Consider a solution consisting of the following two buffer systems: H2CO3 ? HCO3 - + H+ pKa = 6.4 H2PO4 - ? HPO4 2- + H+ pKa = 7.2 At pH 6.4, which one of the following is true about the relative amounts of acid and conjugate base present? (1) [H2CO3] > [HCO3 -] and [H2PO4 -] > [HPO4 2-] (2) [H2CO3] = [HCO3 -] and [H2PO4 -] > [HPO4 2-] (3) [H2CO3] = [HCO3 -] and [H2PO4 -] < [HPO4 2-] (4) [H2CO3] < [HCO3 -] and [H2PO4 -] < [HPO4 2-] (5) [H2CO3] > [HCO3 -] and [H2PO4 -] < [HPO4 2-]
Explanation / Answer
(3) [H2CO3] = [HCO3 -] and [H2PO4 -] < [HPO4 2-] is the answer