Chemistry
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.
Read more about this topic: Hydrogen Chloride
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