Why is NaHCO3 a base?


(I need someone to explain it using the ka values)


H2CO3 <--> HcO3- + H+ ka = 4.3x10^-7

HCO3- <--> CO3^2- + H+ ka = 5.61x10^-11


if I underestand correctly, the kb for the second equation is greater than the ka. Thus the reaction will not proceed forward, but rather produce more HCO3-. This is a basic tendency. Why is it more powerful than the first reaction?