Question

Aspirin (C9H8O4) can be prepared by the reaction of salicylic acid (C7H6O3) with acetic anhydride (in
excess) in the presence of phosphoric acid as catalyst. Initially 5.1 g salicylic acid was used, after
purification; 5.10 g of solid (Aspirin) was collected.
(a) Calculate the theoretical yield. (6 marks)
(b) Calculate the percentage yield for aspirin. (4 marks)
The following equation is balanced as follow:
Salicylic Acid(C7H6O3) Acetic Anhydride Aspirin(C9H8O4) Acetic Acid
1: 1 :1 :1

Answer 1

To save time in typing let's call salicylic acid something like SA. The molar mass of SA is 138.1 but you should confirm that.
mols SA = grams/molar mass = 5.10/138 = about 0.037 but you should recalculate and add another significant figure.
Looking at the equation, 1 mol SA produces 1 mol aspirin so you will get 0.037 mols aspirin. g aspirin = mols aspirin x molar mass aspirin = ?. This is the theoretical yield (TY).
b. The actual yield (AY) is 5.10 grams. %yield = (AY/TY)*100 = ?
Post your work if you get stuck.