Suppose you prepare a sample of paracetamol by reacting 10.0g of p-aminophenol with 15.0g of acetic anhydride. You obtain 10.8g of pure paracetamol as a product. What is the percentage yeild of the reaction?
1. Write and balance the equation.
2. Convert g to mols for each reactant. mols = grams/molar mass = ?
3. Using the coefficients in the balanced equation, convert mols each reactant to mols product. You will likely obtain two different values for mols of the product. The SMALLER one is the correct value for mols product obtained and the reagent responsible for that is the limiting reagent.
4. Convert smaller number of mols to grams. grams = mols x molar mass. This is the theoretical yield (TY)
5. The actual yield (AY) is 10.8 g from the problem.
6. %yield = (AY/TY)*100 = ?
Post your work if you get stuck.
To calculate the percentage yield of the reaction, you need to compare the actual yield (the amount obtained experimentally) with the theoretical yield (the amount expected based on stoichiometry and assuming 100% efficiency).
1. Calculate the molecular weight of p-aminophenol (C6H7NO):
- C: 6 * 12.01 = 72.06 g/mol
- H: 7 * 1.01 = 7.07 g/mol
- N: 1 * 14.01 = 14.01 g/mol
- O: 1 * 16.00 = 16.00 g/mol
Total = 109.14 g/mol
2. Calculate the molecular weight of acetic anhydride (C4H6O3):
- C: 4 * 12.01 = 48.04 g/mol
- H: 6 * 1.01 = 6.06 g/mol
- O: 3 * 16.00 = 48.00 g/mol
Total = 102.10 g/mol
3. Calculate the molecular weight of paracetamol (C8H9NO2):
- C: 8 * 12.01 = 96.08 g/mol
- H: 9 * 1.01 = 9.09 g/mol
- N: 1 * 14.01 = 14.01 g/mol
- O: 2 * 16.00 = 32.00 g/mol
Total = 151.18 g/mol
4. Calculate the stoichiometry of the reaction by balancing the chemical equation:
p-aminophenol (C6H7NO) + acetic anhydride (C4H6O3) → paracetamol (C8H9NO2) + acetic acid (C2H4O2)
- From the balanced equation, we can see that the molar ratio between p-aminophenol and paracetamol is 1:1.
5. Calculate the theoretical yield of paracetamol:
- Convert the mass of p-aminophenol used to moles:
Moles of p-aminophenol = mass / molecular weight
Moles of p-aminophenol = 10.0 g / 109.14 g/mol = 0.0916 mol
- Theoretical yield of paracetamol = Moles of p-aminophenol * molecular weight of paracetamol
Theoretical yield of paracetamol = 0.0916 mol * 151.18 g/mol = 13.82 g
6. Calculate the percentage yield:
- Percentage yield = (Actual yield / Theoretical yield) * 100
- Percentage yield = (10.8 g / 13.82 g) * 100
- Percentage yield = 78.06%
Therefore, the percentage yield of the reaction is approximately 78.06%.