Question

A student collects 0.513 g acetaminophen when 0.387 g of p-aminophenol reacts with 0.500 ml acetic anhydride (density= 1.08 g/mL). Calculate the percent yield of the acetaminophen

Answer 1

Ans. The balanced reaction for synthesis of acetaminophen (paracetamol) is as follow-

C6H7NO + C₄H₆O₃ ------> C₈H₉NO₂ + CH₃COOH       - reaction 1

C₆H₇NO = p-aminophenol

C₄H₆O₃= acetic anhydride

C8H9NO₂ = acetaminophen (paracetamol)

CH₃COOH = Acetic acid

Theoretical molar ratio of reactants = p-aminophenol: Acetic anhydride = 1 : 1

# Moles of p-aminophenol taken = Mass/ molar mass

                                                = 0.387 g / (109.13 g/mol)

                                                = 0.003546 mol

Mass of acetic anhydride = Volume x Density

                                                = 0.500 mL x (1.08 g/ mL)

                                                = 0.540 g

            Moles of acetic anhydride = 0.540 g / (102.09 g/ mol) = 0.00529 mol

Theoretical molar ratio of reactants = p-aminophenol: Acetic anhydride

= 0.00355 mol / 0.00529

= 1 : 1.5

Comparing the theoretical and experimental molar ratio, the moles of acetic anhydride is greater than 1.0 when that of p-aminophenol is kept constant at 1.0 mol.

So,

            Acetic anhydride is the reagent in excess

            p-aminophenol is the limiting reagent.

# The stoichiometry of product follows the stoichiometry of limiting reactant.

# According to stoichiometry of balanced reaction, 1 mol p-aminophenol produces 1 mol acetaminophen. So, theoretically, 1 mol p-aminophenol shall produce 1 mol acetaminophen.

So,

Theoretical moles of acetaminophen produced = 0.00355 mol

Theoretical mass of acetaminophen produced = Moles x Molar mass

                                                                        = 0.00355 mol x (151.17 g/ mol)

                                                                        = 0.536 g

Therefore, theoretical yield of reaction = 0.536 g

# From data provided-

Actual yield of acetaminophen = 0.513 g

Now,

            % yield of synthesis = (Actual yield / Theoretical yield) x 100

                                                = (0.513 g / 0.536 g) x 100

                                                = 95.71 %