petroleum Petroleum, also known as crude oil and oil, is a naturally occurring, yellowish-black liquid A liquid is a nearly incompressible fluid In physics, a fluid is a ...

Oil production
may be stimulated by injecting hydrochloric acid into the rock formation of an
oil well An oil well is a boring Boring may refer to: *Something that causes boredom Engineering and science * Boring (earth), drilling a hole, tunnel, or well in the earth ** Tunnel boring machine, a machine used in boring tunnels * Boring (manufactu ...

oil well
, dissolving a portion of the rock, and creating a large-pore structure. Oil well acidizing is a common process in the
North Sea oil North Sea oil is a mixture of hydrocarbon In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s ...
production industry. Hydrochloric acid has been used for dissolving calcium carbonate, e.g. such things as de-scaling kettles and for cleaning mortar off brickwork. When used on brickwork the reaction with the mortar only continues until the acid has all been converted, producing
calcium chloride Calcium chloride is an inorganic compound, a salt with the chemical formula CaCl2. It is a white coloured crystalline solid at room temperature, and it is highly soluble in water. It can be created by neutralising hydrochloric acid with calc ...

calcium chloride
,
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
, and water:
: CaCO3 + 2 HCl -> CaCl2 + CO2 + H2O Many chemical reactions involving hydrochloric acid are applied in the production of food, food ingredients, and
food additive Food is any substance consumed to provide nutritional support for an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology ...
s. Typical products include
aspartame Aspartame is an artificial non-saccharide is a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar formed when two monosaccharides are joined by glycosidic linkage. Like monosaccharides, disaccharides are s ...

aspartame
,
fructose Fructose, or fruit sugar, is a ketonic simple sugar Monosaccharides (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a cou ...

fructose
,
citric acid Citric acid is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, ...

citric acid
,
lysine Lysine (symbol Lys or K) is an α-amino acid Amino acids are organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, ...

lysine
,
hydrolyzed vegetable protein Hydrolyzed vegetable protein (HVP) products are foodstuffs obtained by protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a ...
as food enhancer, and in
gelatin Gelatin or gelatine (from la, gelatus meaning "stiff" or "frozen") is a translucent, colorless, flavorless food ingredient, commonly derived from collagen taken from animal body parts. It is brittle when dry and rubbery when moist. It may also ...
production. Food-grade (extra-pure) hydrochloric acid can be applied when needed for the final product.


Presence in living organisms

Gastric acid Gastric acid, gastric juice, or stomach acid, is a digestive fluid formed within the stomach lining. With a pH between 1 and 3, gastric acid An acid is a or capable of donating a (hydrogen ion H+) (a ), or, alternatively, capable of for ...
is one of the main secretions of the stomach. It consists mainly of hydrochloric acid and acidifies the stomach content to a pH of 1 to 2. Chloride (Cl) and hydrogen (H+) ions are secreted separately in the stomach fundus region at the top of the stomach by
parietal cell Parietal cells (also known as oxyntic cells) are epithelial cells Epithelium () is one of the four basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological ...

parietal cell
s of the
gastric mucosa The gastric mucosa is the mucous membrane layer of the stomach, which contains the glands and the gastric pits. In humans, it is about 1 mm thick, and its surface is smooth, soft, and velvety. It consists of simple columnar epithelium, lamina ...
into a secretory network called canaliculi before it enters the stomach lumen. Gastric acid acts as a barrier against
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...
s to prevent infections and is important for the digestion of food. Its low pH denatures
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

protein
s and thereby makes them susceptible to degradation by
digestive enzyme Digestive may refer to: Biology *Digestion Digestion is the breakdown of large insoluble food Food is any substance consumed to provide nutritional Nutrition is the biochemical Biochemistry or biological chemistry, is the study of c ...
s such as
pepsin Pepsin is an endopeptidase that breaks down proteins into smaller peptides. It is produced in the gastric chief cells of the stomach lining and is one of the main digestive enzymes in the digestive systems of humans and many other animals, where ...

pepsin
. The low pH also activates the enzyme precursor
pepsinogen Pepsin is an endopeptidase that breaks down protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions w ...
into the active enzyme pepsin by self-cleavage. After leaving the stomach, the hydrochloric acid of the
chyme Chyme or chymus (; from Ancient Greek, Greek χυμός ''khymos'', "juice") is the semi-fluid mass of partly digested food that is expelled by a person's stomach, through the pyloric valve, into the duodenumduodenum The duodenum is the first section of the small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from foo ...

