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Acid Base Tritration Ex3.docx

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University of Toronto St. George
C Jung

1000388671 Experiment 3 Acid-Base Titrations Introduction The purpose of this experiment is to analyze the properties of the acid base reactions, in particular the differences between the strong acid-strong base and weak acid-strong acid. This is accomplished by titration of a weak and strong acid (HCOOH and HCl respectively) with a strong base (NaOH), and measuring the change in pH through the pH meter and phenolphthalein. Results figure#1figure #2 Discussion Through the use of figure #2 the experimental Ka of the HCOOH-NaOH reaction resulted in 3.23*10 . This is 80% accurate in respect to the literature Ka value of 1.8*10 , determined via equation [24] in the Chemistry Lab Manual. The sources of error include: (1) The piecewise manner of attaining the data, causing rounding errors; an error that can be solved by continuously adding the titrant and measuring the pH of the solution. (2) Uneven mixing of the acids and bases resulting in slightly different pH levels throughout the beaker; which may be alleviated via more efficient mixing method. (3) Possible impurities in the acid and base solutions; (4) Delayed color change at equivalence point as a result of phenolphthalein. (5) Human error of adding more/less NaOH then recorded, as well as failure to note the light pink color of phenolphthalein exactly when it surfaces. When the results of the two measuring methods were compared they displayed a marginal variation in volume of NaOH present at equivalence point (differing by only 0.2mL at most), however the pH value associated with the equivalence point was always higher in the titration curve then phenolphthalein (by 2.09 and 2.19 in HCl-NaOH and HCOOH-NaOH respectably). The small variation in the volume of NaOH present at equivalence point was expected to be the same due since a proportional amount of moles of acid and base are needed to reach the equivalence point, therefore the same proportion of volumes of both substances are needed to
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