the potential of an electrode depends on the concentrations of one or more
species present in the solution in which the electrode is immersed
the potential, E, of the glass electrode depends on the
hydronium ion concentrations
Combination electrodes are available which combine the functions of the
calomel reference electrode, the internal reference in the glass electrode, and the concentration of H3O^+ in the analyte solution change
the initial pH of a water solution of sodium carbonate is about
10.5 due to hydrolysis of the CO3^2- ion
The continued addition of HCl titrant results in
a more rapid drop in pH to slightly above 7
The first inflection point in the curve corresponds to first
equivalence point at about pH 8
The second equivalence point occurs in
in pH 4
The endpoints for the first and second equivalence point volumes are
determined graphically using the 1st and second derivatives of the titration curve.
The reaction for the first equivalence point is:
CO3^2- (aq)+H2O (l) ---> HCO3^- (aq)+OH^- (aq)
for the second equivalence point reaction:
HCO3^- (aq)+ H3O^+ (aq) --->H2CO3 (aq) +H2O (l)