My question concerns polyprotic acids.

Question

Formulate a reasoning for the stepwise ionization and subsequent weakening of the acid for polyprotic acids.

Answer 1

The Ka for each succeeding step in the ionization of a polyprotic acid gets smaller and smaller because as each proton (H⁺) is "removed" the attraction between the remaining proton(s) is greater. The negative charge of the resulting anion causes the covalent bond between the remaining H atom(s) to keep the H⁺ from being ionized. This appears as a lower Ka, meaning the [H⁺] decreases with each step.