Question

0.01 M solution of carbonic acid dissociates, and [HCO₃^-] = 0.000066M, then what is the K_a of carbonic acid?

Answer 1

[HCO₃^-] = [H⁺] = 0,000066 M

[H₂CO₃] = C(H₂CO₃) - [H₂CO₃] = 0,01 - 0,000066 = 0,009934 M

K_{a1, H2CO3} = $\frac{[HCO3^-][H^+]}{[H2CO3]} = \frac{[0,00066]^{2}}{[0,009934]} = 4,38 * 10^{-7}$