weak ka

Acid strength is the tendency of an acid, symbolised by the chemical formula




HA



{\displaystyle {\ce {HA}}}
, to dissociate into a proton,





H

+





{\displaystyle {\ce {H+}}}
, and an anion,





A

−





{\displaystyle {\ce {A-}}}
. The dissociation of a strong acid in solution is effectively complete, except in its most concentrated solutions.





HA
⟶

H

+


+

A

−





{\displaystyle {\ce {HA -> H+ + A-}}}
Examples of strong acids are hydrochloric acid





(
HCl
)




{\displaystyle {\ce {(HCl)}}}
, perchloric acid





(

HClO

4





)




{\displaystyle {\ce {(HClO4)}}}
, nitric acid





(

HNO

3





)




{\displaystyle {\ce {(HNO3)}}}
and sulfuric acid





(

H

2






SO

4





)




{\displaystyle {\ce {(H2SO4)}}}
.
A weak acid is only partially dissociated, with both the undissociated acid and its dissociation products being present, in solution, in equilibrium with each other.





HA






↽




−








−




⇀







H

+


+

A

−





{\displaystyle {\ce {HA <=> H+ + A-}}}
Acetic acid (





CH

3





COOH



{\displaystyle {\ce {CH3COOH}}}
) is an example of a weak acid. The strength of a weak acid is quantified by its acid dissociation constant,




K


a





{\displaystyle K_{{\ce {a}}}}
value.
The strength of a weak organic acid may depend on substituent effects. The strength of an inorganic acid is dependent on the oxidation state for the atom to which the proton may be attached. Acid strength is solvent-dependent. For example, hydrogen chloride is a strong acid in aqueous solution, but is a weak acid when dissolved in glacial acetic acid.

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