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.,