What is the Difference Between Oleum and Sulfuric Acid

Oleum and sulfuric acid are both highly corrosive substances commonly used in industrial applications such as manufacturing, chemical synthesis, and battery production. While both are forms of sulfuric acid, there is a difference between oleum and sulfuric acid in composition and concentration.

What is the difference between oleum and sulfuric acid? Oleum is a solution of sulfur trioxide in concentrated sulfuric acid, whereas sulfuric acid is a strong mineral acid.

Key Areas Covered

1. What is Oleum 
      – Definition, Features 
2. What is Sulfuric Acid
      – Definition, Features 
3. Similarities Between Oleum and Sulfuric Acid
      – Outline of Common Features
4. Difference Between Oleum and Sulfuric Acid
      – Comparison of Key Differences
5. FAQ: Oleum and Sulfuric Acid
      – Answers to Frequently Asked Questions

Key Terms

H2SO4, H2S2O7, Fuming Sulfuric Acid, Oleum, Sulfuric Acid Anhydride, Sulfuric Acid

Difference Between Oleum and Sulfuric Acid  - Comparison Summary

What is Oleum

Oleum, also known as fuming sulfuric acid or sulfuric acid anhydride, is a potent chemical compound primarily composed of sulfur trioxide (SO3) dissolved in concentrated sulfuric acid. This highly reactive substance is notable for its corrosive properties and its importance in various industrial processes.

With a molecular formula of H2S2O7, oleum is a colorless to pale yellow liquid that emits white fumes in moist air, hence its name “fuming” sulfuric acid. Its reactivity stems from the presence of sulfur trioxide, which readily reacts with water to form sulfuric acid, releasing heat in the process. Due to its highly exothermic nature, oleum must be handled with extreme caution, requiring specialized equipment and expertise to ensure safety.


Oleum has extensive uses in the production of detergents, explosives, and pharmaceuticals. It serves as a crucial intermediate in the synthesis of various organic compounds, including dyes, perfumes, and plastics. Additionally, oleum plays a vital role in the petrochemical industry, where it is utilized in the sulfonation of organic compounds to produce surfactants and lubricant additives.

Despite its utility, oleum poses significant hazards to both human health and the environment. Exposure to oleum can cause severe burns, respiratory irritation, and other adverse health effects. Accidental release into the environment can lead to soil and water contamination, endangering ecosystems and public health.

To mitigate these risks, strict safety protocols and regulatory measures govern the handling, transportation, and storage of oleum. Personnel working with oleum must undergo rigorous training on handling procedures and emergency response protocols to minimize the likelihood of accidents and mitigate their impact if they occur.

What is Sulfuric Acid

Sulfuric acid, chemically represented as H2SO4, is one of the most essential and widely used industrial chemicals globally. It acts as a precursor to many other chemical compounds and has applications across various industries.

With its strong acidic properties, sulfuric acid is utilized extensively in the production of fertilizers, particularly phosphoric acid for phosphate fertilizers, and ammonium sulfate for nitrogen fertilizers. It plays a crucial role in the manufacture of detergents, dyes, drugs, and explosives. Moreover, it is a key component in the refining of petroleum and the processing of ores to extract metals such as copper, zinc, and lead.

Sulfuric Acid

In addition to its industrial applications, sulfuric acid is utilized in laboratories as a dehydrating agent and a catalyst in various chemical reactions. Its ability to remove water molecules from compounds makes it valuable in organic synthesis processes.

However, despite its widespread utility, sulfuric acid poses significant environmental and health risks. Its corrosive nature can cause severe burns upon contact with skin and eyes, and inhalation of its vapors can lead to respiratory irritation. Moreover, accidental spills or releases of sulfuric acid can result in environmental contamination, leading to soil and water pollution.

Efforts to mitigate the adverse effects of sulfuric acid include strict safety regulations in its handling, storage, and transportation. Additionally, advancements in technology have led to the development of more efficient and environmentally friendly processes for its production and utilization.

Similarities Between Oleum and Sulfuric Acid

  1. Oleum and sulfuric acid are both highly corrosive and strong acids.
  2. Both substances are widely used in industrial processes, such as in the production of chemicals, detergents, and batteries.

Difference Between Oleum and Sulfuric Acid


  • Oleum is a solution of sulfur trioxide (SO3) in concentrated sulfuric acid (H2SO4), commonly used in chemical synthesis and industrial processes due to its high reactivity. On the other hand, sulfuric acid is a strong mineral acid with the chemical formula H2SO4, widely utilized in various industrial applications such as chemical synthesis, mineral processing, and battery production.


  • Sulfuric acid is typically available in aqueous solution with concentrations ranging from 10% to 98%, whereas oleum is a more concentrated form of sulfuric acid with concentrations exceeding 100%.


  • Oleum is formed by dissolving sulfur trioxide in concentrated sulfuric acid, whereas sulfuric acid is typically produced through the contact process, where sulfur dioxide is oxidized to sulfur trioxide and then dissolved in water to form sulfuric acid.


  • Oleum is more reactive than sulfuric acid due to its higher concentration of sulfur trioxide.


In summary, oleum and sulfuric acid, both highly corrosive acids used in industries, have notable differences. Oleum, a concentrated form of sulfuric acid with dissolved sulfur trioxide, is highly reactive and used in various industrial processes but poses significant health and environmental risks. On the other hand, sulfuric acid, produced through the contact process, is utilized as a precursor in fertilizer, detergent, and pharmaceutical manufacturing, though it also carries its own risks.

FAQ: Oleum and Sulfuric Acid

1. Which gas dissolves in concentrated H2SO4 to give oleum?

Oleum is formed by dissolving sulfur trioxide gas in concentrated sulfuric acid, resulting in a highly reactive solution used in chemical synthesis and industrial processes. This dissolution process creates oleum, considered a solution of SO3 in sulfuric acid, through the introduction of SO3 gas into a sulfuric acid solution.

2. Is oleum stronger than sulphuric acid?

Yes, oleum is generally considered stronger than sulfuric acid due to the presence of excess sulfur trioxide (SO3) in its composition. This additional SO3 makes the conjugate base of oleum more stable compared to the conjugate base of sulfuric acid, resulting in increased acidity and reactivity.

3. What is the use of oleum?

Oleum has significant use as a reagent in various chemical processes. One notable application is in the secondary nitration of nitrobenzene, where oleum serves as a catalyst or reactant. This process is crucial in the synthesis of compounds used in the manufacture of dyes, pharmaceuticals, and other organic chemicals.

4. What are the hazards of oleum?

One of the primary hazards of oleum is its reactivity with a wide range of materials, including combustible substances, reducing agents, and organic materials. This reactivity can lead to fire or explosion hazards if not handled properly.


1. “Oleum.” National Library of Medicine. 
2. “Sulfuric Acid.” National Library of Medicine. 

Image Courtesy:

1. “Oleum fuming” By W. Oelen (CC BY-SA 3.0) via Commons Wikimedia
2. “Sulphuric acid on a piece of towel” By Toxic Walker – Own work (CC BY-SA 3.0) via Commons Wikimedia

About the Author: Hasini A

Hasini is a graduate of Applied Science with a strong background in forestry, environmental science, chemistry, and management science. She is an amateur photographer with a keen interest in exploring the wonders of nature and science.

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