Carbonic acid, H₂CO₃, is a diprotic acid with ionization constants:K_a1 = 4.5 × 10^-7, K_a2 = 4.7 × 10^-11.What is the value of the ratio, [H₂CO₃]/[HCO₃^-], in a solution containing both species that is maintained at pH = 7.00 by means of a buffer?

Question

Quizplus · Accepted Answer

The correct answer is D.The ratio [H2CO3]/[HCO3-] can be calculated using the Henderson-Hasselbalch equation:pH = pKa + log([A-]/[HA])where pKa is the dissociation constant of the acid, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the acid.In this case, the pH is 7.00, pKa1 = 4.5 × 10^-7, and pKa2 = 4.7 × 10^-11. Substituting these values into the Henderson-Hasselbalch equation, we get:7.00 = 4.5 × 10^-7 + log([HCO3-]/[H2CO3])Solving for [H2CO3]/[HCO3-], we get:[H2CO3]/[HCO3-] = 10^(7.00 - 4.5 × 10^-7) = 0.22

Carbonic Acid, H2CO3, Is a Diprotic Acid with Ionization Constants:Ka1

Carbonic Acid, H₂CO₃, Is a Diprotic Acid with Ionization Constants:K_a1