Aspirin (C9H8O4) is synthesized by the reaction of salicylic acid (C7H6O3) with acetic anhydride, C4H6O3.
2C7H6O3 + C4H6O3 −→ 2C9H8O4 + H2O
When 19 g of C7H6O3 and 19 g of C4H6O3
react, which is the limiting reagent?
mols SA = 19/molar mass SA.
mols AA = 19/molar mass AA.
Convert mols of SA to mols of aspirin (use the coefficients in the equation).
Convert mols AA to mols of aspirin(use the coefficients here too).
The reagent giving the smallest number for mols aspirin is the limiting reagent and the smallest number is the correct value for mols aspirin formed in the reaction.
How do you convert it to moles of asprin?
Use the coefficients in the balanced equation.
mols SA x (2 mols aspirin/2 mols SA) = mols SA x 2/2 = ? mols aspirin.
mols AA x (2 mols aspirin/1 mol AA) = mols AA x 2/1 = ? mols aspirin.
To determine the limiting reagent, we need to compare the amount of product that can be formed from each reactant.
Step 1: Calculate the moles of each reactant
- Convert the given masses of each reactant to moles using their molar masses.
- The molar mass of salicylic acid (C7H6O3) is (12.01 * 7) + (1.01 * 6) + (16.00 * 3) = 138.12 g/mol.
- The molar mass of acetic anhydride (C4H6O3) is (12.01 * 4) + (1.01 * 6) + (16.00 * 3) = 102.09 g/mol.
Moles of salicylic acid (C7H6O3):
m = 19 g
Molar mass = 138.12 g/mol
moles = m / Molar mass = 19 g / 138.12 g/mol = 0.1376 mol
Moles of acetic anhydride (C4H6O3):
m = 19 g
Molar mass = 102.09 g/mol
moles = m / Molar mass = 19 g / 102.09 g/mol = 0.1862 mol
Step 2: Convert reactants to the moles ratio based on the balanced equation
From the balanced equation, we can see that the stoichiometric ratio of salicylic acid to aspirin is 2:2, meaning 2 moles of salicylic acid react to form 2 moles of aspirin.
Similarly, the stoichiometric ratio of acetic anhydride to aspirin is 1:2.
Since the balanced equation already indicates that 2 moles of salicylic acid are required to form 2 moles of aspirin, we can see that salicylic acid is the limiting reagent.