So negative log of this guy is the same as saying positive log of the reciprocal of this guy. So the concentration of conjugate base divided by the concentration of conjugate acid. So Now, A final formula states we find that PH is equal to. Remember, negative log of Ka is simply PKA. And we get PH is equal to PKA plus log of the ratio of conjugate base over conjugate acid. And this is our Henderson half of block formula.