Hydrochloric acid

Hydrochloric acid or muriatic acid is a colorless inorganic chemical system with the formula H
. Hydrochloric acid has a distinctive pungent smell. It is classified as strongly acidic and can attack the skin over a wide composition range, since the hydrogen chloride completely dissociates in aqueous solution.

Hydrochloric acid is the simplest chlorine-based acid system containing water. It is a solution of hydrogen chloride and water, and a variety of other chemical species, including hydronium and chloride ions. It is an important chemical reagent and industrial chemical, used in the production of polyvinyl chloride for plastic. In households, diluted hydrochloric acid is often used as a descaling agent. In the food industry, hydrochloric acid is used as a food additive and in the production of gelatin. Hydrochloric acid is also used in leather processing.

Hydrochloric acid was discovered by the alchemist Jabir ibn Hayyan around the year 800 AD.[7][8] It was historically called acidum salis and spirits of salt because it was produced from rock salt and "green vitriol" (Iron(II) sulfate) (by Basilius Valentinus in the 15th century) and later from the chemically similar common salt and sulfuric acid (by Johann Rudolph Glauber in the 17th century). Free hydrochloric acid was first formally described in the 16th century by Libavius. Later, it was used by chemists such as Glauber, Priestley, and Davy in their scientific research. Unless pressurized or cooled, hydrochloric acid will turn into a gas if there is around 60% or less of water. Hydrochloric acid is also known as hydronium chloride, in contrast to its anhydrous parent known as hydrogen chloride, or dry HCl.

Hydrochloric acid
3D model of hydrogen chloride
3D model of water
3D model of the chloride anion
3D model of the hydronium cation
Sample of hydrochloric acid in a bottle
IUPAC name
Other names
  • Muriatic acid[1]
  • Spirits of salt[2]
    Hydronium chloride
    Chlorhydric Acid
ECHA InfoCard 100.210.665
EC Number 231-595-7
E number E507 (acidity regulators, ...)
UN number 1789
Appearance Colorless, transparent liquid
Melting point Concentration-dependent – see table
Boiling point Concentration-dependent – see table
log P 0.00[4]
Acidity (pKa) −5.9 (HCl gas)[5]
A09AB03 (WHO) B05XA13 (WHO)
Safety data sheet See: data page
GHS pictograms GHS-pictogram-exclamGHS-pictogram-acid
GHS signal word Danger[6]
H290, H314, H335[6]
P260, P280, P303+361+353, P305+351+338[6]
NFPA 704
Related compounds
Related compounds
Supplementary data page
Refractive index (n),
Dielectric constantr), etc.
Phase behaviour
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).


Hydrochloric acid was known to European alchemists as spirits of salt or acidum salis (salt acid). Both names are still used, especially in other languages, such as German: Salzsäure, Dutch: Zoutzuur, Swedish: Saltsyra, Turkish: Tuz Ruhu, Polish: kwas solny, Bulgarian: солна киселина, Russian: соляная кислота, Chinese: 鹽酸, Korean: 염산, and Taiwanese: iâm-sng. Gaseous HCl was called marine acid air.

The old (pre-systematic) name muriatic acid has the same origin (muriatic means "pertaining to brine or salt", hence muriate means hydrochloride), and this name is still sometimes used.[1][9] The name hydrochloric acid was coined by the French chemist Joseph Louis Gay-Lussac in 1814.[10]


Hydrochloric acid has been an important and frequently used chemical from early history and was discovered by the alchemist Jabir ibn Hayyan around the year 800 AD.[11][8]

Aqua regia, a mixture consisting of hydrochloric and nitric acids, prepared by dissolving sal ammoniac in nitric acid, was described in the works of Pseudo-Geber, a 13th-century European alchemist.[12][13][14][15][16] Other references suggest that the first mention of aqua regia is in Byzantine manuscripts dating to the end of the 13th century.[17][18][19][20]

Free hydrochloric acid was first formally described in the 16th century by Libavius, who prepared it by heating salt in clay crucibles.[21] Other authors claim that pure hydrochloric acid was first discovered by the German Benedictine monk Basil Valentine in the 15th century,[22] when he heated common salt and green vitriol,[23] whereas others argue that there is no clear reference to the preparation of pure hydrochloric acid until the end of the 16th century.[17]

In the 17th century, Johann Rudolf Glauber from Karlstadt am Main, Germany used sodium chloride salt and sulfuric acid for the preparation of sodium sulfate in the Mannheim process, releasing hydrogen chloride gas. Joseph Priestley of Leeds, England prepared pure hydrogen chloride in 1772,[24] and by 1808 Humphry Davy of Penzance, England had proved that the chemical composition included hydrogen and chlorine.[25]

During the Industrial Revolution in Europe, demand for alkaline substances increased. A new industrial process developed by Nicolas Leblanc of Issoudun, France enabled cheap large-scale production of sodium carbonate (soda ash). In this Leblanc process, 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 vented into the air. 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.[14][26]

