Question

Aspirin is produced by the reaction of salicylic acid (C7H6O3 . M = 138.1 g/mol) and acetic anhydride(C4H6O3, M = 102.1 g/mol).

                  C7H6O3(s) + C4H6O3(l) → C9H8O4(s) + C2H4O2(l)

If 2.04 g of C9H8O4 (M = 180.2 g/mol) is produced from the reaction of 3.00 g C7H6O3 and 5.40 g C4H6O3, what is the percent yield?

Answer 1

Number of moles of C7H6O3 =mass/ molar mass
                                                      = 3 / 138.1
                                                        = 0.0217 mol

Number of moles of C4H6O3=mass/ molar mass
                                                      = 5.4 / 102.1
                                                        = 0.0529 mol

According to reaction, 1 mol of each should react.
So C7H6O3   acts as limiting agent.
Number of moles of C9H8O4 should be produced theoretically = 0.0217 mol
mass of C9H8O4 produced theoretically = Molar mass * number of moles
                                                                        = 180.2 * 0.0217
                                                                         = 3.91 gm

But actually produced = 2.04 gm

percentage yield = actual yield * 100 / theoretical yield
                              = 2.04*100 / 3.91
                              = 52.2 %