pKa values of phosphoric acid are 2.2,7.2 and 12.7.A phosphate buffer of pH = 7.4 can be prepared using

Question

Quizplus · Accepted Answer

To prepare a phosphate buffer of pH=7.4, we need to have both the conjugate acid-base pairs, i.e., H₂PO₄- /HPO₄²- with a pKa close to 7.4. 
Among the given options, the best choice is (A) H₂PO₄- and HPO₄²-, as their pKa values are 7.2 and 12.7, respectively. By choosing an appropriate ratio of these two species, we can prepare a buffer with a pH close to 7.4. 
Option (B) cannot be the best choice, as the pKa values of HPO₄²- and PO₄³- are greater than 12 and lower than 7, respectively. 
Option (C) cannot be the choice for preparing a phosphate buffer, as HCl is not related to the phosphate buffer system.

PKa Values of Phosphoric Acid Are 2