When benzene sulphonic acid and p-nitrophenol are treated with NaHCO3 the gases released, respectively, are:

PhSO3HI+NaHCO3→PhSO3Na+H2O+CO2p−NO2II−C6H4−OH+NaHCO3→p−NO2−C6H4ONa+H2O+CO2HCO3−+H+→H2O+CO2↑Since both (I) and (II) are stronger acids than H2CO3, they are capable of evolving CO2 with NaHCO3.