Is nitric acid the strongest acid and acetic acid the weakest?

1 Answer
Mar 3, 2017

Answer:

Far from it!

Explanation:

The strongest acid

Probably the strongest common acid is perchloric acid, #"HClO"_4 ("p"K_text(a) = "-10")#.

It is #10^7# times as strong as sulfuric acid, #"H"_2"SO"_4 ("p"K_text(a) = "-3")# which, in turn, is 50 times stronger than nitric acid, #"HNO"_3 ("p"K_text(a) = "-1.3")#.

However, the strongest acid known is fluoroantimonic acid, #"H"_2"SbF"_6#. Its Hammett acidity function, #H_0 = "-31.3"#. This makes it more than #10^19# times as strong as sulfuric acid.

The weakest acid

The weakest common acid is probably #"HCN" color(white)(l)("p"K_text(a) = 9.2)#.

Acetic acid (#"p"K_"a" = 4.8#) is 25 000 times stronger than #"HCN"#.

However, the weakest acids are probably the alkanes (#"p"K_"a" ≈ 50#)

The weakest acid is probably cyclopentane. Its Bordwell #"p"K_"a" = 59#.

Even ethylene (#"p"K_"a" = 50#) is a billion times more acidic than cyclopentane.