2. Phosphoric acid (H3PO4) is a triprotic acid with thefollowing pKa values: pKa1 = 2.15 pKa2 = 7.20 pKa3 = 12.35
a). You wish to prepare a 1.000 L of a 0.0450 M phosphate bufferat pH 6.8. Which of the following salts do you use (PICK 2) andwhat mass of each salt will you add to the mixture? H3PO4 (M.W.=97.995) KH2PO4 (M.W.=136.086) Na2HPO4 (M.W.=141.959) AlPO4(M.W.=121.953) 2
b). A concentrated phosphate buffer known as “phosphate bufferedsaline†(or PBS) is made with the salts you choose from above inaddition to NaCl and KCl. The 10x concentrated solution has a pH~6.8 and the 1x concentrated (i.e., diluted with water) solution is~7.1. Why?
c). You accidently grabbed the 10x concentrated phosphatebuffered saline (or 10xPBS) instead of the 1xPBS solution and startto adjust the pH of your buffer with NaOH to reach your desiredbuffer pH. You notice it is taking much more base than with yourusual 1xPBS buffer. Why?
