Hydrochloric acid



Hydrochloric acid
IUPAC name Hydrochloric acid
Other names Muriatic acid, Spirit of salt
Identifiers
CAS number 7647-01-0
RTECS number MW4025000
Properties
Molecular formula HCl in water (H2O)
Molar mass 36.46 g/mol (HCl)
Appearance Clear colorless to
light-yellow liquid
Melting point

−26 °C (247 K)
38% solution.

Boiling point

110 °C (383 K),
20.2% solution;
48 °C (321 K),
38% solution.

Solubility in water Miscible.
Acidity (pKa) −8.0
Viscosity 1.9 mPa·s at 25 °C,
31.5% solution
Hazards
MSDS External MSDS
MSDS External MSDS
Main hazards Corrosive
NFPA 704
 
3
1
 
R-phrases R34, R37
S-phrases S45
Flash point Non-flammable.
Related Compounds
Other anions HF, HBr, HI
Related acids Hydrobromic acid
Sulfuric acid
Supplementary data page
Structure and
properties 		εr, etc.
Thermodynamic
data 		Phase behaviour
Solid, liquid, gas
Spectral data MS
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Hydrochloric acid is the aqueous liquid.

Hydrochloric acid, or muriatic acid by its historical but still occasionally-used name, has been an important and frequently-used chemical from early history, and was discovered by the Davy in order to help establish modern chemical knowledge.

From the Industrial Revolution, it became an important industrial chemical for many applications, including the large-scale production of gelatin and other ingredients in food, and leather processing. About 20 million metric tonnes of HCl gas are produced annually.

History

Hydrochloric acid was first discovered around 800 AD by the philosopher's stone.

  In the Middle Ages, hydrochloric acid was known to European alchemists as spirit of salt or acidum salis. 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"), and this name is still sometimes used. Notable production was recorded by chlorine.

During the Industrial Revolution in Europe, demand for Leblanc process, salt is converted to soda ash, using sulfuric acid, limestone, and coal, releasing hydrogen chloride as a by-product. Until the Alkali Act of 1863, excess HCl was vented to 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.

When early in the twentieth century the Leblanc process was effectively replaced by the industrial organic compounds production.

Hydrochloric acid is listed as a Table II precursor under the 1988 Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances because of its use in the production of heroin, cocaine, and methamphetamine.[1]

Chemistry

  Hydrogen chloride (HCl) is a monoprotic acid, which means it can dissociate (i.e., ionize) only once to give up one H+ ion (a single hydronium ion, H3O+:

HCl + H2O ⇌ H3O+ + Cl−

The other ion formed is Cl−, the strong acid, since it is fully dissociated in water.

Monoprotic acids have one concentration) equals HCl molarity is excellent, agreeing to four significant digits.

Of the seven common strong acids in chemistry, all of them catalyst for some chemical reactions.

Physical properties

The physical properties of hydrochloric acid, such as concentration or molarity of HCl in the acid solution. They can range from those of water at 0% HCl to values for fuming hydrochloric acid at over 40% HCl.

Conc. (w/w)
c : kg HCl/kg  		Conc. (w/v)
c : kg HCl/m3 		Conc.
Baumé
 Density
ρ : kg/l 		Molarity
M 		 pH 
 Viscosity
η : mPa·s 		Specific
heat
s : kJ/(kg·K) 		Vapor
pressure
PHCl : Pa 		Boiling
point
b.p. 		Melting
point
m.p.
10% 104.80 6.6 1.048 2.87 M -0.5 1.16 3.47 0.527 103 °C -18 °C
20% 219.60 13 1.098 6.02 M -0.8 1.37 2.99 27.3 108 °C -59 °C
30% 344.70 19 1.149 9.45 M -1.0 1.70 2.60 1,410 90 °C -52 °C
32% 370.88 20 1.159 10.17 M -1.0 1.80 2.55 3,130 84 °C -43 °C
34% 397.46 21 1.169 10.90 M -1.0 1.90 2.50 6,733 71 °C -36 °C
36% 424.44 22 1.179 11.64 M -1.1 1.99 2.46 14,100 61 °C -30 °C
38% 451.82 23 1.189 12.39 M -1.1 2.10 2.43 28,000 48 °C -26 °C
The reference pressure for the above table are 20 °C and 1 atmosphere (101 kPa).

