What range of pKa values is characteristic of weak acids?

Weak acids are characterized by their ability to partially dissociate in solution, which is quantitatively represented by their pKa values. The pKa is the negative logarithm of the acid dissociation constant (Ka), and it indicates the strength of an acid; lower pKa values correspond to stronger acids, while higher pKa values indicate weaker acids.

The range of pKa values associated with weak acids generally falls between 5 and 9. This range implies that these acids do not completely dissociate in solution, maintaining a significant proportion of their molecules in the undissociated form. Consequently, when weak acids are dissolved in water, they establish an equilibrium between the undissociated acid and its ions, which is a defining characteristic of weak acids.

In contrast, very strong acids usually have pKa values lower than 3, indicating that they dissociate almost completely in solution. Highly weak acids or very weak acids tend to have pKa values above 9. Therefore, the range of 5 to 9 effectively represents the typical behavior of weak acids in aqueous solutions, highlighting their partial ionization and equilibrium characteristics.