You need a system of H3PO4 with K2HPO4 buffer, adjust the pH with H3PO4. This buffer has 7.2 as one of the pKa, so has a useful range of 6.2 to 8.2.
Hope this helps
Could a buffer system employing H3PO4 as the weak acid and H2PO4^- as the weak base be used as a buffer system within cells? Explain.
I know the answer is no but I'm not really quite sure how to explain why.
3 answers
I believe Sofia has the right idea but has answered the wrong question. If one uses H3PO4/NaH2PO4 (that's the question, not H3PO4/K2KPO4), the optimum operating range for the system is +/- 1 pH unit of pk3 (not k2). pK3 for H3PO4 is 12.35. Since the cell operational range is about 6.8 to 7.4 the H3PO4/NaH2PO4 does not fall within that range and that is why the buffer system is not appropriate for that purpose.
Thank you both so much! This makes much more sense then what I was trying to read from the textbook.