answer. Calculate the pKaof acetic acid from the midpoint data using the Henderson-Hasselbach equations in the Background section. Finally, find the average calculated molarity, percent by mass concentration, and pKafor acetic acid based on the provided data. Data Data Table 3 Vinegar Sample 1 Vinegar Sample 2 Vinegar Sample 3 Initial pH Reading pH = 3.211 pH = 3.102 pH = 3.105 Initial Buret Reading 2.89 mL 3.00 mL 1.61 mL Midpoint pH Reading pH = 4.895 pH = 4.687 Midpoint Buret Reading 12.92 mL 9.50 mL Final pH Reading pH = 8.238 pH = 8.531 pH = 8.934 Final Buret Reading 20.12 mL 20.31 mL 19.00 mL Volume of NaOH Consumed 17.23 mL 17.31 mL 17.39 mL Calculated Molarity of Acetic Acid in the Vinegar Sample 5.96 M 5.79 M 10.8 M Volume NaOH Consumed at Midpoint Reading 9.92 mL 7.89 mL Moles of NaOH Consumed at Midpoint Reading [A–] 0.00992 mol 0.00789 mol Moles of Acetic Acid Remaining at Midpoint [HA] 0.00739 mol 0.00950 mol Calculated p K a 3.55 4.06 Average calculated molarity of acetic acid = (5.96 + 5.79 +10.8)/3 = 7.52 M Average acetic acid concentration expressed in percent by mass = 5.07 % Average value of pK a of acetic acid based on provided experimental data = (3.55 +4.06)/2 = 3.81 Percent error for pK a of acetic acid = [(3.81 – 3.55)/3.88 + (4.06 – 3.81)/3.81]/2 x 100 % = 6.70 % References Carolina Distance Learning Investigation Manual, ‘Determination of Acetic Acid Concentration’ Link 5
*results and discussion included below in post lab and discussion questions. Pre-laboratory Question1.Write the balanced equation for the neutralization of acetic acid by sodium hydroxide. O 2.The Food and Drug Administration (FDA) mandates that all vinegar sold in the United Statesmust have a minimum concentration of 4% acetic acid by mass. Calculate the minimum molarity of acetic acid in vinegar according to this standard. Assume the density of vinegar isthe same as for water. = 0.67 mol/L 3.Calculate the mass of NaOH required to make 0.40 L of a 0.50 M solution. 4.Read through the laboratory procedures and then diagram the procedures using illustrations and/or a flow chart to describe the steps. Ensure that your diagrams are labelled with quantities and descriptions.Place the 10 mL graduate cylinder onto the electronic balance, tare the balance. Then, add 5 mL of vinegar and 2 drops of phenolphthalein into the cylinder. Transfer 10mL of 1 M NaOH to a small plastic cup. Use the NaOH in the small cup to fill the syringe, try to removeas many bubbles as possible. Record the initial volume of NaOH. Add the NaOH to the 6
vinegar solution, using the syringe, drop by drop. Swirl after every drop till the solution becomes pink. Record the final volume of NaOH. Laboratory Questions
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