# Equivalence point was determined the half equivalence

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equivalence point was determined. The half-equivalence point is the half-way point of the equivalence point which is where both the weak acid and the base had equal concentrations. By observing Henderson-Hasselbalch’s equation, pH = p K a + log A ¿ ¿ ¿ ¿ , if the acid and base are identical, they will have a 1:1 ratio, resulting in the pH being equal to the p K a (the log 1 is equal to zero). (The three titration curves and three second derivative curves from the Part A Data Analysis can be found at the beginning of the worksheet.)
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 21.83 10.92 3.12 2 19.06 9.53 3.56 3 19.74 9.87 3.74 Average 20.21 10.12 3.47 8 A. M. Bohnsack Spring 2019 (revised Z. Baranová)
Worksheet & Grading Rubric – Weak Acids and Buffers 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?
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.