Hydrochloric gas Hydrochloride
3D model (JSmol)
ECHA InfoCard 100.028.723
EC Number 231-595-7
RTECS number MW4025000
UN number 1050
InChI=1S/HCl/h1H N Key: VEXZGXHMUGYJMC-UHFFFAOYSA-N Y
InChI=1/HCl/h1H Key: VEXZGXHMUGYJMC-UHFFFAOYAT
Molar mass 36.46 g/mol
Appearance Colorless gas
Odor pungent; sharp and burning
Density 1.49 g L−1
Melting point −114.22 °C (−173.60 °F; 158.93 K)
Boiling point −85.05 °C (−121.09 °F; 188.10 K)
823 g/L (0 °C) 720 g/L (20 °C) 561 g/L (60 °C)
Solubility soluble in methanol, ethanol, ether
Vapor pressure 4352 kPa (at 21.1 °C)
Acidity (pKa) -3.0; -5.9 (±0.4) 
Basicity (pKb) 17.0
1.0004456 (gas) 1.254 (liquid)
Viscosity 0.311 cP (−100 °C)
Specific heat capacity (C)
0.7981 J K−1 g−1
Std molar entropy (So298)
186.902 J K−1 mol−1
Std enthalpy of formation (ΔfHo298)
–92.31 kJ mol−1
Std enthalpy of combustion (ΔcHo298)
–95.31 kJ mol−1
A09AB03 (WHO) B05XA13 (WHO)
Safety data sheet JT Baker MSDS
GHS signal word Danger
GHS hazard statements
H280, H314, H331
GHS precautionary statements
P261, P280, P305+351+338, P310, P410+403
0 3 1 ACID
Lethal dose or concentration (LD, LC):
LD50 (median dose)
238 mg/kg (rat, oral)
LC50 (median concentration)
3124 ppm (rat, 1 hr) 1108 ppm (mouse, 1 hr)
LCLo (lowest published)
1300 ppm (human, 30 min) 4416 ppm (rabbit, 30 min) 4416 ppm (guinea pig, 30 min) 3000 ppm (human, 5 min)
US health exposure limits (NIOSH):
C 5 ppm (7 mg/m3)
C 5 ppm (7 mg/m3)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
The compound hydrogen chloride has the chemical formula HCl and as
such is a hydrogen halide. At room temperature, it is a colorless gas,
which forms white fumes of hydrochloric acid upon contact with
atmospheric water vapor.
1.1 Structure and properties
2.1 Direct synthesis 2.2 Organic synthesis 2.3 Laboratory methods
3 Applications 4 History 5 Safety 6 See also 7 References 8 External links
HCl + H2O → H3O+ + Cl−
The resulting solution is called hydrochloric acid and is a strong acid. The acid dissociation or ionization constant, Ka, is large, which means HCl dissociates or ionizes practically completely in water. Even in the absence of water, hydrogen chloride can still act as an acid. For example, hydrogen chloride can dissolve in certain other solvents such as methanol and protonate molecules or ions, and can also serve as an acid-catalyst for chemical reactions where anhydrous (water-free) conditions are desired.
HCl + CH3OH → CH3O+H2 + Cl−
Because of its acidic nature, hydrogen chloride is a corrosive substance, particularly in the presence of moisture. Structure and properties
The structure of solid DCl, as determined by neutron diffraction of DCl powder at 77 K. DCl was used instead of HCl because the deuterium nucleus is easier to detect than the hydrogen nucleus. The "infinite" chains of DCl are indicated by the dashed lines.
Frozen HCl undergoes phase transition at 98.4 K. X-ray powder diffraction of the frozen material shows that the material changes from an orthorhombic structure to a cubic one during this transition. In both structures the chlorine atoms are in a face-centered array. However, the hydrogen atoms could not be located. Analysis of spectroscopic and dielectric data, and determination of the structure of DCl (deuterium chloride) indicates that HCl forms zigzag chains in the solid, as does HF (see figure on right).
