Question

A student measures out exactly 0.105 g of salicylic acid and runs the experiment as dictated in the lab manual. They obtain 0.111 g of aspirin. What is the percent yield for their reaction?

Answer 1

Answer: The percent yield of the reaction is 8.10 %.

Explanation:

To calculate the number of moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$      .....(1)

Given mass of salicylic acid = 0.105g

Molar mass of salicylic acid = 138.12 g/mol

Putting values in equation 1, we get:

$\text{Moles of salicylic acid}=\frac{0.105g}{138.12g/mol}=0.0079mol$

The chemical equation for the formation of aspirin from salicylic acid follows:

$\text{Salicylic acid + Acetic anhydride}\rightarrow \text{Aspirin + Acetic acid}$

By Stoichiometry of the reaction:

1 mole of salicylic acid produces 1 mole of aspirin

So, 0.0076 moles of salicylic acid will produce = $\frac{1}{1}\times 0.0076=0.0076mol$ of aspirin

Now, calculating the mass of aspirin from equation 1, we get:

Molar mass of aspirin = 180.16 g/mol

Moles of aspirin = 0.0076 moles

Putting values in equation 1, we get:

$0.0076mol=\frac{\text{Mass of aspirin}}{180.16g/mol}\\\\\text{Mass of aspirin}=(0.0076mol\times 180.16g/mol)=1.37g$

To calculate the percentage yield of aspirin, we use the equation:

$\%\text{ yield}=\frac{\text{Experimental yield}}{\text{Theoretical yield}}\times 100$

Experimental yield of aspirin = 0.111 g

Theoretical yield of aspirin = 1.37 g

Putting values in above equation, we get:

$\%\text{ yield of aspirin}=\frac{0.111g}{1.37g}\times 100\\\\\% \text{yield of aspirin}=8.10\%$

Hence, the percent yield of the reaction is 8.10 %.