I understand the henderson-hasselbalch equation, and how the pH of a solution depends on the ratio of acid to its conjugate base. However, I dont understand how this concept can be related to solutions that are extremely diluted. For example, lets say you have 0.00001M acid+c.base. According to Henderson-Hasselbalch, the pH will still = pKa, since the log ratio is equal to 1. But does this make sense logically? I mean with that little acid, there are so little H+ ions dissociated, so how can the pH possibly equal the pKa (especially if the pKa is very low for that specific acid)??