Question

Enter your answer in the provided box. The pH of a bicarbonate-carbonic acid buffer is 5.41. Calculate the ratio of the concentration of carbonic acid (H2CO3) to that of the bicarbonate ion (HCO3−). (Ka1 of carbonic acid is 4.2 × 10−7.)

Answer 1

9.332 = [H₂CO₃] / [HCO₃⁻]

Step-by-step explanation:

It is possible to find the ratio of carbonic acid:bicarbonate ion using Henderson-Hasselbalch formula:

pH = pka+ log₁₀ [HCO₃⁻] / [H₂CO₃]

If pH of the solution is 5.41 and pKa of the solution is -logKa = 6.38.

Replacing:

5.41 = 6.38 + log₁₀ [HCO₃⁻] / [H₂CO₃]

-0.97 = log₁₀ [HCO₃⁻] / [H₂CO₃]

0.107 = [HCO₃⁻] / [H₂CO₃]

This is the ratio of bicarbonate ion:carbonic acid, now, the ratio of carbonic acid:bicarbonate ion is:

1 / 0.107 = 9.332 = [H₂CO₃] / [HCO₃⁻]