Aspirin is prepared by heating salicylic acid, C7H6O3, with acetic anhydride, C4H603. The other product produced is acetic acid, C2H402.
C7H6O3+C4H6)3->C9H8O4+C2H4O2
What is the theoretical yield in grams of aspirin, C9H8O4, when 2.00 grams of salicylic acid is heated with 4.00g of acetic anhydride? If the actual yield of aspirin is 2.10g, what is the percentage yield?
71.3%
Чокх
To find the theoretical yield of aspirin, first write out the balanced chemical equation for the reaction:
C7H6O3 + C4H6O3 → C9H8O4 + C2H4O2
From the balanced equation, we can see that the molar ratio between salicylic acid and aspirin is 1:1. This means that 1 mole of salicylic acid will produce 1 mole of aspirin.
Step 1: Convert the mass of salicylic acid to moles.
Given: Mass of salicylic acid = 2.00 grams
Molar mass of salicylic acid (C7H6O3) = 138.12 g/mol (the sum of the atomic masses of carbon, hydrogen, and oxygen in the compound)
Moles of salicylic acid = (mass of salicylic acid) / (molar mass of salicylic acid)
= 2.00 g / 138.12 g/mol
Step 2: Determine the limiting reactant.
Next, we need to determine which reactant is limiting. To do this, compare the moles of each reactant to their respective stoichiometric coefficients in the balanced equation.
Given: Mass of acetic anhydride = 4.00 grams
Molar mass of acetic anhydride (C4H6O3) = 102.09 g/mol
Moles of acetic anhydride = (mass of acetic anhydride) / (molar mass of acetic anhydride)
= 4.00 g / 102.09 g/mol
By comparing the moles of salicylic acid and acetic anhydride, we can determine the limiting reactant. The reactant that produces fewer moles of product is the limiting reactant.
Step 3: Calculate the moles of aspirin produced.
Since the molar ratio between salicylic acid and aspirin is 1:1, the number of moles of aspirin will be equal to the number of moles of salicylic acid.
Moles of aspirin = Moles of salicylic acid
= (2.00 g / 138.12 g/mol)
Step 4: Convert moles of aspirin to grams.
To find the theoretical yield, multiply the moles of aspirin by its molar mass.
Molar mass of aspirin (C9H8O4) = 180.16 g/mol
Theoretical yield = Moles of aspirin × Molar mass of aspirin
= (2.00 g / 138.12 g/mol) × 180.16 g/mol
Now, to calculate the percentage yield:
Given: Actual yield = 2.10 grams
Percentage yield = (Actual yield / Theoretical yield) × 100
= (2.10 g / Theoretical yield) × 100
Simply substitute the value of the theoretical yield obtained earlier into this equation to find the percentage yield.
This is a limiting reagent problem because amounts for BOTH reactants are given.
AH = acetic anhydride.
SA = salicylic acid
ASA = aspirin
mols AH = grams/molar mass = ?
mols SA = grams/molar mass = ?
Using the coefficients in the balanced equation, convert mols AH to mols of ASA.
Do the same and convert mols SA to mols ASA.
It is quite likely that the two values will not agree which means one of them is wrong; the correct value in limiting reagent problems is ALWAYS the smaller value and the reagent producing that value is the limiting reagent.
Now convert mols of the product to grams by g = mols x molar mass. This is the theoretical yield (TY).
The actual yield in the problem is given as 2.10g (AY).
%yield = (AY/TY)*100 = ?