Disulfuric acid

Disulfuric acid
Names
	IUPAC name Disulfuric acid
	Other names Pyrosulfuric acid, Oleum
Identifiers
CAS Number	7783-05-3 ;
3D model (JSmol)	Interactive image; Interactive image; Interactive image;
ChEBI	CHEBI:29211 ;
ChemSpider	56433 ;
ECHA InfoCard	100.029.069
EC Number	231-976-8;
MeSH	Pyrosulfuric+acid
PubChem CID	62682;
UNII	NTC1O8E83E ;
CompTox Dashboard (EPA)	DTXSID7064817 ;
	InChI InChI=1S/H2O7S2/c1-8(2,3)7-9(4,5)6/h(H,1,2,3)(H,4,5,6) Key: VFNGKCDDZUSWLR-UHFFFAOYSA-N ; InChI=1/H2O7S2/c1-8(2,3)7-9(4,5)6/h(H,1,2,3)(H,4,5,6) Key: VFNGKCDDZUSWLR-UHFFFAOYAZ;
	SMILES OS(=O)(=O)OS(O)(=O)=O; OS(=O)(=O)OS(=O)(=O)O; O=S(=O)(O)OS(=O)(=O)O;
Properties
Chemical formula	H2O7S2
Molar mass	178.13 g·mol−1
Appearance	colorless
Melting point	36 °C (97 °F; 309 K)
Acidity (pKa)	2.5 (20 °C; in conc. H2SO4)
Conjugate base	Disulfate
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Disulfuric acid (alternative spelling disulphuric acid) or pyrosulfuric acid (alternative spelling pyrosulphuric acid), also named oleum, is a sulfur oxoacid. It is a major constituent of fuming sulfuric acid, oleum, and this is how most chemists encounter it. As confirmed by X-ray crystallography, the molecule consists of a pair of SO₂(OH) groups joined by an oxide.