Hydrogen chloride is produced by combining chlorine and hydrogen:Īs the reaction is exothermic, the installation is called an HCl oven or HCl burner. Joseph Priestley of Leeds, England prepared pure hydrogen chloride in 1772, and by 1808 Humphry Davy of Penzance, England had proved that the chemical composition included hydrogen and chlorine. 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. Most hydrogen chloride produced on an industrial scale is used for hydrochloric acid production. While the spring constants are nearly identical, the disparate reduced masses of H 35Cl and H 37Cl cause 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. Naturally abundant chlorine consists of two isotopes, 35Cl and 37Cl, in a ratio of approximately 3:1. The latter can even be made of quartz as the HCl absorption lies in a window of transparency for this material. 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 value of the rotational constant B is much smaller than the vibrational one ν o, such that a much smaller amount of energy is required to rotate the molecule for a typical molecule, this lies within the microwave region. Including anharmonicity the vibrational energy can be written as.Į v = h ν e ( v + 1 2 ) + h x e ν e ( v + 1 2 ) 2 At room temperature, almost all molecules are in the ground vibrational state v = 0. 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). Infrared (IR) absorption spectrum One doublet in the IR spectrum resulting from the isotopic composition of chlorine
Solubility of HCl (g/L) in common solvents Temperature (☌) 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). However, the hydrogen atoms could not be located. In both structures the chlorine atoms are in a face-centered array. X-ray powder diffraction of the frozen material shows that the material changes from an orthorhombic structure to a cubic one during this transition. The extensible linear structure is indicated by the dashed lines.įrozen HCl undergoes phase transition at 98.4 K. DCl was used instead of HCl because the deuterium nucleus is easier to detect than the hydrogen nucleus. The structure of solid DCl, as determined by neutron diffraction of DCl powder at 77 K. Hydrogen chloride can protonate molecules or ions and can also serve as an acid- catalyst for chemical reactions where anhydrous (water-free) conditions are desired.īecause of its acidic nature, hydrogen chloride is a corrosive substance, particularly in the presence of moisture. For example, hydrogen chloride can dissolve in certain other solvents such as methanol: Even in the absence of water, hydrogen chloride can still act as an acid. The acid dissociation or ionization constant, K a, is large, which means HCl dissociates or ionizes practically completely in water. The resulting solution is called hydrochloric acid and is a strong acid. Upon contact, H 2O and HCl combine to form hydronium cations + and chloride anions Cl − through a reversible chemical reaction: In part because of its high polarity, HCl is very soluble in water (and in other polar solvents). 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.
The chlorine atom is much more electronegative than the hydrogen atom, which makes this bond polar. Hydrogen chloride is a diatomic molecule, consisting of a hydrogen atom H and a chlorine atom Cl connected by a polar covalent bond. Reactions Hydrochloric acid fumes turning pH paper red showing that the fumes are acidic Hydrochloric acid, the aqueous solution of hydrogen chloride, is also commonly given the formula HCl.
Hydrogen chloride gas and hydrochloric acid are important in technology and industry. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. The compound hydrogen chloride has the chemical formula HCl and as such is a hydrogen halide.