I am doing a lab to determine the concentration of H3PO4 and NaH2PO4. I have already done the lab, and calculated Ka1 and Ka2 from my results, but ran into a problem. I need help in how I would prepare a phosphate buffer, pH 7.00, about .05M using activity coefficients. We haven't really go over it in class yet and the book is a confusing me a bit. A nudge in the right direction would help.