Question

The pH of blood plasma is 7.40. The principal buffer system is HCO3?/H2CO3. Calculate the ratio [HCO3?]/[H2CO3] in blood plasma. (Ka of H2CO3, carbonic acid, is 4.5 × 10?7) Enter your answer in the provided box.

Answer 1

The pH of blood constituents of the bicarbonate buffering system, pKa and ratio of Bicarbonate to carbonic acid is releted to the Henderson–Hasselbalch equation as:

pH = pKa_{carbonic acid} + log₁₀ [HCO^-₃ / H₂CO₃]

Since pKa = - log₁₀ Ka

Buffer reaction is : H₂CO₃   $\rightarrow$ ? HCO^-₃ + H⁺

Steps:

Given pH of blood plasma: 7.40

Ka of H₂CO₃ : 4.5 X 10⁷

Find :  ratio [HCO₃^-]/[H₂CO₃]

1.Put the all values given in H. H. equation then

pH = pKa_{carbonic acid} + log₁₀ [HCO^-₃ / H₂CO₃]

7.40 = - log₁₀ (4.5 X 10⁷) + log₁₀ [HCO^-₃ / H₂CO₃]

7.40 + log₁₀ (4.5 X 10⁷) = log₁₀ [HCO^-₃ / H₂CO₃]

7.40 + log₁₀ (4.5) + 7 log₁₀ 10 = log₁₀ [HCO^-₃ / H₂CO₃]

7.40 + 0.6532 + 7 ( log₁₀ 10 = 1) = log₁₀ [HCO^-₃ / H₂CO₃]

15.0532 =  log₁₀ [HCO^-₃ / H₂CO₃]

log₁₀ [HCO^-₃ / H₂CO₃] = 15.0532

[HCO^-₃ / H₂CO₃] = Anti log (15.0532)

[HCO^-₃ / H₂CO₃] = 1130316324738697.8

hence [HCO^-₃ / H₂CO₃] = 11.30 X 10¹⁴