Hydrogen chloride

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Structural formula
Structure of hydrogen chloride
Surname Hydrogen chloride
other names
  • Hydrochloric acid anhydrous
  • Hydrogen chloride ( IUPAC )
  • Hydrochloric acid gas
  • Hydrogen chloride
  • Chlorane
Molecular formula HCl
Brief description

colorless, pungent smelling gas

External identifiers / databases
CAS number 7647-01-0
EC number 231-595-7
ECHA InfoCard 100.028.723
PubChem 313
Wikidata Q211086
Molar mass 36.46 g mol −1
Physical state



1.64 kg m −3 (gas density, 0 ° C)

Melting point

−114.8 ° C

boiling point

−85.0 ° C

Vapor pressure

4.26 M Pa (20 ° C)

pK s value



easily in water (720 g l −1 at 20 ° C)

Dipole moment

1.1086 (3) D (3.698 · 10 −30  C  ·  m )

safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary
06 - Toxic or very toxic 05 - Corrosive 04 - gas bottle


H and P phrases H: 331-314-280
EUH: 071
P: 260-280-304 + 340-303 + 361 + 353-305 + 351 + 338-315-405-403

DFG / Switzerland: 2 ml m −3 or 3 mg m −3

Thermodynamic properties
ΔH f 0

−92.3 kJ / mol

As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Hydrogen chloride ( molecular formula HCl, systematically also referred to as hydrogen chloride or hydrogen chloride ) is a colorless, pungent smelling gas that dissolves very easily in water . Aqueous solutions of hydrogen chloride are called hydrochloric acid or hydrochloric acid. If you inhale the gas, hydrochloric acid is produced in the lungs, which leads to severe burns, since hydrochloric acid is a very strong acid .

He was portrayed by Humphry Davy in 1808.

Extraction and presentation

Hydrogen chloride is produced in the laboratory from concentrated sulfuric acid and sodium chloride :

Sodium chloride and sulfuric acid react to form sodium sulfate and hydrogen chloride

Instead of using sulfuric acid, sodium hydrogen sulfate can also be used. For this purpose, a mixture of sodium chloride and sodium hydrogen sulfate is heated dry. In order to keep the reaction going, the resulting hydrogen chloride gas has to be removed.

In the chemical industry, hydrogen chloride occurs mainly as a by-product in the chlorination of organic compounds or is obtained with the chlorine- explosive gas reaction (ignition of a mixture of hydrogen and chlorine, for example by exposure).

Hydrogen and chlorine react to form hydrogen chloride

In the photochlorination or sulfochlorination of hydrocarbons, hydrogen chloride is produced as a by-product:

Overview reaction of the Reed reaction


The systematic designation hydrogen chloride uses the syllable chloride to express that the chlorine atom in the molecular compound carries a negative partial charge , similar to chloride ions , which have a negative ionic charge .

Hydrogen chloride has a slightly higher density than air . In one liter of water , 520 l dissolve at 0  ° C when heated, which corresponds to 850 g of HCl gas. At 20 ° C, 442 liters of hydrogen chloride dissolve in one liter of water. In humid air, HCl gas forms a mist of fine hydrochloric acid droplets.

Its specific heat capacity c p is 799 J / (kg K).

Biological importance

Hydrogen chloride, in the form of hydrochloric acid, is a component of the gastric juice of omnivorous animals and also causes food to be denatured in the human stomach .


In addition to its diverse uses as an acid, pure hydrogen chloride is also used as a chlorinating agent in the oxychlorination of ethene to vinyl chloride .

safety instructions

Hydrogen chloride is corrosive and toxic in high concentrations. However, poisoning is very rare. Inhalation can cause irritation and chemical burns to the mucous membranes and the respiratory tract, which can lead to acute bronchitis or pneumonia . If it comes into contact with skin and clothing, the acid can be washed out thoroughly and completely with water.

Web links

Commons : Hydrogen Chloride  - Collection of pictures, videos and audio files

Individual evidence

  1. entry to HYDROCHLORIC ACID in CosIng database of the European Commission, accessed on 21 March 2020th
  2. a b c d e f g h i Entry on hydrogen chloride in the GESTIS substance database of the IFA , accessed on February 1, 2016(JavaScript required) .
  3. Robert Anthony Robinson, Roger G. Bates: Dissociation constant of hydrochloric acid from partial vapor pressures over hydrogen chloride-lithium chloride solutions . In: Analytical Chemistry , 43 (7), 1971, pp. 969-970.
  4. David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Dipole Moments, pp. 9-51.
  5. Entry on Hydrogen chloride in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
  6. Swiss Accident Insurance Fund (Suva): Limit values ​​- current MAK and BAT values (search for 7647-01-0 or hydrogen chloride ), accessed on November 2, 2015.
  7. David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Standard Thermodynamic Properties of Chemical Substances, pp. 5-8.