Asprin, C9H8O4, is prepared by reacting salicylic acid, C7H6O3, with acetic anhydride, C4H6O3.

The other product is acetic acid C2H4O2,

C9h8o4 + C4H6O3 -> C9H8O4 + C2H4O2

when 2.00 g of salicylic acid is heated with 4.00 g of acetic anhydride.

If the actual yield of aspirin is 2.1 g, what is the percentage yield?

2 answers

This is a limiting regent(LR) problem. Your equation is wrong; i.e., you started with aspirin to form aspirin. You meant to start with salicylic acid (SA). I will shorten these formulas to
C7H6O3 + C4H6O3 -> C9H8O4 + C2H4O2
SA + AH(acetic anhydride) => ASA(aspirin) = HAc(acetic acid)

mols SA = grams/molar mass = ?
mols AH = grams/molar mass = ?

Find the LR this way.
Convert mols SA to mols ASA. That's done by using the coefficients in the balanced equation; i.e., mols SA x (1 mol ASA/1 mol SA) = ? mols ASA.
Do the same and convert mols AH to mols ASA.
The SMALLER number always wins in LR problems and the LR is the reagent producing the smaller mols product.
Now convert mols ASA (the product you want) to grams. g = mols x molar mass = ?. This is the theoretical yield (TY). The actual yield (AY) in the problem is given as 2.1 g.
% yield = (AY/TY)*100 = ?
Post your work if you get stuck.
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