Question: what is the limiting reactant in an alka-seltzer tablet?
Answer: Eventually, the acid (H+) will be in excess, and the NaHCO3 contained in the Alka Seltzer tablet becomes the limiting reactant. Since the amount of NaHCO3 in an Alka Seltzer tablet is fixed, no additional CO2 will be generated with increasing amounts of vinegar.