In the 20th century, the Leblanc process was effectively replaced by the 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 industrial organic compounds production.[14][26][27]

Since 1988, 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 because of its use in the production of heroin, cocaine, and methamphetamine.[28]

Structure and reactions

Hydrochloric acid is the salt of hydronium ion, H3O+ and chloride. It is usually prepared by treating HCl with water.[29][30]

However, the speciation of hydrochloric acid is more complicated than this simple equation implies. The structure of bulk water is infamously complex, and likewise, the formula H3O+ is also a gross oversimplification of the true nature of the solvated proton, H+(aq), present in hydrochloric acid. A combined IR, Raman, X-ray and neutron diffraction study of concentrated solutions of 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 different ways. (In H5O2+, the proton is sandwiched midway between two water molecules at 180°). The author suggests that H3O+ may become more important in dilute HCl solutions.[31] (See Hydronium for further discussion of this issue.)

Hydrochloric acid is a strong acid, since it is completely dissociated in water.[29][30] It can therefore be used to prepare salts containing the Cl anion called chlorides.

As a strong acid, hydrogen chloride has a large Ka. Theoretical attempts to assign the pKa of hydrogen chloride have been made, with the most recent estimate being −5.9.[5] However, it is important to distinguish between hydrogen chloride gas and hydrochloric acid. Due to the leveling effect, 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 pH, indicating that Cl is a very weak conjugate base and that HCl is fully dissociated in aqueous solution. Dilute solutions of HCl have a pH close to that predicted by assuming full dissociation into hydrated H+ and Cl.[32]

Of the six common strong mineral acids in chemistry, hydrochloric acid is the monoprotic acid least likely to undergo an interfering oxidation-reduction reaction. It is one of the least hazardous strong acids to handle; despite its acidity, it consists of 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, make hydrochloric acid an excellent acidifying reagent.

Hydrochloric acid is the preferred acid in titration for determining the amount of bases. Strong acid titrants give more precise results due to a more distinct endpoint. Azeotropic, or "constant-boiling", hydrochloric acid (roughly 20.2%) can be used as a primary standard in quantitative analysis, although its exact concentration depends on the atmospheric pressure when it is prepared.[33]

Hydrochloric acid is frequently used in chemical analysis to prepare ("digest") samples for analysis. Concentrated hydrochloric acid dissolves many metals and forms oxidized metal chlorides and hydrogen gas. It also reacts with basic compounds such as calcium carbonate or copper(II) oxide, forming the dissolved chlorides that can be analyzed.[29][30]

Physical properties

Concentration Density Molarity pH Viscosity Specific
kg HCl/kg  kg HCl/m3 Baumé kg/L mol/L mPa·s kJ/(kg·K) kPa °C °C
10% 104.80 6.6 1.048 2.87 −0.5 1.16 3.47 1.95 103 −18
20% 219.60 13 1.098 6.02 −0.8 1.37 2.99 1.40 108 −59
30% 344.70 19 1.149 9.45 −1.0 1.70 2.60 2.13 90 −52
32% 370.88 20 1.159 10.17 −1.0 1.80 2.55 3.73 84 −43
34% 397.46 21 1.169 10.90 −1.0 1.90 2.50 7.24 71 −36
36% 424.44 22 1.179 11.64 −1.1 1.99 2.46 14.5 61 −30
38% 451.82 23 1.189 12.39 −1.1 2.10 2.43 28.3 48 −26
The reference temperature and pressure for the above table are 20 °C and 1 atmosphere (101.325 kPa).
Vapour pressure values are taken from the International Critical Tables and refer to the total vapour pressure of the solution.
Phase diagram HCl H2O s l
Melting temperature as a function of HCl concentration in water[34][35]

Physical properties of hydrochloric acid, such as boiling and melting points, density, and pH, depend on the concentration or molarity 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.[29][30][36]

Hydrochloric acid as the binary (two-component) mixture of HCl and H2O has a constant-boiling azeotrope at 20.2% HCl and 108.6 °C (227 °F). There are four constant-crystallization eutectic points for hydrochloric acid, between the crystal form of HCl·H2O (68% HCl), HCl·2H2O (51% HCl), HCl·3H2O (41% HCl), HCl·6H2O (25% HCl), and ice (0% HCl). There is also a metastable eutectic point at 24.8% between ice and the HCl·3H2O crystallization.[36]


Hydrochloric acid is prepared by dissolving 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.

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 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.[14] 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 at 2 million metric tons annually (2 Mt/year), calculated as HCl gas, Georgia Gulf Corporation, Tosoh Corporation, Akzo Nobel, 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.[14]


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.[14]

Pickling of steel

One of the most important applications of hydrochloric acid is in the pickling of steel, to remove rust or iron oxide scale from iron or steel before subsequent processing, such as extrusion, rolling, galvanizing, and other techniques.[14][27] Technical quality HCl at typically 18% concentration is the most commonly used pickling agent for the pickling of carbon steel grades.

