Hydrogen chloride

Hydrogen chloride

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Not to be confused with hydrochloric acid.

Hydrogen chloride

IUPAC name[hide]

Hydrogen chloride[1]

Other names[hide]

Hydrochloric acid gas

Hydrochloride

Identifiers

CAS number 7647-01-0 Yes

ChemSpider 307 Yes

UNII QTT17582CB Yes

EC number 231-595-7

UN number 1050

KEGG D02057 Yes

MeSH Hydrochloric+acid

ChEBI CHEBI:17883 Yes

ChEMBL CHEMBL1231821

RTECS number MW4025000

ATC code A09AB03,B05XA13

Beilstein Reference 1098214

Gmelin Reference 322

Jmol-3D images Image 1

SMILES

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InChI

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Properties

Molecular formula HCl

Molar mass 36.46 g mol−1

Appearance Colorless gas

Odor pungent

Density 1.490 g cm−3

Melting point

-114.22 °C, 159 K, -174 °F

Boiling point

-85.05 °C, 188 K, -121 °F

Solubility in water 82.3 g/100 mL (0 °C)

72.0 g/100 mL (20 °C)

56.1 g/100 mL (60 °C)

Solubility soluble in methanol, ethanol, ether

Vapor pressure 4352 kPa (at 21.1 °C)[2]

Acidity (pKa) -7.0[3]

Basicity (pKb) 21.0

Refractive index (nD) 1.0004456 (gas)

1.254 (liquid)

Viscosity 0.311 cP (-100 °C)

Structure

Molecular shape linear

Dipole moment 1.05 D

Thermochemistry

Std enthalpy of

formation ΔfHo298 –92.31 kJ mol−1

Std enthalpy of

combustion ΔcHo298 –95.31 kJ mol−1

Standard molar

entropy So298 186.902 J K−1 mol−1

Specific heat capacity, C 0.7981 J K−1 g−1

Hazards

MSDS JT Baker MSDS

GHS pictograms The corrosion pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The skull-and-crossbones pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)

GHS signal word Danger

GHS hazard statements H280, H314, H331

GHS precautionary statements P261, P280, P305+351+338, P310, P410+403

EU Index 017-002-00-2

EU classification Toxic T Corrosive C

R-phrases R23, R35

S-phrases (S1/2), S9, S26, S36/37/39, S45

NFPA 704

NFPA 704.svg031ACID

LD50 238 mg/kg (rat, oral)

Related compounds

Related compounds Hydrogen fluoride

Hydrogen bromide

Hydrogen iodide

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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Infobox references

The compound hydrogen chloride has the chemical formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. 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.

Contents [hide]

1 Chemistry

1.1 Structure and properties

2 Production

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

Chemistry[edit]

Hydrochloric acid fumes turning pH paper red showing that the fumes are acidic

Hydrogen chloride is a diatomic molecule, consisting of a hydrogen atom H and a chlorine atom Cl connected by a covalent single bond. Since the chlorine atom is much more electronegative than the hydrogen atom, the covalent bond between the two atoms is quite polar. Consequently, the molecule has a large dipole moment with a negative partial charge δ– at the chlorine atom and a positive partial charge δ+ at the hydrogen atom. In part because of its high polarity, HCl is very soluble in water (and in other polar solvents).

Upon contact, H2O and HCl combine to form hydronium cations H3O+ and chloride anions Cl– through a reversible chemical reaction:

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, protonate molecules or ions, and 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 corrosive, particularly in the presence of moisture.

Structure and properties[edit]

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.[4] 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).[5]

Solubility of HCl (g/L) in common solvents[6]

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 below, 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. To promote an HCl molecule to the v = 1 state, we would expect to see an infrared absorption about 2880 cm−1. 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 rotation of the molecules. Because of quantum mechanical selection rules, only certain rotational modes are

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