Discussion of Titration of ColaThe technical objectives of the titration of cola in this experiment is to conduct a pH titration of phosphoric acid in a cola drink with standardized base to determine the concentration of phosphoric acid in cola drink and determine the acid dissociation constants of phosphoric acid. Ultimately, the extent of ionization of phosphoric acid is measured. The pH and volume of titrant at the first equivalence point was 3.72 at 6.50 mL and the pH and volume of titrant added to the second equivalence point was 6.92 at 17.50 mL. The equivalence points were identified by observing where in-between the first derivative line there are peaks. However, the data obtained did not produce a good second equivalence point that can be easily discerned and had to be estimated. The pKa1 for phosphoric acid determined algebraically from the initial pH and first equivalence point of the titrant was pKa=−log(Ka)=2.16.The concentration of H3PO40.010M NaOH x6.50mL=M2x20mL H3P O4x=3.25x10−4MThe pKa1value in item iii−¿H2PO4¿¿+¿H3O¿¿¿K a1=¿+¿H3O¿¿¿
−¿H2PO4¿¿[H3PO4]=¿pKa=−log(Ka)=2.16The pKa1and pKa2determined graphically from the titration curve are 2.75 and 6.23. These pKavalues were determined by observing the halfway points of the graph, where pH = pKa1and pH = pKa2. By observing the derivative line of the graph, the pKa1and pKa2values can be determined by observing these halfway points in between the peaks of the derivative line. Discussion of Titration AccuracyThe algebraic method is the more accurate method for determining the pKa1because it has a smaller percent error (0%), which shows that it is the more appropriate measure of accuracy. This is also because the data recorded is not very accurate because the phosphoric acid was not well enough titrated to show a distinct pKa2value. error graphically=[experimental−literature]literature=2.75−2.162.16x100=27.31error algebraically=[experimental−literature]literaturex100=2.16−2.162.16x100=0ReferencesBottomley, L.; Bottomley, L. A.; CHEM 1211K/1212K, Chemical Principles I & II Laboratory Manual, 2015-2016; Hayden-McNeil Publishing: Plymouth, 2016, pp 197-209.
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- Fall '12
- pH, Sodium hydroxide, Phosphoric acid