The spent acid has long been reused 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:[14]

By recuperation of the spent acid, a closed acid loop is established.[27] The iron(III) oxide by-product of the regeneration process is valuable, used in a variety of secondary industries.[14]

Production of organic compounds

Another major use of hydrochloric acid is in the production of organic compounds, such as vinyl chloride and dichloroethane for PVC. This is often captive use, consuming locally produced hydrochloric acid that never actually reaches the open market. Other organic compounds produced with hydrochloric acid include bisphenol A for polycarbonate, activated carbon, and ascorbic acid, as well as numerous pharmaceutical products.[27]

(dichloroethane by oxychlorination)

Production of inorganic compounds

Numerous products can be produced with hydrochloric acid in normal acid-base reactions, resulting in inorganic compounds. These include water treatment chemicals such as iron(III) chloride and polyaluminium chloride (PAC).

(iron(III) chloride from magnetite)

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

Other inorganic compounds produced with hydrochloric acid include road application salt calcium chloride, nickel(II) chloride for electroplating, and zinc chloride for the galvanizing industry and battery production.[27]

(calcium chloride from limestone)

pH control and neutralization

Hydrochloric acid can be used to regulate the acidity (pH) of solutions.

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 waste streams and swimming pool pH control.[27]

Regeneration of ion exchangers

High-quality hydrochloric acid is used in the regeneration of ion exchange resins. Cation exchange is widely used to remove ions such as Na+ and Ca2+ from aqueous solutions, producing demineralized water. The acid is used to rinse the cations from the resins.[14] 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.[14]


Hydrochloric acid is used for a large number of small-scale applications, such as leather processing, purification of common salt, household cleaning,[37] and building construction.[27] Oil production may be stimulated by injecting hydrochloric acid into the rock formation of an 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 production industry.[14]

Hydrochloric acid has been used for dissolving calcium carbonate, i.e. such things as de-scaling kettles and for cleaning mortar off brickwork, but it is a hazardous liquid which must be used with care. When used on brickwork the reaction with the mortar only continues until the acid has all been converted, producing calcium chloride, carbon dioxide, and water:

Many chemical reactions involving hydrochloric acid are applied in the production of food, food ingredients, and food additives. Typical products include aspartame, fructose, citric acid, lysine, hydrolyzed vegetable protein as food enhancer, and in gelatin production. Food-grade (extra-pure) hydrochloric acid can be applied when needed for the final product.[14][27]

Presence in living organisms

Stomach mucosal layer labeled
Diagram of alkaline mucous layer in stomach with mucosal defense mechanisms

Gastric acid 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.[38][39]

Chloride (Cl) and hydrogen (H+) ions are secreted separately in the stomach fundus region at the top of the stomach by parietal cells of the gastric mucosa into a secretory network called canaliculi before it enters the stomach lumen.[40]

Gastric acid acts as a barrier against microorganisms to prevent infections and is important for the digestion of food. Its low pH denatures proteins and thereby makes them susceptible to degradation by digestive enzymes such as pepsin. The low pH also activates the enzyme precursor pepsinogen into the active enzyme pepsin by self-cleavage. After leaving the stomach, the hydrochloric acid of the chyme is neutralized in the duodenum by sodium bicarbonate.[38]

The stomach itself is protected from the strong acid by the secretion of a thick mucus layer, and by secretin induced buffering with sodium bicarbonate. Heartburn or peptic ulcers can develop when these mechanisms fail. Drugs of the antihistaminic and proton pump inhibitor classes can inhibit the production of acid in the stomach, and antacids are used to neutralize excessive existing acid.[38][41]


UN transport pictogram - 8
Hazard C
Classification[42] R-Phrases
10–25% Irritant (Xi) R36/37/38
> 25% Corrosive (C) R35 R37

Concentrated hydrochloric acid (fuming hydrochloric acid) forms acidic mists. Both the mist and the solution have a corrosive effect on human tissue, with the potential to damage respiratory organs, eyes, skin, and intestines irreversibly. Upon mixing hydrochloric acid with common oxidizing chemicals, such as sodium hypochlorite (bleach, NaClO) or potassium permanganate (KMnO4), the toxic gas chlorine is produced.

Personal protective equipment such as latex gloves, protective eye goggles, and chemical-resistant clothing and shoes will minimize risks when handling hydrochloric acid. The United States Environmental Protection Agency rates and regulates hydrochloric acid as a toxic substance.[43]

The UN number or DOT number is 1789. This number will be displayed on a placard on the container.