Temperature (°C) 0 20 30 50
Water 823 720 673 596
Methanol 513 470 430
Ethanol 454 410 381
Ether 356 249 195
Infrared (IR) absorption spectrum
One doublet in the IR spectrum resulting from the isotopic composition of chlorine
The infrared spectrum of gaseous hydrogen chloride, shown on the left, consists of a number of sharp absorption lines grouped around 2886 cm−1 (wavelength ~3.47 µm). At room temperature, almost all molecules are in the ground vibrational state v = 0. Including anharmonicity the vibrational energy can be written as.
v i b
displaystyle E_ mathrm vib =hnu _ e cdot left(v+ tfrac 1 2 right)+hx_ e nu _ e cdot left(v+ tfrac 1 2 right)^ 2
To promote an HCl molecule from the v = 0 to the v = 1 state, we would expect to see an infrared absorption about νo = νe + 2xeνe = 2880 cm−1. However, this absorption corresponding to the Q-branch is not observed due to it being forbidden by symmetry. Instead, two sets of signals (P- and R-branches) are seen owing to a simultaneous change in the rotational state of the molecules. Because of quantum mechanical selection rules, only certain rotational transitions are permitted. The states are characterized by the rotational quantum number J = 0, 1, 2, 3, ... selection rules state that ΔJ is only able to take values of ±1.
E ( J
r o t
= h ⋅ B ⋅ J ( J + 1 )
displaystyle E(J)_ mathrm rot =hcdot Bcdot J(J+1)
The value of the rotational constant B is much smaller than the vibrational one νo, such that a much smaller amount of energy is required to rotate the molecule; for a typical molecule, this lies within the microwave region. However, the vibrational energy of HCl molecule places its absorptions within the infrared region, allowing a spectrum showing the rovibrational transitions of this molecule to be easily collected using an infrared spectrometer with a gas cell. The latter can even be made of quartz as the HCl absorption lies in a window of transparency for this material. Naturally abundant chlorine consists of two isotopes, 35Cl and 37Cl, in a ratio of approximately 3:1. While the spring constants are identical within experimental error, the reduced masses are different causing measurable differences in the rotational energy, thus doublets are observed on close inspection of each absorption line, weighted in the same ratio of 3:1.
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Most hydrogen chloride produced on an industrial scale is used for hydrochloric acid production. Direct synthesis
Flame inside HCl oven
In the chlor-alkali industry, brine (mixture of sodium chloride and water) solution is electrolyzed producing chlorine (Cl2), sodium hydroxide, and hydrogen (H2):
2 NaCl + 2 H2O → Cl2 + 2 NaOH + H2
The pure chlorine gas can be combined with hydrogen to produce hydrogen chloride in the presence of UV light:
Cl2(g) + H2(g) → 2 HCl(g)
