Please help me solve this and show me how you got the answer. Thank you!

Question

A student prepared aspirin using 2.019 g of salicylic acid and 5.2 ml of acetic anhydride (d=1.08g/ml)

1. Which reactant is limiting? salicylic acid or acetic anhydride

2. What is the theoretical yield of aspirin

3. If the student obtained 1.789 g of aspirin, what is the percent yield?

Answer 1

The balanced chemical reaction is

 

   2 C₇H₆O₃ + (CH₃ CO)₂O ==>   2 C₉H₈O₄ + H₂O

 

    So the molar ratio at stoichiometry is  two moles acid to one mole acetic anhydride.     The next step is to work out the molar masses of the molecules.   My result  is

 

   MM   salicylic acid =   138

   MM   acetic anhydride =  102

   MM  aspirin =  180

 

   The mass of salicylic acid available is 2.019 g   which is   0.01463 moles

   The mass of acetic anhydride available is  5.2 x 1.08 = 5.616 g   which is   0.05506 moles

 

   Since the molar ratio is 2 moles acid to one mole anhydride,   salicylic acid is the limiting reactant.

 

  Since two moles of aspirin will be produced from 2 moles of salicylic acid  (i.e. 1 to 1),  0.01463  moles of the acid will produce  0.01463 moles of aspirin.      This is 2.633 g of aspirin (the theoretical yield).

 

  The percent yield is  100 x (1.789/ 2.633) = 68%