Question

What molar ratio of HPO4 2- to H2PO4 - in solution would produce a pH of 7.0? Phosphoric acid (H3PO4), a triprotonic acid, has pKa values: 2.14, 6.86, and 12.4. Only one of the pKa values is relevant here. how do i know which pka value to use.. please explain

Answer 1

use 6.86 because it is the one which has a pKa close to 7.4 which is the blood pH