Objectives the objective of part a is to standardize

Objectives
The objective of part A is to standardize a sodium hydroxide solution via titration using a visual
indicator. The visual indicator used in this experiment is phenolphthalein.
The objective of part B is to conduct a pH titration of phosphoric acid in a cola drink with
standardized base to determine the concentration of phosphoric acid in a cola drink and determine the
acid dissociation constants of phosphoric acid. In addition, the extent of ionization of phosphoric acid
will be determined.
Discussion for Part A
The measured concentration of the NaOH was around 0.012053 M in the first trial and around
0.012011 in the second trial. These measurements are very accurate and precise, as the measurements
don’t vary significantly and both these measurements are very close to the actual concentration of
NaOH, which is around 0.01 M.
Errors relevant in this part of the experiment primarily involve how titration is done and how the
equivalence point is determined. A visual indicator, phenolphthalein, is used to determine the pH of the
solution. This involves observations of how colored the solution is at a certain point, which gives way to
measurement and observation error. The pH cannot be accurately determined since it is solely based on
the observation of this color. In addition, relevant errors include possible contamination of the solution.
The concentrations of the solutions may not have been as perfect as intended, due to contaminants in
the air.
Discussion for Part B
The titration curve shows three steps in the neutralization reaction of the triprotic phosphoric
acid and sodium hydroxide. There are two equivalence points, at which the moles of strong base is
equal to the moles of acid in the solution. There are also three points in the titration curve at which the
pH of the solution is equal to the pK
a
of each step of the dissociation of the triprotic phosphoric acid.
Based on graphical analysis, the pK
a1
value observed was 3.06 and the pK
a2
value was observed
to be 6.43. The literature values were pK
a1
as 2.12 and pK
a2
as 7.21. The pK
a
values in this case were
slightly off. However, the shape of the titration curve accurately represented the titration curve of a
triprotic acid.