# Relative strength of acids and Bases

In practice _{} is used to define the strength only of those acids that are weaker than _{} and _{} is used to define the strength of only those bases that are weaker than _{}. For two weak acids _{} and _{} of ionisation constant _{} and _{} respectively at the same concentration _{}, we have,

_{}

Similarly, relative strengths of any two weak bases at the same concentration are given by the ratio of the square-roots of their dissociation constants. i.e.,

_{}