chem quest: percent yield?

Question

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

C7H6O3(s) + C4H6O3(λ) → C9H8O4(s) + C2H4O2(λ).

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?

a.68.0%
b.14.2%
c.24.3%
d.52.1%
e.21.4%

Answer 1

no, it not that simple.
substances react not in gram equivalents, but in mol equivalents. in this case 1 mol of acid reacts with 1 mol of anhydride to form 1 mol of aspirin.
u know the amounts used, and u know the molecular weights of all substances. u have to figure how many moles of each u have, and what is the maximum possible yield.
u have 0.02172 moles acid and 0.05 moles anhydride. so, theoretically, u should get the same amount of aspirin, namely 0.02172 moles. but u have only 0.1132 moles (divide mas by mol. weight).
so ur yield is almost half of what it should be.

Answer 2

I want to say C but that's providing you just add 3.00 and 5.40. It might not be that simple.

(2.04/8.4) * 100 = 24.3%

Edit: Yeah I knew it wasn't that simple. But mols throw me off.