See also


  1. ^ a b "Hydrochloric Acid". Archived from the original on 15 October 2010. Retrieved 16 September 2010.
  2. ^ "spirits of salt". Retrieved 29 May 2012.
  3. ^ Henri A. Favre; Warren H. Powell, eds. (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. Cambridge: The Royal Society of Chemistry. p. 131.
  4. ^ "Hydrochloric acid_msds".
  5. ^ a b Trummal, Aleksander; Lipping, Lauri; Kaljurand, Ivari; Koppel, Ilmar A.; Leito, Ivo (2016-05-06). "Acidity of Strong Acids in Water and Dimethyl Sulfoxide". The Journal of Physical Chemistry A. 120 (20): 3663–3669. doi:10.1021/acs.jpca.6b02253. ISSN 1089-5639. PMID 27115918.
  6. ^ a b c Sigma-Aldrich Co., Hydrochloric acid. Retrieved on 2017-11-29.
  7. ^ "Human Metabolome Database: Showing metabocard for Hydrochloric acid (HMDB0002306)". www.hmdb.ca. Retrieved 2017-11-04.
  8. ^ a b Pubchem. "hydrochloric acid". pubchem.ncbi.nlm.nih.gov. Retrieved 2017-11-04.
  9. ^ "Muriatic Acid" (PDF). PPG Industries. 2005. Archived from the original (PDF) on 2 July 2015. Retrieved 10 September 2010.
  10. ^ Gay-Lussac (1814) "Mémoire sur l'iode" (Memoir on iodine), Annales de Chemie, 91 : 5–160. From page 9: " … mais pour les distinguer, je propose d'ajouter au mot spécifique de l'acide que l'on considère, le mot générique de hydro; de sorte que le combinaisons acide de hydrogène avec le chlore, l'iode, et le soufre porteraient le nom d'acide hydrochlorique, d'acide hydroiodique, et d'acide hydrosulfurique; … " ( … but in order to distinguish them, I propose to add to the specific suffix of the acid being considered, the general prefix hydro, so that the acidic combinations of hydrogen with chlorine, iodine, and sulfur will bear the name hydrochloric acid, hydroiodic acid, and hydrosulfuric acid; … )
  11. ^ "Human Metabolome Database: Showing metabocard for Hydrochloric acid (HMDB0002306)". www.hmdb.ca. Retrieved 2017-11-04.
  12. ^ Bauer, Hugo (2009). A history of chemistry. BiblioBazaar, LLC. p. 31. ISBN 978-1-103-35786-4.
  13. ^ Karpenko, V.; Norris, J.A. (2001). "Vitriol in the history of chemistry" (PDF). Chem. Listy. 96: 997.
  14. ^ a b c d e f g h i j k l m "Hydrochloric Acid". Chemicals Economics Handbook. SRI International. 2001. pp. 733.4000A–733.3003F.
  15. ^ Norton, S. (2008). "A Brief History of Potable Gold". Molecular Interventions. 8 (3): 120–3. doi:10.1124/mi.8.3.1. PMID 18693188.
  16. ^ Thompson, C. J. S. (2002). "Alchemy and Alchemists" (Reprint of the edition published by George G. Harrap and Co., London, 1932 ed.). Dover Publications, Inc., Mineola, NY: 61, 18.
  17. ^ a b Forbes, Robert James (1970). A short history of the art of distillation: from the beginnings up to the death of Cellier Blumenthal. BRILL. ISBN 978-90-04-00617-1.
  18. ^ Myers, R. L. (2007). The 100 most important chemical compounds: a reference guide. Greenwood Publishing Group. p. 141. ISBN 978-0-313-33758-1.
  19. ^ Datta, N. C. (2005). The story of chemistry. Universities Press. p. 40. ISBN 978-81-7371-530-3.
  20. ^ Pereira, Jonathan (1854). The elements of materia medica and therapeutics, Volume 1. Longman, Brown, Green, and Longmans. p. 387.
  21. ^ Leicester, Henry Marshall (1971). The historical background of chemistry. Courier Dover Publications. p. 99. ISBN 978-0-486-61053-5. Retrieved 19 August 2010.
  22. ^ Waite, A. E. (1992). Secret Tradition in Alchemy (public document ed.). Kessinger Publishing.
  23. ^ Von Meyer, Ernst Sigismund (1891). A History of Chemistry from Earliest Times to the Present Day. London, New York, Macmillan. p. 51.
  24. ^ Priestley, Joseph (1772). "Observations on different kinds of air [i.e., gases]". Philosophical Transactions of the Royal Society of London. 62: 147–264 (234–244). doi:10.1098/rstl.1772.0021.
