So PKA is equal to negative log of Ka, and this is the definition of PH. Negative log of the H plus concentration is equal to PH. And this we leave as it is. Now, if we take this expression, the log and bring it to the left side, we get our Henderson Hasselbalk equation. So what this equation tells us is the PH of our solution that contains that Buffet system is equal to the PKA value of that particular asset that is used in that buffer system, plus the log of the ratio of the conjugate base to its acid. Now, why is this equation a useful equation?