For the synthesis of aspirin, how do you calculate the percent yield if the reaction produces 4.70 grams of aspirin. The reaction, using molecular...

Aspirin (C9H8O4) is generated from salicyclic
acid (C7H6O3) and acetic anhydride (C4H6O3) using the following synthesis reaction:

C7H6O3  + C4H6O3  -----> C9H8O4  +  C2H4O2

and since acetic
anhydride is in excess, salicylic acid will be the limiting agent.

Using
stoichiometry: 1 mole of salicylic acid generates 1 mole aspirin. 

So, 180 gm
aspirin can be generated from 138 gm salicylic acid.

Using the information
from your other question where 4 gm salicylic acid was available and the aspirin yield was 4 x
180/138 gm = 5.22 gm 

and in this case, 4.7 gm aspirin was generated, i.e.
the reaction was not perfect (< 100% efficiency).

Theoretical yield = 5.22
gm

Actual yield = 4.7 gm

% yield = Actual
yield/theoretical yield    x100 = 4.7 x 100/5.22 =
90.04%