Question 5.SP.20: Acetaminophen, the active ingredient in Tylenol, can be prep...
Acetaminophen, the active ingredient in Tylenol, can be prepared by the chemical reaction given below. What is the percent yield when 60.0 g of 4-aminophenol reacts with acetyl chloride to form 70.0 g of acetaminophen?
To find the theoretical yield, convert grams of reactant to grams of product, following the three steps in
Sample Problem 5.17. Then, use the formula, percent yield = (actual yield/theoretical yield) × 100%.
[1] Convert the number of grams of reactant to the number of moles of reactant using the reactant’s molar mass.
• Use the molar mass of the reactant, 4-aminophenol, to write a conversion factor. Multiply the number of grams of reactant by the conversion factor to give the number of moles of reactant.
\begin{matrix} \text{Grams of reactant} & & \text{molar mass conversion factor} & &\text{Moles of reactant}\\ \\ 60.0 \cancel{g}\text{ 4-aminophenol}& \times & \frac{\text{1 mol 4-aminophenol}}{109.1 \cancel{g}\text{4-aminophenol}} &= & 0.550 \text{ mol 4-aminophenol} \end{matrix}
[2] Convert the number of moles of reactant to the number of moles of product using a mole–mole conversion factor.
• Use the coefficients in the balanced chemical equation to write a mole–mole conversion factor—one mole of 4-aminophenol forms one mole of acetaminophen. Multiply the number of moles of reactant by the conversion factor to give the number of moles of product.
\begin{matrix} \text{Moles of reactant} & & \text{mole-mole conversion factor} & &\text{Moles of product}\\ \\ 0.550 \cancel{mol} \text{4-aminophenol}& \times & \frac{\text{1 mol acetaminophen}}{1 \cancel{mol}\text{ 4-aminophenol}} &= & \text{0.550 mol acetaminophen} \end{matrix}
[3] Convert the number of moles of product to the number of grams of product using the product’s molar mass.
• Use the molar mass of the product to write a conversion factor. Multiply the number of moles of product (from step [2]) by the conversion factor to give the number of grams of product.
\begin{matrix} \text{Moles of product} & & \text{molar mass conversion factor} & &\text{Grams of product}\\ \\ 0.550 \cancel{mol} \text{ acetaminophen }& \times & \frac{\text{151.2 g acetaminophen}}{1 \cancel{mol}\text{ acetaminophen}} &= & \text{83.2 g acetaminophen} \\ \\&&&& \text{Theoretical yield} \end{matrix}
[4] Use the theoretical yield and the given actual yield to calculate the percent yield.
\begin{matrix} \text{Percent yield}&= & \frac{\text{ actual yield (g)}}{\text{theoretical yield (g)}} & \times &100\% \\ \\ &= & \frac{\text{70.0 g}}{\text{83.2 g}}& \times & 100\% & =&84.1\% \end{matrix}