What is buffer capacity?

The buffer capacity is the amount of acid or base a buffer can accept until it can no longer maintain a constant pH.

Direct definition: "The buffer capacity is the amount of acid or base a buffer can accept until it can no longer maintain a constant . It is a value that quantifies the amount of ##H_3O^+## and ##OH^-## that a solution is capable of neutralizing before the weak acid or conjugate base is used up and the pH of the solution begins to change sharply."

Now what does that mean?

Alright, so we know that it has the word "capacity" so we know its associated to a limit. So the limit of a buffer, or how far a buffer system can be "pushed" before it breaks and is ineffective right? You can think about your temper for example! Lets say your temper is at a level of 0 and you have a younger brother that keeps poking you and running off. Your "buffer capacity" is the amount of pokes it takes until your temper rises. If you get poked a few times I mean you might shrug it off, temper levels may rise to around maybe 1, 2, or 3? seems reasonable. But if you get poked lets say 50 times your temper will be at a 5 and you may end up yelling at your younger brother to STOP!!!!

Same thing applies to a buffer (however it is less vocal)! Lets say the pH of a buffer is sitting at 5. There is only a certain amount of volume of acid that can be added that if you add anymore, then the buffer system will break it can't handle that much acid and will not stabilize back to a level of 5. Same applies if a base is added - if you add over a certain volume of base then the buffer system will break and will not be able to stabilize back to (for this example) a pH of 5.