Question

Aspirin can be prepared from salicylic acid ( C 7 H 6 O 3 CX7HX6OX3), which has a molar mass of 138.12 g/mol, and acetic anhydride ( C 4 H 6 O 3 CX4HX6OX3), which has a molar mass of 102.04 g/mol. The density of acetic anhydride is 1.082 g/mL. C 7 H 6 O 3 + C 4 H 6 O 3 ⟶ C 9 H 8 O 4 + C 2 H 3 O 2 CX7HX6OX3+CX4HX6OX3⟶CX9HX8OX4+CX2HX3OX2 What is the theoretical yield, in grams, of aspirin ( C 9 H 8 O 4 CX9HX8OX4), which has a molar mass of 180.15 g/mol, possible when reacting 3.20 g of salicylic acid with 3.71 mL of acetic anhydride? Type answer:

Answer 1

Answer: The theoretical yield of aspirin is 4.14 g

Explanation:

To calculate the moles :

$\text{Moles of solute}=\frac{\text{given mass}}{\text{Molar Mass}}$  $\text{Moles of salicylic acid}=\frac{3.20g}{138.12g/mol}=0.023moles$

mass of acetic anhydride = $density\times volume =1.082g/ml\times 3.71ml=4.01g$

$\text{Moles of acetic anhydride}=\frac{4.01g}{102.04g/mol}=0.039moles$

$C_9H_6O_3+C_4H_6O_3\rightarrow C_9H_8O_4+C_2H_3O_2$  

According to stoichiometry :

1 mole of salycylic acid require 1 mole of acetic anhydride

Thus 0.023 moles of  salycylic acid require=$\frac{1}{1}\times 0.023=0.023moles$  of acetic anhydride

Thus salycylic acid is the limiting reagent as it limits the formation of product and acetic anhydride is the excess reagent.

As 1 mole of salycylic give = 1 mole of aspirin

Thus 0.023 moles of salycylic acid give =$\frac{1}{1}\times 0.023=0.023moles$  of aspirin

Mass of aspirin = $moles\times {\text {Molar mass}}=0.023moles\times 180.15g/mol=4.14g$

Thus theoretical yield of aspirin is 4.14 g