H2CO3⇌H++HCO3−K1=4.2×10−7 HCO3−⇌H++CO32−K2=4.8×10−11 Second dissociation constant (K2) is much smaller than the first one (K1). Just a small fraction of total HCO3− formed will undergo second stage of ionization. Hence in saturated solution [H+]≫>>[CO32−];[CO32−]≠0.034M [HCO32−]>>[CO32−] and [H+]≈[HCO3−]