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Exp 2 Lab Report - Investigation of the Relationship...

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Investigation of the Relationship Between Equilibrium Constants and Initial Concentrations Using the Law of Mass Action Jubilee Ngo TA: Christine Huang Section: A00 Chemistry 100A at University of California, San Diego 9500 Gilman Drive, La Jolla, California 92093 13 July 2006 Abstract Determination of the equilibrium constant, K c , of the esterification reaction of ethyl alcohol (C 2 H 5 OH) and acetic acid (CH 3 COOH) to produce ethyl acetate (CH 3 COOC 2 H 5 ) using the Law of Mass Action was the main purpose of this experiment. First, five solutions created by mixing different volumes of acetic acid, ethyl alcohol, ethyl acetate, and water were allowed to reach equilibrium, with the addition of hydrochloric acid as the catalyst. Using recorded mass percents, densities, and molar masses of each substance, initial moles were calculated and then titrations with standardized NaOH were performed to allow for the calculation of the equilibrium moles, and hence, concentrations of each substance. Finally, these concentrations were used in the Law of Mass Action to obtain the equilibrium constants of each solution. The average K c is determined to be 5.527 ± 0.632. Because of the small standard deviation value, the independence of K c of the initial concentrations of reactants and products is observed even though various errors throughout the experiment asserts that the result does not represent the true equilibrium constant value of the esterification reaction. Result As Table 1 reveals, the equilibrium directions flasks b-f are all to the left, except for the flask f, whose direction is to the right. These directions are determined by the initial volume of each substances added, also guided by LeChatelier’s Principle. The mass percents and densities of all of the substances involved in the esterification reaction are recorded from the labels in Table 3 while only HCl was experimentally determined (see Table 2), which turned out to be 2.98 M. The standardization of NaOH by titration with KHP is recorded in Table 4. Take special notice that the average NaOH concentration was 1.912 ± 0.023 M. The most important results are in Table 6 and Table 7. Table 6 shows the initial moles of each substance of the reaction; except for water, the initial moles of all of the other substances were calculated using the mass percents, densities, and molar masses recorded in Table 3 and the initial volumes of each substance added according to Table 1. The calculation of the initial moles of water is more complicated
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