The strength of a weak acid is best described using the value of its acid dissociation constant (acid ionisation constant), K a (or pK a). Unless you have been given a list of acids to memorise as weak, very weak etc, these terms are quite arbitrary, and should only be used to compare the strength of one acid with another. You will also see comparative terms such as weak, very weak, and, very, very weak (even feeble) used to describe this continuum of weakness. We have chosen to use the terms "weak" for those that undergo very little dissociation, and the term "moderately weak" for those that are not so "weak". The term "weak" is not well defined, that is, a weak acid is one that only partially dissociates (ionises).įor this reason there is a continuum of weakness of acid, that is, some weak acids are weaker than others. The term "strong" is quite well defined for a dilute solution of monoprotic acid, such an acid is strong if its percentage dissociation (ionisation) is approximately 100%. (See the tutorial on Acid and Base Definitions)Ģ. The terms "acid" and "base" refer to a Brønsted-Lowry acid and a Brønsted-Lowry base.
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