 What is a buffer and what is buffer capacity? We're going to look at a common buffer of acetic acid and sodium acetate. In the first test tube I'm going to put 1.0 molar acetic acid sodium acetate buffer. In the second test tube, I'm going to put the same buffer but a different concentration. This is a 0.01 molar buffer. Made from, again, acetic acid and sodium acetate. And in the third test tube, I'm going to put just deionized water. Same amount. To each of the three test tubes, I'm going to add some universal indicator. And we'll need to stir these a bit so you see that the first two are red indicating that they're acidic. These two are in the pH range of one to two. This is in the pH range of about six. So what I'm going to do is add sodium hydroxide, 0.1 molar. And I want you to observe what happens in each one when I add only one drop of 0.1 molar sodium hydroxide. In the first test tube, you see virtually no change. In the second test tube, virtually no change. But in the water, just one drop has turned it to purple. So this is not a buffered solution and you can see just one drop of the sodium hydroxide has made this very basic. Definite change in the second one. So even though these are the same buffer system, this one is more concentrated and with only 11 drops, we've got a change. 25 drops, we've pushed it way over the edge. We've destroyed the buffer, the capacity of the second one and the first one is still unchanged. So a buffer is able to mediate or keep the pH from changing very much. We could do the reverse of that by adding acid. This is already acidic. So if we add acid to that, you get no change. If we add acid back to this one, we can push it back in the opposite direction because we were just slightly basic. If we add acid to this one, water, you can see it only took one drop to change that. So water is not buffered and one or two drops of acid or base will change the pH dramatically. And this weak buffered solution, it has a buffer capacity of controlling the pH, but it's easily destroyed. In this case, 25 drops of a .1 molar solution pushed the acid into a basic solution. In this concentrated buffer, one molar, we added 25 drops of base and still didn't change the pH of the solution dramatically.