Hydrochloric acid, with the chemical formula HCl and CAS number 7647-01-0, is an aqueous solution of hydrogen chloride available in varying concentrations. It is a strong inorganic acid with high corrosivity and irritancy. Hydrochloric acid can chemically react with many metals, metal oxides, bases, and most salts; it neutralizes with alkaline substances, but shows no reactivity with nonmetals such as phosphorus and sulfur. As an important inorganic chemical raw material, hydrochloric acid is widely used in industries such as pharmaceuticals and dyes, and also serves as an extractant and cleaning agent for metal surfaces.