Hydrochloric acid as the binary (two-component) mixture of HCl and H2O has a constant-boiling ice (0% HCl). There is also a metastable eutectic point at 24.8% between ice and the HCl·3H2O crystallization

Production

Main article: hydrogen chloride

Hydrochloric acid is prepared by dissolving hydrogen chloride in water. Hydrogen chloride can be generated in many ways, and thus several different precursors to hydrochloric acid exist. The large-scale production of hydrochloric acid is almost always integrated with other industrial scale chemicals production.

Industrial market

Hydrochloric acid is produced in solutions up to 38% HCl (concentrated grade). Higher vapors. Solutions for household purposes, mostly cleaning, are typically 10% to 12%, with strong recommendations to dilute before use.

Major producers worldwide include 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 of all 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. The application often determines the required product quality.

Regeneration of ion exchangers

An important application of high-quality hydrochloric acid is the regeneration of demineralized water.

Na+ is replaced by H3O+
Ca2+ is replaced by 2 H3O+

Ion exchangers and demineralized water are used in all chemical industries, drinking water production, and many food industries.

pH Control and neutralization

A very common application of hydrochloric acid is to regulate the pH) 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 waste streams and swimming pool treatment.

Pickling of steel

Pickling is an essential step in galvanizing, and other techniques. Technical-quality HCl at typically 18% concentration is the most commonly-used pickling agent for the pickling of carbon steel grades.

Fe2O3 + Fe + 6 HCl → 3 FeCl2 + 3 H2O

The heavy-metal levels in the pickling liquor has decreased this practice.

In recent years, the steel pickling industry has, however, 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 ferric oxide by product of the regeneration process is a valuable by-product, used in a variety of secondary industries.

HCl is not a common pickling agent for stainless steel grades.

Production of inorganic compounds

Numerous products can be produced with hydrochloric acid in normal iron(III) chloride and polyaluminium chloride (PAC).

Fe2O3 + 6 HCl → 2 FeCl3 + 3 H2O

Both iron(III) chloride and PAC are used as wastewater treatment, drinking water production, and paper production.

Other inorganic compounds produced with hydrochloric acid include road application salt battery production.

Production of organic compounds

The largest hydrochloric acid consumption is in the production of pharmaceutical products.

Other applications

Hydrochloric acid is a fundamental chemical, and as such it is used for a large number of small-scale applications, such as leather processing, household cleaning, and building construction. In addition, a way of stimulating oil production is 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.

Many chemical reactions involving hydrochloric acid are applied in the production of food, food ingredients, and food additives. Typical products include gelatin production. Food-grade (extra-pure) hydrochloric acid can be applied when needed for the final product.

Presence in living organisms

Physiology and pathology

Hydrochloric acid constitutes the majority of digestive fluid. In a complex process and at a large energy burden, it is secreted by parietal cells (also known as oxyntic cells). These cells contain an extensive secretory network (called canaliculi) from which the HCl is secreted into the lumen of the stomach. They are part of the fundic glands (also known as oxyntic glands) in the stomach.

Safety mechanisms that prevent the damage of the epithelium of digestive tract by hydrochloric acid are the following:

  • Negative regulators of its release
  • A thick mucus layer covering the epithelium
  • Sodium bicarbonate secreted by gastric epithelial cells and pancreas
  • The structure of epithelium (tight junctions)
  • Adequate blood supply
  • Prostaglandins (many different effects: they stimulate mucus and bicarbonate secretion, maintain epithelial barrier integrity, enable adequate blood supply, stimulate the healing of the damaged mucous membrane)

When, due to different reasons, these mechanisms fail, heartburn or peptic ulcers can develop. Drugs called antacids neutralize existing acid.

