Aspirin can be made in the laboratory by reacting acetic anhydride ( C 4 H 6 O 3

Question

Aspirin can be made in the laboratory by reacting acetic anhydride (C 4H 6O 3) with salicylic acid (C 7H 6O 3) to form aspirin (C 9H 8O 4) and acetic acid (C 2H 4O 2). The balanced equation is
C 4H 6O 3+C 7H 6O 3?C 9H 8O 4+C 2H 4O 2
In a laboratory synthesis, a student begins with 2.80mL of acetic anhydride (density=1.08g/ml) and 1.24g of salicylic acid. Once the reaction is complete, the student collects 1.24g of aspirin.

Determine the limiting reactant for the reaction.

Determine the theoretical yield of aspirin for the reaction.

Explanation / Answer

C4H6O3 = 102 g/mol

C7H6O3 = 108 g/mol

C9H8O4 = 180 g/mol

C2H4O2 = 60 g/mol

Convert 2.8 mL acetic anhydride to g:

1.08 g/mL * 2.8 mL = 3.024 g

Now convert all grams to moles:

3.024g acetic anhydride * 1mol/102g = .029647 mol

1.24g salicylic acid * 1mol/108g = .01148 mol

1.24g aspirin * 1mol/180g = .006889 mol

From the above balanced equation, everything has a coefficient of 1, so in a perfect world, once all of the .01148 moles of salicylic acid (lowest moles on the reactant side and therefore the limiting reactant since the ratio is 1:1) has completely reacted then we should have .01148 moles of aspirin (that's the theoretical yield).

.01148 mol aspirin * 180g/1mol = 2.067 g aspirin (theoretical)

percent yield is:

[actual yield]/[theoretical yield] x 100%

[.006889 mol collected]/[.01148 mol expected] x 100% = 60% yield

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