As the reaction is exothermic, the installation is called an HCl oven or HCl burner. The resulting hydrogen chloride gas is absorbed in deionized water, resulting in chemically pure hydrochloric acid. This reaction can give a very pure product, e.g. for use in the food industry. Organic synthesis The largest production of hydrochloric acid is integrated with the formation of chlorinated and fluorinated organic compounds, e.g., Teflon, Freon, and other CFCs, as well as chloroacetic acid and PVC. Often this production of hydrochloric acid is integrated with captive use of it on-site. In the chemical reactions, hydrogen atoms on the hydrocarbon are replaced by chlorine atoms, whereupon the released hydrogen atom recombines with the spare atom from the chlorine molecule, forming hydrogen chloride. Fluorination is a subsequent chlorine-replacement reaction, producing again hydrogen chloride:
R−H + Cl2 → R−Cl + HCl R−Cl + HF → R−F + HCl
The resulting hydrogen chloride gas is either reused directly or absorbed in water, resulting in hydrochloric acid of technical or industrial grade. Laboratory methods Small amounts of HCl gas for laboratory use can be generated in an HCl generator by dehydrating hydrochloric acid with either sulfuric acid or anhydrous calcium chloride. Alternatively, HCl can be generated by the reaction of sulfuric acid with sodium chloride:
NaCl + H2SO4 → NaHSO4 + HCl
This reaction occurs at room temperature. Provided there is NaCl remaining in the generator and it is heated above 200 °C, the reaction proceeds further:
NaCl + NaHSO4 → HCl + Na2SO4
For such generators to function, the reagents should be dry. HCl can also be prepared by the hydrolysis of certain reactive chloride compounds such as phosphorus chlorides, thionyl chloride (SOCl2), and acyl chlorides. For example, cold water can be gradually dripped onto phosphorus pentachloride (PCl5) to give HCl:
PCl5 + H2O → POCl3 + 2 HCl
High-purity streams of the gas require lecture bottles or cylinders, both of which can be expensive. In comparison, the use of a generator requires only apparatus and materials commonly available in a laboratory. Applications Most hydrogen chloride is used in the production of hydrochloric acid. It is also an important reagent in other industrial chemical transformations, e.g.:
Hydrochlorination of rubber Production of vinyl and alkyl chlorides
In the semiconductor industry, it is used to both etch semiconductor
crystals and to purify silicon via trichlorosilane (SiHCl3).
It may also be used to treat cotton to delint it, and to separate it
from wool.
In the laboratory, anhydrous forms of the gas are particularly useful
for generating chloride-based Lewis acids, which must be absolutely
dry for their Lewis sites to function. It can also be used to dry the
corresponding hydrated forms of these materials by passing it over as
they are heated; the materials would otherwise fume HCl gas themselves
and decompose. Neither can these hydrates be dried using standard
Alchemists of the
This "acetylene process" has been replaced by a process which adds Cl2
to one of the double bonds in 1,3-butadiene instead, and subsequent
elimination produces HCl instead, as well as chloroprene.
Chloride, inorganic salts of hydrochloric acid Gastric acid, hydrochloric acid secreted into the stomach to aid digestion of proteins Hydrochloride, organic salts of hydrochloric acid
^ "hydrogen chloride (CHEBI:17883)". Chemical Entities of Biological
Interest (ChEBI). UK: European Bioinformatics Institute.
^ Haynes, William M. (2010). Handbook of Chemistry and Physics (91
