 Diagrammatically, it looks a little bit like this, so you can see from the diagram that the concentrations of both the acid and the conjugate base are equal. And so therefore, just to reiterate that, when we look at the Ka value, if I simplify that just down to the protons, the hydrogen ions rather than writing them as hydroniums because we know that the water is going to disappear anyway, then you can see maybe a little clearer on this slide than on the previous slide that the concentration of this and this are the same. So whatever those values are, they'll cancel out. So we have a direct relationship between the Ka value and the H plus value, and so therefore the pKa is a nice relevant one for us to talk about when we're looking at buffer solutions. But what's the purpose? What's the point of this? The point of this is if we add an acid, so if we add a source of H plus ions, what we're going to do is we're going to increase the concentration of the H plus ions, and Le Chatelier's principle says that the system will shift to counter that to try and push us back in the opposite direction, and so therefore we will have a shift in the equilibrium in this case to the left to increase the concentration of the reactants. Likewise, if we were to add a base, add a source of hydroxide ions, what these are going to do is they're going to neutralize the protons, neutralize the hydronium ions, drop the concentration of those, therefore what we're going to need to do is we're going to need to, by Le Chatelier's principle, shift that equilibrium, which is actually going to shift it this time to the right. Decrease the acid concentration and increase the concentration of the products, the H plus and the H3C00-. Now this type of situation, buffers work for small changes in pH over a reasonable range, but not too much. If you start pouring too much sulfuric acid into your swimming pool, you will badly affect the pH and you won't be able to recover it just with the use of a buffer. So buffer solutions allow us to have some resistance to changes in pH over a small range, and they're a very useful thing in a number of important natural systems, and we'll look at those natural systems in the final video. Thank you for watching.