duodenum
by
bicarbonate In inorganic chemistry, bicarbonate (International Union of Pure and Applied Chemistry, IUPAC-recommended nomenclature: hydrogen carbonate) is an intermediate form in the deprotonation of carbonic acid. It is a Polyatomic ion, polyatomic anion w ...

bicarbonate
. The stomach itself is protected from the strong acid by the
secretion Secretion is the movement of material from one point to another, such as a secreted chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up ...
of a thick
mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membrane A mucous membrane or mucosa is a biological membrane, membrane that lines various cavities in the body and covers the surface of internal organs. It consists o ...
layer, and by
secretin Secretin is a hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellular organisms, that are transported to distant organs to regulate physiology and / or behavior. Hor ...
induced buffering with
sodium bicarbonate Sodium bicarbonate ( IUPAC name: sodium hydrogen carbonate), commonly known as baking soda or bicarbonate of soda, is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cation (Na+) and a bicarbonate anion ( HCO3 ...

sodium bicarbonate
.
Heartburn Heartburn, also known as pyrosis, cardialgia or acid indigestion, is a burning sensation in the central chest or upper central abdomen. The discomfort often rises in the chest and may radiate to the neck, throat, or angle of the arm. Heartbur ...
or
peptic ulcer Peptic ulcer disease (PUD) is a break in the inner Gastric mucosa, lining of the stomach, the first part of the small intestine, or sometimes the lower esophagus. An ulcer in the stomach is called a gastric ulcer, while one in the first part of t ...

peptic ulcer
s can develop when these mechanisms fail. Drugs of the antihistaminic and
proton pump inhibitor Proton-pump inhibitors (PPIs) are members of a class of medications whose main action is a profound and prolonged reduction of stomach acid production. Within the class of medications, there is no clear evidence that one agent works better than ...
classes can inhibit the production of acid in the stomach, and
antacid An antacid is a substance which neutralizes stomach acidity and is used to relieve heartburn Heartburn, also known as pyrosis, cardialgia or acid indigestion, is a burning sensation in the central chest or upper central abdomen. The disc ...
s are used to neutralize excessive existing acid.


Safety

Being a strong acid, hydrochloric acid is corrosive to living tissue and to many materials, but not to rubber. Typically, rubber protective gloves and related protective gear are used when handling concentrated solutions. Hydrochloric acid has been listed as a Table II precursor under the 1988
United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances The United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances of 1988 is one of three major drug control treaties currently in force. It provides additional legal mechanisms for enforcing the 1961 Single Conv ...
because of its use in the production of
heroin Heroin, also known as diacetylmorphine and diamorphine among other names, is an opioid Opioids are substances that act on opioid receptor Opioid receptors are a group of inhibitory G protein-coupled receptors with opioids as ligands. T ...

heroin
,
cocaine Cocaine (from , from , ultimately from Quechuan languages, Quechua: ''kúka'') is a tropane alkaloid and stimulant drug obtained primarily from the leaves of two coca species native to South America, ''Erythroxylum coca'' and ''Erythroxylu ...

cocaine
, and
methamphetamine Methamphetamine (contracted from ) is a potent central nervous system (CNS) stimulant that is mainly used as a recreational drug use, recreational drug and less commonly as a second-line treatment for attention deficit hyperactivity disord ...

methamphetamine
.


See also

*
Chloride The chloride ion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects th ...

Chloride
, inorganic salts of hydrochloric acid *
HydrochlorideIn chemistry, a hydrochloride is an acid salt resulting, or regarded as resulting, from the reaction of hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution ...
, organic salts of hydrochloric acid *
Aqua regia ''Aqua regia'' (; from Latin, "regal water" or "Royal water") is a mixture of nitric acid and hydrochloric acid, optimally in a molar concentration, molar ratio of 1:3.The relative concentrations of the two acids in water differ; values could be ...

Aqua regia


References


External links


NIST WebBook, general link


an

at ''
The Periodic Table of Videos ''The Periodic Table of Videos'' (usually shortened to ''Periodic Videos'') is a series of videos about chemical elements 400px, The periodic table of the chemical elements In chemistry Chemistry is the scientific discipline involved ...
'' (University of Nottingham) * Calculators
surface tensions
an
densities, molarities and molalities
of aqueous HCl ; General safety information





; Pollution information

{{DEFAULTSORT:Hydrochloric Acid Mineral acids Alchemical substances Chlorides Nonmetal halides Photographic chemicals Stomach Solutions E-number additives