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Weak acid

A weak acid is an acid that does not ionise in a solution to a significant extent; that is, if the acid was represented by the general formula HA, then in aqueous solution a significant amount of undissociated HA still remains. Weak acids in water dissociate as

\mathrm{ HA_{(aq)} \, \leftrightarrow \, H^+\,_{(aq)} +\, A^-\,_{(aq)} }.

The equilibrium concentrations of reactants and products are related by the Acidity constant expression, (Ka):

\mathrm{ K_a\, =\, \frac {[H^+\,][A^-\,]}{[HA]} }

The greater the value of Ka, the more the formation of H+ is favored, and the lower the pH of the solution. The Ka of weak acids varies between 1.8×10-16 and 55.5. Acids with a Ka less than 1.8×10-16 are weaker acids than water. Acids with a Ka of greater than 55.5 are strong acids and almost totally dissociate when dissolved in water. The vast majority of acids are weak acids. Organic acids are a large subset of weak acids. Common household weak organic acids include acetic acid found in vinegar, and citric acid found in lemons; weak mineral acids include boric acid used as an antiseptic and eyewash and phosphoric acid that appears in many soft drinks.

See also

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Weak_acid". A list of authors is available in Wikipedia.
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