Search results
Results from the WOW.Com Content Network
Nitric acid, with a pK value of around −1.7, behaves as a strong acid in aqueous solutions with a pH greater than 1. [23] At lower pH values it behaves as a weak acid. pK a values for strong acids have been estimated by theoretical means. [24] For example, the pK a value of aqueous HCl has been estimated as −9.3.
Acid strength is the tendency of an acid, symbolised by the chemical formula HA, to dissociate into a proton, H +, and an anion, A −.The dissociation or ionization of a strong acid in solution is effectively complete, except in its most concentrated solutions.
A strong superacid of this kind is fluoroantimonic acid. Another group of superacids, the carborane acid group, contains some of the strongest known acids. Finally, when treated with anhydrous acid, zeolites [ citation needed ] (microporous aluminosilicate minerals) will contain superacidic sites within their pores.
Sulfonic acids are strong acids. They are commonly cited as being around a million times stronger than the corresponding carboxylic acid. For example, p-Toluenesulfonic acid and methanesulfonic acid have pK a values of −2.8 and −1.9, respectively, while those of benzoic acid and acetic acid are 4.20 and 4.76, respectively.
Fluoroantimonic acid is a mixture of hydrogen fluoride and antimony pentafluoride, containing various cations and anions (the simplest being H 2 F + and SbF − 6).This mixture is a superacid stronger than pure sulfuric acid, by many orders of magnitude, according to its Hammett acidity function.
Although hydrofluoric acid is regarded as a weak acid, it is very corrosive, even attacking glass when hydrated. [20] Dilute solutions are weakly acidic with an acid ionization constant K a = 6.6 × 10 −4 (or pK a = 3.18), [10] in contrast to corresponding solutions of the other hydrogen halides, which are strong acids (pK a < 0).
Nitric acid is normally considered to be a strong acid at ambient temperatures. There is some disagreement over the value of the acid dissociation constant, though the pK a value is usually reported as less than −1. This means that the nitric acid in diluted solution is fully dissociated except in extremely acidic solutions.
Citric acid also dissolves in absolute (anhydrous) ethanol (76 parts of citric acid per 100 parts of ethanol) at 15 °C. It decomposes with loss of carbon dioxide above about 175 °C. Citric acid is a triprotic acid, with pK a values, extrapolated to zero ionic strength, of 3.128, 4.761, and 6.396 at 25 °C. [21]