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Report Form for Phosphoric Acid Titration Curves Chemistry 112 Lab Section 005 November 4, 2014 A. The research questions for this lab are: 1. What

how exactly did they solve for the pKa for both and Ka for both and the average M in H3PO4?

Report Form for Phosphoric Acid Titra±on Curves Chemistry 112 Lab Sec±on 005 November 4, 2014 A. The research ques±ons for this lab are: 1. What is the ini±al concentra±on of the H 3 PO 4 ? 2. What are pK a1 & pK a2 (and Ka 1 & Ka 2 ) for H 3 PO 4 ? 3. What are the H 3 PO 4 concentra±ons in my so² drink? B. Observa±ons & Results Tables Summarize your data in the following tables. Table 1. Phosphoric Acid Titra±on Data and Concentra±on Results. [NaOH] (M) Equiv point pH at equiv point NaOH vol to reach equiv point (mL) NaOH moles (mol) H 3 PO 4 moles (mol) Star±ng [H 3 PO 4 ] (M) Average [H 3 PO 4 ] (M) 0.1023 1 st 4.5 pH 12.75 1.304 x 10 -3 1.304 x 10 -3 0.043 0.048 2 nd 10 pH 15.50 1.586 x 10 -3 1.586 x 10 -3 0.053 Table 2. Phosphoric Acid Equilibrium Constants. Equil # pKa Ka 1 2.25 5.62 x 10 -3 2 7.25 5.62 x 10 -8 Table 3. Cola So² Drink Titra±on Data and Concentra±on Results for SodaStream Dr. Pete [NaOH] (M) Equiv point pH at equiv point NaOH vol to reach equiv point (mL) NaOH moles (mol) H 3 PO 4 moles (mol) Star±ng [H 3 PO 4 ] (M) Average [H 3 PO 4 ] (M) 0.05115 1 st 4.5 pH 2.25 1.151 x 10 -4 1.151 x 10 -4 2.88 x 10 -3 4.32 x 10 -3 2 nd 9.35 pH 4.50 2.302 x 10 -4 2.302 x 10 -4 5.75 x 10 -3
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Table 4. Phosphoric Acid Concentra±on in Various Cola Sof Drinks Cola name [H 3 PO 4 ] (M) SodaStream Cherry Cola 0.01183 SodaStream Cherry Cola 0.00475 SodaStream Cherry Cola 0.0703 SodaStream Cherry Cola 0.00607 SodaStream Cherry Cola 0.01022 SodaStream Cherry Cola 0.007665 SodaStream Dr. Pete 0.00432 SodaStream Dr. Pete 0.00430 C. Complete claims For each oF the research ques±ons above. Include appropriate units. 1. The ini±al concentra±on oF the H 3 PO 4 solu±on is 0.048 M. 2. The pK a1 is 2.25, the pK a2 is 7.25, the K a1 is 5.62 x 10 -3 , and the K a2 is 5.62 x 10 -8 For H 3 PO 4 . 3. The H 3 PO 4 concentra±ons in my sof drink (SodaStream Dr. Pete) are 2.88 x 10 -3 M For the ²rst equivalence point and 5.75 x 10 -3 For the second equivalence point. D. Evidence 1. The pH oF the solu±on beFore adding any NaOH was low because H 3 PO 4 is acidic. In my notebook I wrote down that the ini±al pH oF the H 3 PO 4 solu±on was 1.17. IF you take the nega±ve log oF what I Found to be the ini±al concentra±on oF H3PO4 you get 1.31875, or 1.3 when considering signi²cant ²gures. This shows that the ini±al concentra±on that I experimentally Found gives a pH Fairly close to what the ini±al pH was. 2. The K a values that I got From my experiment are Fairly close to those given in the book, and the pH values derived From those K a values are even more similar when compared. This means that the pK a values are more accurate than the K a values, but they are both s±ll Fairly close to the values provided by my book. 3. When I average the two equivalence concentra±ons that I obtained For my sof drink I get 4.32 x 10 -3 M. The nega±ve log oF this concentra±on gives me a value oF 2.3645, or 2.4 when accoun±ng For signi²cant ²gures, which is the pH. I didn’t write down the ini±al pH, but on my ±tra±on curve the ini±al pH oF my sof drink is above 2.00 pH by a bit and appears to be somewhere close to 2.5. This shows that the ini±al concentra±on that I experimentally Found gives a pH Fairly close to what the ini±al pH appears to be on the graph in my notebook.
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I am attaching a phosphoric acid titration curve for your reference. If you have the first equivalence point. Then half the... View the full answer

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