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Theoretical and Percent Yield

Solution to Practice Problem

Find the limiting reagent

molar mass of p-aminophenol =109.1g/mol
molar mass of acetic anhydride = 102.1 g/mol
moles of p-aminophenol = mass/molar mass
                                  = 0.157g/(109.1g/mol)
                                  = 0.00144 mol
moles of acetic anhydride = mass/molar mass
                                         = 0.486g/(102.1g/mol)
                                         = 0.00476 mol
From the balanced chemical equation we know that for every mole of p-aminophenol and acetic acid one mole of acetaminophen is produced.
Since there are more moles of acetic anhydride than p-aminophenol, p-aminophenol is used up first as the reaction proceeds.  We can conclude that acetic anhydride is in excess and p-aminophenol is the limiting reagent.
Therefore # moles of p-aminophenol = # of acetaminophen produced

Finding the Theoretical Yield
Theoretical Yield = moles of acetamiophen x molar mass of acetaminophen
                         = 0.00144 mol x 151.2g/mol

                         = 0.217 g


Finding the Percent Yield
Percent Yield =         Actual Yield        x 100%
                            Theoretical Yield
                    =            0.198g      x 100 %
                    =  91.2 %

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