9. Polyprotic Acid-Base Equilibria
Polyprotic Acids and Bases
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We've looked at the polyprotic acid form. Now, let's look at the polyprotic base form. Here, we're dealing with a 3 minus. We have the potential of absorbing or accepting 3 H+ ions. Here, we're dealing with the basic form where it has no acidic hydrogens on it. Here, it's going to just accept an H+ from water thereby creating HA2- By doting in H plus away, water itself becomes Oh minus. Now because we're talking about accepting the first acidic hydrogen, we're dealing with Kb 1. So here would be 2 minuteus times Oh minus divided by a3 minuteus. Here, we're now going to deal with 2 minus. With 2 minus, water is now going to donate a second H plus over to it to make it into H2A- and Oh- Here we have H2A- times Oh minus divided by H a 2 minus. Finally, this one that we created can react with a third water molecule to produce these new products times Oh minus divided by H2A minus. Realize here by examining the polyprotic acid form and and the polyprotic base form, we've gone through a lot of different variations of our polyprotic species. We've gone through the fully protonated version in this acid form which could have lost an H plus to become H2A-. That could have continued to lose another H plus to become H a2-. And then finally, we have a3- after it's lost all of its H plus. This understanding will help us realize the connections between the different forms of these compounds and the different Ka and Kb values that are associated with them. Click on to the next video to look at the final portion when talking about polyprotic species.
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