  25. ^ Davy, Humphry (1808). "Electro-chemical researches, on the decomposition of the earths; with observations on the metals obtained from the alkaline earths, and on the amalgam procured from ammonia". Philosophical Transactions of the Royal Society of London. 98: 333–370. doi:10.1098/rstl.1808.0023. p. 343: When potassium was heated in muriatic acid gas [i.e., gaseous hydrogen chloride], as dry as it could be obtained by common chemical means, there was a violent chemical action with ignition; and when the potassium was in sufficient quantity, the muriatic acid gas wholly disappeared, and from one-third to one-fourth of its volume of hydrogene was evolved, and muriate of potash [i.e., potassium chloride] was formed. (The reaction was: 2HCl + 2K → 2KCl + H2)
  26. ^ a b Aftalion, Fred (1991). A History of the International Chemical Industry. Philadelphia: University of Pennsylvania Press. ISBN 978-0-8122-1297-6.
  27. ^ a b c d e f g h Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 946–48. ISBN 978-0-08-037941-8.
  28. ^ "List of precursors and chemicals frequently used in the illicit manufacture of narcotic drugs and psychotropic substances under international control" (PDF) (Annex to Form D ("Red List")) (Eleventh ed.). International Narcotics Control Board. January 2007. Archived from the original (PDF) on 2008-02-27.
  29. ^ a b c d Lide, David (2000). CRC Handbook of Chemistry and Physics (81st ed.). CRC Press. ISBN 978-0-8493-0481-1.
  30. ^ a b c d Perry, R.; Green D.; Maloney J. (1984). Perry's Chemical Engineers' Handbook (6th ed.). McGraw-Hill Book Company. ISBN 978-0-07-049479-4.
  31. ^ Agmon, Noam (January 1998). "Structure of Concentrated HCl Solutions". The Journal of Physical Chemistry A. 102 (1): 192–199. CiteSeerX doi:10.1021/jp970836x. ISSN 1089-5639.
  32. ^ McCarty, Christopher G.; Vitz, Ed (May 2006). "pH Paradoxes: Demonstrating That It Is Not True That pH ≡ −log[H+]". Journal of Chemical Education. 83 (5): 752. doi:10.1021/ed083p752. ISSN 0021-9584.
  33. ^ Mendham, J.; Denney, R. C.; Barnes, J. D.; Thomas, M. J. K.; Denney, R. C.; Thomas, M. J. K. (2000). Vogel's Quantitative Chemical Analysis (6th ed.). New York: Prentice Hall. ISBN 978-0-582-22628-9.
  34. ^ "Systemnummer 6 Chlor". Gmelins Handbuch der Anorganischen Chemie. Chemie Berlin. 1927.
  35. ^ "Systemnummer 6 Chlor, Ergänzungsband Teil B – Lieferung 1". Gmelins Handbuch der Anorganischen Chemie. Chemie Weinheim. 1968.
  36. ^ a b Aspen Properties. binary mixtures modeling software (calculations by Akzo Nobel Engineering ed.). Aspen Technology. 2002–2003.
  37. ^ Simhon, Rachel (13 September 2003). "Household plc: really filthy bathroom". The Daily Telegraph. London. Retrieved 31 March 2010.
  38. ^ a b c Maton, Anthea; Jean Hopkins; Charles William McLaughlin; Susan Johnson; Maryanna Quon Warner; David LaHart; Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. ISBN 978-0-13-981176-0.
  39. ^ Haas, Elson. "Digestive Aids: Hydrochloric acid". healthy.net.
  40. ^ Arthur, C.; Guyton, M. D.; Hall, John E. (2000). Textbook of Medical Physiology (10th ed.). W.B. Saunders Company. ISBN 978-0-7216-8677-6.
  41. ^ Bowen, R. (18 March 2003). "Control and Physiologic Effects of Secretin". Colorado State University. Retrieved 16 March 2009.
  42. ^ "Council Directive 67/548/EEC of 27 June 1967 on the approximation of laws, regulations and administrative provisions relating to the classification, packaging and labelling of dangerous substances". EUR-lex. Retrieved 2 September 2008.
  43. ^ "HCl score card". United States Environmental Protection Agency. Retrieved 12 September 2007.

