Given the pK_a values for phosphoric acid of 2.14, 6.86 and 12.4, what is the ratio of HPO₄^2-/H₂PO₄^- in a typical muscle cell where the pH is 7.2? A)0.46 B)2.2 C)6.3 * 10^-6 D)1.1 * 10⁵ E)none of the above

Question

Quizplus · Accepted Answer

At pH 7.2, the dominant species of phosphoric acid are HPO4^2- and H2PO4^-. The ratio of these species is given by the Henderson-Hasselbalch equation: ratio = [HPO4^2-]/[H2PO4^-] = 10^(pH-pKa2), where pKa2 = 6.86 for phosphoric acid. Thus, ratio = 10^(7.2-6.86) = 10^0.34 ≈ 2.2.

Given the PKa Values for Phosphoric Acid of 2

Given the PK_a Values for Phosphoric Acid of 2