One method for determining the purity of aspirin (C₉H₈O₄) is to hydrolyze it with NaOH solution and then to titrate the remaining NaOH. The reaction of aspirin with NaOH is as follows:

A sample of aspirin with a mass of 1.427 g was boiled in 50.00 mL of 0.500 M NaOH. After the solution was cooled, it took 31.92 mL of 0.289 M HCl to titrate the excess NaOH. Calculate the purity of the aspirin. What indicator should be used for this titration? Why?

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C,H,O4(s) + 2OH(aq) Aspirin Boil C₂H5O3(aq) + C₂H₂O₂ (aq) + H₂O(1) 10 min Salicylate ion Acetate ion