Question

1. What is the theoretical yield of aspirin when reacting 3.08 g of salicylic acid with an excess of acetic anhydride? Report your answer to 3 significant figures.

2. If you prepare 3.45 kg of aspirin from an industrial process with a theoretical yield of 4.38 kg of aspirin, what is the percent yield of the process? Report your answer to 3 significant figures.

3. What is the yield of aspirin when reacting excess salicylic acid with 1.11 mL of acetic anhydride? The density of acetic anhydride is 1.082 g/mL. Report your answer to 3 significant figures.

Answer 1

1) The theoretical yield of a reaction can be calculated using following formula

Theoretical yield = (mass of salicylic acid x molecular weight of aspirin) / molecular weight of salicylic acid

The molar mass of aspirin and salicylic acid is 180.158 g/mol and 138.12 g/mol

Therefore,

Theoretical yield = (3.08 g x 180.158 g/mol) / 138.12 g/mol

= 4.017 g

2) The % yield can be calculated using following formula

% yield = (Obtained yield / Theoretical yield) x 100

= (3.45 Kg/ 4.38 Kg) x 100

= 78.7 %

3) Let us first convert the mL of acetic anhydride into grams of acetic anhydride by using density

mass of acetic anhydride = density x volume

= 1.082 g/mL x 1.11 mL

= 1.2 g

Now the yield of aspirin can be calculated using following formula

Theoretical yield = (mass of acetic anhydride x molecular weight of aspirin) / molar mass of acetic anhydride

The molar mass of aspirin and acetic anhydride is 180.158 g/mol and 102.09 g/mol

Therefore,

Theoretical yield = (1.2 g x 180.158 g/mol) / 102.09 g/mol

= 2.11 g