Question

Near the endpoint of the Na₂CO₃-HCl titration, it is necessary to heat the analyte solution almost to boiling to remove the _____ produced by the titration reaction.

a. bicarbonate ion
b. water
c. carbon dioxide
d. sodium chloride

Answer 1

Na₂CO₃(aq) + HCl(aq) = NaHCO₃(aq) + NaCl(aq)

NaHCO₃(aq) + HCl(aq) = NaCl(aq) + CO₂(g) + H₂O(l)

In the titration, Na₂CO₃ first reacts with HCl to produce NaHCO₃ and NaCl, and in the second step, NaHCO₃ again reacts with HCl to give NaCl, CO₂ and water.

So it is necessary to remove the CO₂ produced and hence the analyte is heated before the endpoint.

CO₂ produced in the titration forms carbonic acid and cause detectable errors in the titration, so it is necessary to remove the produced CO₂ by heating the analyte during titration.