im sorry, it means the pKa2 for the phosphate buffer is 6.86 (the one that has been given to us to use) I used the Henderson Hasselbalch equation to get the ratios for the pH when its at 7.4 and 6.7 but I dont know what to do from there. I kind of worked it out, not sure if its correct and got 37 mL of HCl to be added.
Borek if its not too much could you explain how i should go about doing this?