External links

General safety information
Pollution information

3-MCPD (3-monochloropropane-1,2-diol or 3-chloropropane-1,2-diol) is an organic chemical compound which is the most common member of chemical food contaminants known as chloropropanols. It is suspected to be carcinogenic in humans.

It is primarily created in foods during protein hydrolysis when hydrochloric acid is added at high temperature to speed up the breakdown of proteins into amino acids. As a byproduct of this process, chloride can react with the glycerol backbone of lipids to produce 3-MCPD. 3-MCPD can also occur in foods which have been in contact with materials containing epichlorohydrin-based wet-strength resins which are used in the production of some tea bags and sausage casings.In 2009, 3-MCPD was found in some East Asian and Southeast Asian sauces such as oyster sauce, Hoisin sauce, and soy sauce. Using hydrochloric acid rather than traditional slow fermentation is a far cheaper and faster method but unavoidably creates chloropropanols. A 2013 European Food Safety Authority report indicated margarine, vegetable oils (excluding walnut oil), preserved meats, bread, and fine bakery wares as major sources in Europe.3-MCPD can also be found in many paper products treated with polyamidoamine-epichlorohydrin wet-strength resins.


An acid is a molecule or ion capable of donating a hydron (proton or hydrogen ion H+), or, alternatively, capable of forming a covalent bond with an electron pair (a Lewis acid).The first category of acids is the proton donors or Brønsted acids. In the special case of aqueous solutions, proton donors form the hydronium ion H3O+ and are known as Arrhenius acids. Brønsted and Lowry generalized the Arrhenius theory to include non-aqueous solvents. A Brønsted or Arrhenius acid usually contains a hydrogen atom bonded to a chemical structure that is still energetically favorable after loss of H+.

Aqueous Arrhenius acids have characteristic properties which provide a practical description of an acid. Acids form aqueous solutions with a sour taste, can turn blue litmus red, and react with bases and certain metals (like calcium) to form salts. The word acid is derived from the Latin acidus/acēre meaning sour. An aqueous solution of an acid has a pH less than 7 and is colloquially also referred to as 'acid' (as in 'dissolved in acid'), while the strict definition refers only to the solute. A lower pH means a higher acidity, and thus a higher concentration of positive hydrogen ions in the solution. Chemicals or substances having the property of an acid are said to be acidic.

Common aqueous acids include hydrochloric acid (a solution of hydrogen chloride which is found in gastric acid in the stomach and activates digestive enzymes), acetic acid (vinegar is a dilute aqueous solution of this liquid), sulfuric acid (used in car batteries), and citric acid (found in citrus fruits). As these examples show, acids (in the colloquial sense) can be solutions or pure substances, and can be derived from acids (in the strict sense) that are solids, liquids, or gases. Strong acids and some concentrated weak acids are corrosive, but there are exceptions such as carboranes and boric acid.

The second category of acids are Lewis acids, which form a covalent bond with an electron pair. An example is boron trifluoride (BF3), whose boron atom has a vacant orbital which can form a covalent bond by sharing a lone pair of electrons on an atom in a base, for example the nitrogen atom in ammonia (NH3). Lewis considered this as a generalization of the Brønsted definition, so that an acid is a chemical species that accepts electron pairs either directly or by releasing protons (H+) into the solution, which then accept electron pairs. However, hydrogen chloride, acetic acid, and most other Brønsted-Lowry acids cannot form a covalent bond with an electron pair and are therefore not Lewis acids. Conversely, many Lewis acids are not Arrhenius or Brønsted-Lowry acids. In modern terminology, an acid is implicitly a Brønsted acid and not a Lewis acid, since chemists almost always refer to a Lewis acid explicitly as a Lewis acid.

Americium dioxide

Americium dioxide (AmO2) is a black

compound of americium. In the solid state AmO2 adopts the fluorite, CaF2 structure. It is used as a source of alpha particles.

Aqua regia

Aqua regia (; from Latin, lit. "regal water" or "king's water") is a mixture of nitric acid and hydrochloric acid, optimally in a molar ratio of 1:3. Aqua regia is a yellow-orange (sometimes red) fuming liquid, so named by alchemists because it can dissolve the noble metals gold and platinum, though not all metals.

Condensed tannin

Condensed tannins (proanthocyanidins, polyflavonoid tannins, catechol-type tannins, pyrocatecollic type tannins, non-hydrolyzable tannins or flavolans) are polymers formed by the condensation of flavans. They do not contain sugar residues.They are called proanthocyanidins as they yield anthocyanidins when depolymerized under oxidative conditions. Different types of condensed tannins exist, such as the procyanidins, propelargonidins, prodelphinidins, profisetinidins, proteracacinidins, proguibourtinidins or prorobinetidins. All of the above are formed from flavan-3-ols, but flavan-3,4-diols, called (leucoanthocyanidin) also form condensed tannin oligomers, e.g. leuco-fisetinidin form profisetinidin, and flavan-4-ols form condensed tannins, e.g. 3',4',5,7-flavan-4-ol form proluteolinidin (luteoforolor). One particular type of condensed tannin, found in grape, are procyanidins, which are polymers of 2 to 50 (or more) Catechin units joined by carbon-carbon bonds. These are not susceptible to being cleaved by hydrolysis.

While many hydrolyzable tannins and most condensed tannins are water-soluble, several tannins are also highly octanol-soluble. Some large condensed tannins are insoluble. Differences in solubilities are likely to affect their biological functions.

Descaling agent

A descaling agent or chemical descaler is a chemical substance used to remove limescale from metal surfaces in contact with hot water, such as in boilers, water heaters, and kettles. Descaling agents are typically acidic compounds such as hydrochloric acid that react with the alkaline carbonate compounds present in the scale, producing carbon dioxide gas and a soluble salt. Strongly acidic descaling agents are often corrosive to the eyes and skin.

