Titration curves HCl and Naoh

Titration curves HCl and Naoh - Abstract: Experiment 3 used...

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Abstract: Experiment 3 used titration curves of 2M HCl and 2M NaOH to identify the unknown amino acid. The initial pH of the dissolved solid amino acid in deionized water was5.82 and 6.21 respectively and titrated to accordingly to acidic end at pH 1.0 and basic end at pH 12.0. The pKa’s were experimentally found to be 2.20, 9.50 and the molecular weight was 122.0 g/mole. The accepted pKa’s values were 2.09, 9.10 and the accepted molecular weight was 119 g/mole. The identity of the amino acid was established to be Threonine. The titration of NaCl indicated that salt buffer had the capability to control the titration curve. This step was followed up by the titration of the prepared buffer consisting Sodium Acetate and Acetic acid. The calculated buffer capacities for each titration showed a close relationship between the concentration of the buffers and their capacities. Introduction: Titration is a technique which relying on the concentration and the graphical analysis of the pH with respect to volume of the standard base or acid titrant to determine the reaction’s completion. In this experiment, an unknown amino acid was dissolved then titrated with 2M HCl and NaOH. The pH were recorded using the BECKMAN Φ31 pH meter after each addition of the titrant into the unknown analyte and an analysis of the graphical data set to determine the identity of the unknown amino acid. 5.00M Sodium chloride was titrated using 0.100M acetic acid to examine the ionic strength affecting the pKa of a weak acid. Then an amount of 20 mL deionized H 2 O was titrated with 0.100M Acetic acid. This titration was done as control to see how weak acid changes the solution activity.
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A specific pH 4.5 specifically was assigned and prepared to obtain a 500 mL of 100 mM acetate buffer. This buffer was titrated using already diluted titrant of 0.2M HCl and 0.2M NaOH. The results indicated how well the buffer was made and the buffer capacity. This prepared buffer showed experimentally that the capability to resist the change in pH, therefore the titration curves were different from what expected from the titration of the unknown amino acid done above. Procedures: In part A of this experiment, an amount of unknown solid amino acid (401.2 mg) was dissolved completely in 20 mL of deionized water at room temperature. The pH meter was standardized by placing in already made buffers of oH 4.0 and pH 7.0 for the acid titration; pH 7.0 and pH 10.0 for base titration. After the mixture became clear, a magnetic stir bar was placed into the container and spun on a stir plate with the pH probe submerged on the side wall. The solution was titrated with 2.0M HCl until the overall pH approached 12.0 (Table 1). Another amount of unknown solid amino acid (411.0 mg), was also dissolved in 20 mL of deionized water and then titrated with 2.0M NaOH until the pH approached 1.0 (Table 2). The titrations were repeated using water blank, 20 mL, instead of the unknown mixture used previously. In part B, an amount of 0.100M acetic acid was added into a 100 mL beaker along with a
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This note was uploaded on 04/03/2012 for the course CHEM 131A taught by Professor Nemes during the Spring '12 term at San Jose State University .

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Titration curves HCl and Naoh - Abstract: Experiment 3 used...

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