Question

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.

Answer 1

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

Answer 2

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.

Answer 3

Thank you both so much! This makes much more sense then what I was trying to read from the textbook.