How is the weakest acid identified in terms of Kb?

To determine the strength of an acid, we look at the acid dissociation constant, Ka, which measures the extent to which an acid donates protons in solution. However, when identifying the weakest acid in terms of Kb, we need to consider the relationship between Kb and Ka through the water ion product, Kw.

A weak acid corresponds to a small Ka value because it only partially dissociates in solution. Conversely, Kb measures the strength of a base and refers to the base's ability to gain protons to form its conjugate acid. If we have a weak acid, it will have a larger Kb for its conjugate base, indicating a weaker acid associated with a smaller Ka.

Thus, the weakest acid corresponds to the smallest Kb for its conjugate base when considering the acid-base equilibrium. In summary, the identification of the weakest acid in terms of Kb is based on the concept that a weaker acid yields a stronger conjugate base, leading to smaller values of Kb, which aligns with the idea of acid strength being inversely related to its base's Kb value. Therefore, the smallest Kb correlates with the weakest acid.