Any acid stronger than 100 % pure sulfuric acid is a superacid.
Superacids are so powerful that we cannot use #"p"K_text(a)# values to measure their acidities.
Instead, we must use Hammett #H_0# values.
#H_0# is similar to #"p"K_text(a)# in that it is a logarithmic scale and a more negative value means a stronger acid.
Here is a table of some superacids.
#ulbb("Acid"color(white)(mmmmmm)"Structure"color(white)(mml)H_0color(white)(m))#
#("Sulfuric"color(white)(mmmmm)"H"_2"SO"_4color(white)(mmmml)"-12.0")#
#"Chlorosulfuric"color(white)(mml)"ClSO"_3"H"color(white)(mmmll)"-12.8"#
#"Triflic"color(white)(mmmmmml)"CF"_3"SO"_3"H"color(white)(mmll)"-14.1"#
#"Oleum"color(white)(mmmmmm)"H"_2"O"_4"·SO"_3color(white)(mmll)"-15"#
#"Fluorosulfuric"color(white)(mml)"FSO"_3"H"color(white)(mmmm)"-15.1"#
#"Carborane"color(white)(mmmm)"HCHB"_11"F"_11color(white)(mm)"-18.0"#
#"Magic"color(white)(mmmmmml)"FSO"_3"H·.SbF"_5color(white)(m)"-19.2"#
#"Fluoroantimonic"color(white)(m)"H"_2"F·SbF"_6color(white)(mmm)"-31.3"#
Thus, the most powerful acid is over #10^19# times as strong as 100 % sulfuric acid.
