[wils0645]

I bubbled 5% CO2 through a needle into 30 mL of phosphate buffered saline open to atmosphere (25C) for approximately one hour and reduced the pH from 7.40 to 6.48. I was wondering if I can find the concentration of CO2 in the solution over time with one known (pH) using the Henderson-Haselbalch equation? pKa for phosphoric acid is 7.199. Since CO2+ H20->H+ HCO3- is an addition of a weak acid into the solution, how can I determine the CO2 concentration over time? Would I need the flow rate of CO2 infusion into the solution?  The phosphate buffered saline consists of 138 mM of NaCl, 10mM phosphate, 2.7 mM KCl.  [HPO4 2- = .0061, H2PO4- = .0039].