Calculate the theoretical yield of aspirin ( C9H8O4).

Question

Aspirin can be synthesized in the lab by combining salicylic acid (C7H6O3) and acetic anhydride (C4H6O3) to form aspirin (C9H8O4) and acetic acid (C2H4O2). The balanced equation for this reaction is

C7H6O3+C4H6O3⟶C9H8O4+C2H4O2

A student started with 3.19 mL acetic anhydride (density=1.08 g/mL) and 2.12 g salicylic acid. The student synthesized 2.11g of aspirin.

Answer 1

C7H6O3 + C4H6O3 ==> C9H8O4 + C2H4O2 ... balanced equation

SA................AA.................Aspirin........acetic acid

Find the limiting reactant. An easy way is to simply divide moles of each reactant by the coefficient in the balanced equation. In this case, both coefficients are 1 so we can just compare moles of each reactant.

For SA we have: 2.12 g SA x 1 mol / 138 g = 0.0154 mols

For AA we have: 3.19 mls x 1.08 g / ml x 1 mol / 102 g = 0.0338 mols

Salicylic acid is limiting

Next, use mols SA to find mols of aspirin formed (theoretical yield)

Theoretical yield = 0.0154 mols SA x 1 mol aspirin / mol SA x 180.2 g aspirin/mol = 2.78 g aspirin

Finally, find the % yield

% yield = actual yield / theoretical yield (x100%) = 2.11 g / 2.78 g (x100%) = 75.9% yield