ed.). Boca Raton, Florida: CRC Press. p. 4–67.
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H3AsO3 H3AsO4 HAt HSO3F HBF4 HBr HBrO HBrO2 HBrO3 HBrO4 HCl HClO HClO2 HClO3 HClO4 HCN HCNO H2CrO4/H2Cr2O7 H2CO3 H2CS3 HF HFΟ HI HIO HIO2 HIO3 HIO4 HMnO4 H2MoO4 HNC NaHCO3 HNCO HNO HNO2 HNO3 H2N2O2 HNO5S H3NSO3 H2O H2O2 H2O3 H3PO2 H3PO3 H3PO4 H4P2O7 H5P3O10 H2PtCl6 H2S H2S2 H2Se H2SeO3 H2SeO4 H4SiO4 H2SiF6 HSCN HNSC H2SO3 H2SO4 H2SO5 H2S2O3 H2S2O6 H2S2O7 H2S2O8 CF3SO3H H2Te H2TeO3 H6TeO6 H4TiO4 H2Po HCo(CO)4
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Molecules detected in outer space
Acetonitrile Cyanobutadiynyl radical E-Cyanomethanimine Cyclopropenone Diacetylene Ethylene Formamide HC4N Ketenimine Methanethiol Methanol Methyl isocyanide Pentynylidyne Propynal Protonated cyanoacetylene
Acetic acid Aminoacetonitrile Cyanoallene Ethanimine Glycolaldehyde Heptatrienyl radical Hexapentaenylidene Methylcyanoacetylene Methyl formate Propenal
Acetamide Cyanohexatriyne Cyanotriacetylene Dimethyl ether Ethanol Methyldiacetylene Octatetraynyl radical Propene Propionitrile
Ten atoms or more
Ethyl methyl ether
Atomic and molecular astrophysics
Diffuse interstellar band
Earliest known life forms
Extraterrestrial liquid water
Helium hydride ion
Iron–sulfur world theory
Molecules in stars
Nexus for Exoplanet System Science
PAH world hypothesis
Polycyclic aromatic hydrocarbon
Book:Chemistry Category:Astrochemistry Category:Molecules Portal:Astrobiology Portal:Astronomy Portal:Chemistry
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ClF ClF3 ClF5 ClNO3 ClO Cl2O2 ClO2 ClO2F ClO3F Cl2O Cl2O4 Cl2O6 Cl2O7 HCl SiCl4
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Binary compounds of hydrogen
Alkali metal hydrides
LiH NaH KH RbH CsH
Lithium hydride, LiH ionic metal hydride
Beryllium hydride Left (gas phase): BeH2 covalent metal hydride Right: (BeH2)n (solid phase) polymeric metal hydride
Methane, CH4 covalent nonmetal hydride
Ammonia, NH3 covalent nonmetal hydride
Water, H2O covalent nonmetal hydride
Alkaline earth hydrides
BeH MgH CaH SrH BaH
BeH2 MgH2 CaH2 SrH2 BaH2
Group 13 hydrides
BH3 B2H6 B2H2 B2H4
B2H2 B2H4 B4H10 B5H9 B5H11 B6H10 B6H12 B10H14 B18H22
Group 14 hydrides
CH4 C2H6 C3H8 C4H10 C5H12 C6H14 C7H16 C8H18 C9H20 C10H22 more...
C2H4 C3H6 C4H8 C5H10 C6H12 C7H14 C8H16 C9H18 C10H20 more...
C2H2 C3H4 C4H6 C5H8 C6H10 C7H12 C8H14 C9H16 C10H18 more...
SiH4 Si2H6 Si3H8 Si4H10 Si5H12 Si6H14 Si7H16 Si8H18 Si9H20 Si10H22 more...
GeH4 Ge2H6 Ge3H8 Ge4H10 Ge5H12
CH CH2 CH3 C2H Cycloalkanes Cycloalkenes Annulenes Many more
NH3 N2H4 N3H5 N4H6 N5H7 N6H8 N7H9 N8H10 N9H11 N10H12 more...
N2H2 N3H3 N4H4
PH3 P2H4 P3H5 P4H6 P5H7 P6H8 P7H9 P8H10 P9H11 P10H12 more...
P2H2 P3H3 P4H4
H2O H2O2 H2O3 H2O4 H2O5 H2O6 H2O7 H2O8 H2O9 H2O10 more...
H2S H2S2 H2S3 H2S4 H2S5 H2S6 H2S7 H2S8 H2S9 H2S10 more...
HO HO2 HO3 H2O+–O– H2S=S (HS)2S+–S– HS HDO D2O T2O
HF HCl HBr HI HAt
Transition metal hydrides
ScH2 YH2 YH3 TiH2 ZrH2 HfH2 VH VH2 NbH NbH2 TaH CrH CrH2 CrHx NiH PdHx (x < 1) FeH FeH2 FeH5 CuH ZnH2 CdH2 HgH2
LaH2 LaH3 CeH2 CeH3 PrH2 PrH3 NdH2 NdH3 SmH2 SmH3 EuH2 GdH2 GdH3 TbH2 TbH3 DyH2 DyH3 HoH2 HoH3 ErH2 ErH3 TmH2 TmH3 YbH2 YbH2.5 LuH2 LuH3
AcH2 ThH2 Th4H15 PaH3 UH3 NpH2 NpH3 PuH2 PuH3 AmH2 AmH3 CmH2