Hydrochloric acid
Hydrochloric acid is the salt of the protonated water and chloride. Its ions are often written as H3O+ Cl-, although the cation is in fact often bonded to other water molecules. A combined IR, Raman, X-ray, and neutron diffraction study of concentrated hydrochloric acid revealed that the primary form of H+(aq) in these solutions is H5O2+, which, along with the chloride anion, is hydrogen-bonded to neighboring water molecules in several ways. (See Hydronium for further discussion of this issue.)