Weak acid 166506 223519498 2008-07-04T12:32:47Z 122.53.239.140 /* Explanation */ {{Acids_and_Bases}} A '''weak acid''' is an [[acid]] that does not completely donate all of its hydrogens when dissolved in water. These acids have higher [[pH]] compared to [[strong acids]], which release all of their hydrogens when dissolved in water. ==Explanation== Weak acids do not [[ionization|ionize]] 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 <math>\mathrm{ HA_{(aq)} \, \leftrightarrow \, H^+\,_{(aq)} +\, A^-\,_{(aq)} }.</math> The equilibrium concentrations of reactants and products are related by the [[Acidity constant]] expression, (K<sub>a</sub>): <math>\mathrm{ K_a\, =\, \frac {[H^+\,][A^-\,]}{[HA]} }</math> The greater the value of K<sub>a</sub>, the more the formation of H<sup>+</sup> is favored, and the lower the [[pH]] of the solution. The K<sub>a</sub> of weak acids varies between 1.8&times;10<sup>-16</sup> and 55.5. Acids with a K<sub>a</sub> less than 1.8&times;10<sup>-16</sup> are weaker acids than water. Acids with a K<sub>a</sub> of greater than 55.5 are [[strong acids]] and almost totally dissociate when dissolved in water and sea level magnitude ==Examples== The vast majority of acids are weak acids. Organic acids are a large subset of weak acids. However, there are some [[mineral acid]]s in this field. *[[acetic acid]] *[[citric acid]] *[[boric acid]] *[[phosphoric acid]] *[[hydrofluoric acid]] ==See also== * [[Strong acid]] * [[Weak base]] [[Category:Acids]] [[es:Ácido débil]] [[fr:Acide faible]] [[hr:Slaba kiselina]] [[id:Asam lemah]] [[it:Acidi deboli]] [[nl:Zwak zuur]] [[fi:Heikko happo]] [[sv:Svag syra]] [[zh:弱酸]]