HCl, anhydrous hydrochloric acid. Its molecular weight is 36. 47 g/mol; it is a colorless, corrosive gas. Hydrogen chloride is a covalent bonded nonflammable gas and ionises almost completely when dissolved in water. When dissolved in water, hydrogen chloride forms a strong acid, hydrochloric acid. In the stratosphere, HCl acts as a reservoir species temporarily removing chlorine radicals from a catalytic ozone destruction cycle. (See ozone and chlorine. )