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acid base lab - Acidity Constant from a Titration Curve...

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Acidity Constant from a Titration Curve G00458510 Connie Jamieson 10/13/2011 Chemistry 212 section 205 T/A: Tiffany Ha Lab Partner: John Mullen
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Calculations: V ml at equivalence point for HCl: Theoretical endpoint for HCl: 25.0ml Percent error: 3.6% V ml at equivalence point for acetic acid: Theoretical endpoint for acetic acid: 25.0ml Percent error: 0.4% pK a = pH so K a for acetic acid from titration curve = K a = 10 -pKa = 2.0 x 10 -5 Raw Data Table: Titration of a Strong Acid (0.100M HCL) with a Strong Base (0.100M NaOH)
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Total Volume of 0.100M NaOH (ml) added to 25.0ml 0.100 HCL pH of Solution 0.0 0.97 2.0 0.98 4.1 1.05 6.6 1.14 8.0 1.19 10.2 1.28 12.0 1.39 13.1 1.47 14.6 1.55 16.0 1.63 17.0 1.77 17.5 1.75 18.1 1.8 18.5 1.82 19.1 1.95 19.6 1.96 20.0 2.03 20.6 2.08 21.5 2.3 22.0 2.4 22.5 2.62 23.0 2.95 23.5 3.81 24.0 6.85 24.1 7.03 26.1 11.63 27.1 11.84 28.0 11.98 Table 2 Raw Data Table: Titration of a Weak Acid (0.100M Acetic Acid ) with a Strong Base (0.100M NaOH)
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Total Volume of 0.100M NaOH (ml) added to 25.0ml 0.100 Acetic Acid pH of Solution 0.0 2.72 2.0 3.39 4.0 3.63 6.0 3.93 8.0 4.13 10.0 4.26 12.0 4.38 14.0 4.53 15.0 4.56 16.0 4.68 17 4.72 17.5 4.8 18 4.84 18.5 4.91 19 4.93 19.5 4.98 20 5.04 20.5 5.09 21 5.17 21.5 5.25 22 5.32 22.5 5.44 23 5.55 23.5 5.69 24 5.91 24.5 6.32 24.9 7.15 25.5 10.24 26.5 11.07 27.5 11.54 Table 3 the equivalence point was higher when graph was analyzed. Conclusion/Discussion: The purpose of this experiment was to perform two different acid/base titrations and then plot the pH of the acid solution against the amount of base added during the titration, this type of
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graph is a titration curve. Titration is a quantitative measurement of an analyte in solution by reacting it completely with a standardized reagent. Acids and bases react until one of the reactants is consumed completely a phenolphthalein indicator, which is colorless in acidic and neutral solutions and pink in basic solution and has a pH range between 8.3-10.0, was used as well as a pH meter to directly read the pH of the test solution. The first titration was preformed with a strong acid 0.100M HCL with a strong base 0.100M NaOH. The point at which all of the analyte is consumed by titrant is called the equivalence point. Figure 1 shows the titration of 0.100M HCL with 0.100M NaOH. For this titration, the equivalence point occurred at a pH of 7.00 which corresponded. This value was found by both measuring the pH during titration and using an indicator pH was 7.03 by this method refer to table 2. The equivalence point was also determined by the titration curve graph. This was achieved by plotting the points from the titration and then using geometric method of analysis. Using a ruler draw lines that follow the flat more horizontal part of the curve continue by drawing a line that follows the flat vertical part of the curve. Then measure the distance between the top intersection and the bottom intersection. The geometric center of this line is the equivalence point.
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