Objectives The objective of part A is to standardize a sodium hydroxide

Objectives the objective of part a is to standardize

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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.
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  • Fall '12
  • SOPER
  • Sodium hydroxide, Phosphoric acid

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