Phosphoric Acid Titration Curves - Phosphoric Acid Titration Curves Taylor Black Cassie Pressnall CHEM 112L 005 A Research Questions a What is the exact

Phosphoric Acid Titration Curves - Phosphoric Acid...

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Phosphoric Acid Titration Curves Taylor Black Cassie Pressnall CHEM 112L & 005 March 29, 2016 A. Research Questions a. What is the exact initial concentration of the H 3 PO 4 solution? b. What are the pK a1 & pK a2 for H 3 PO 4 ? c. What are K a1 & K a2 for H 3 PO 4 ? d. What is the H 3 PO 4 concentration in my soft drink? B. Observations & Results Table 1. Phosphoric Acid Titration Data and Concentration Results [NaOH] (M) Equivalenc e point pH at equivalenc e point NaOH volume to reach equivalence point (mL) NaOH Moles (mol) H 3 PO 4 Moles (mol) Starting [H 3 PO 4 ] (M) Average [H 3 PO 4 ] (M) 0.103 M 1 st 4.33 13.0 mL 0.001339 0.001339 0.0446 0.0455 2 nd 9.48 26.5 mL 0.001391 0.001391 0.0464 Table 2. Phosphoric Acid Equilibrium Constants Table 3. Cola Soft Drink Titration Data and Concentration Results for Cherry Cola Graphs attached to the back Calculations and analysis are in notebook pages C. Claims Equivalence # pK a K a 1 2.22 pH 6.03x10^ -3 2 7.12 pH 7.60x10^ -8 [NaOH] (M) Equivalence point pH at equivalence point NaOH volume to reach equivalence point (mL) NaOH Moles (mol) H3PO4 Moles (mol) Starting [H3PO4] in this cola (M) Average [H3PO4] in this cola (M) 0.0515 M 1 st 5.52 8.0 mL 0.000412 0.000412 0.103 0.0544 2 nd 7.48 12.5 mL 0.000231 0.000231 0.00579
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a. The exact initial concentration of H 3 PO 4 is 0.0455 M. b. The pKa1 for H 3 PO 4 is 2.22 pH and the pKa2 for H 3 PO 4 is 7.12 pH. c. The K a1 for H 3 PO 4 is 6.03x10^ -3 and the K a2 for H 3 PO 4 is 7.6x10^ -8 . d. The H 3 PO 4 concentration in Cherry Cola is 0.0544 M. D. Evidence a. The exact initial concentration of H 3 PO 4 is 0.0455 M in my experiment. I found this by using the concentration of the 0.103 M NaOH times the number of liters added to reach each equivalence point. That gave me the number of moles of NaOH added to reach the 1 st equivalence point. Since the balanced chemical reaction is a 1:1 ratio that also gave me the number of H 3 PO 4 moles titrated. Since 0.013 L of NaOH to reach the first equivalence point and 0.0135 L of NaOH were added to reach the 2 nd equivalence point the two concentrations for H 3 PO 4 are slightly different. In order to get from moles to molarity. The moles of the H 3 PO 4 had to be divided by the liters of the acid added to get the Molarity. The concentration for the first equivalence point being 0.0446 M, and the concentration for the second equivalence point being 0.0464 M. The average of the two molarities of H 3 PO 4 is 0.0455.
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  • Fall '11
  • HeatherRankin
  • Chemistry, pH, Pk, Equivalence point, Equivalence, cherry cola

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