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 colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. The compound hydrogen chloride has the chemical formula H Cl and as such is a hydrogen halide.
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