# Experiment 18.pdf - Toni McDonald Experiment 18 Pre-Lab...

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Toni McDonald Experiment 18: Pre-Lab March 27, 2020 Buffer Solutions Objective: To find the pKa of acetic acid by multiple methods. To determine if the acetic acid/sodium acetate buffer solution is able to resist changes in pH. Variables: Independent: pH of the solutionsDependent: the pKa of acetic acidHypothesis: 1.The pKa value of aceic acid is 4.8. The value will be experimentally calculated through two different methods. Using methods of titration with NaOH and acetic acid, we will find the pH of a buffer solution. In the first method, the value of pKa of acetic acid will be found by measuring the pH of acetic acid, which would be approximately 2.88. This casr involves using te formula for Ka and then converting it to pKa using the formula, pKa = -logKa. After, use pH to find the concentration of H3O+ using the equation [H3O+]=10^-pH; this should be 1.3 * 10^-3M. Since the concentration of acetate and hydronium are equal, we can solve for Ka by multiplying both concentrations and dividing it by the average molarity of acetic acid from the 3 trials. Additionally, the concentration of acetic acid will be 0.1012 M, unchanged. In the second method, the pKa value of acetic acid is determined by making a buffer solution. In this case, a specific solution can be made such that the pH is equal to the pKa, making it easy to measure the pH and have the pKa.