10 After you determine the volume of the equivalence points determine the pH at

# 10 after you determine the volume of the equivalence

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pH increase because you are going through two equivalence points. 10. After you determine the volume of the equivalence points, determine the pH at half equivalence point. Find the pH associated with the volume ½ way between 0 mL of NaOH and the volume at 1 st equivalence point. Then find the pH associated with the volume ½ way between the volume of the first equivalence point and the second. 11. Print a copy of the graph of pH vs . volume. Then print a copy of the NaOH volume data and the pH data for the titration. To print you must connect the Labquest 2 to the printer via the USB cable, Select File, then Print, then Graph. HP LaserJet P2035 [USB] should appear in the top selection. Checkmark the box for “Print Graph Title” and enter a title. Checkmark the “Print Footer” and enter your name and your partner(s). Select Print. 12. Dispose of the beaker contents into the waste container. Rinse the pH Sensor and return it to the storage solution. Repeat the necessary steps to test a new sample of the cola if time allows. Prelaboratory assignment Exp. 8 Phosphoric Acid in Cola Name:____________________ Date:____________ Lab Section:________________ 1. The phosphoric acid in a 100.00-mL sample of Cola drink was titrated with 0.1025 M NaOH. If the first equivalence point occurred after 16.11 mL of base was added, and the second equivalence point occurred after 32.55 mL of base was added, calculate the molar concentrations of H 3 PO 4 in the Cola sample based on: a. The first equivalence point b. The second equivalence point. c.What is the average concentration? 2.Based on the average concentration in question 1c, if you were able to titrate to the third equivalence point of H3PO4, What would thetotalvolume of NaOH you would need? 3. Based on question 1. How many moles, of NaOH were added when: a. pH = p K a1 b. pH = p K a2 4.One source in the literature quotes 0.54 g/L as being the concentration of phosphoric acid, H3PO4, in Cola. What is it in molarity? Show your calculations and include units. 1. Use your printed graph and data table to confirm the volume of NaOH titrant you recorded before and after the large increase in pH values upon the addition of 0.5 mL of NaOH solution. (Remember to include your graphs with the report sheets) 2. Determine the volume of NaOH added at each equivalence point. To do this, add the two NaOH values determined above and divide by two. 3. Calculate the number of moles of NaOH used. 4. See the equation for the neutralization reaction given in the introduction. Determine the number of moles of H 3 PO 4 reacted.  #### You've reached the end of your free preview.

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• Spring '12
• NidhalMarashi
• pH, Sodium hydroxide
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