ionic equation for acetic acid and sodium carbonate-bicarbonate buffer

Question

I'm stuck on finding the total ionic equation for mixing sodium carbonate with bicarbonate buffer solution when mixed with a) vinegar and b) ammonia. Also looking for the net ionic equations of these reactions.

Answer 1

The buffer reaction between bicarbonate and carbonate is:

HCO₃^- (aq) <==> CO₃^2- (aq)

As per the Bronsted-Lowry definition of an acid/base, HCO₃^- will act as an acid since it contains a hydrogen in its molecule and can donate protons. On the other hand, CO₃^2- will act as a base since it can accept protons.

a) Vinegar contains acetic acid (HC₂H₃O₂; a weak acid = proton donor). When added to the buffer, will it react with HCO₃^- (acid) or CO₃^2- (base)?? Hint: Will an acid (acetic) react with another acid (HCO₃^-)? The answer is NO, therefore, acetic acid will react with CO₃^2- and convert it to HCO₃^-. In the reaction, acetic acid is converted to the acetate anion (C₂H₃O₂^-). The net ionic equation for this reaction (read from right to left) is:

HCO₃^- (aq) + C₂H₃O₂^- (aq) <==> CO₃^2- (aq) + HC₂H₃O₂ (aq)

b) Ammonia (NH₃) is a weak base (proton acceptor). Here again, will NH₃ (a base) react with HCO₃^- (acid) or CO₃^2- (base)? As you may have predicted, NH₃ will react with HCO₃^- to form CO₃^2-. In the reaction, NH₃ accepts the proton from HCO₃^- to give the ammonium cation (NH₄⁺). The net ionic equation for this reaction (read from left to right) is:

HCO₃^- (aq) + NH₃ (aq) <==> CO₃^2- (aq) + NH₄⁺ (aq)