Notable descaling agents include acetic acid, citric acid, glycolic acid, formic acid, phosphoric acid, sulfamic acid and hydrochloric acid.

There are many companies offering inhibited or "buffered" acids that inhibit the corrosive effect of the acids on various materials. Typically about a 10% concentration of hydrochloric acid with a corrosion inhibitor and some added penetrating and wetting agents added. This allows for a better cleaning of machinery and especially heat exchangers because often the scale in mixed up with silica and other contaminants. These additives reduce the corrosion on the metals and cut through and loosen up these other materials mixed with the scale for faster and more thorough cleaning.


Effervescence is the escape of gas from an aqueous solution and the foaming or fizzing that results from that release. The word effervescence is derived from the Latin verb fervere (to boil), preceded by the adverb ex. It has the same linguistic root as the word fermentation.

Effervescence can also be observed when opening a bottle of champagne, beer or carbonated beverages such as soft drinks. The visible bubbles are produced by the escape from solution of the dissolved gas (which itself is not visible while dissolved in the liquid).

Although CO2 is most common for beverages, nitrogen gas is sometimes deliberately added to certain beers. The smaller bubble size creates a smoother beer head. Due to the poor solubility of nitrogen in beer, kegs or widgets are used for this.

In the laboratory, a common example of effervescence is seen if hydrochloric acid is added to a block of limestone. If a few pieces of marble or an antacid tablet are put in hydrochloric acid in a test tube fitted with a bung, effervescence of carbon dioxide can be witnessed.

This process is generally represented by the following reaction, where a pressurized dilute solution of carbonic acid in water releases gaseous carbon dioxide at decompression:

In simple terms, it is the result of the chemical reaction occurring in the liquid which produces a gaseous product.

Gastric acid

Gastric acid, gastric juice, or stomach acid, is a digestive fluid formed in the stomach and is composed of hydrochloric acid (HCl), potassium chloride (KCl), and sodium chloride (NaCl). The acid plays a key role in digestion of proteins, by activating digestive enzymes, and making ingested proteins unravel so that digestive enzymes break down the long chains of amino acids.

Gastric acid is produced by cells in the lining of the stomach, which are coupled in feedback systems to increase acid production when needed. Other cells in the stomach produce bicarbonate, a base, to buffer the fluid, ensuring that it does not become too acidic. These cells also produce mucus, which forms a viscous physical barrier to prevent gastric acid from damaging the stomach. The pancreas further produces large amounts of bicarbonate and secretes bicarbonate through the pancreatic duct to the duodenum to completely neutralize any gastric acid that passes further down into the digestive tract.

The main constituent of gastric acid is hydrochloric acid which is produced by parietal cells (also called oxyntic cells) in the gastric glands in the stomach. Its secretion is a complex and relatively energetically expensive process. Parietal cells contain an extensive secretory network (called canaliculi) from which the hydrochloric acid is secreted into the lumen of the stomach. The pH of gastric acid is 1.5 to 3.5 in the human stomach lumen, the acidity being maintained by the proton pump H+/K+ ATPase. The parietal cell releases bicarbonate into the bloodstream in the process, which causes a temporary rise of pH in the blood, known as an alkaline tide.

The highly acidic environment in the stomach lumen causes proteins from food to lose their characteristic folded structure (or denature). This exposes the protein's peptide bonds. The gastric chief cells of the stomach secrete enzymes for protein breakdown (inactive pepsinogen, and in infancy rennin). Hydrochloric acid activates pepsinogen into the enzyme pepsin, which then helps digestion by breaking the bonds linking amino acids, a process known as proteolysis. In addition, many microorganisms have their growth inhibited by such an acidic environment, which is helpful to prevent infection.

Globe rupture

Globe rupture is an ophthalmologic condition when the integrity of the outer membranes of the eye are disrupted by blunt or penetrating trauma, usually resulting from a full-thickness injury to the cornea or sclera. It may also result from damage caused by chemicals such as strong acids (hydrochloric acid, sulfuric acid, hydrofluoric acid etc.) or industrial chemicals such as lewisite.

During a globe rupture, the outer membranes of the eye are completely or partially compromised, and the vitreous and/or aqueous humour drain through the site of the rupture, causing the eye to 'deflate'.

If not treated swiftly, severe damage can result. In many cases, globe ruptures are untreatable without enucleating the affected eye socket and replacing the eye with an ocular prosthesis. However, with modern diagnostic techniques, surgical approaches, and rehabilitation, in many cases eyes can be salvaged with retention of vision.


A glucoside is a glycoside that is derived from glucose. Glucosides are common in plants, but rare in animals. Glucose is produced when a glucoside is hydrolysed by purely chemical means, or decomposed by fermentation or enzymes.

