When we get to the equivalence point, we will have added 2 volumes of 0.1 M NaOH per unit volume of the original sulfuric acid. The pKa for chloroacetic acid is 2.865. This is actually a rerun of Pb. We've used the approximation that neutral molecules have unit activity coefficients. If the resolution of the meter is 0.02 pH units, you couldn't tell the difference.
Precision has to do with reproducibility.
So as long as the matrix composition is constant, precision can not be effected by ionic strength. Ionic strength shifts equilibria for both the titrand and the indicator, so if the charge on the indicator and the charge on the analyte are the same, ionic strength effects should track each other. There are five blatant errors in the procedure which anyone who's had a month of Quantitative Analysis should be able to spot. A handful of ore is mixed with tapwater and swirled for several hours to dissolve. Should precisely weigh the specimen on an analytical balance.