oleum

Also known as fuming sulfuric acid, fuming sulphuric acid, Nordhausen acid

Oleum (Latin oleum, meaning oil), or fuming sulfuric acid, is a term referring to solutions of various compositions of sulfur trioxide in sulfuric acid, or sometimes more specifically to disulfuric acid (also known as pyrosulfuric acid).

Chemical data

Formula: H2O7S2
Molecular weight: 178.15 g/mol
IUPAC name: sulfuric acid;sulfur trioxide
SMILES: OS(=O)(=O)O.O=S(=O)=O
InChIKey: HIFJUMGIHIZEPX-UHFFFAOYSA-N
Polar surface area: 135 Å²
H-bond donors: 2
H-bond acceptors: 7
Formal charge: 0

via PubChem

Wikidata facts

Mass: 98.082
Image: Oleum fuming.jpg

Show 7 more facts

chemical formula: H₂SO₄
pKa: -3
refractive index: 1.397
density: 1.8356
boiling point: 279.6
melting point: -10.38
electric dipole moment: 2.72

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Article

8 sections

Contents

Production
Applications
Sulfuric acid production
As an intermediate for transportation
Organic chemistry research
Explosives manufacture
Carbon snake
References

Oleums can be described by the formula ySO3·H2O where y is the total molar mass of sulfur trioxide content. The value of y can be varied, to include different oleums. They can also be described by the formula H2SO4·xSO3 where x is now defined as the molar free sulfur trioxide content. Oleum is generally assessed according to the free SO3 content by mass. It can also be expressed as a percentage of sulfuric acid strength; for oleum concentrations, that would be over 100%. For example, 10% oleum can also be expressed as H2SO4·0.13611SO3, 1.13611SO3·H2O or 102.25% sulfuric acid. The conversion between % acid and % oleum is: \%\,\text{acid} = 100 + \frac{18}{80} \times \%\,\text{oleum} For x = 1 and y = 2 the empirical formula H2S2O7 for disulfuric (pyrosulfuric) acid is obtained. Pure disulfuric acid is a solid at room temperature, melting at 36 °C and rarely used either in the laboratory or industrial processes — although some research indicates that pure disulfuric acid has never been isolated yet.