where water autoprotolysis is negligible and the fractional dissociation of HA is small, we obtain the common "weak" acid equation
or, equivalently,
when:
where water autoprotolysis is still negligible but the fractional dissociation becomes large, the "weak" acid behaves like a "strong" acid.
both conditions are satisfied simultaneously.
For values of Ka < 10-7, these two conditions cannot be satisfied simultaneously.
(or equivalently, when:
)
AND
where water autoprotolysis is the dominant source of H+, we have:
