Condition For NaHCO3 to react to form CO2 with organic acids?

Question

My professor told us the following: NaHCO3 will react to evolveCO2 whenever the acidic nature of the reactant exceeds the acidic nature of benzoic acid. I want to know why this is. And is the given statement valid? He didn't give us the reason.

Answer 1

For the basic nature of sodium bicarbonate: While sodium bicarbonate is a base, but it is not necessarily a strong base like sodium hydroxide. Due to the resonance within the bicarbonate structure, the anion is shared between the two oxygens making the anion less basic. Here this statement is true that it will not deprotonate everything. I'm not sure of the exact pKa value where it stops being basic, but certainly below pKa of about 5 (benzoic acid) will be able to act as a base.

In terms of the evolution of CO2 this is correct. As the bicarbonate is protonated it forms carbonic acid, which is relatively unstable. Carbonic acid readily decomposes to form CO2 and water.