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One of the most common ways to identify, purify, and analyze drugs is through ac

ID: 1057135 • Letter: O

Question

One of the most common ways to identify, purify, and analyze drugs is through acid-base titration. Aspirin, is a well-known drug used to treat common aches and pains, and is actually a weak acid. As a result, it can be titrated with a sodium hydroxide (NaOH), and phenolphthalein, which is used as an indicator. An aspirin sample thus can be neutralized by the reaction shown below. Determine the mass (in g) of an unknown sample of aspirin which is dissolved in 25.00 mL of water, and is titrated to the end point using 32.50 mL of a 0.100 M NaOH solution. Aspirin has only 1 acidic hydrogen per molecule, and the molar mass of aspirin is 180.16 g/mol. Given the mass you calculated above, determine the concentration (molarity) of the aspirin in the unknown sample that was titrated.

Explanation / Answer

HC9H7O4 + NaOH ---------> NaC9H7O4 + H2O

1 moles      1 moles

no of moles of NaOH    = molarity * volume in L

                                     = 0.1*0.0325   = 0.00325 moles

no of moles of NaOH   = no of moles of asprine

no of moles of asprine   = 0.00325 moles

mass of asprine                = no of moles * gram molar mass

                                         = 0.00325*180.16   = 0.586g   = 586mg

molarity of asprine         = no of moles/volume of solution in L

                                       = 0.00325/0.025   = 0.13M >>>> answer

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