Sulfuric acid, H2SO4, is a strong mineral acid, which is a viscous (thick and syrupy), oily liquid that has for years been the most widely used chemical in the world. Normally found in a liquid state, sulfuric acid has a density of 1.84 g/cm3 and is soluble in water. Its melting point is about 50°F (10°C) and its boiling point is approximately 640°F (337°C). In the 2000s, over 165 million tonnes (metric tons; which is equivalent to 364 billion lb [165 billion kg]) of sulfuric acid are produced each year. It is considered the second most produced chemical, besides drinkable water. It is also one of the least expensive acids, which makes it a favorite of industries around the world. It is used in the production of fertilizers and as an industrial catalyst (a substance which speeds up chemical reactions). It is also used in large amounts in oil refining and waste-water processing.
Today, it is generally considered that sulfuric acid was first called oil of vitriol when Islamic alchemist, astronomer, and physicist Jabir ibn Hayyan (c. 721−c. 815) discovered it in the eighth century. European alchemists also called it oil of vitriol, along with spirit of vitriol and vitriol. It was a very popular chemical to alchemists across Asia and Europe from the eighth century to the sixteenth century, and in later centuries by chemists. In the seventeenth century, German-Dutch alchemist and chemist Johann Glauber (1604−1670) combined sulfur with saltpeter (potassium nitrate) and heated the combination with steam to make sulfuric acid. Around 1735, sulfuric acid was first mass produced by English pharmacist Joshua Ward in glass containers. Then, about 15 years later, English inventor John Roebuck (1718−1794) used a lead chamber process that made its production more efficient and less costly. The process was improved upon over the next eighty years. In 1831, English merchant Peregrine Phillips designed the contact process for producing sulfuric acid. His patented process is now the standard way of producing sulfuric acid in the 2000s.
One of the major uses of sulfuric acid is in the production of fertilizers. Phosphate rock is treated with sulfuric acid to produce water soluble phosphates, which are essential for plant growth and survival. It is also the acid used in car batteries. Automobile batteries contain lead, lead oxide, and sulfuric acid. These lead storage batteries are used because they can not only provide the electric current needed to start a car, but can be recharged by the car’s electrical system while the car is running.
Sulfuric acid is one of the major components of acid rain. Coal contains sulfur as a natural impurity and when coal is burned sulfur dioxide (SO2) and sulfur trioxide (SO3) gases are produced. Sulfur trioxide then reacts with water in the air, creating sulfuric acid. This acid rain can damage buildings, corrode metal, and destroy plant and animal life. Acid rain is an increasing problem not only in major industrialized nations, but also in neighboring countries that are downwind, since pollutants produced by a country do not stay in the air above that country.
One of the major industrial uses of sulfuric acid is as a dehydrating agent (a substance that removes water from other substances). Sulfuric acid is an extremely effective dehydrating agent. Upon contact with living tissue it kills cells by removing water from them.
Some historians credit the discovery of sulfuric acid to the Islamic scientist Mohammad Ibn Zakariya al-Razi (864-930 ce), while others claim the first mention of the compound to have been by the Islamic writer Geber (probably born about 1270). In any case, European scientists apparently did not discover sulfuric acid on their own until the sixteenth century, when the Belgian scientist Johann Baptista van Helmont (1579–1644) described its preparation by adding water to the gas formed when sulfur was burned. The discovery of sulfuric acid proved to be an important development in the early history of modern chemistry. For the first time, it gave chemists an acid far stronger than the vinegar with which they previously had to work in analyzing mixtures and making new chemical compounds.
The first commercially successful method for making sulfuric acid was developed in 1746 by English physician, chemist, and inventor John Roebuck (1718–1794). Roebuck's method is called the lead chamber process because the acid is made in large containers lined with lead. The lead chamber process involves three primary steps: the combustion of sulfur to produce sulfur dioxide; the conversion of sulfur dioxide to sulfur trioxide; and the reaction of sulfur trioxide with water to make sulfuric acid:
S + O2 → SO2
2SO2 + O2 → SO3
SO3 + H2O → H2SO4
The most important single use of sulfuric acid is for the production of phosphoric acid (H3PO4), which in turn is used to make fertilizers. About 70 percent of all the sulfuric acid used in the United States goes to this application. Some other uses of sulfuric acid include: