The pH of blood is 7.35. It is maintained in part by the buffer system composed of carbonic acid (H₂CO₃) and the bicarbonate (hydrogen carbonate, HCO₃^-) ion. What is the ratio of [bicarbonate]/[carbonic acid] at this pH? For carbonic acid, K_a1 = 4.2 × 10^-7. A) [bicarbonate]/[carbonic acid] = 0.11 B) [bicarbonate]/[carbonic acid] = 0.38 C) [bicarbonate]/[carbonic acid] = 2.65 D) [bicarbonate]/[carbonic acid] = 9.4 E) None of these choices are correct.

Question

Quizplus · Accepted Answer

Using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]), where pKa = -log(Ka). For carbonic acid, pKa = -log(4.2 × 10^-7) ≈ 6.38. Substituting the values, 7.35 = 6.38 + log([HCO3-]/[H2CO3]), solving gives [HCO3-]/[H2CO3] ≈ 9.4.

The PH of Blood Is 7