Chemistry / Unit 10 Chem 1853 short lesson, about 20 seconds
Polyprotic Acids: Stepwise Ionization
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The idea
A polyprotic acid loses protons through separate equilibria, each with its own Ka, and each successive Ka is dramatically smaller than the one before.
In practice
Phosphoric acid ionizes in three steps, Ka1 near 10⁻³, Ka2 near 10⁻⁸, Ka3 near 10⁻¹³.
Where people slip
Treating the steps as equally significant ignores how the later ionizations are suppressed by the earlier ones.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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