What is the of 1.07M solution of carbonic acid? K a1 =4.3*10^ -7 K a2 =5.6*10^ -11

Question

What is the of 1.07M solution of carbonic acid? K a1 =4.3*10^ -7 K a2 =5.6*10^ -11

Answer 1

Are you asking what the pH is?

For diprotic (or polyprotic) acids, when the Ka values differ by more than 10³, we generally ignore the 2nd Ka as it contributes little to the [H⁺] and hence to the overall pH. I will adopt that policy here.

H₂CO₃ = H⁺ + HCO₃^-

Ka = [H⁺][HCO₃^-] / [H₂CO₃]

4.3x10^-7 = (x)(x) /1.07

x² = 4.6x10^-7

x = 6.8x10^-4 M = [H⁺]

pH = -log [H⁺]

pH = 3.17