4. Calculate the pH of a 25 ml solution containing 0.5 g of codeine (MW = 299.36) and 1.7 g of codeine phosphate (MW = 406.37). The pKa of codeine is 7.9. a. Ans = 7.5 5. Calculate the percent ionized and unionized of cefazolin at pH 3 (pKa = 2.1; salt form is cefazolin sodium). a. Ans: ionized 89%; unionized = 11% 6. Calculate the ratio of ionized unionized forms of phenytoin at pH 7.4 (pKa 8.32; salt form is phenytoin sodium). a. Ans: ionized : unionized = 0.12 : 1 %3D %3D