HCl

Hydrochloric acid or hydrogen chloride, a colourless gas with a pungent odour; its aqueous solution is known as hydrochloric acid. Hydrogen chloride is produced by burning hydrogen and chlorine together and is also a by-product of the chlorination of organic compounds.

HCl is used in the production of the plastic PVC, ferric chloride (needed for waste water purification) and silicones.