When creating a titration curve for a weak base, the pH of theinitial solution requires setting up a table showing the initial,change, and equilibrium values for each species and plugging theseinto the equilibrium constant expression. The expression for thebicarbonate ion is Ka1=[H2CO3][H+][HCO3−] For an anion that canboth hydrolyze and produce H+, the pH of a concentrated solutioncan be more easily approximated using the equation pH=12(pKa1+pKa2)During the titration before the equivalence point, provided thatthe concentration of acid is significantly more than theconcentration of base, the Henderson-Hasselbalch equation can beused to approximate the pH: pH=pKa+log[base][acid] At theequivalence point, the solution is no longer a buffer, but containsthe weak acid H2CO3. The change in concentration of the bicarbonateion is significant, and the equilibrium constant expression for Ka1must again be used to find the concentration of hydronium ions.After the equivalence point, the strong acid will control thepH.
Part A
A 10.0-mL sample of 1.0 M NaHCO3 is titrated with 1.0 M HCl(hydrochloric acid). Approximate the titration curve by plottingthe following points: pH after 0 mL HCl added, pH after 1.0 mL HCladded, pH after 9.5 mL HCl added, pH after 10.0 mL HCl added(equivalence point), pH after 10.5 mL HCl added, and pH after 12.0mL HCl added.
