What is the Difference Between Oleum and Sulfuric Acid?

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The main difference between oleum and sulfuric acid lies in their composition and properties.

Oleum:

  • Also known as fuming sulfuric acid, it is a solution of sulfur trioxide (SO3) in sulfuric acid.
  • The chemical formula for oleum is ySO3·H2O, where y represents the total molar content of sulfur trioxide.
  • Oleum is an oily, colored, or cloudy liquid due to the presence of impurities.
  • It generates strong fumes when exposed to air and is diluted with considerable heat generation when in contact with water.
  • Oleum is generally less corrosive to metals than sulfuric acid because there is no free water to attack surfaces.

Sulfuric Acid:

  • An inorganic acid, it is produced by the contact process from elementary sulfur.
  • Sulfuric acid is an aqueous solution of sulfuric acid and has a strong acidic nature.
  • It is a clear, oily, colorless to slightly clouded liquid that is well miscible with water.
  • Sulfuric acid is hygroscopic and has corrosive effects, carbonizing most organic substances.
  • It is widely used in various applications, such as fertilizer production, oil refining, wastewater processing, and chemical synthesis.

In summary, oleum is a solution of sulfur trioxide in sulfuric acid, while sulfuric acid is a standalone inorganic acid. Oleum has a more complex composition and is generally less corrosive than sulfuric acid.

Comparative Table: Oleum vs Sulfuric Acid

Here is a table comparing the differences between oleum and sulfuric acid:

Property Oleum Sulfuric Acid
Definition Oleum is a mixture of sulfuric acid with up to 80% free sulfur trioxide, also known as "fuming sulfuric acid" Sulfuric acid is a highly water-soluble, hygroscopic, and strong acidic compound with the molecular formula H2SO4
Chemical Formula ySO3.H2O, where "y" represents the total molar content of sulfur trioxide H2SO4
Molar Mass Varies depending on the concentration of sulfur trioxide 98.07 g/mol
Boiling Point Varies depending on the concentration of sulfur trioxide 337°C (639°F)
Melting Point Varies depending on the concentration of sulfur trioxide 10°C (50°F) for pure sulfuric acid
Concentration 10% oleum can also be expressed as H2SO4.0.13611SO3, 1.13611SO3.H2O, or 102.25% sulfuric acid Less concentrated sulfuric acid is sometimes erroneously called "oleum"
Applications Oleum is an important intermediate in the manufacture of sulfuric acid due to its high enthalpy of hydration Sulfuric acid is used in a wide range of applications, such as fertilizer production, oil refining, wastewater processing, and chemical synthesis

The key difference between oleum and sulfuric acid lies in the concentration of sulfur trioxide in the compound. Oleum is a mixture of sulfuric acid with up to 80% free sulfur trioxide, while sulfuric acid itself contains sulfur trioxide in a less concentrated form.