And then finally, the last type, we just said strong acid and weak base, so let's reverse it, weak acid and strong base. Example here, we could have 1. Let's do a different number 2.50 molar HF now, that's a weak acid, and 1.0 Molar NaOH. Now, our weak acid is definitely larger in amount. So again here, we need the weak species higher in amount. So this would be a buffer. Got to remember that.
So if we go back, the first way is to mix a weak acid and conjugate base. Here, they could be equal to or different from each other but the good buffers are within the range of 101. In the next two, the weak species has to be higher than the strong species. Otherwise, it won't be a buffer. You have to remember all three cases because you'll be tested on them. And if you don't know which is which, you won't be able to get the correct answer. So just remember, with a weak base, they can be equal, they can be different. As long as it's within the range of 101, it's a good buffer. If it's outside that range, it's a bad buffer.
Case 23, the weak species have to be higher than the strong species. The strong species cannot be equal to or greater. If it is, the buffer gets destroyed. Remember these principles, and they'll help guide you to see if you have a buffer or not.