In some instances, the stomach does not produce enough hydrochloric acid. These pathologic states are denoted by the terms hypochlorhydria and achlorhydria. They have the potential to lead to gastroenteritis.

Chemical weapons

membranes so that the lung becomes filled with fluid (pulmonary edema).

Hydrochloric acid is also partly responsible for the harmful or blistering effects of mustard gas. In the presence of water, such as on the moist surface of the eyes or lungs, mustard gas breaks down forming hydrochloric acid.

Safety

Dangerous goods labels
Dangerous goods label for hydrochloric acid: corrosive  

Hydrochloric acid in high concentrations 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. Upon mixing hydrochloric acid with common oxidizing chemicals, such as chlorine is produced. To minimize the risks while working with hydrochloric acid, appropriate precautions should be taken, including wearing rubber or PVC gloves, protective eye goggles, and chemical-resistant clothing.

The hazards of solutions of hydrochloric acid depend on the concentration. The following table lists the EU classification of hydrochloric acid solutions:

Concentration
by weight 		Classification R-Phrases
10%–25% Irritant (Xi) R36/37/38
>25% Corrosive (C) R34 R37

The Environmental Protection Agency rates and regulates hydrochloric acid as a toxin.[3]

See also

Related chemical substances
  • Hydrochloride, organic salts of hydrochloric acid
  • HClO Hypochlorous acid, and its salt hypochlorite
  • HClO2 Chlorous acid, and its salt chlorite
  • HClO3 Chloric acid, and its salt chlorate
  • HClO4 perchlorate

Notes and references

Notes
  1. ^ List of precursors and chemicals frequently used in the illicit manufacture of narcotic drugs and pychotropic substances under international control (PDF). International Narcotics Control Board.
  2. ^ Dissociation constants pKa and pKb. ChemBuddy.com.
  3. ^ HCl score card. Environmental Protection Agency. Retrieved on 2007-09-12.
References
  • (2001) "Hydrochloric Acid", Chemicals Economics Handbook. SRI International, p. 733.4000A-733.3003F. 
  • Van Dorst, W.C.A.; et al. (2004). technical product brochure Hydrochloric Acid, public document, Akzo Nobel Base Chemicals. 
  • Van Dorst, W.C.A. (1996–2002). various technical papers, not for open publication, Akzo Nobel Base Chemicals. 
  • Lide, David (1980–1981). CRC Handbook of Chemistry and Physics, 61st edition, CRC Press. 
  • Aspen Technology, Aspen Properties, binary mixtures modeling software, calculations by Akzo Nobel Engineering, 2002–2003
  • Evison, D (2002). "Chemical weapons". BMJ: 324(7333):332-5. PMID 11834561.
  • Arthur, C.; M.D. Guyton, John E. Hall (2000-08-15). Textbook of Medical Physiology, 10th edition, W.B. Saunders Company. ISBN 0-7216-8677-X. 
  • Perry, R; Green D, Maloney J (1984). Perry's Chemical Engineers' Handbook, 6th edition, McGraw-Hill Book Company. ISBN 0-07-049479-7. 
General safety information
  • EPA Hazard Summary
  • NIH Description and Hazard Summary
  • Hydrochloric acid MSDS by Jones-Hamilton
  • Hydrochloric acid MSDS by Hampton Research
  • Hydrochloric acid MSDS by American Bioanalytical
  • Hydrochloric acid MSDS by Georgia Institute of Technology
  • Hydrochloric acid MSDS by Akzo Nobel
Manufacturer information
  • Hydrochloric acid product information of Akzo Nobel
  • Hydrochloric acid product information of Tessenderlo
  • Hydrochloric acid product information of Solvay
  • Dow Chemical
  • Chlor-Alkali information of Tosoh
  • Hydrochloric acid product information of Bayer MaterialScience in North America
Pollution information
  • National Pollutant Inventory - Hydrochloric Acid Fact Sheet
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Hydrochloric_acid". A list of authors is available in Wikipedia.