The name was originally given to plant products of this nature, in which the other part of the molecule was, in the greater number of cases, an aromatic aldehydic or phenolic compound (exceptions are sinigrin and jalapin or scammonin). It has now been extended to include synthetic ethers, such as those obtained by acting on alcoholic glucose solutions with hydrochloric acid, and also the polysaccharoses, e.g. cane sugar, which appear to be ethers also. Although glucose is the most common sugar present in glucosides, many are known which yield rhamnose or iso-dulcite; these may be termed pentosides. Much attention has been given to the non-sugar parts (aglyca) of the molecules; the constitutions of many have been determined, and the compounds synthesized; and in some cases the preparation of the synthetic glucoside effected.

The simplest glucosides are the alkyl ethers which have been obtained by reacting hydrochloric acid on alcoholic glucose solutions. A better method of preparation is to dissolve solid anhydrous glucose in methanol containing hydrochloric acid. A mixture of alpha- and beta-methylglucoside results.

Classification of the glucosides is a matter of some intricacy. One method based on the chemical constitution of the non-glucose part of the molecules has been proposed that posits four groups: (I) alkyl derivatives, (2) benzene derivatives, (3) styrolene derivatives, and (4) anthracene derivatives. A group may also be constructed to include the cyanogenic glucosides, i.e. those containing prussic acid. Alternate classifications follow a botanical classification, which has several advantages; in particular, plants of allied genera contain similar compounds. In this article the chemical classification will be followed, and only the more important compounds will be discussed herein.

Hydrochloric acid (data page)

This page provides supplementary chemical data on Hydrochloric acid.

Hydrochloric acid regeneration

Hydrochloric acid regeneration or HCl regeneration refers to a chemical process for the reclamation of bound and unbound HCl from metal chloride solutions such as hydrochloric acid.


In chemistry, a hydrochloride is an acid salt resulting, or regarded as resulting, from the reaction of hydrochloric acid with an organic base (e.g. an amine). An alternative name is chlorhydrate, which comes from French. An archaic alternative name is muriate, derived from hydrochloric acid's ancient name: muriatic acid.

For example, reacting pyridine (C5H5N) with hydrochloric acid (HCl) yields its hydrochloride salt, pyridinium chloride. The molecular formula is either written as C5H5N·HCl or as C5H5NH+ Cl−.

Hydrogen chloride

The compound hydrogen chloride has the chemical formula HCl and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride gas and hydrochloric acid are important in technology and industry. Hydrochloric acid, the aqueous solution of hydrogen chloride, is also commonly given the formula HCl.

Kipp's apparatus

Kipp's apparatus, also called Kipp generator, is an apparatus designed for preparation of small volumes of gases. It was invented around 1844 by the Dutch pharmacist Petrus Jacobus Kipp and widely used in chemical laboratories and for demonstrations in schools into the second half of the 20th century.

It later fell out of use, at least in laboratories, because most gases then became available in small gas cylinders. These industrial gases are much purer and drier than those initially obtained from a Kipp apparatus without further processing.

Mineral acid

A mineral acid (or inorganic acid) is an acid derived from one or more inorganic compounds. All mineral acids form hydrogen ions and the conjugate base when dissolved in water.

Organoyttrium chemistry

Organoyttrium chemistry is the study of compounds containing carbon-yttrium bonds. They are studied in academic research, but have not received widespread use otherwise. These compounds use YCl3 as a starting material, which is in turn obtained in a reaction of Y2O3 with concentrated hydrochloric acid and ammonium chloride.

Parietal cell

Parietal cells (also known as oxyntic or delomorphous cells) are the epithelial cells that secrete hydrochloric acid (HCl) and intrinsic factor. These cells are located in the gastric glands found in the lining of the fundus and in the cardia of the stomach. They contain an extensive secretory network (called canaliculi) from which the HCl is secreted by active transport into the stomach. The enzyme hydrogen potassium ATPase (H+/K+ ATPase) is unique to the parietal cells and transports the H+ against a concentration gradient of about 3 million to 1, which is the steepest ion gradient formed in the human body. Parietal cells are primarily regulated via histamine, acetylcholine and gastrin signaling from both central and local modulators (see 'Regulation').


Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids.

The term tannin (from Anglo-Norman tanner, from Medieval Latin tannāre, from tannum, oak bark) refers to the use of oak and other bark in tanning animal hides into leather. By extension, the term tannin is widely applied to any large polyphenolic compound containing sufficient hydroxyls and other suitable groups (such as carboxyls) to form strong complexes with various macromolecules.

The tannin compounds are widely distributed in many species of plants, where they play a role in protection from predation (including as pesticides) and might help in regulating plant growth. The astringency from the tannins is what causes the dry and puckery feeling in the mouth following the consumption of unripened fruit, red wine or tea. Likewise, the destruction or modification of tannins with time plays an important role when determining harvesting times.

Tannins have molecular weights ranging from 500 to over 3,000 (gallic acid esters) and up to 20,000 (proanthocyanidins).

Digestives, including enzymes (A09)
Acid preparations

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