1. The problem statement, all variables and given/known data We have the buffer Tricine 0.1M and pKa=8.15 and the pH=8.8 2. Relevant equations what are the molar conc. of tricine+ (the protonated form of tricine) and tricine0 (the deprotonated form of tricine)? 3. The attempt at a solution Well, if you go to henderson-hassalbach equation you get: 8.8=8.15+log X/0.1-X where X is the molar conc. of both H3O+ and tricine0 at equillibrium, further solving gives X=0.082M But I don't understand - if the pH is given to me can't I find X, which is also the H3O+ conc. at equillibrium, from 8.8=-log[H3O+]? If I do that, I'll get a very different answer to X... why is that?