 There's something else that we can look at is polyprotism. Polyprotism sounds a bit like what it says, so protons and poly means many, so really more than one. I mean, for it to be poly, you'd want more than two, but sulfuric acid is a good example here because it's a species that has more than one proton, and therefore it often will form an anethyprotic species. So the example that I've looked at here is phosphoric acid. This one here is phosphoric acid, and you can see that phosphoric acid has three protons. So in actual fact, if we were to combine it with water as a liquid, and we'll regard each of these as the acid sequence. So here's an acid, meaning that the water would be the base. So we would get H2PO4, this is an ion with a one minus charge, and that would form an H3O plus ion. So that's the first one. Then there would be a second ionization, which would involve the H2PO4 minus. Again, if we put that with water, with water acting as the Bronsted Larry base, then we would have HPO4 two minus aqueous, and another H3O plus aqueous. And then of course we can do, this is also acting as an acid, then we can do a third ionization with the HPO4 two minus, and it will also combine with the H2O, again acting as a base, this time forming the PO4 three minus ion, the phosphate ion, and another hydronium ion. Now we can add these together, and you'll see that if we were to add them together and cancel out the like species, then what we would end up with is three water molecules and three of the hydroniums as well as the phosphate ion. What you can see is with each of these, the corresponding species here is a conjugate base, which also is then acting as an acid here, here's a conjugate base, but also acting as an acid here. So these are our amphiprotic species, and we can see them when we pull some of these different polyprotic species apart and go through their ionization sequences. There are two examples that you need to look at for each of these. You may want to pause the video at this point and see if you can work them out yourselves or you may get a chance to do this in class just to have a look. The key to this of course is that the first thing we want to do is we want to ionize each of these. So this is sodium ion and a bicarbonate ion, both of these obviously in solution. The important thing about these is from our NAG-SAG, this is a group one, and potassium is a group one, and we know that all group one salts are soluble. So the second thing we want to do is we want to get the potassium ions out of here and leave our H2PO4-ion here as well. So once you've isolated each of these two, then what you can do is then go through the sequence that I just showed you in the previous couple of slides to show that these ions in solution can act as both proton donors and proton acceptors, and that's our definition of anti-protic species. Have a look at a couple of examples and make sure that you can demonstrate each of these. Simplest thing as I said is to add them to water and show the conjugate pairs of each of these species with an acid and its conjugate base, and then acting as a base with its conjugate acid. Thanks for watching and thanks Nelson.