## Chemistry: Molecular Approach (4th Edition)

For most polyprotic acids, the $K_a$ for the first ionization is much larger than the same for the second ionization or even a third one if it is possible. Therefore, the amount of $H_3O^+$ produced by the second and third ionization is much smaller than the same produced by the first one. In addition to that, the formation of $H_3O^+$ by the first ionization shifts the equilibrium to the left (Le Chatelier's principle), reducing even more the other ionizations, and making them even more negligible.
For most polyprotic acids, the $K_a$ for the first ionization is much larger than the same for the second ionization or even a third one if it is possible. Therefore, the amount of $H_3O^+$ produced by the second and third ionization is much smaller than the same produced by the first one. In addition to that, the formation of $H_3O^+$ by the first ionization shifts the equilibrium to the left (Le Chatelier's principle), reducing even more the other ionizations, and making them even more negligible.