# Part a preparation and standardization of naoh 6 pts

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PART A: Preparation and Standardization of NaOH (6 pts) Table 1 : NaOH volumes at the equivalence and half-equivalence points of each acetic acid titration, obtained from the second derivative curves. Trial NaOH volume (mL) at equivalence point NaOH volume (mL) at half-equivalence point pH at half- equivalence point 1 10.10 5.055 4.484 2 10.00 5.009 4.477 3 10.02 5.012 4.478 Average 10.04 5.025 4.479 2. (4 pts) Calculate the K a of your acetic acid solution. Discuss this calculation. Based on the value of K a , is acetic acid a strong acid or a weak acid? Why?
13 A. M. Bohnsack Spring 2019 (revised Z. Baranová)
Worksheet & Grading Rubric – Weak Acids and Buffers 3. (3 pts) Calculate the number of moles of acetic acid that were present in the original buffer solution prepared in Step 18 of the procedure. Assume no change in volume upon addition of sodium acetate trihydrate. Discuss this calculation.
4. (3 pts) Calculate the number of moles of acetate that were present in the original buffer solution prepared in Step 18 of the procedure. The molecular mass of sodium acetate trihydrate is 136.08 g/mol. Discuss this calculation.
5. (3 pts) Use the Henderson–Hasselbalch equation to calculate the theoretical pH of the buffer solution (prior to the addition of NaOH) using the values obtained in Discussion Questions 3 and 4 and the theoretical value of K a for acetic acid, 1.8 10 –5 . Discuss this calculation.
6. (2 pts) What was the measured pH of the buffer solution prior to the addition of NaOH? Use the theoretical pH calculated in Discussion Question 5 and the following equation to determine and discuss the % error of your results:
7. (3 pts) During the addition of NaOH in Part B , which buffer species reacted with the NaOH? Provide the balanced formula unit equation for this reaction. 14 A. M. Bohnsack Spring 2019 (revised Z. Baranová)
Worksheet & Grading Rubric – Weak Acids and Buffers During the addition of NaOH in Part B acetic acid was the buffer series being neutralized. The balanced formula unit equation for this reaction: NaOH (aq) +C 2 H 4 O 2(aq) →NaC 2 H 3 O 2(aq) +H 2 O (l) . PART B: Buffered Acetic Acid vs. NaOH (5 pts) Table 2 : Relevant volumes and pH readings during the NaOH titration of the buffer. Titration Conditions NaOH added (mL) pH Initial 0 mL 4.848 pH Buffering capacity reached 7.87 mL 5.848 pH Equivalence point 9.77 mL 8.88 pH
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