To solve this part of the workshop you will need the following equations: pH = -

Question

To solve this part of the workshop you will need the following equations: pH = -log [H_3O^*]; pOH = - log [OH]; pH + pOH = 14; K_a x K_b = K_w; pH = pK_a +log ([Base]/[Acid]) Iog((Basc]/(Acid J) Reconsider the titration curve in Problem 1 and complete the table below. The table asks you to consider several points along the titration curve. Each point represents the solution after a fixed amount of 0.2 M NaOH has been added to the 25 mL benzoic acid. The first point occurs before any NaOH has been added, the next after the midpoint but before the equivalence point, the next at the equivalence point and the last after the equivalence point for each point you should (a) list the major speeds in solution, (b) identify the pH active species and find its concentration, (c) determine the pH of the resulting solution. You calculated the starting concentration of benzoic add in problem 1. Think about each point on the curve as a chemical reaction between the NaOH that you have added and the benzoic add that you started with. To receive credit for this problem you must show ALL your calculations. Use the next page if you need more space!

Explanation / Answer

Titration of 25 ml of benzoic acid with 0.2 M NaOH

NaOH (ml)      major species present           [pH-active species]                 pH

      0.0                      C6H5COOH                             H+                               2.45

     20.0                     C6H5COO-            C6H5COOH, C6H5COO-             4.80

     30.75                   C6H5COO-                        C6H5COO-                       8.60

      40.0                    C6H5COO-                              OH-                            12.66

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