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_4 H_6 O_3) with salicylic acid (C_7 H_6 O_3) to form aspirin (C_9 H_8 O_4) and acetic acid (C_2 H_4 O_2). The balance equation is: C_4 H_6 O_3 + C_7 H_6 O_3 rightarrow C_9 H_8 O_4 + C_2 H_4 O_2 In a laboratory synthesis, a student begins with 5.00 ml of acetic anhydride (density = 1.08 g/ml) and 2.08 g of salicylic acid. Once the reaction is complete, the student collects 2, 010 mg of aspirin. Determine the limiting reactant (i.e., the one that is used up first), theoretical yield aspirin, and percent yield for the reaction. a. limiting reactant ________ b. theoretical yield _________ c. percent yield

Explanation / Answer

Ans A

5 ml or 0.005 l of acetic anhydride with density 1.08g/ml has a mass of,

1.08 = M/ 5

M = 5.4 g

molar mass of acetic anhydride = 102 g/mol

5.4 g of acetic anhydride = 5.4/102 = 0.053 moles

molar mass of salicylic acid = 138.12 g/ mol

so 2.08 g = 0.015 moles

Now in the reaction , equimolar ratios of both the reactants have been used,

so clearly salicylic acid is the limiting reagent.

Ans B.

As salicylic acid is the limiting reagent , so 0.015 moles of aspirin is formed.

The molar mass of aspirin is 180.16 g/mol

so amount of aspirin formed = 180.16 * 0.015 =2.702 g

so the theoretical yield of aspirin = 2702 mg

Ans C.

Percent yield = (Actual yield / theoretical yield ) / x 100

= (2010 / 2702) x 100

percent yield = 74.39 %

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