Exercise 8.71 Aspirin can be made in the laboratory by reacting acetic anhydride

Question

Exercise 8.71 Aspirin can be made in the laboratory by reacting acetic anhydride (C4H6O3) with salicylic acid (C7H6O3) to form aspirin (C9H8O4) and acetic acid (C2H4O2). The balanced equation is C4H6O3 + C7H6O3 right arrow C9H8O4 + C2H4O2 In a laboratory synthesis, a student begins with 2.80 mL of acetic anhydride (density = 1.08 g/ml) and 1.24 g of salicylic acid. Once the reaction is complete, the student collects 1.23 g of aspirin. Part B Determine the theoretical yield of aspirin for the reaction. Part C Determine the percent yield of aspirin for the reaction.

Explanation / Answer

molarmass of aspirin = 180.157 g/mol

molarmass of aceticanhydride = 102.09 g·mol1 .

No of mol of aceticanhydride = (2.8*1.08)/102.09 = 0.03 mol

No of mol of salicylicacid = 1.24/138.121   = 0.009 mol

limiting reagent is salicylicacid

No of mol of aspirin produced = 0.009 mol

mass of aspirin produced = 0.009*180.157 = 1.62 grams

Theoretical yield of aspirin = 1.62 grams

practical yield = 1.23 grams

percent yield = practical yield/Theoretical yield*100

    = 1.23/1.62*100 = 75.9%

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