What is "superacid"

n. (context chemistry English) any medium having a very high acidity; typically a solution of a strong Lewis acid in a Brønsted acid.

According to the classical definition, a superacid is an acid with an acidity greater than that of 100% pure sulfuric acid, which has a Hammett acidity function (H) of −12. According to the modern definition, superacid is a medium in which the chemical potential of the proton is higher than in pure sulfuric acid. Commercially available superacids include trifluoromethanesulfonic acid (CFSOH), also known as triflic acid, and fluorosulfuric acid (HSOF), both of which are about a thousand times stronger (i.e. have more negative H values) than sulfuric acid. Strong superacids are prepared by the combination of a strong Lewis acid and a strong Brønsted acid. A particularly strong superacid is fluoroantimonic acid.