This is probably a stupid question. Stems from AAMC 5 number 15: The pka for the dissociation of H2PO4 to HPO4 is 6.7. What is the initial ratio of [HPO4]/[H2PO4] in the buffer solution of experiment 1? (experiment 1 states the solution was buffered at PH 8.7) I thought in a buffer, the acid and conj. base concentrations are equal, but in the answer solution, the henderson hasselbach equation is used to calculate the ratio (which I thought would have been 1 in a buffer). What am I not understanding in this concept? Thanks.