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?

everyone!

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