Question: why is hco3 a weak acid?
Answer: The Na+ comes from NaOH, the HCO3- comes from carbonic acid, H2CO3. ... H2CO3 is a weak acid and does not completely dissociate. The product, HCO3-, is not stable and can react again with water to contribute to the pH. HCO3- will act as a base by plucking off the proton from H2O, and forming a basic solution.