Sulfuric Acid
Overview
Sulfuric acid (sul-FUR-ik AS-id) is a colorless to dark brown, dense, oily liquid that mixes completely with water. Its color depends on its purity, with compounds of sulfur adding a darker color to the colorless pure product. Sulfuric acid is also available in a form known as fuming sulfuric acid, a solution of sulfur trioxide in sulfuric acid with the chemical formula xH2SO4·ySO3. Sulfuric acid is the most commonly manufactured chemical in the world. In 2004, the chemical industry produced 37,515,000 metric tons (41,266,000 short tons), of which more than half was used in the manufacture of fertilizers.
Key Facts
Other Names:
Hydrogen sulfate; oil of vitriol
Formula:
H2SO4
Elements:
Hydrogen, sulfur, oxygen
Compound Type:
Acid (inorganic)
State:
Liquid
Molecular Weight:
98.08 g/mol
Melting Point:
10.31°C (50.56°F)
Boiling Point:
337°C (639°F)
Solubility:
Completely miscible with water
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.
How It Is Made
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
Although the process looks fairly simple, the reactions are actually somewhat complex because of other compounds needed to make the reactions occur.
The second method for making sulfuric acid is known as the contact process. It was invented about 1830 by an English vinegar merchant from Bristol, Peregrine Phillips. The chemical reactions involved in Phillips' process are identical to those in the lead chamber process, but they are carried out over a catalyst of finely divided platinum metal. Phillips found that the yield obtained (the amount of raw material converted to useful product) was much higher than with the lead chamber process.
As it happens, little attention was paid to Phillips' discovery because there was not much demand for sulfuric acid at the time. It was not until the invention of synthetic dyes a few decades later that the compound became commercially important. But even then, the lead chamber process was the preferred method for making sulfuric acid. Over time, improvements were made in the contact process, and it gradually became more and more popular. Today, nearly all of the sulfuric acid produced is manufactured by some modification of Peregrine Phillips' method.
Common Uses and Potential Hazards
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:
- As the electrolyte in lead storage batteries (the liquid through which charged particles flow);
- For the processing of gasoline and other petrochemicals, as a way of removing impurities present in the products;
- As a cleaning agent for metal surfaces, especially prior to their being plated with a second metal;
- In the manufacture of explosives, dyes, glues, pigments, rayon, and films;
- As a catalyst in a variety of industrial chemical and research chemical reactions; and
- In the processing of ores in preparation for the extraction of metals.
Interesting Facts
- Sulfuric acid's common name is oil of vitriol. That name comes from the fact that it was once produced from either iron(II) sulfate, known as "green vitriol," or from copper(II) sulfate, known as "blue vitriol."
- The conversion of sulfur dioxide to sulfur trioxide in the manufacture of sulfuric acid does not occur very readily. That step controls the efficiency with which the acid can be made. Phillips' great breakthrough was to find a catalyst that made that reaction take place more easily. Later, researchers found an even more efficient catalyst, vanadium pentoxide (V2O5). Today, vanadium pentoxide is still the most popular catalyst in the production of sulfuric acid.
Words to Know
A material that increases the rate of a chemical reaction without undergoing any change in its own chemical structure. Able to be mixed; especially applies to the mixing of one liquid with another.Sulfuric acid is a highly corrosive material that causes severe damage to the skin, eyes, and respiratory system. If spilled on the skin or eyes, it can cause inflammation, burns, and blistering, and cause serious damage to one's vision. If swallowed, it causes severe burns of the gastrointestinal tract and irreversible damage to tissue and organs. Any accident in which sulfuric acid is inhaled, swallowed, or spilled on the body requires immediate medical attention.
For Further Information
"Chemical of the Week: Sulfuric Acid." Science is Fun. http://scifun.chem.wisc.edu/chemweek/Sulf&top/Sulf&Top.html (accessed on November 15, 2005).
"Chronic Toxicity Summary: Sulfuric Acid." Office of Environmental Health Hazard, State of California. http://www.oehha.org/air/chronic_rels/pdf/sulfuric.pdf (accessed on November 15, 2005).
"Sulfuric Acid." In World of Scientific Discovery. 2nd ed. Detroit: Gale Group, 1999.
"Sulfuric Acid." National Safety Council. http://www.nsc.org/library/chemical/sulfuric.htm (accessed on November 15, 2005).
"Sulfuric Acid: Production and Uses." Aus-e-tute. http://www.ausetute.com.au/sulfacid.html (accessed on November 15, 2005).
See Also
Phosphoric Acid; Sulfur Dioxide
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