Hydrogen chloride
![Hydrochloric acid fumes turning pH paper red showing that the fumes are acidic](/Images/godic/202501/04/Hydrochloric_acid_010747.jpg")
![The structure of solid DCl, as determined by neutron diffraction of DCl powder at 77 K. DCl was used instead of HCl because the deuterium nucleus is easier to detect than the hydrogen nucleus. The](/Images/godic/202501/04/DCl_Neutron_powder0747.png")
![](/Images/godic/202501/04/DCl_Neutron_powder,_side0747.png")
![Infrared (IR) absorption spectrum](/Images/godic/202501/04/HCl20747.jpg")
The compound hydrogen chloride has the chemical formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry. Hydrochloric acid, the aqueous solution of hydrogen chloride, is also commonly given the formula HCl.